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  • 1. Anton, Arthur Markus
    et al.
    Frenzel, Falk
    Yuan, Jiayin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tress, Martin
    Kremer, Friedrich
    Hydrogen bonding and charge transport in a protic polymerized ionic liquid2020In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 16, no 26, p. 6091-6101Article in journal (Refereed)
    Abstract [en]

    Hydrogen bonding and charge transport in the protic polymerized ionic liquid poly[tris(2-(2-methoxyethoxy)ethyl)ammoniumacryloxypropyl sulfonate] (PAAPS) are studied by combining Fourier transform infrared (FTIR) and broadband dielectric spectroscopy (BDS) in a wide temperature range from 170 to 300 K. While the former enables to determine precisely the formation of hydrogen bonds and other moiety-specific quantized vibrational states, the latter allows for recording the complex conductivity in a spectral range from 10(-2)to 10(+9) Hz. A pronounced thermal hysteresis is observed for the H-bond network formation in distinct contrast to the reversibility of the effective conductivity measured by BDS. On the basis of this finding and the fact that the conductivity changes with temperature by orders of magnitude, whereas the integrated absorbance of the N-H stretching vibration (being proportional to the number density of protons in the hydrogen bond network) changes only by a factor of 4, it is concluded that charge transport takes place predominantly due to hopping conduction assisted by glassy dynamics (dynamic glass transition assisted hopping) and is not significantly affected by the establishment of H-bonds.

  • 2. Aristov, Maria
    et al.
    Eichhorn, Ralf
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Bechinger, Clemens
    Separation of chiral colloidal particles in a helical flow field2013In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 9, no 8, p. 2525-2530Article in journal (Refereed)
    Abstract [en]

    Stereoisomeric molecules with opposite chirality, so-called enantiomers, often vary regarding their sensory, pharmacological and toxicological properties. Such enantiomer specific effects play a central role in the development, testing and evaluation of drugs, pesticides and food related products. Accordingly, efficient techniques for separation of chiral mixtures into enantiopure compounds are of enormous practical relevance. Most current enantiomer separation methods are based on enantioselective interactions with an auxiliary substance which has to be developed and optimized for different chiral molecules in an elaborate and costly process. Here, we experimentally demonstrate the separation of micron-sized chiral particles in a helical fluid flow which is created inside a microfluidic device patterned with slanted grooves. We observe that the retention time of particles in a helical flow field strongly depends on their chirality which leads to an effective chiral separation within the channel. Our experimental results are confirmed by numerical calculations which demonstrate how the coupling of rotational and translational degrees of freedom leads to differences in the trajectories of particles with opposite chirality. Since our separation mechanism does not rely on material specific interactions, this offers considerable advantages over existing methods. We expect that our approach can be also applied at nanometre length scales by using channels with smaller diameters and with an optimized geometry.

  • 3.
    Elias-Wolff, Federico
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lindén, Martin
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brandt, Erik G.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Curvature sensing by cardiolipin in simulated buckled membranes2019In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 15, no 4, p. 792-802Article in journal (Refereed)
    Abstract [en]

    Cardiolipin is a non-bilayer phospholipid with a unique dimeric structure. It localizes to negative curvature regions in bacteria and is believed to stabilize respiratory chain complexes in the highly curved mitochondrial membrane. Cardiolipin's localization mechanism remains unresolved, because important aspects such as the structural basis and strength for lipid curvature preferences are difficult to determine, partly due to the lack of efficient simulation methods. Here, we report a computational approach to study curvature preferences of cardiolipin by simulated membrane buckling and quantitative modeling. We combine coarse-grained molecular dynamics with simulated buckling to determine the curvature preferences in three-component bilayer membranes with varying concentrations of cardiolipin, and extract curvature-dependent concentrations and lipid acyl chain order parameter profiles. Cardiolipin shows a strong preference for negative curvatures, with a highly asymmetric chain order parameter profile. The concentration profiles are consistent with an elastic model for lipid curvature sensing that relates lipid segregation to local curvature via the material constants of the bilayers. These computations constitute new steps to unravel the molecular mechanism by which cardiolipin senses curvature in lipid membranes, and the method can be generalized to other lipids and membrane components as well.

  • 4.
    Ermilova, Inna
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cholesterol in phospholipid bilayers: positions and orientations inside membranes with different unsaturation degrees2019In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 15, no 1, p. 78-93Article in journal (Refereed)
    Abstract [en]

    Cholesterol is an essential component of all animal cell membranes and plays an important role in maintaining the membrane structure and physical–chemical properties necessary for correct cell functioning. The presence of cholesterol is believed to be responsible for domain formation (lipid rafts) due to different interactions of cholesterol with saturated and unsaturated lipids. In order to get detailed atomistic insight into the behaviour of cholesterol in bilayers composed of lipids with varying degrees of unsaturation, we have carried out a series of molecular dynamics simulations of saturated and polyunsaturated lipid bilayers with different contents of cholesterol, as well as well-tempered metadynamics simulations with a single cholesterol molecule in these bilayers. From these simulations we have determined distributions of cholesterol across the bilayer, its orientational properties, free energy profiles, and specific interactions of molecular groups able to form hydrogen bonds. Both molecular dynamics and metadynamics simulations showed that the most unsaturated bilayer with 22:6 fatty acid chains shows behaviour which is most different from other lipids. In this bilayer, cholesterol is relatively often found in a “flipped” configuration with the hydroxyl group oriented towards the membrane middle plane. This bilayer has also the highest (least negative) binding free energy among liquid phase bilayers, and the lowest reorientation barrier. Furthermore, cholesterol molecules in this bilayer are often found to form head-to-tail contacts which may lead to specific clustering behaviour. Overall, our simulations support ideas that there can be a subtle interconnection between the contents of highly unsaturated fatty acids and cholesterol, deficiency or excess of each of them is related to many human afflictions and diseases.

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  • 5.
    He, Andong
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Wettlaufer, John
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Hertz beyond belief2014In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 10, no 13, p. 2264-2269Article in journal (Refereed)
    Abstract [en]

    We examine the validity of Hertz's linear elastic theory for central collisions of spheres using a viscoelastic model. This model explains why Hertz's theory is accurate in predicting the collision time and maximum contact area even when 40% of the kinetic energy is lost due to viscous dissipation. The main reason is that both the collision time and maximum contact area have a very weak dependence on the impact velocity. Moreover, we show that colliding objects exhibit an apparent size-dependent yield strength, which results from larger objects dissipating less energy at a given impact velocity.

  • 6. Helden, Laurent
    et al.
    Eichhorn, Ralf
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Bechinger, Clemens
    Direct measurement of thermophoretic forces2015In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 11, no 12, p. 2379-2386Article in journal (Refereed)
    Abstract [en]

    We study the thermophoretic motion of a micron sized single colloidal particle in front of a flat wall by evanescent light scattering. To quantify thermophoretic effects we analyse the nonequilibrium steady state (NESS) of the particle in a constant temperature gradient perpendicular to the confining walls. We propose to determine thermophoretic forces from a generalized potential associated with the probability distribution of the particle position in the NESS. Experimentally we demonstrate, how this spatial probability distribution is measured and how thermophoretic forces can be extracted with 10 fN resolution. By varying temperature gradient and ambient temperature, the temperature dependence of Soret coefficient ST(T) is determined for r = 2.5 mm polystyrene and r = 1.35 mm melamine particles. The functional form of ST(T) is in good agreement with findings for smaller colloids. In addition, we measure and discuss hydrodynamic effects in the confined geometry. The theoretical and experimental technique proposed here extends thermophoresis measurements to so far inaccessible particle sizes and particle solvent combinations.

  • 7. Jativa, Fernando
    et al.
    Schütz, Christina
    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).
    Zhang, Xuehua
    Wicklein, Bernd
    Confined self-assembly of cellulose nanocrystals in a shrinking droplet2015In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 11, no 26, p. 5374-5380Article in journal (Refereed)
    Abstract [en]

    We have studied how cellulose nanocrystals (CNC) self-assemble into liquid crystalline phases in shrinking, isolated droplets. By adjusting the water dissolution rate of an aqueous CNC droplet immersed in a binary toluene-ethanol mixture we can control the final morphology of the consolidated microbead. At low ethanol concentration in the surrounding fluid dense microbeads of spherical morphology are produced while collapsed core-shell particles are obtained at high ethanol concentration. Polarized light microscopy was used to follow the spatial evolution and coalescence of birefringent spheroids during droplet shrinkage. Electron microscopy reveals the resultant nematic microstructure. This method of confined CNC assembly provides thus the possibility to prepare ordered microbeads, which can be useful as templates or for their optical properties.

  • 8. Korolev, Nikolay
    et al.
    Allahverdi, Abdollah
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nordenskioeld, Lars
    The polyelectrolyte properties of chromatin2012In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 8, no 36, p. 9322-9333Article, review/survey (Refereed)
    Abstract [en]

    Double helical DNA is a negatively charged polyelectrolyte and exists in the nucleus of living cells as chromatin, a highly compacted but dynamic complex with histone proteins. The first level of DNA compaction is the linear array of the nucleosome core particles (NCP), which is a well-defined structure of 145-147 bp DNA with the histone octamer, connected by linker DNA. Higher levels of chromatin compaction include two routes which may overlap: intramolecular folding of the nucleosome array resulting in formation of the 30 nm fibre and intermolecular aggregation (self-association) between different arrays (or distant fibres of the same chromosome). This review describes how the polyelectrolyte properties of chromatin are illustrated by experimental results of folding and self-association of well-defined model chromatin, in the form of recombinant nucleosome arrays, and how these properties can be understood from computer modelling. Chromatin compaction shows considerable similarities to DNA condensation. However, the structure of condensed chromatin is sensitive to the detailed molecular features of the nucleosome-nucleosome interactions which include the influence of the histone tails and their modifications.

  • 9.
    Lyubartsev, Alexander P.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Rabinovich, Alexander L.
    Recent development in computer simulations of lipid bilayers2011In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 7, no 1, p. 25-39Article, review/survey (Refereed)
    Abstract [en]

    Rapid development of computer power during the last decade has made molecular simulations of lipid bilayers feasible for many research groups, which, together with the growing general interest in investigations of these very important biological systems has lead to tremendous increase of the number of research on the computational modeling of lipid bilayers. In this review, we give account of the recent progress in computer simulations of lipid bilayers covering mainly the period of the last 5 years, and covering several selected subjects: development of the force fields for lipid bilayer simulations, studies of the role of lipid unsaturation, the effect of cholesterol and other inclusions on properties of the bilayer, and use of coarse-grained models.

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  • 10.
    Mancarella, Francesco
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Style, Robert W.
    Wettlaufer, John S.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Yale University, USA.
    Interfacial tension and a three-phase generalized self-consistent theory of non-dilute soft composite solids2016In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 12, no 10, p. 2744-2750Article in journal (Refereed)
    Abstract [en]

    In the dilute limit Eshelby's inclusion theory captures the behavior of a wide range of systems and properties. However, because Eshelby's approach neglects interfacial stress, it breaks down in soft materials as the inclusion size approaches the elastocapillarity length L equivalent to gamma/E. Here, we use a three-phase generalized self-consistent method to calculate the elastic moduli of composites comprised of an isotropic, linear-elastic compliant solid hosting a spatially random monodisperse distribution of spherical liquid droplets. As opposed to similar approaches, we explicitly capture the liquid-solid interfacial stress when it is treated as an isotropic, strain-independent surface tension. Within this framework, the composite stiffness depends solely on the ratio of the elastocapillarity length L to the inclusion radius R. Independent of inclusion volume fraction, we find that the composite is stiffened by the inclusions whenever R < 3L/2. Over the same range of parameters, we compare our results with alternative approaches (dilute and Mori-Tanaka theories that include surface tension). Our framework can be easily extended to calculate the composite properties of more general soft materials where surface tension plays a role.

  • 11.
    Mancarella, Francesco
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Wettlaufer, John S.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Yale University, USA; University of Oxford, UK.
    Surface tension and a self-consistent theory of soft composite solids with elastic inclusions2017In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 13, no 5, p. 945-955Article in journal (Refereed)
    Abstract [en]

    The importance of surface tension effects is being recognized in the context of soft composite solids, where they are found to significantly affect the mechanical properties, such as the elastic response to an external stress. It has recently been discovered that Eshelby's inclusion theory breaks down when the inclusion size approaches the elastocapillary length L = gamma/E, where gamma is the inclusion/host surface tension and E is the host Young's modulus. Extending our recent results for liquid inclusions, here we model the elastic behavior of a non-dilute distribution of isotropic elastic spherical inclusions in a soft isotropic elastic matrix, subject to a prescribed infinitesimal far-field loading. Within our framework, the composite stiffness is uniquely determined by the elastocapillary length L, the spherical inclusion radius R, and the stiffness contrast parameter C, which is the ratio of the inclusion to the matrix stiffness. We compare the results with those from the case of liquid inclusions, and we derive an analytical expression for elastic cloaking of the composite by the inclusions. Remarkably, we find that the composite stiffness is influenced significantly by surface tension even for inclusions two orders of magnitude more stiff than the host matrix. Finally, we show how to simultaneously determine the surface tension and the inclusion stiffness using two independent constraints provided by global and local measurements.

  • 12. Marichez, Vincent
    et al.
    Tassoni, Alessandra
    Cameron, Robert P.
    Barnett, Stephen M.
    Eichhorn, Ralf
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Genet, Cyriaque
    Hermans, Thomas M.
    Mechanical chiral resolution2019In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 15, no 23, p. 4593-4608Article, review/survey (Refereed)
    Abstract [en]

    Mechanical interactions of chiral objects with their environment are well-established at the macroscale, like a propeller on a plane or a rudder on a boat. At the colloidal scale and smaller, however, such interactions are often not considered or deemed irrelevant due to Brownian motion. As we will show in this tutorial review, mechanical interactions do have significant effects on chiral objects at all scales, and can be induced using shearing surfaces, collisions with walls or repetitive microstructures, fluid flows, or by applying electrical or optical forces. Achieving chiral resolution by mechanical means is very promising in the field of soft matter and to industry, but has not received much attention so far.

  • 13. Metere, Alfredo
    et al.
    Oleynikov, Peter
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Dzugutov, Mikhail
    Lidin, Sven
    A smectic dodecagonal quasicrystal2016In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 12, no 43, p. 8869-8875Article in journal (Refereed)
    Abstract [en]

    We report a solid smectic phase that exhibits dodecagonal global order. It is composed of axially stacked hexagonally ordered particle layers, and its 12-fold rotational symmetry induced by the 301 rotation of adjacent layers with respect to each other. A quasicrystal was produced in a molecular-dynamics simulation of a single-component system of particles interacting via a spherically-symmetric potential. It was formed as a result of a first-order phase transition from an isotropic liquid state that occurred under constant-density cooling. This finding implies that a similarly structured quasicrystal can possibly be produced by the same class of systems as those forming smectic-B crystals. This quasicrystal can also be expected to arise in a system of spherically-shaped colloidal particles with appropriately tuned potential.

  • 14.
    Metere, Alfredo
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sarman, Sten
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Oppelstrup, Tomas
    Dzugutov, Mikhail
    Formation of a Columnar Liquid Crystal in a Simple One-Component System of Particles2015In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 11, no 23, p. 4606-4613Article in journal (Refereed)
    Abstract [en]

    We report a molecular dynamics simulation demonstrating that a columnar liquid crystal, commonly formed by disc-shaped molecules, can be formed by identical particles interacting via a spherically symmetric potential. Upon isochoric cooling from a low-density isotropic liquid state the simulated system performed a weak first order phase transition which produced a liquid crystal phase composed of parallel particle columns arranged in a hexagonal pattern in the plane perpendicular to the column axis. The particles within columns formed a liquid structure and demonstrated a significant intracolumn diffusion. Further cooling resulted in another first-order transition whereby the column structure became periodically ordered in three dimensions transforming the liquid-crystal phase into a crystal. This result is the first observation of a liquid crystal formation in a simple one-component system of particles. Its conceptual significance is in that it demonstrated that liquid crystals that have so far only been produced in systems of anisometric molecules, can also be formed by mesoscopic soft-matter and colloidal systems of spherical particles with appropriately tuned interatomic potential.

  • 15.
    Mocci, Francesca
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Insight into nucleic acid counterion interactions from inside molecular dynamics simulations is worth its salt2012In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 8, no 36, p. 9268-9284Article, review/survey (Refereed)
    Abstract [en]

    Nucleic acids are highly charged polyelectrolytes. Their interactions with counterions are of great importance for their structural stability, conformational behaviour and biological functions. Molecular modelling and simulation techniques, particularly molecular dynamics, have been highly useful for studies of interactions between DNA, water and ions at the molecular level, allowing us to explain many experimental observations, or to obtain information not accessible experimentally. In this review we focus on both atomistic and coarse-grained molecular simulation studies concerning the interactions of DNA with different types of counterions, with emphasis on recent studies, still open questions, limits of the method and possible further developments.

  • 16.
    Munier, Pierre
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Di, Andi
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hadi, Seyed Ehsan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kapuscinski, Martin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Segad, Mo
    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).
    Assembly of cellulose nanocrystals and clay nanoplatelets studied by time-resolved X-ray scattering2021In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 17, no 23, p. 5747-5755Article in journal (Refereed)
    Abstract [en]

    Time-resolved small-angle X-ray scattering (SAXS) was used to probe the assembly of cellulose nanocrystals (CNC) and montmorillonite (MNT) over a wide concentration range in aqueous levitating droplets. Analysis of the SAXS curves of the one-component and mixed dispersions shows that co-assembly of rod-like CNC and MNT nanoplatelets is dominated by the interactions between the dispersed CNC particles and that MNT promotes gelation and assembly of CNC, which occurred at lower total volume fractions in the CNC:MNT than in the CNC-only dispersions. The CNC dispersions displayed a d proportional to phi(-1/2) scaling and a low-q power-law exponent of 2.0-2.2 for volume fractions up to 35%, which indicates that liquid crystal assembly co-exists and competes with gelation.

  • 17.
    Munier, Pierre
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, 10691, Sweden.
    Hadi, Seyed Ehsan
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, 10691, Sweden;Wallenberg Wood Science Center, Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, 10691, Sweden.
    Segad, Mo
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, 10691, Sweden.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University, Stockholm, 10691, Sweden.
    Rheo-SAXS study of shear-induced orientation and relaxation of cellulose nanocrystal and montmorillonite nanoplatelet dispersions2022In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 18, no 2, p. 390-396Article in journal (Refereed)
  • 18.
    Munier, Pierre
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hadi, Seyed Ehsan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Wallenberg Wood Science Center, Sweden.
    Segad, Mo
    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).
    Rheo-SAXS study of shear-induced orientation and relaxation of cellulose nanocrystal and montmorillonite nanoplatelet dispersions2022In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 18, no 2, p. 390-396Article in journal (Refereed)
    Abstract [en]

    The development of robust production processes is essential for the introduction of advanced materials based on renewable and Earth-abundant resources. Cellulose nanomaterials have been combined with other highly available nanoparticles, in particular clays, to generate multifunctional films and foams. Here, the structure of dispersions of rod-like cellulose nanocrystals (CNC) and montmorillonite nanoplatelets (MNT) was probed using small-angle X-ray scattering within a rheological cell (Rheo-SAXS). Shear induced a high degree of particle orientation in both the CNC-only and CNC:MNT composite dispersions. Relaxation of the shear-induced orientation in the CNC-only dispersion decayed exponentially and reached a steady-state within 20 seconds, while the relaxation of the CNC:MNT composite dispersion was found to be strongly retarded and partially inhibited. Viscoelastic measurements and Guinier analysis of dispersions at the shear rate of 0.1 s(-1) showed that the addition of MNT promotes gel formation of the CNC:MNT composite dispersions. A better understanding of shear-dependent assembly and orientation of multi-component nanoparticle dispersions can be used to process materials with improved mechanical and functional properties.

  • 19.
    Murtola, Teemu
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Vuorela, Timo A.
    Hyvonen, Marja T.
    Marrink, Siewert-Jan
    Karttunen, Mikko
    Vattulainen, Ilpo
    Low density lipoprotein: structure, dynamics, and interactions of apoB-100 with lipids2011In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 7, no 18, p. 8135-8141Article in journal (Refereed)
    Abstract [en]

    Low-density lipoprotein (LDL) transports cholesterol in the bloodstream and plays an important role in the development of cardiovascular diseases, in particular atherosclerosis. Despite its importance to health, the structure of LDL is not known in detail. This is worrying since the lack of LDL's structural information makes it more difficult to understand its function. In this work, we have combined experimental and theoretical data to construct LDL models comprised of the apoB-100 protein wrapped around a lipid droplet of about 20 nm in size. The models are considered by near-atomistic multi-microsecond simulations to unravel structural as well as dynamical properties of LDL, with particular attention paid to lipids and their interactions with the protein. We find that the distribution and the ordering of the lipids in the LDL particle are rather complex. The previously proposed 2- and 3- layer models turn out to be inadequate to describe the properties of the lipid droplet. At the surface of LDL, apoB-100 is found to interact favorably with cholesterol and its esters. The interactions of apoB-100 with core molecules, in particular cholesteryl esters, are rather frequent and arise from hydrophobic amino acids interacting with the ring of cholesteryl esters, and also in part from the rather loose packing of lipids at the surface of the lipoparticle. The loose packing may foster the function of transfer proteins, which transport lipids between lipoproteins. Finally, the comparison of the several apoB-100 models in our study suggests that the properties of lipids in LDL are rather insensitive to the conformation of apoB-100. Altogether, the findings pave the way for further studies of LDL to better understand the central steps in the emergence of atherosclerosis.

  • 20. Rosti, Marco Edoardo
    et al.
    Pramanik, Satyajit
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Brandt, Luca
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    The breakdown of Darcy's law in a soft porous material2020In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 16, no 4, p. 939-944Article in journal (Refereed)
    Abstract [en]

    We perform direct numerical simulations of the flow through a model of deformable porous medium. Our model is a two-dimensional hexagonal lattice, with defects, of soft elastic cylindrical pillars, with elastic shear modulus G, immersed in a liquid. We use a two-phase approach: the liquid phase is a viscous fluid and the solid phase is modeled as an incompressible viscoelastic material, whose complete nonlinear structural response is considered. We observe that the Darcy flux (q) is a nonlinear function - steeper than linear - of the pressure-difference (Delta P) across the medium. Furthermore, the flux is larger for a softer medium (smaller G). We construct a theory of this super-linear behavior by modelling the channels between the solid cylinders as elastic channels whose walls are made of material with a linear constitutive relation but can undergo large deformation. Our theory further predicts that the flow permeability is an universal function of Delta P/G, which is confirmed by the present simulations.

  • 21. Style, Robert W.
    et al.
    Wettlaufer, John S.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Yale University, USA; University of Oxford, England.
    Dufresne, Eric R.
    Surface tension and the mechanics of liquid inclusions in compliant solids2015In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 11, no 4, p. 672-679Article in journal (Refereed)
    Abstract [en]

    Eshelby's theory of inclusions has wide-reaching implications across the mechanics of materials and structures including the theories of composites, fracture, and plasticity. However, it does not include the effects of surface stress, which has recently been shown to control many processes in soft materials such as gels, elastomers and biological tissue. To extend Eshelby's theory of inclusions to soft materials, we consider liquid inclusions within an isotropic, compressible, linear-elastic solid. We solve for the displacement and stress fields around individual stretched inclusions, accounting for the bulk elasticity of the solid and the surface tension (i.e. isotropic strain-independent surface stress) of the solid-liquid interface. Surface tension significantly alters the inclusion's shape and stiffness as well as its near-and far-field stress fields. These phenomena depend strongly on the ratio of the inclusion radius, R, to an elastocapillary length, L. Surface tension is significant whenever inclusions are smaller than 100L. While Eshelby theory predicts that liquid inclusions generically reduce the stiffness of an elastic solid, our results show that liquid inclusions can actually stiffen a solid when R < 3L/2. Intriguingly, surface tension cloaks the far-field signature of liquid inclusions when R = 3L/2. These results are have far-reaching applications from measuring local stresses in biological tissue, to determining the failure strength of soft composites.

  • 22.
    Sune, Marc
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Arratia, Cristóbal
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Bonfils, Anthony
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Vella, Dominic
    Wettlaufer, John
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Wrinkling composite sheets2023In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 19, no 45, p. 8729-8743Article in journal (Refereed)
    Abstract [en]

    We examine the buckling shape and critical compression of confined inhomogeneous composite sheets lying on a liquid foundation. The buckling modes are controlled by the bending stiffness of the sheet, the density of the substrate, and the size and the spatially dependent elastic coefficients of the sheet. We solve the beam equation describing the mechanical equilibrium of a sheet when its bending stiffness varies parallel to the direction of confinement. The case of a homogeneous bending stiffness exhibits a degeneracy of wrinkled states for certain lengths of the confined sheet; we explain this degeneracy using an asymptotic analysis valid for long sheets, and show that it corresponds to the switching of the sheet between symmetric and antisymmetric buckling modes. This degeneracy disappears for spatially dependent elastic coefficients. Medium length sheets buckle similarly to their homogeneous counterparts, whereas the wrinkled states in large length sheets concentrate the bending energy towards the soft regions of the sheet. We examine the buckling shape and critical compression of confined inhomogeneous composite sheets lying on a liquid foundation.

  • 23.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stanford University, USA.
    Zhu, You-Liang
    Lu, Zhong-Yuan
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden.
    Electrostatic interactions in soft particle systems: mesoscale simulations of ionic liquids2018In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 14, no 21, p. 4252-4267Article in journal (Refereed)
    Abstract [en]

    Computer simulations provide a unique insight into the microscopic details, molecular interactions and dynamic behavior responsible for many distinct physicochemical properties of ionic liquids. Due to the sluggish and heterogeneous dynamics and the long-ranged nanostructured nature of ionic liquids, coarse-grained mesa-scale simulations provide an indispensable complement to detailed first-principles calculations and atomistic simulations allowing studies over extended length and time scales with a modest computational cost. Here, we present extensive coarse-grained simulations on a series of ionic liquids of the 1-alkyl-3-methylimidazolium (alkyl = butyl, heptyl-, and decyl-) family with Cl, [BF4], and [PF6] counterions. Liquid densities, microstructures, translational diffusion coefficients, and re-orientational motion of these model ionic liquid systems have been systematically studied over a wide temperature range. The addition of neutral beads in cationic models leads to a transition of liquid morphologies from dispersed apolar beads in a polar framework to that characterized by bi-continuous sponge-like interpenetrating networks in liquid matrices. Translational diffusion coefficients of both cations and anions decrease upon lengthening of the neutral chains in the cationic models and by enlarging molecular sizes of the anionic groups. Similar features are observed in re-orientational motion and time scales of different cationic models within the studied temperature range. The comparison of the liquid properties of the ionic systems with their neutral counterparts indicates that the distinctive microstructures and dynamical quantities of the model ionic liquid systems are intrinsically related to Coulombic interactions. Finally, we compared the computational efficiencies of three linearly scaling O(NlogN) Ewald summation methods, the particle-particle particle-mesh method, the particle-mesh Ewald summation method, and the Ewald summation method based on a non-uniform fast Fourier transform technique, to calculate electrostatic interactions. Coarse-grained simulations were performed using the GALAMOST and the GROMACS packages and hardware efficiently utilizing graphics processing units on a set of extended [1-decyl-3-methylimidazolium][BF4] ionic liquid systems of up to 131072 ion pairs.

  • 24. Zhu, Lailai
    et al.
    Rorai, Cecilia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). KTH Mechanics, Sweden.
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Brandt, Luca
    A microfluidic device to sort capsules by deformability: a numerical study2014In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 10, no 39, p. 7705-7711Article in journal (Refereed)
    Abstract [en]

    Guided by extensive numerical simulations, we propose a microfluidic device that can sort elastic capsules by their deformability. The device consists of a duct embedded with a semi-cylindrical obstacle, and a diffuser which further enhances the sorting capability. We demonstrate that the device can operate reasonably well under changes in the initial position of the capsule. The efficiency of the device remains essentially unaltered under small changes of the obstacle shape (from semi-circular to semi-elliptic cross-section). Confinement along the direction perpendicular to the plane of the device increases its efficiency. This work is the first numerical study of cell sorting by a realistic microfluidic device.

1 - 24 of 24
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