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  • 1.
    Agthe, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Plivelic, Tomas S.
    Labrador, Ana
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Following in Real Time the Two-Step Assembly of Nanoparticles into Mesocrystals in Levitating Drops2016In: Nano Letters, ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 11, p. 6838-6843Article in journal (Refereed)
    Abstract [en]

    Mesocrystals composed of crystallographically aligned nanocrystals are present in biominerals and assembled materials which show strongly directional properties of importance for mechanical protection and functional devices. Mesocrystals are commonly formed by complex biomineralization processes and can also be generated by assembly of anisotropic nanocrystals. Here, we follow the evaporation-induced assembly of maghemite nanocubes into mesocrystals in real time in levitating drops. Analysis of time-resolved small-angle X-ray scattering data and ex situ scanning electron microscopy together with interparticle potential calculations show that the substrate-free, particle-mediated crystallization process proceeds in two stages involving the formation and rapid transformation of a dense, structurally disordered phase into ordered mesocrystals. Controlling and tailoring the particle-mediated formation of mesocrystals could be utilized to assemble designed nanoparticles into new materials with unique functions.

  • 2.
    Agthe, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wetterskog, Erik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mouzon, Johanne
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Dynamic growth modes of ordered arrays and mesocrystals during drop-casting of iron oxide nanocubes2014In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 16, no 8, p. 1443-1450Article in journal (Refereed)
    Abstract [en]

    The growth modes of self-assembled mesocrystals and ordered arrays from dispersions of iron oxide nanocubes with a mean edge length of 9.6 nm during controlled solvent removal have been investigated with a combination of visible light video microscopy, atomic force microscopy and scanning electron microscopy. Mesocrystals with translational and orientational order of sizes up to 10 mu m are formed spontaneously during the final, diffusion-controlled, drop-casting stage when the liquid film is very thin and the particle concentration is high. Convection-driven deposition of ordered nanocube arrays at the edge of the drying droplet is a manifestation of the so called coffee-ring effect. Dendritic growth or fingering of rapidly growing arrays of ordered nanocubes could also be observed in a transition regime as the growth front moves from the initial three-phase contact line towards the centre of the original droplet.

  • 3. Aulin, Christian
    et al.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lindström, Tom
    High strength, flexible and transparent nanofibrillated cellulose-nanoclay biohybrid films with tunable oxygen and water vapor permeability2012In: NANOSCALE, ISSN 2040-3364, Vol. 4, no 20, p. 6622-6628Article in journal (Refereed)
    Abstract [en]

    A novel, technically and economically benign procedure to combine vermiculite nanoplatelets with nanocellulose fibre dispersions into functional biohybrid films is presented. Nanocellulose fibres of 20 nm diameters and several micrometers in length are mixed with high aspect ratio exfoliated vermiculite nanoplatelets through high-pressure homogenization. The resulting hybrid films obtained after solvent evaporation are stiff (tensile modulus of 17.3 GPa), strong (strength up to 257 MPa), and transparent. Scanning electron microscopy (SEM) shows that the hybrid films consist of stratified nacre-like layers with a homogenous distribution of nanoplatelets within the nanocellulose matrix. The oxygen barrier properties of the biohybrid films outperform commercial packaging materials and pure nanocellulose films showing an oxygen permeability of 0.07 cm(3) mu m m(-2) d(-1) kPa(-1) at 50% relative humidity. The oxygen permeability of the hybrid films can be tuned by adjusting the composition of the films. Furthermore, the water vapor barrier properties of the biohybrid films were also significantly improved by the addition of nanoclay. The unique combination of excellent oxygen barrier behavior and optical transparency suggests the potential of these biohybrid materials as an alternative in flexible packaging of oxygen sensitive devices such as thin-film transistors or organic light-emitting diode displays, gas storage applications and as barrier coatings/laminations in large volume packaging applications.

  • 4. Bender, Philipp
    et al.
    Wetterskog, Erik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hermann, Raphael P.
    Brückel, Thomas
    Wiedenmann, Albrecht
    Disch, Sabrina
    Shape-induced superstructure formation in concentrated ferrofluids under applied magnetic fields2022In: Journal of applied crystallography, ISSN 0021-8898, E-ISSN 1600-5767, Vol. 55, no 6, p. 1613-1621Article in journal (Refereed)
    Abstract [en]

    The field-induced ordering of concentrated ferrofluids based on spherical and cuboidal maghemite nanoparticles is studied using small-angle neutron scattering, revealing a qualitative effect of the faceted shape on the interparticle interactions as shown in the structure factor and correlation lengths. Whereas a spatially disordered hard-sphere interaction potential with a short correlation length is found for ∼9 nm spherical nanoparticles, nanocubes of a comparable particle size exhibit a more pronounced interparticle interaction and the formation of linear arrangements. Analysis of the anisotropic two-dimensional pair distance correlation function gives insight into the real-space arrangement of the nanoparticles. On the basis of the short interparticle distances found here, oriented attachment, i.e. a face-to-face arrangement of the nanocubes, is likely. The unusual field dependence of the interparticle correlations suggests a field-induced structural rearrangement.

  • 5.
    Bergström, Lennart
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sturm Nee Rosseeva, Elena V.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cölfen, Helmut
    Mesocrystals in Biominerals and Colloidal Arrays2015In: Accounts of Chemical Research, ISSN 0001-4842, E-ISSN 1520-4898, Vol. 48, no 5, p. 1391-1402Article, review/survey (Refereed)
    Abstract [en]

    Mesocrystals, which originally was a term to designate superstructures of nanocrystals with a common crystallographic orientation, have now evolved to a materials concept. The discovery that many biominerals are mesocrystals generated a large research interest, and it was suggested that mesocrystals result in better mechanical performance and optical properties compared to single crystalline structures. Mesocrystalline biominerals are mainly found in spines or shells, which have to be mechanically optimized for protection or as a load-bearing skeleton. Important examples include red coral and sea urchin spine as well as bones. Mesocrystals can also be formed from purely synthetic components. Biomimetic mineralization and assembly have been used to produce mesocrystals, sometimes with complex hierarchical structures. Important examples include the fluorapatite mesocrystals with gelatin as the structural matrix, and mesocrystalline calcite spicules with impressive strength and flexibility that could be synthesized using silicatein protein fibers as template for calcium carbonate deposition. Self-assembly of nanocrystals can also result in mesocrystals if the nanocrystals have a well-defined size and shape and the assembly conditions are tuned to allow the nanoparticles to align crystallographically. Mesocrystals formed by assembly of monodisperse metallic, semiconducting, and magnetic nanocrystals are a type of colloidal crystal with a well-defined structure on both the atomic and mesoscopic length scale. Mesocrystals typically are hybrid materials between crystalline nanoparticles and interspacing amorphous organic or inorganic layers. This structure allows to combine disparate materials like hard but brittle nanocrystals with a soft and ductile amorphous material, enabling a mechanically optimized structural design as realized in the sea urchin spicule. Furthermore, rnesocrystals can combine the properties of individual nanocrystals like the optical quantum size effect, surface plasmon resonance, and size dependent magnetic properties with a mesostructure and morphology tailored for specific applications. Indeed, mesocrystals composed of crystallographically aligned polyhedral or rodlike nanocrystals with anisotropic properties can be materials with strongly directional properties and novel collective emergent properties. An additional advantage of mesocrystals is that they can combine the properties of nanoparticles with a structure on the micro- or macroscale allowing for much easier handling. In this Account, we propose that mesocrystals are defined as a nanostructured material with a defined long-range order on the atomic scale, which can be inferred from the existence of an essentially sharp wide-angle diffraction pattern (with sharp Bragg peaks) together with clear evidence that the material consists of individual nanoparticle building units. We will give several examples of mesocrystals and discuss the structural characteristics for biominerals, biomimetic materials, and colloidal arrays of nanocrystals. The potential of the mesocrystal materials concept in other areas will be discussed and future developments envisioned.

  • 6. Boily, Jean-Francois
    et al.
    Yesilbas, Merve
    Uddin, Munshi Md. Musleh
    Lu, Baiqing
    Trushkina, Yulia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Thin Water Films at Multifaceted Hematite Particle Surfaces2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 48, p. 13127-13137Article in journal (Refereed)
    Abstract [en]

    Mineral surfaces exposed to moist air stabilize nanometer- to micrometer-thick water films. This study resolves the nature of thin water film formation at multifaceted hematite (alpha-Fe2O3) nanoparticle surfaces with crystallographic faces resolved by selected area electron diffraction. Dynamic vapor adsorption (DVA) in the 0-19 Torr range at 298 K showed that these particles stabilize water films consisting of up to 4-5 monolayers. Modeling of these data predicts water loadings in terms of an adsorption regime (up to 16 H2O/nm(2)) involving direct water binding to hematite surface sites, and of a condensation regime (up to 34 H2O/nm(2)) involving water binding to hematite-bound water nanodusters. Vibration spectroscopy identified the predominant hematite surface hydroxo groups (-OH, mu-OH, mu(3)-OH) through which first layer water molecules formed hydrogen bonds, as well as surface iron sites directly coordinating water molecules (i.e., as geminal eta-(OH2)(2) sites). Chemometric analyses of the vibration spectra also revealed a strong correspondence in the response of hematite surface hydroxo groups to DVA-derived water loadings. These findings point to a near-saturation of the hydrogen-bonding environment of surface hydroxo groups at a partial water vapor pressure of similar to 8 Torr (similar to 40% relative humidity). Classical molecular dynamics (MD) resolved the interfacial water structures and hydrogen bonding populations at five representative crystallographic faces expressed in these nanoparticles. Simulations of single oriented slabs underscored the individual roles of all (hydro)oxo groups in donating and accepting hydrogen bonds with first layer water in the adsorption regime. These analyses pointed to the preponderance of hydrogen bond-donating -OH groups in the stabilization of thin water films. Contributions of mu-OH and mu(3)-OH groups are secondary, yet remain essential in the stabilization of thin water films. MD simulations also helped resolve crystallographic controls on water water interactions occurring in the condensation regime. Water water hydrogen bond populations are greatest on the (001) face, and decrease in importance in the order (001) > (012) approximate to (110) > (014) >> (100). Simulations of a single (similar to 5 nm x similar to 6 nm x similar to 6 nm) nanometric hematite particle terminated by the (001), (110), (012), and (100) faces also highlighted the key roles that sites at particle edges play in interconnecting thin water films grown along contiguous crystallographic faces. Hydroxo water hydrogen bond populations showed that edges were the preferential loci of binding. These simulations also suggested that equilibration times for water binding at edges were slower than on crystallographic faces. In this regard, edges, and by extension roughened surfaces, are expected to play commanding roles in the stabilization of thin water films. Thus, in focusing on the properties of nanometric-thick water layers at hematite surfaces, this study revealed the nature of interactions between water and multifaced particle surfaces. Our results pave the way for furthering our understanding of mineral-thin water film interfacial structure and reactivity on a broader range of materials.

  • 7. Disch, S.
    et al.
    Hermann, R. P.
    Wetterskog, Erik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Podlesnyak, A. A.
    An, K.
    Hyeon, T.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brueckel, Th.
    Spin excitations in cubic maghemite nanoparticles studied by time-of-flight neutron spectroscopy2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 6, p. 064402-Article in journal (Refereed)
    Abstract [en]

    We have determined the field dependence of collective magnetic excitations in iron oxide nanoparticles of cubic shape with 8.42(2) nm edge length and a narrow log normal size distribution of 8.2(2)% using time-of-flight neutron spectroscopy. The energy dependence of the uniform precession modes was investigated up to 5 T applied field and yields a Lande factor g = 2.05(2) as expected for maghemite (gamma-Fe2O3) nanoparticles. A large effective anisotropy field of B-A,B-eff = 0.45(16) T was determined, in excellent agreement with macroscopic measurements. This anisotropy is attributed to enhanced shape anisotropy in these monodisperse cubic nanoparticles. The combination of our results with macroscopic magnetization information provides a consistent view of the energy scales of superparamagnetic relaxation and collective magnetic excitations in magnetic nanoparticles.

  • 8. Disch, Sabrina
    et al.
    Wetterskog, Erik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hermann, Raphael P.
    Korolkov, Denis
    Busch, Peter
    Boesecke, Peter
    Lyon, Olivier
    Vainio, Ulla
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brueckel, Thomas
    Structural diversity in iron oxide nanoparticle assemblies as directed by particle morphology and orientation2013In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 5, no 9, p. 3969-3975Article in journal (Refereed)
    Abstract [en]

    The mesostructure of ordered arrays of anisotropic nanoparticles is controlled by a combination of packing constraints and interparticle interactions, two factors that are strongly dependent on the particle morphology. We have investigated how the degree of truncation of iron oxide nanocubes controls the mesostructure and particle orientation in drop cast mesocrystal arrays. The combination of grazing incidence small-angle X-ray scattering and scanning electron microscopy shows that mesocrystals of highly truncated cubic nanoparticles assemble in an fcc-type mesostructure, similar to arrays formed by iron oxide nanospheres, but with a significantly reduced packing density and displaying two different growth orientations. Strong satellite reflections in the GISAXS pattern indicate a commensurate mesoscopic superstructure that is related to stacking faults in mesocrystals of the anisotropic nanocubes. Our results show how subtle variation in shape anisotropy can induce oriented arrangements of nanoparticles of different structures and also create mesoscopic superstructures of larger periodicity.

  • 9. Disch, Sabrina
    et al.
    Wetterskog, Erik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hermann, Raphaël
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Busch, Peter
    Brückel, Thomas
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kamali, Saeed
    Shape Induced Symmetry in Self-Assembled Mesocrystals of Iron Oxide Nanocubes2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 4, p. 1651-1656Article in journal (Refereed)
    Abstract [en]

    Grazing incidence small-angle scattering and electron microscopy have been used to show for the first time that nonspherical nanoparticles can assemble into highly ordered body-centered tetragonal mesocrystals. Energy models accounting for the directionality and magnitude of the van der Waals and dipolar interactions as a function of the degree of truncation of the nanocubes illustrated the importance of the directional dipolar forces for the formation of the initial nanocube clusters and the dominance of the van der Waals multibody interactions in the dense packed arrays.

  • 10. Dish, Sabina
    et al.
    Wetterskog, Erik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hermann, Raphäel P.
    Wiedenmann, A.
    Vainio, U.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brückel, Thomas
    Quantitative spatial magnetization distribution in iron oxide nanocubes and nanospheres by polarized small-angle neutron scattering2012In: New Journal of Physics, E-ISSN 1367-2630, Vol. 14, p. 013025-Article in journal (Refereed)
    Abstract [en]

    By means of polarized small-angle neutron scattering, we have resolved the long-standing challenge of determining the magnetization distribution in magnetic nanoparticles in absolute units. The reduced magnetization, localized in non-interacting nanoparticles, indicates strongly particle shape-dependent surface spin canting with a 0.3(1) and 0.5(1) nm thick surface shell of reduced magnetization found for similar to 9 nm nanospheres and similar to 8.5 nm nanocubes, respectively. Further, the reduced macroscopic magnetization in nanoparticles results not only from surface spin canting, but also from drastically reduced magnetization inside the uniformly magnetized core as compared to the bulk material. Our microscopic results explain the low macroscopic magnetization commonly found in nanoparticles.

  • 11. Estrader, M.
    et al.
    Lopez-Ortega, A.
    Estrade, S.
    Golosovsky, I. V.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vasilakaki, M.
    Trohidou, K. N.
    Varela, M.
    Stanley, D. C.
    Sinko, M.
    Pechan, M. J.
    Keavney, D. J.
    Peiro, F.
    Surinach, S.
    Baro, M. D.
    Nogués, J.
    Robust antiferromagnetic coupling in hard-soft bi-magnetic core/shell nanoparticles2013In: Nature Communications, E-ISSN 2041-1723, Vol. 4, article id 2960Article in journal (Refereed)
    Abstract [en]

    The growing miniaturization demand of magnetic devices is fuelling the recent interest in bi-magnetic nanoparticles as ultimate small components. One of the main goals has been to reproduce practical magnetic properties observed so far in layered systems. In this context, although useful effects such as exchange bias or spring magnets have been demonstrated in core/shell nanoparticles, other interesting key properties for devices remain elusive. Here we show a robust antiferromagnetic (AFM) coupling in core/shell nanoparticles which, in turn, leads to the foremost elucidation of positive exchange bias in bi-magnetic hard-soft systems and the remarkable regulation of the resonance field and amplitude. The AFM coupling in iron oxide-manganese oxide based, soft/hard and hard/soft, core/shell nanoparticles is demonstrated by magnetometry, ferromagnetic resonance and X-ray magnetic circular dichroism. Monte Carlo simulations prove the consistency of the AFM coupling. This unique coupling could give rise to more advanced applications of bi-magnetic core/shell nanoparticles.

  • 12.
    Estrader, Marta
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). University of Barcelona, Spain.
    Lopez-Ortega, Alberto
    Golosovsky, Igor V.
    Estrade, Sonia
    Roca, Alejandro G.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lopez-Conesa, Lluis
    Tobia, Dina
    Winkler, Elin
    Ardisson, Jose D.
    Macedo, Waldemar A. A.
    Morphis, Andreas
    Vasilakaki, Marianna
    Trohidou, Kalliopi N.
    Gukasov, Arsen
    Mirebeau, Isabelle
    Makarova, O. L.
    Zysler, Roberto D.
    Peiro, Francesca
    Baro, Maria Dolors
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nogues, Josep
    Origin of the large dispersion of magnetic properties in nanostructured oxides: FexO/Fe3O4 nanoparticles as a case study2015In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 7, p. 3002-3015Article in journal (Refereed)
    Abstract [en]

    The intimate relationship between stoichiometry and physicochemical properties in transition-metal oxides makes them appealing as tunable materials. These features become exacerbated when dealing with nanostructures. However, due to the complexity of nanoscale materials, establishing a distinct relationship between structure-morphology and functionalities is often complicated. In this regard, in the FexO/Fe3O4 system a largely unexplained broad dispersion of magnetic properties has been observed. Here we show, thanks to a comprehensive multi-technique approach, a clear correlation between the magneto-structural properties in large (45 nm) and small (9 nm) FexO/Fe3O4 core/shell nanoparticles that can explain the spread of magnetic behaviors. The results reveal that while the FexO core in the large nanoparticles is antiferromagnetic and has bulk-like stoichiometry and unit-cell parameters, the FexO core in the small particles is highly non-stoichiometric and strained, displaying no significant antiferromagnetism. These results highlight the importance of ample characterization to fully understand the properties of nanostructured metal oxides.

  • 13. Estradé, S.
    et al.
    Yedra, Ll.
    López-Ortega, A.
    Estrader, M.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Baró, M. D.
    Nogués, J.
    Peiró, F.
    Distinguishing the core from the shell in MnOx/MnOy and FeOx/MnOx core/shell nanoparticles through quantitative electron energy loss spectroscopy (EELS) analysis2012In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, Vol. 43, no 1, p. 30-36Article, review/survey (Refereed)
    Abstract [en]

    The structural and chemical characterization of inverted bi-magnetic MnOx(antiferromagnetic)/MnOy(ferrimagnetic) and FeOx(soft-ferrimagnetic)/MnOx(hard-ferrimagnetic) core/shell nanoparticles has been carried out by means of scanning transmission electron microscopy with electron energy loss spectroscopy analysis, (S)TEM-EELS. Quantitative EELS was applied to assess the local composition of the nanoparticles by evaluating the local Mn oxidation state based on the Mn L-3/L-2 peak intensity ratio and the Mn L-3 peak onset. The analysis allows to unambiguously distinguish the core from the shell and to determine the nature of the involved manganese oxides in both cases. The results evidence that the structure of the nanoparticles is, in fact, more complex than the one designed by the synthesis parameters. 

  • 14. Farhadi-Khouzani, Masoud
    et al.
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Durak, Grażyna M.
    Fornell, Jordina
    Sort, Jordi
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Gebauer, Denis
    A CaCO3/nanocellulose-based bioinspired nacre-like material2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 31, p. 16128-16133Article in journal (Refereed)
    Abstract [en]

    Nacre continues to be an inspiration for the fabrication of strong and tough materials from renewable and earth-abundant raw materials. Herein, we showed how a nacre-like hybrid material based on nanocellulose (NC) and CaCO3 can be prepared via the sequential infiltration of polymer-stabilised CaCO3 liquid precursors into layers of predeposited NC films. Layer-by-layer assembly of the NC films followed by controlled spreading and infiltration with liquid CaCO3 precursors generated a lamellar material with an architecture and iridescent appearance similar to those of nacre. The wettability of the NC films towards the liquid CaCO3 precursors was controlled by hydroxyl and carboxyl functionalization of the NC fibrils and the addition of magnesium ions. The combination of a high stiffness and plasticity of the nacre-like NC/CaCO3 hybrid materials show that excellent mechanical properties can be obtained employing a fibrillar organic constituent that is relatively hard. The fabrication of a nacrelike hybrid material via an aqueous route of assembly and infiltration processing demonstrates how a sustainable composite material with outstanding properties can be produced using the most abundant biopolymer and biomineral on earth.

  • 15.
    Faure, Bertrand
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ahniyaz, Anwar
    Villaluenga, Irune
    Berriozabal, Gemma
    De Miguel, Yolanda R.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Dispersion and surface functionalization of oxide nanoparticles for transparent photocatalytic and UV-protecting coatings and sunscreens2013In: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514, Vol. 14, no 2, p. 023001-Article, review/survey (Refereed)
    Abstract [en]

    This review describes recent efforts on the synthesis, dispersion and surface functionalization of the three dominating oxide nanoparticles used for photocatalytic, UV-blocking and sunscreen applications: titania, zinc oxide, and ceria. The gas phase and liquid phase synthesis is described briefly and examples are given of how weakly aggregated photocatalytic or UV-absorbing oxide nanoparticles with different composition, morphology and size can be generated. The principles of deagglomeration are reviewed and the specific challenges for nanoparticles highlighted. The stabilization of oxide nanoparticles in both aqueous and non-aqueous media requires a good understanding of the magnitude of the interparticle forces and the surface chemistry of the materials. Quantitative estimates of the Hamaker constants in various media and measurements of the isoelectric points for the different oxide nanoparticles are presented together with an overview of different additives used to prepare stable dispersions. The structural and chemical requirements and the various routes to produce transparent photocatalytic and nanoparticle-based UV-protecting coatings, and UV-blocking sunscreens are described and discussed.

  • 16.
    Faure, Bertrand
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hamaker Constants of Iron Oxide Nanoparticles2011In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 14, p. 8659-8664Article in journal (Refereed)
    Abstract [en]

    The Hamaker constants for iron oxide nanoparticles in various media have been calculated using Lifshitz theory. Expressions for the dielectric responses of three iron oxide phases (magnetite, maghemite, and hematite) were derived from recently published optical data. The nonretarded Hamaker constants for the iron oxide nanopartides interacting across water, A(1w1) = 33 - 39 zJ, correlate relatively well with previous reports, whereas the calculated values in nonpolar solvents (hexane and toluene), A(131) = 9 29 zJ, are much lower than the previous estimates, particularly for magnetite. The magnitude of van der Waals interactions varies significantly between the studied phases (magnetite < maghemite < hematite), which highlights the importance of a thorough characterization of the particles. The contribution of magnetic dispersion interactions for particle sizes in the superparamagnetic regime was found to be negligible. Previous conjectures related to colloidal stability and self-assembly have been revisited on the basis of the new Lifshitz values of the Hamaker constants.

  • 17.
    Faure, Bertrand
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wetterskog, Erik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gunnarsson, Klas
    Josten, Elisabeth
    Hermann, Raphael P.
    Brueckel, Thomas
    Andreasen, Jens Wenzel
    Meneau, Florian
    Meyer, Mathias
    Lyubartsev, Alexander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svedlindh, Peter
    2D to 3D crossover of the magnetic properties in ordered arrays of iron oxide nanocrystals2013In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 5, no 3, p. 953-960Article in journal (Refereed)
    Abstract [en]

    The magnetic 2D to 3D crossover behavior of well-ordered arrays of monodomain gamma-Fe2O3 spherical nanoparticles with different thicknesses has been investigated by magnetometry and Monte Carlo (MC) simulations. Using the structural information of the arrays obtained from grazing incidence small-angle X-ray scattering and scanning electron microscopy together with the experimentally determined values for the saturation magnetization and magnetic anisotropy of the nanoparticles, we show that MC simulations can reproduce the thickness-dependent magnetic behavior. The magnetic dipolar particle interactions induce a ferromagnetic coupling that increases in strength with decreasing thickness of the array. The 2D to 3D transition in the magnetic properties is mainly driven by a change in the orientation of the magnetic vortex states with increasing thickness, becoming more isotropic as the thickness of the array increases. Magnetic anisotropy prevents long-range ferromagnetic order from being established at low temperature and the nanoparticle magnetic moments instead freeze along directions defined by the distribution of easy magnetization directions.

  • 18. Golosovsky, IV
    et al.
    Salazar-Alvarez, G
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Lopez-Ortega, A
    Gonzalez, MA
    Sort, J
    Estrader, M
    Surinach, S
    Baro, MD
    Nogues, J
    Magnetic Proximity Effect Features in Antiferromagnetic/FerrimagneticCore-Shell Nanoparticles2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 24, p. 247201-Article in journal (Refereed)
  • 19.
    Guccini, Valentina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Carlson, Annika
    Yu, Shun
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lindbergh, Göran
    Wreland Lindström, Rakel
    Salazar-­‐Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Highly proton conductive membranes based on carboxylated cellulose nanofibres and their performance in proton exchange membrane fuel cellsManuscript (preprint) (Other academic)
  • 20.
    Guccini, Valentina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center (WWSC), Sweden.
    Carlson, Annika
    Yu, Shun
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center (WWSC), Sweden.
    Lindbergh, Göran
    Wreland Lindström, Rakel
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center (WWSC), Sweden.
    Highly proton conductive membranes based on carboxylated cellulose nanofibres and their performance in proton exchange membrane fuel cells2019In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 43, p. 25032-25039Article in journal (Refereed)
    Abstract [en]

    The performance of thin carboxylated cellulose nanofiber-based (CNF) membranes as proton exchange membranes in fuel cells has been measured in situ as a function of CNF surface charge density (600 and 1550 mu mol g(-1)), counterion (H+ or Na+), membrane thickness and fuel cell relative humidity (RH 55 to 95%). The structural evolution of the membranes as a function of RH, as measured by Small Angle X-ray Scattering, shows that water channels are formed only above 75% RH. The amount of absorbed water was shown to depend on the membrane surface charge and counter ions (H+ or Na+). The high affinity of CNF for water and the high aspect ratio of the nanofibers, together with a well-defined and homogenous membrane structure, ensures a proton conductivity exceeding 1 mS cm(-1) at 30 degrees C between 65 and 95% RH. This is two orders of magnitude larger than previously reported values for cellulose materials and only one order of magnitude lower than Nafion 212. Moreover, the CNF membranes are characterized by a lower hydrogen crossover than Nafion, despite being approximate to 30% thinner. Thanks to their environmental compatibility and promising fuel cell performance the CNF membranes should be considered for new generation proton exchange membrane fuel cells.

  • 21.
    Guccini, Valentina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kumar, Sugam
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Trushkina, Yulia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nagy, Gergely
    Schütz, Christina
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tuning the magnetic alignment of cellulose nanocrystals from perpendicular to parallel using lepidocrocite nanoparticlesManuscript (preprint) (Other academic)
  • 22.
    Guccini, Valentina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Yu, Shun
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Agthe, Michael
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Trushkina, Yulia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fall, Andreas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Inducing nematic ordering of cellulose nanofibers using osmotic dehydration2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 48, p. 23157-23163Article in journal (Refereed)
    Abstract [en]

    The formation of nematically-ordered cellulose nanofiber (CNF) suspensions with an order parameter f(max) approximate to 0.8 is studied by polarized optical microscopy, small-angle X-ray scattering (SAXS), and rheological measurements as a function of CNF concentration. The wide range of CNF concentrations, from 0.5 wt% to 4.9 wt%, is obtained using osmotic dehydration. The rheological measurements show a strong entangled network over all the concentration range whereas SAXS measurements indicate that at concentrations >1.05 wt% the CNF suspension crosses an isotropic-anisotropic transition that is accompanied by a dramatic increase of the optical birefringence. The resulting nanostructures are modelled as mass fractal structures that converge into co-existing nematically-ordered regions and network-like regions where the correlation distances decrease with concentration. The use of rapid, upscalable osmotic dehydration is an effective method to increase the concentration of CNF suspensions while partly circumventing the gel/glass formation. The facile formation of highly ordered fibers can result in materials with interesting macroscopic properties.

  • 23.
    Guccini, Valentina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Aalto University, Finland.
    Yu, Shun
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). RISE Research Institute of Sweden, Sweden.
    Meng, Zhoujun
    Kontturi, Eero
    Demmel, Franz
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden.
    The Impact of Surface Charges of Carboxylated Cellulose Nanofibrils on the Water Motions in Hydrated Films2022In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 23, no 8, p. 3104-3115Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibrils (CNFs) with carboxylated surface ligands are a class of materials with tunable surface functionality, good mechanical properties, and bio-/environmental friendliness. They have been used in many applications as scaffold, reinforcing, or functional materials, where the interaction between adsorbed moisture and the CNF could lead to different properties and structures and become critical to the performance of the materials. In this work, we exploited multiple experimental methods to study the water movement in hydrated films made of carboxylated CNFs prepared by TEMPO oxidation with two different surface charges of 600 and 1550 μmol·g–1. A combination of quartz crystal microbalance with dissipation (QCM-D) and small-angle X-ray scattering (SAXS) shows that both the surface charge of a single fibril and the films’ network structure contribute to the moisture uptake. The films with 1550 μmol·g–1 surface charges take up twice the amount of moisture per unit mass, leading to the formation of nanostructures with an average radius of gyration of 2.1 nm. Via the nondestructive quasi-elastic neutron scattering (QENS), a faster motion is explained as a localized movement of water molecules inside confined spheres, and a slow diffusive motion is found with the diffusion coefficient close to bulk water at room temperature via a random jump diffusion model and regardless of the surface charge in films made from CNFs. 

  • 24.
    Hao, Wenming
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Björnerbäck, Fredrik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Trushkina, Yulia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bengoechea, Mikel Oregui
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Barth, Tanja
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    High-Performance Magnetic Activated Carbon from Solid Waste from Lignin Conversion Processes. 1. Their Use As Adsorbents for CO22017In: ACS Sustainable Chemistry and Engineering, E-ISSN 2168-0485, Vol. 5, no 4, p. 3087-3095Article in journal (Refereed)
    Abstract [en]

    Lignin is naturally abundant and a renewable [GRAPHICS] precursor with the potential to be used in the production of both chemicals and materials. As many lignin conversion processes suffer from a significant production of solid wastes in the form of hydrochars, this study focused on transforming hydrochars into magnetic activated carbons (MAC). The hydrochars were produced via hydrothermal treatment of lignins together with formic acid. The activation of the hydrochars was performed chemically with KOH with a focus on the optimization of the MACs as adsorbents for CO2. MACs are potentially relevant to carbon capture and storage (CCS) and gas purification processes. In general, the MACs had high specific surface areas (up to 2875 m(2)/g), high specific pore volumes, and CO2 adsorption capacities of up to 6.0 mmol/g (I atm, 0 degrees C). The textual properties of the MACs depended on the temperature of the activation. MACs activated at a temperature of 700 degrees C had very high ultramicropore volumes, which are relevant for potential adsorption-driven separation of CO2 from N-2. Activation at 800 degrees C led to MACs with larger pores and very high specific surface areas. This temperature-dependent optimization option, combined with the magnetic properties, provided numerous potential applications of the MACs besides those of CCS. The hydrochar was derived from eucalyptus lignin, and the corresponding MACs displayed soft magnetic behavior with coercivities of <100 Oe and saturation magnetization values of 1-10 emu/g.

  • 25. Ishikawa, Mai
    et al.
    Oaki, Yuya
    Tanaka, Yoshihisa
    Kakisawa, Hideki
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Imai, Hiroaki
    Fabrication of nanocellulose-hydroxyapatite composites and their application as water-resistant transparent coatings2015In: Journal of materials chemistry. B, ISSN 2050-750X, E-ISSN 2050-7518, Vol. 3, no 28, p. 5858-5863Article in journal (Refereed)
    Abstract [en]

    Nanosized composite rods similar to 300 nm in length and similar to 20 nm in width were produced by deposition of 22-77 wt% of a c-axis-oriented hydroxyapatite (HA) on cellulose nanocrystals (CNCs). The CNCs functionalized with sulphonic groups were covered with the HA nanocrystals through controlled nucleation and growth under a moderately supersaturated condition in a solution system based on a simulated body fluid. Water-resistant transparent coatings 2-4 mm thick were obtained via evaporation-induced assembly of CNC-HA nanocomposites by casting their suspension on a glass substrate and the subsequent growth of HA nanocrystals by vapour hydrothermal treatment. The composite coatings exhibited improved mechanical strength compared to that of crustacean exoskeletons, and potential for bone regeneration.

  • 26. Josten, Elisabeth
    et al.
    Wetterskog, Erik
    Glavic, Artur
    Boesecke, Peter
    Feoktystov, Artem
    Brauweiler-Reuters, Elke
    Rücker, Ulrich
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brückel, Thomas
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Superlattice growth and rearrangement during evaporation-induced nanoparticle self-assembly2017In: Scientific Reports, E-ISSN 2045-2322, Vol. 7, article id 2802Article in journal (Refereed)
    Abstract [en]

    Understanding the assembly of nanoparticles into superlattices with well-defined morphology and structure is technologically important but challenging as it requires novel combinations of in-situ methods with suitable spatial and temporal resolution. In this study, we have followed evaporation-induced assembly during drop casting of superparamagnetic, oleate-capped gamma-Fe2O3 nanospheres dispersed in toluene in real time with Grazing Incidence Small Angle X-ray Scattering (GISAXS) in combination with droplet height measurements and direct observation of the dispersion. The scattering data was evaluated with a novel method that yielded time-dependent information of the relative ratio of ordered (coherent) and disordered particles (incoherent scattering intensities), superlattice tilt angles, lattice constants, and lattice constant distributions. We find that the onset of superlattice growth in the drying drop is associated with the movement of a drying front across the surface of the droplet. We couple the rapid formation of large, highly ordered superlattices to the capillary-induced fluid flow. Further evaporation of interstitital solvent results in a slow contraction of the superlattice. The distribution of lattice parameters and tilt angles was significantly larger for superlattices prepared by fast evaporation compared to slow evaporation of the solvent.

  • 27. Kim, Hyeyun
    et al.
    Endrődi, Balázs
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cornell, Ann
    One-Step Electro-Precipitation of Nanocellulose Hydrogels on Conducting Substrates and Its Possible Applications: Coatings, Composites, and Energy Devices2019In: ACS Sustainable Chemistry and Engineering, E-ISSN 2168-0485, Vol. 7, no 24, p. 19415-19425Article in journal (Refereed)
    Abstract [en]

    TEMPO-oxidized cellulose nanofibrils (TOCN) are pH-responsive biopolymers which undergo sol-gel transition at acidic conditions (pH < 4) due to charge neutralization. Electronically conducting materials can be coated by such gels during aqueous electrolysis, when an electrochemical reaction generates a local pH decrease at the electrode surface. In this work, electro-precipitation of different TOCN gels has been performed on oxygen evolving anodes. We demonstrate that TOCN hydrogels can be electrochemically coated on the surface of any conductive material with even complex 3D shape. Further, not only TOCN but also micro- or nanosized particles containing TOCN composites can be coated on the electrode surface, and coatings containing multiple layers of different composites can be also produced. We demonstrate that this simple and facile electrocoating technique can be subject to various applications, such as coatings making electrodes selective for the hydrogen evolution reaction, as well as a new eco-friendly aqueous-based synthesis of Li-ion battery electrodes.

  • 28. Kim, Hyeyun
    et al.
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH Royal Institute of Technology, Sweden.
    Lu, Huiran
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH Royal Institute of Technology, Sweden.
    Lindbergh, Göran
    Cornell, Ann
    Lithium Ion Battery Separators Based On Carboxylated Cellulose Nanofibers From Wood2019In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 2, no 2, p. 1241-1250Article in journal (Refereed)
    Abstract [en]

    Carboxylated cellulose nanofibers, prepared by TEMPO-mediated oxidation (TOCN), were processed into asymmetric mesoporous membranes using a facile paper-making approach and investigated as lithium ion battery separators. Membranes made of TOCN with sodium carboxylate groups (TOCN-COO-Na+) showed capacity fading after a few cycles of charging and discharging. On the other hand, its protonated counterpart (TOCN-COOH) showed highly improved electrochemical and cycling stability, displaying 94.5% of discharge capacity maintained after 100 cycles at 1 C rate of charging and discharging. The asymmetric surface porosity of the membranes must be considered when assembling a battery cell as it influences the rate capabilities of the battery. The wood-based TOCN-membranes have a good potential as an ecofriendly alternative to conventional fossil fuel-derived separators without adverse side effects.

  • 29. Kim, Jong Min
    et al.
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kim, Dongwon
    Oh, Jiseop
    Park, Seungman
    Jeon, Youngmoo
    Hwang, Taejin
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Piao, Yuanzhe
    A novel textile-like carbon wrapping for highperformance silicon anodes in lithium-ion batteries2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 26, p. 12475-12483Article in journal (Refereed)
    Abstract [en]

    Carbon coating is essential for active materials in electrochemical applications that are often insulators or poor conductors. A conventional conformal carbon coating can hinder the ion diffusion to and from the active material and form an isolated conducting network. Especially, active materials with very large volume expansion, e.g., silicon, can destroy the carbon coating during lithiation, which makes conformal carbon coating inappropriate. This paper presents a novel textile-like carbon wrapping that provides efficient electron and ion diffusion paths via a wide-range carbon network and pores. The textile-like carbon wrapping can reduce the electrical contact loss during cycling through the wide-range carbon network, which makes it a suitable carbon coating for materials that undergo volume expansion. A textile-like carbon-wrapped silicon is formed by pyrolysis of a dried suspension of silicon nanoparticles mixed with enzymatically hydrolyzed cellulose nanofibers. It shows excellent electrochemical performance compared to a conformal carbon-coated silicon. It exhibits a reversible specific capacity of 680mA h g(-1) at 8.0 A g(-1) and shows excellent cycling stability (capacity retention of 94.5% after 500 cycles at 2.0 A g(-1)) with high Si content (95.71 wt%). Therefore, this novel textile-like carbon wrapping can be utilized in many electrochemical applications instead of the conventional carbon coating, especially for active materials that undergo large volume expansion.

  • 30. Kim, Jong Min
    et al.
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Seong, Kwang-dong
    Oh, Jiseop
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Piao, Yuanzhe
    Extensively interconnected silicon nanoparticles via carbon network derived from ultrathin cellulose nanofibers as high performance lithium ion battery anodes2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 118, p. 8-17Article in journal (Refereed)
    Abstract [en]

    Silicon is a good alternative to conventional graphite anode but it has bad cycling and rate performance. To overcome these severe problems, extensively interconnected silicon nanoparticles using carbon network derived from ultrathin cellulose nanofibers were synthesized. Ultrathin cellulose nanofibers, an abundant and sustainable material, entangle each silicon nanoparticle and become extensively interconnected carbon network after pyrolysis. This wide range interconnection provides an efficient electron path by decreasing the likelihood that electrons experience contact resistivity and also suppresses the volume expansion of silicon during lithiation. In addition, Ultrathin cellulose nanofibers are carboxylated and therefore adhesive to silicon nanoparticles through hydrogen bonding. This property makes ultrathin cellulose the perfect carbon source when making silicon composites. As a consequence, it exhibits 808 mAh g(-1) of the reversible capacity after 500 cycles at high current density of 2 A g(-1) with a coulombic efficiency of 99.8%. Even at high current density of 8 A g(-1), it shows a high reversible discharge capacity of 464 mAh g(-1). Moreover, extensively interconnected carbon network prevents the formation of a brittle electrode with a water-based binder. Therefore, this remarkable material has a huge potential for LIBs applications.

  • 31. Kozin, Philipp A.
    et al.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Boily, Jean-Francois
    Oriented Aggregation of Lepidocrocite and Impact on Surface Charge Development2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 30, p. 9017-9021Article in journal (Refereed)
    Abstract [en]

    The impact of lepidocrocite (gamma-FeOOH) nanoparticle aggregation on mineral surface charge development was resolved in aqueous solutions of NaCl and NaClO4. Synthetic rod-like particles exhibiting charged edge (100) and neutrally/low-charged (010) faces self-aggregated in salt-free solutions. Aggregation was notably imaged by high-resolution transmission electron microscopy, and inferred by decreases in N-2(g)-B.E.T. specific surface area from 94 m(2)/g to 77 m(2)/g after 12 months, and to 66 m(2)/g after 33 months storage. Potential determining (H+, OH-) ions loadings in the 4-11 pH range were unchanged only if the particles remained aggregated in NaCI but only if they were disaggregated in NaClO4. These differences, alongside molecular simulations and experimental ion loadings resolved in other studies from our group, point to important controls on background electrolyte ion identity on the aggregation and charge development in lepidocrocite. These results may apply further to other mineral surfaces of comparable surface (hydr)oxo populations.

  • 32. Krycka, K. L.
    et al.
    Borchers, J. A.
    Laver, M.
    Salazar Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Lopez-Ortega, A.
    Estrader, M.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Surinach, S.
    Baro, M. D.
    Sort, J.
    Nogues, J.
    Correlating material-specific layers and magnetic distributions within onion-like Fe3O4/MnO/gamma-Mn2O3 core/shell nanoparticles2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 17, p. 17B531-Article in journal (Refereed)
    Abstract [en]

    The magnetic responses of two nanoparticle systems comprised of Fe3O4/gamma-Mn2O3 (soft ferrimagnetic, FM/hard FM) and Fe3O4/MnO/gamma-Mn2O3 (soft FM/antiferromagnetic, AFM/hard FM) are compared, where the MnO serves to physically decouple the FM layers. Variation in the temperature and applied field allows for Small Angle Neutron Scattering (SANS) measurements of the magnetic moments both parallel and perpendicular to an applied field. Data for the bilayer particle indicate that the graded ferrimagnetic layers are coupled and respond to the field as a single unit. For the trilayer nanoparticles, magnetometry suggests a Curie temperature (T-C) approximate to 40 K for the outer gamma-Mn2O3 component, yet SANS reveals an increase in the magnetization associated with outer layer that is perpendicular to the applied field above T-C during magnetic reversal. This result suggests that the gamma-Mn2O3 magnetically reorients relative to the applied field as the temperature is increased above 40 K.

  • 33. Krycka, Kathryn L.
    et al.
    Borchers, Julie A.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lopez-Ortega, Alberto
    Estrader, Marta
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Estrade, Sonia
    Winkler, Elin
    Daniel Zysler, Roberto
    Sort, Jordi
    Peiro, Francesca
    Dolors Baro, Maria
    Kao, Chi-Chang
    Nogues, Josep
    Resolving Material-Specific Structures within Fe3O4 vertical bar gamma-Mn2O3 Core vertical bar Shell Nanoparticles Using Anomalous Small-Angle X-ray Scattering2013In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 7, no 2, p. 921-931Article in journal (Refereed)
    Abstract [en]

    Here it is demonstrated that multiple-energy, anomalous small-angle X-ray scattering (ASAXS) provides significant enhancement in sensitivity to internal material boundaries of layered nanoparticles compared with the traditional modeling of a single scattering energy, even for cases in which high scattering contrast naturally exists. Specifically, the material-specific structure of monodispersed Fe3O4 vertical bar gamma-Mn2O3 core vertical bar shell nanoparticles is determined, and the contribution of each component to the total scattering profile is identified with unprecedented clarity. We show that Fe3O4 vertical bar gamma-Mn2O3 core vertical bar shell nanoparticles with a diameter of 8.2 +/- 0.2 nm consist of a core with a composition near Fe3O4 surrounded by a (MnxFe1-x)(3)O-4 shell with a graded composition, ranging from x approximate to 0.40 at the Inner shell toward x approximate to 0.46 at the surface. Evaluation of the scattering contribution arising from the interference between material-specific layers additionally reveals the presence of Fe3O4 cores without a coating shell. Finally, it is found that the material-specific scattering profile shapes and chemical compositions extracted by this method are independent of the original input chemical compositions used in the analysis, revealing multiple-energy ASAXS as a powerful tool for determining internal nanostructured morphology even if the exact composition of the individual layers is not known a priori.

  • 34.
    Limaye, Mukta
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden; Indian Institute of Science Education & Research, India.
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Kriechbaum, Konstantin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wohlert, Jakob
    Bacsik, Zoltán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wohlert, Malin
    Xia, Wei
    Pléa, Mama
    Dembele, Cheick
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Functionalization and patterning of nanocellulose films by surface-bound nanoparticles of hydrolyzable tannins and multivalent metal ions2019In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 41, p. 19278-19284Article in journal (Refereed)
    Abstract [en]

    Inspired by the Bogolanfini dyeing technique, we report how flexible nanofibrillated cellulose (CNF) films can be functionalized and patterned by surface-bound nanoparticles of hydrolyzable tannins and multivalent metal ions with tunable colors. Molecular dynamics simulations show that gallic acid (GA) and ellagic acid (EA) rapidly adsorb and assemble on the CNF surface, and atomic force microscopy confirms that nanosized GA assemblies cover the surface of the CNF. CNF films were patterned with tannin-metal ion nanoparticles by an in-fibre reaction between the pre-impregnated tannin and the metal ions in the printing ink. Spectroscopic studies show that the Fe-III/II ions interact with GA and form surface-bound, stable GA-Fe-III/II nanoparticles. The functionalization and patterning of CNF films with metal ion-hydrolyzable tannin nanoparticles is a versatile route to functionalize films based on renewable materials and of interest for biomedical and environmental applications.

  • 35.
    Limaye, Mukta V.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Dembele, Aissata
    Plea, Mama
    Andersson, Linnea
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    On the role of tannins and iron in the Bogolan or mud cloth dyeing process2012In: Textile research journal, ISSN 0040-5175, E-ISSN 1746-7748, Vol. 82, no 18, p. 1888-1896Article in journal (Refereed)
    Abstract [en]

    We have investigated the chemistry of the Bogolan or mud cloth dyeing process, a traditional technique of coloring cotton cloths deeply rooted in Mali. Textiles produced by the traditional Bogolan process, using tannin-rich plant extract and iron-rich clay-based mud, were compared using infrared (IR) spectroscopy, scanning electron microscopy (SEM) and X-ray absorption near-edge spectroscopy (XANES) with cotton fibers that were impregnated with tannin and iron salt solutions. IR spectroscopy in both reflective mode on the cloth and cotton and in transmission mode on single fibers, together with SEM, showed that gallic and tannic acid adsorb and precipitate onto the cotton fiber surface. IR spectroscopy and comparison with tannin and iron solution-impregnated cotton showed that the black color of the traditional Bogolan cloth is dominated by the formation of iron-tannin complexes. The presence of iron in the Bogolan cloth was confirmed using XANES data, supporting the notion that iron has been transferred from the iron-rich clay-based mud to the cloth. The chemistry of Bogolan cloth is not only historically and culturally significant and of importance in textile conservation, but may also inspire future research on sustainable dyeing and processing techniques based on natural products.

  • 36. Limaye, Mukta V.
    et al.
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wohlert, Jakob
    Bacsik, Zoltán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wohlert, Malin
    Xia, Wei
    Eisenhofer, Stefan
    Pléa, Mama
    Dembelé, Cheik
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bogolanfini dyeing – a traditional nanotechnology from West AfricaManuscript (preprint) (Other academic)
  • 37.
    Liu, Yingxin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH, Sweden.
    Agthe, Michael
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salajková, Michaela
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH, Sweden.
    Fall, Andreas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH, Sweden.
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Assembly of cellulose nanocrystals in a levitating drop probed by time-resolved small angle X-ray scattering2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 38, p. 18113-18118Article in journal (Refereed)
    Abstract [en]

    Assembly of bio-based nano-sized particles into complex architectures and morphologies is an area of fundamental interest and technical importance. We have investigated the assembly of sulfonated cellulose nanocrystals (CNC) dispersed in a shrinking levitating aqueous drop using time-resolved small angle X-ray scattering (SAXS). Analysis of the scaling of the particle separation distance (d) with particle concentration (c) was used to follow the transition of CNC dispersions from an isotropic state at 1-2 vol% to a compressed nematic state at particle concentrations above 30 vol%. Comparison with SAXS measurements on CNC dispersions at near equilibrium conditions shows that evaporation-induced assembly of CNC in large levitating drops is comparable to bulk systems. Colloidal states with d vs. c scalings intermediate between isotropic dispersions and unidirectional compression of the nematic structure could be related to the biphasic region and gelation of CNC. Nanoscale structural information of CNC assembly up to very high particle concentrations can help to fabricate nanocellulose-based materials by evaporative methods.

  • 38.
    Liu, Yingxin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, KTH, Sweden.
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, KTH, Sweden.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, KTH, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Assembly, Gelation, and Helicoidal Consolidation of Nanocellulose Dispersions2019In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, no 10, p. 3600-3606Article in journal (Refereed)
    Abstract [en]

    The ability to probe the assembly, gelation, and helicoidal consolidation of cellulose nanocrystal (CNC) dispersions at high concentrations can provide unique insight into the assembly and can assist optimized manufacturing of CNC-based photonic and structural materials. In this Feature Article, we review and discuss the concentration dependence of the structural features, characterized by the particle separation distance and the helical pitch, at CNC concentrations (c) that range from the isotropic state, over the biphasic range, to the fully liquid crystalline state. The structure evolution of CNC dispersions probed by time resolved small-angle X-ray scattering during evaporation-induced assembly highlighted the importance of gelation and consolidation at high concentrations. We briefly discuss how the homogeneity of helicoidal nanostructures in dry CNC films can be improved and present an outlook for future work.

  • 39. Lopez-Ortega, Alberto
    et al.
    Estrader, Marta
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Roca, Alejando G.
    Nogues, Josep
    Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles2015In: Physics reports, ISSN 0370-1573, E-ISSN 1873-6270, Vol. 553, p. 1-32Article, review/survey (Refereed)
    Abstract [en]

    The applications of exchange coupled bi-magnetic hard/soft and soft/hard ferromagnetic core/shell nanoparticles are reviewed. After a brief description of the main synthesis approaches and the core/shell structural morphological characterization, the basic static and dynamic magnetic properties are presented. Five different types of prospective applications, based on diverse patents and research articles, are described: permanent magnets, recording media, microwave absorption, biomedical applications and other applications. Both the advantages of the core/shell morphology and some of the remaining challenges are discussed.

  • 40.
    Lopez-Ortega, Alberto
    et al.
    Campus Universitat Autnoma de Barcelona.
    Tobia, Dina
    CNEA-CONICET.
    Winkler, Elin
    CNEA-CONICET.
    Golosovsky, Igor V.
    S:t Petersburg University.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Estrade, Sonia
    Universitat de Barcelona.
    Estrader, Marta
    Universitat de Barcelona.
    Sort, Jordi
    Universitat Autnoma de Barcelona..
    Gonzalez, Angel
    Institut Laue Langevin.
    Surinach, Santiago
    Universitat Autnoma de Barcelona.
    Arbiol, Jordi
    Universitat Autnoma de Barcelona.
    Peiro, Francesca
    Universitat de Barcelona.
    Zysler, Roberto D.
    CNEA-CONICET.
    Dolors Baro, Maria
    Universitat Autnoma de Barcelona.
    Nogues, Josep
    Universitat Autnoma de Barcelona.
    Size-Dependent Passivation Shell and Magnetic Properties in Antiferromagnetic/Ferrimagnetic Core/Shell MnO Nanoparticles2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 27, p. 9398-9407Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of bimagnetic core/shell nanoparticles consisting of an antiferromagnetic MnO core and a ferrimagnetic passivation shell have been investigated. It is found that the phase of the passivation shell (gamma-Mn2O3 or Mn3O4) depends on the size of the nanoparticles. Structural and magnetic characterizations concur that while the smallest nanoparticles have a predominantly gamma-Mn2O3 shell, larger ones have increasing amounts of Mn3O4. A considerable enhancement of the Neel temperature, T-N, and the magnetic anisotropy of the MnO core for decreasing core sizes has been observed. The size reduction also leads to other phenomena such as persistent magnetic moment in MnO up to high temperatures and an unusual temperature behavior of the magnetic domains.

  • 41. Lu, Huiran
    et al.
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH Royal Institute of Technology, Sweden.
    Kim, Hyeyun
    Salazar-Alyarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH Royal Institute of Technology, Sweden.
    Lindbergh, Göran
    Cornell, Ann
    Effects of Different Manufacturing Processes on TEMPO-Oxidized Carboxylated Cellulose Nanofiber Performance as Binder for Flexible Lithium-Ion Batteries2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 43, p. 37712-37720Article in journal (Refereed)
    Abstract [en]

    Carboxylated cellulose nanofibers (CNF) prepared using the TEMPO-route are good binders of electrode components in flexible lithium-ion batteries (LIB). However, the different parameters employed for the defibrillation of CNF such as charge density and degree of homogenization affect its properties when used as binder. This work presents a systematic study of CNF prepared with different surface charge densities and varying degrees of homogenization and their performance as binder for flexible LiFePO4 electrodes. The results show that the CNF with high charge density had shorter fiber lengths compared with those of CNF with low charge density, as observed with atomic force microscopy. Also, CNF processed with a large number of passes in the homogenizer showed a better fiber dispersibility, as observed from rheological measurements. The electrodes fabricated with highly charged CNF exhibited the best mechanical and electrochemical properties. The CNF at the highest charge density (ISSO mu mol g(-1)) and lowest degree of homogenization (3 + 3 passes in the homogenizer) achieved the overall best performance, including a high Young's modulus of approximately 311 MPa and a good rate capability with a stable specific capacity of 116 mAh g(-1) even up to 1 C. This work allows a better understanding of the influence of the processing parameters of CNF on their performance as binder for flexible electrodes. The results also contribute to the understanding of the optimal processing parameters of CNF to fabricate other materials, e.g., membranes or separators.

  • 42.
    Mayence, Arnaud
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wang, Dong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Oleynikov, Peter
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Probing planar defects in nanoparticle superlattices by 3D small-angle electron diffraction tomography and real space imaging2014In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 6, no 22, p. 13803-13808Article in journal (Refereed)
    Abstract [en]

    We demonstrate how the acquisition and processing of 3D electron diffraction data can be extended to characterize structural features on the mesoscale, and show how lattice distortions in superlattices of self-assembled spherical Pd nanoparticles can be quantified by three-dimensional small-angle electron diffraction tomography (3D SA-EDT). Transmission electron microscopy real space imaging and 3D SA-EDT reveal a high density of stacking faults that was related to a competition between fcc and hcp arrangements during assembly. Information on the orientation of the stacking faults was used to make analogies between planar defects in the superlattices and Shockley partial dislocations in metallic systems.

  • 43.
    Olsson, R T
    et al.
    KTH.
    Azizi Samir, M A S
    Nanocomposites and Bioconcepts s.a.r.l., N170 Tanalt Alhouda (Agadir), .
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Belova, L
    KTH.
    Ström, V
    KTH.
    Berglund, L A
    KTH.
    Ikkala, O
    Helsinki University of Technology/Aalto University School of Science and Technology, Molecular Materials, Department of Applied Physics.
    Nogués, J
    Universitat Autònoma de Barcelona.
    Gedde, U W
    KTH.
    Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates2010In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 5, p. 584-588Article in journal (Refereed)
    Abstract [en]

    Nanostructured biological materials inspire the creation of materials with tunable mechanical properties. Strong cellulose nanofibrils derived from bacteria or wood can form ductile or tough networks that are suitable as functional materials. Here, we show that freeze-dried bacterial cellulose nanofibril aerogels can be used as templates for making lightweight porous magnetic aerogels, which can be compacted into a stiff magnetic nanopaper. The 20-70-nm-thick cellulose nanofibrils act as templates for the non-agglomerated growth of ferromagnetic cobalt ferrite nanoparticles (diameter, 40-120 nm). Unlike solvent-swollen gels and ferrogels, our magnetic aerogel is dry, lightweight, porous (98%), flexible, and can be actuated by a small household magnet. Moreover, it can absorb water and release it upon compression. Owing to their flexibility, high porosity and surface area, these aerogels are expected to be useful in microfluidics devices and as electronic actuators.

  • 44. Park, Ji Hyun
    et al.
    Noh, JungHyun
    Schütz, Christina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Salazar Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Scalia, Giusy
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lagerwall, Jan P. F.
    Macroscopic Control of Helix Orientation in Films Dried from Cholesteric Liquid-Crystalline Cellulose Nanocrystal Suspensions2014In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 7, p. 1477-1484Article in journal (Refereed)
    Abstract [en]

    The intrinsic ability of cellulose nanocrystals (CNCs) to self-organize into films and bulk materials with helical order in a cholesteric liquid crystal is scientifically intriguing and potentially important for the production of renewable multifunctional materials with attractive optical properties. A major obstacle, however, has been the lack of control of helix direction, which results in a defect-rich, mosaic-like domain structure. Herein, a method for guiding the helix during film formation is introduced, which yields dramatically improved uniformity, as confirmed by using polarizing optical and scanning electron microscopy. By raising the CNC concentration in the initial suspension to the fully liquid crystalline range, a vertical helix orientation is promoted, as directed by the macroscopic phase boundaries. Further control of the helix orientation is achieved by subjecting the suspension to a circular shear flow during drying.

  • 45. Roldan, M. A.
    et al.
    Mayence, Arnaud
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    López-Ortega, A.
    Ishikawa, R.
    Salafranca, J.
    Estrader, M.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Baró, M. D.
    Nogués, J.
    Pennycook, S. J.
    Varela, M.
    Probing the metastability of core|shell nanoparticle systems at atomic resolutionManuscript (preprint) (Other academic)
  • 46.
    Salazar-Alvarez, German
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Geshev, Julian
    Agramunt-Puig, Sebastia
    Navau, Carles
    Sanchez, Alvaro
    Sort, Jordi
    Nogues, Josep
    Tunable High-Field Magnetization in Strongly Exchange-Coupled Freestanding Co/CoO Core/Shell Coaxial Nanowires2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 34, p. 22477-22483Article in journal (Refereed)
    Abstract [en]

    The exchange bias properties of Co/CoO coaxial core/shell nanowires were investigated with cooling and applied fields perpendicular to the wire axis. This configuration leads to unexpected exchange-bias effects. First, the magnetization value at high fields is found to depend on the field-cooling conditions. This effect arises from the competition between the magnetic anisotropy and the Zeeman energies for cooling fields perpendicular to the wire axis. This allows imprinting predefined magnetization states to the antiferromagnetic (AFM) shell, as corroborated by micromagnetic simulations. Second, the system exhibits a high-field magnetic irreversibility, leading to open hysteresis loops attributed to the AFM easy axis reorientation during the reversal (effect similar to athermal training). A distinct way to manipulate the high-field magnetization in exchange-biased systems, beyond the archetypical effects, was thus experimentally and theoretically demonstrated.

  • 47.
    Salazar-Alvarez, German
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Lidbaum, Hans
    Lopez-Ortega, Alberto
    Estrader, Marta
    Leifer, Klaus
    Sort, Jordi
    Surinach, Santiago
    Dolors Baro, Maria
    Nogues, Josep
    Two-, Three-, and Four-Component Magnetic Multilayer Onion Nanoparticles Based on Iron Oxides and Manganese Oxides2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 42, p. 16738-16741Article in journal (Refereed)
    Abstract [en]

    Magnetic multilayered, onion-like, hetero-structured nanoparticles are interesting model systems for studying magnetic exchange coupling phenomena. In this work, we synthesized heterostructured magnetic nanopartides composed of two, three, or four components using iron oxide seeds for the subsequent deposition of manganese oxide. The MnO layer was allowed either to passivate fully in air to form an outer layer of Mn(3)O(4) or to oxidize partially to form MnO vertical bar Mn(3)O(4) double layers. Through control of the degree of passivation of the seeds, particles with up to four different magnetic layers can be obtained (i.e., FeO vertical bar Fe(3)O(4)vertical bar MnO vertical bar Mn(3)O(4)). Magnetic characterization of the samples confirmed the presence of the different magnetic layers.

  • 48.
    Schütz, Christina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Agthe, Michael
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fall, Andreas B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Salajkova, Michaela
    Plivelic, Tomas S.
    Lagerwall, Jan P. F.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rod Packing in Chiral Nematic Cellulose Nanocrystal Dispersions Studied by Small-Angle X-ray Scattering and Laser Diffraction2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 23, p. 6507-6513Article in journal (Refereed)
    Abstract [en]

    The packing of cellulose nanocrystals (CNC) in the anisotropic chiral nematic phase has been investigated over a wide concentration range by small-angle X-ray scattering (SAXS) and laser diffraction. The average separation distance between the CNCs and the average pitch of the chiral nematic phase have been determined over the entire isotropic-anisotropic biphasic region. The average separation distances range from 51 nm, at the onset of the anisotropic phase formation, to 25 nm above 6 vol % (fully liquid crystalline phase) whereas the average pitch varies from approximate to 15 mu m down to approximate to 2 mu m as phi increases from 2.5 up to 6.5 vol %. Using the cholesteric order, we determine that the twist angle between neighboring CNCs increases from about 1 degrees up to 4 degrees as phi increases from 2.5 up to 6.5 vol %. The dependence of the twisting on the volume fraction was related to the increase in the magnitude of the repulsive interactions between the charged rods as the average separation distance decreases.

  • 49.
    Schütz, Christina
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden .
    Sort, Jordi
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Oliynyk, Vitaliy
    Pellicer, Eva
    Fall, Andreas
    Wågberg, Lars
    Berglund, Lars
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Hard and Transparent Films Formed by Nanocellulose-TiO2 Nanoparticle Hybrids2012In: PLOS ONE, E-ISSN 1932-6203, Vol. 7, no 10, article id e45828Article in journal (Refereed)
    Abstract [en]

    The formation of hybrids of nanofibrillated cellulose and titania nanoparticles in aqueous media has been studied. Their transparency and mechanical behavior have been assessed by spectrophotometry and nanoindentation. The results show that limiting the titania nanoparticle concentration below 16 vol% yields homogeneous hybrids with a very high Young's modulus and hardness, of up to 44 GPa and 3.4 GPa, respectively, and an optical transmittance above 80%. Electron microscopy shows that higher nanoparticle contents result in agglomeration and an inhomogeneous hybrid nanostructure with a concomitant reduction of hardness and optical transmittance. Infrared spectroscopy suggests that the nanostructure of the hybrids is controlled by electrostatic adsorption of the titania nanoparticles on the negatively charged nanocellulose surfaces.

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  • 50. Sundberg, Johan
    et al.
    Guccini, Valentina
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Håkansson, Karl M. O.
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Toriz, Guillermo
    Gatenholm, Paul
    Controlled molecular reorientation enables strong cellulose fibers regenerated from ionic liquid solutions2015In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 75, p. 119-124Article in journal (Refereed)
    Abstract [en]

    Cellulose is difficult to solubilize and undergoes thermal decomposition prior to melting. In recent years ionic liquids have been evaluated as solvents of cellulose. In the regeneration process the non-solvent governs the resulting material's crystallinity. Water adsorbs to amorphous cellulose, acts as plasticizer and lowers the T-g, hence the degree of crystallinity will affect the potential strain induced reorientation. We prepared regenerated cellulose fibers form ionic liquid using different non-solvents. The influence of shear forces upon cellulose chain alignment during extrusion was simulated in silica based upon rheological measurements. The regenerated fibers had different physical, morphological and mechanical properties. Molecular re-orientation in fibers induced by mechanical strain, at humidities above the Tg, resulted in much improved mechanical properties with the Young's modulus reaching 23.4 +/- 0.8 GPa and the stress at break 504.6 +/- 51.9 MPa, which is comparable to commercially available cellulose fibers.

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