Change search
Refine search result
1 - 16 of 16
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Sarman, Sten
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wang, Yong-Lei
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Non-Newtonian rheological properties of shearing nematic liquid crystal model systems based on the Gay-Berne potential2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 25, p. 16615-16623Article in journal (Refereed)
    Abstract [en]

    The viscosities and normal stress differences of various liquid crystal model systems based on the Gay-Berne potential have been obtained as functions of the shear rate in the non-Newtonian regime. Various molecular shapes such as regular convex calamitic and discotic ellipsoids and non-convex shapes such as bent core molecules and soft ellipsoid strings have been examined. The isotropic phases were found to be shear thinning with the shear rate dependence of the viscosity following a power law in the same way as alkanes and other non-spherical molecules. The nematic phases turned out to be shear thinning but the logarithm of the viscosity proved to be an approximately linear function of the square root of the shear rate. The normal stress differences were found to display a more or less parabolic dependence on the shear rate in the isotropic phase whereas this dependence was linear at low to intermediate shear rates in the nematic phase.

  • 2.
    Sarman, Sten
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wang, Yong-Lei
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Self-diffusion in the non-Newtonian regime of shearing liquid crystal model systems based on the Gay-Berne potential2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 5, article id 054901Article in journal (Refereed)
    Abstract [en]

    The self-diffusion coefficients of nematic phases of various model systems consisting of regular convex calamitic and discotic ellipsoids and non-convex bodies such as bent-core molecules and soft ellipsoid strings have been obtained as functions of the shear rate in a shear flow. Then the self-diffusion coefficient is a second rank tensor with three different diagonal components and two off-diagonal components. These coefficients were found to be determined by a combination of two mechanisms, which previously have been found to govern the self-diffusion of shearing isotropic liquids, namely, (i) shear alignment enhancing the diffusion in the direction parallel to the streamlines and hindering the diffusion in the perpendicular directions and (ii) the distortion of the shell structure in the liquid whereby a molecule more readily can escape from a surrounding shell of nearest neighbors, so that the mobility increases in every direction. Thus, the diffusion parallel to the streamlines always increases with the shear rate since these mechanisms cooperate in this direction. In the perpendicular directions, these mechanisms counteract each other so that the behaviour becomes less regular. In the case of the nematic phases of the calamitic and discotic ellipsoids and of the bent core molecules, mechanism (ii) prevails so that the diffusion coefficients increase. However, the diffusion coefficients of the soft ellipsoid strings decrease in the direction of the velocity gradient because the broadsides of these molecules are oriented perpendicularly to this direction due the shear alignment (i). The cross coupling coefficient relating a gradient of tracer particles in the direction of the velocity gradient and their flow in the direction of the streamlines is negative and rather large, whereas the other coupling coefficient relating a gradient in the direction of the streamlines and a flow in the direction of the velocity gradient is very small.

  • 3.
    Sarman, Sten
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wang, Yong-Lei
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Thermomechanical coupling in coarse grained cholesteric liquid crystal model systems with pitches of realistic length2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 25, p. 16822-16829Article in journal (Refereed)
    Abstract [en]

    Thermomechanical coupling in cholesteric liquid crystals, i.e. when a temperature gradient parallel to the cholesteric axis rotates the director, has been studied in a model system of soft ellipsoids where the interaction potential has been augmented by a chiral potential. More specifically, the cross coupling coefficient between the temperature gradient and the director angular velocity, or Leslie coefficient, has been obtained as a function of the pitch by evaluating the corresponding Green-Kubo relation by molecular dynamics simulation. The product of the Leslie coefficient and the pitch has been found to be constant within the statistical uncertainty. This is in accordance with a symmetry condition originally proposed by de Gennes and it means that the Leslie coefficient of systems with longer pitches can be obtained from systems with shorter pitches. Since the pitches of realistic systems are usually very long, it becomes possible to study thermomechanical coupling in these systems which otherwise would have required prohibitively long simulations. Since we also have obtained rather accurate data on the cross correlation function between the director angular velocity and the heat current density, it becomes possible to analyse the mechanism of thermomechanical coupling to some extent.

  • 4. Shin, Jae Yoon
    et al.
    Wang, Yong-Lei
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stanford University, United States.
    Yamada, Steven A.
    Hung, Samantha T.
    Fayer, Michael D.
    Imidazole and 1-Methylimidazole Hydrogen Bonding and Nonhydrogen Bonding Liquid Dynamics: Ultrafast IR Experiments2019In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 123, no 9, p. 2094-2105Article in journal (Refereed)
    Abstract [en]

    The dynamics of imidazole (IM) and 1-methylimidazole (1-MeIM) in the liquid phase at 95 degrees C were studied by IR polarization selective pump-probe and two-dimensional IR (2D IR) spectroscopies. The two molecules are very similar structurally except that IM can be simultaneously a hydrogen bond donor and acceptor and therefore forms extended hydrogen-bonded networks. The broader IR absorption spectrum and a shorter vibrational lifetime of the vibrational probe, selenocyanate anion (SeCN-), in IM vs 1-MeIM indicate that stronger hydrogen bonding exists between SeCN- and IM. Molecular dynamics (MD) simulations support the strong hydrogen bond formation between SeCN- and IM via the HN moiety. SeCN- makes two H-bonds with IM; it is inserted in the IM H-bonded chains rather than being a chain terminator. The strong hydrogen bonding influenced the reorientation dynamics of SeCN- in IM, leading to a more restricted short time angular sampling (wobbling-in-a-cone). The complete orientational diffusion time in IM is 1.7 times slower than in 1-MeIM, but the slow down is less than expected, considering the 3-fold larger viscosity of IM. The jump reorientation mechanism accounts for the anomalously fast orientational relaxation in IM, and the MD simulations determined the average jump angle of the probe between hydrogen bonding sites. Spectral diffusion time constants obtained from the 2D IR experiments are only modestly slower in IM than in 1-MeIM in spite of the significant increase in viscosity. The results indicate that the spectral diffusion sensed by the SeCN- has IM hydrogen bond dynamics contributions not present in 1-MeIM.

  • 5.
    Wang, Yong-Lei
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Electrostatic Interactions in Coarse-Grained Simulations: Implementations and Applications2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Electrostatic interactions between charged species play a prominent role in determining structures and states of physical system, leading to important technological and biological applications. In coarse-grained simulations, accurate description of electrostatic interactions is crucial in addressing physical phenomena at larger spatial and longer temporal scales.

    In this thesis, we implement ENUF method, an abbreviation for Ewald summation based on non-uniform fast Fourier transform technique, into dissipative particle dynamics (DPD) scheme. With determined suitable parameters, the computational complexity of ENUF-DPD method is approximately described as O(N logN). The ENUF-DPD method is further validated by investigating dependence of polyelectrolyte conformations on charge fraction of polyelectrolyte and counterion valency of added salts, and studying of specific binding structures of dendrimers on amphiphilic membranes.

    In coarse-grained simulations, electrostatic interactions are either explicitly calculated with suitable methods, or implicitly included in effective potentials. The effect of treatment fashion of electrostatic interactions on phase behavior of [BMIM][PF6] ionic liquid (IL) is systematically investigated. Our systematic analyses show that electrostatic interactions should be incorporated explicitly in development of effective potentials, as well as in coarse-grained simulations to improve reliability of simulation results.

    Detailed image of microscopic structures and orientations of [BMIM][PF6] at graphene and vacuum interfaces are investigated by using atomistic simulations. Imidazolium rings and alkyl side chains of [BMIM] lie preferentially flat on graphene surface. At IL-vacuum interface, ionic groups pack closely together to form polar domains, leaving alkyl side chains populated at interface and imparting hydrophobic character. With the increase of IL filmthickness, orientations of [BMIM] change gradually from dominant flat distributions along graphene surface to orientations where imidazolium rings are either parallel or perpendicular to IL-vacuum interface with tilted angles. The interfacial spatial ionic structural heterogeneity formed by ionic groups also contributes to heterogeneous dynamics in interfacial regions.

  • 6.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stellenbosch University, South Africa.
    Interfacial structure and orientation of confined ionic liquids on charged quartz surfaces2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 42, p. 23329-23339Article in journal (Refereed)
    Abstract [en]

    Atomistic molecular dynamics simulations have been performed to study microscopic ionic structures and orientational preferences of absorbed [BMIM] cations and four paired anions ([BF4], [PF6], [TFO] and [TF2N]) on quartz surfaces. Two chemically different quartz surface models were adopted: one is saturated with silanol Si(OH)(2) groups, and the other one is covered by silane SiH2 groups, respectively. Simulation results reveal that dense ionic layers, characterized by distinct mass, number, charge and electron densities, are formed in quartz interfacial region. The orientational preferences of confined ionic groups are characterized with different features depending on the size and shape of anionic groups, and the quartz surface charge. The [BMIM] cations attach exclusively onto the negatively charged Si(OH) (2) surface. The imidazolium rings lie preferentially perpendicular to Si(OH)(2) surface, to which the directly connected methyl and butyl chains are oriented and elongated along Si(OH)(2) surface, respectively. The anions are mainly absorbed on positively charged SiH2 surface. The main axes of asymmetric [TFO] and [TF2N] anions are perpendicular and parallel to SiH2 surface, respectively. Such distinct structural and orientational preferences of confined ionic groups attribute to the strong electrostatic interactions and the formation of hydrogen bonds between confined ionic species and quartz interfacial groups.

  • 7.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Jilin University.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lu, Zhong-Yuan
    Influence of ionic liquid film thickness on ion pair distributionsand orientations at graphene and vacuum interfaces2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 32, p. 13559-13569Article in journal (Refereed)
    Abstract [en]

    Microscopic structures, orientational preferences together with mass, number and electron density distributions of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid (IL) have been studied on a neutral hydrophobic graphene surface, and at the IL–vacuum interface using atomistic Molecular Dynamics simulations. At the IL–graphene interface, distinct mass, number and electron density distributions are observed oscillating into the bulk region with several compact structural layers. The imidazolium ring of [BMIM] cations lies preferentially flat on the graphene surface, with its methyl and butyl side chains elongated along the graphene surface. At the IL–vacuum interface, however, the distributions of [BMIM][PF6] ion pairs are strongly influenced by the thickness of IL film. With the increase of IL film thickness, the orientations of [BMIM] cations at the IL–vacuum interface change gradually from dominant flat distributions along the graphene surface to orientations where the imidazolium rings are either parallel or perpendicular to the IL–vacuum interface with tilted angles. The outmost layers are populated with alkyl groups and imparted with distinct hydrophobic character. The calculated radial distribution functions suggest that ionic structures of [BMIM][PF6] ion pairs in IL–graphene and IL–vacuum interfacial regions are significantly different from each other and also from that in bulk regions.

  • 8.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Jilin University.
    Laaksonen, Aattoo
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lu, Zhong-Yuan
    Implementation of non-uniform FFT based Ewald summation in dissipative particle dynamics method2013In: Journal of Computational Physics, ISSN 0021-9991, E-ISSN 1090-2716, Vol. 235, p. 666-682Article in journal (Refereed)
    Abstract [en]

    The ENUF method, i.e., Ewald summation based on the non-uniform FFT technique (NFFT), is implemented in dissipative particle dynamics (DPD) simulation scheme to fast and accurately calculate the electrostatic interactions at mesoscopic level. In a simple model electrolyte system, the suitable ENUF–DPD parameters, including the convergence parameter α, the NFFT approximation parameter p, and the cut-offs for real and reciprocal space contributions, are carefully determined. With these optimized parameters, the ENUF–DPD method shows excellent efficiency and scales as O(NlogN)O(NlogN). The ENUF–DPD method is further validated by investigating the effects of charge fraction of polyelectrolyte, ionic strength and counterion valency of added salts on polyelectrolyte conformations. The simulations in this paper, together with a separately published work of dendrimer–membrane complexes, show that the ENUF–DPD method is very robust and can be used to study charged complex systems at mesoscopic level.

  • 9.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Lawrence, Rochelle S.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lu, Zhong-Yuan
    Jilin Univ, Inst Theoret Chem, State Key Lab Theoret & Computat Chem, Changchun, Peoples R China.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Molecular Dynamics Study of Aqueous Solution of Polyethylene Oxide: Critical Test of Force Field Models2013In: SOFT MATERERIALS, ISSN 1539-445X, Vol. 11, no 4, p. 371-383Article in journal (Refereed)
    Abstract [en]

    Five differently proposed force fields are compared on their ability to reproduce experimental data of dilute aqueous solutions of polyethylene oxide (PEO). Solution densities, radii of gyration, radial distribution functions, self-diffusion coefficients, and also solvation free energies are evaluated in using atomistic Molecular Dynamics simulations. The chosen force fields are the three ones from Bedrov et al. [J. Phys. Chem. B 1998, 102, 996], including the original force field with the generic combining rule (GEN), one with empirical combination rule (EMP) and quantum chemistry based force field (QC). The other two force fields are the one from Cordeiro et al. [Macromolecules 2010, 43, 1583] (CZMP) and the CHARMM force field. The CZMP force field performs best in reproducing both thermodynamic and dynamic properties of the PEO dilute solution. The QC force field describes the chain dimension and hydrophilic behavior of PEO oligomers reasonably well and also the power-law exponent matches well with experimental results, but it overestimates the interaction strength between PEO and water resulting in slightly higher densities and slower mobilities for PEO oligomers in dilute solution. The CHARMM force field reproduces the densities and self-diffusion coefficients for PEO oligomers quite well, but it gives PEO a semi-hydrophobic character in dilute solution. The original force field, together with the EMP combining rule gives only the thermodynamic properties of PEO dilute solutions in a reasonable agreement with experimental data, but describes neither the thermodynamic nor the dynamic properties of PEO oligomers properly when it is used with the generic combination rule. Simulation results also reveal that CZMP, QC and CHARMM can qualitatively reproduce the solvation free energies for the ether unit in dilute aqueous solution. The influence of different water models on phase behavior of dilute PEO aqueous solution is indistinguishable in our simulations.

  • 10.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lu, Zhong-Yuan
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stellenbosch University, South Africa.
    Heterogeneous dynamics of ionic liquids in confined films with varied film thickness2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 38, p. 20731-20740Article in journal (Refereed)
    Abstract [en]

    Dynamical behavior and characteristics of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid (IL) in confined films with varied film thickness have been investigated using atomistic molecular dynamics simulations. Simulation results indicate that the dynamics of confined ionic groups in interfacial regions is highly heterogeneous and depends strongly on their relative layered positions in the confined IL film. The dynamics and relaxation times of the ionic groups in the bulk region of confined IL films are very similar to that in the corresponding pure bulk simulation. In contrast, the diffusion of the corresponding ionic groups slows down and can be characterized by slaved diffusion while the corresponding relaxation times increase remarkably as these ionic groups come closer to the neutral graphene surface. While at the IL-vacuum interface, the diffusion and relaxation of terminal carbon atoms of butyl chains of [BMIM] cations are much faster than in other layers of the confined IL film and in the bulk region of the simulation system without confinement, due to their librated motion in this interfacial region. The dynamical heterogeneity of the confined ionic groups is intrinsically related to microscopic ionic structures and the orientational preference of [BMIM][PF6] ion pairs in interfacial regions.

  • 11.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Jilin University .
    Lu, Zhong-Yuan
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Specific binding structures of dendrimers on lipid bilayer membranes2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 23, p. 8348-8359Article in journal (Refereed)
    Abstract [en]

    Dissipative particle dynamics simulations are used to study the specific binding structures of polyamidoamine (PAMAM) dendrimers on amphiphilic membranes and the permeation mechanisms. Mutually consistent coarse-grained (CG) models both for PAMAM dendrimers and for dimyristoylphosphatidylcholine (DMPC) lipid molecules are constructed. The PAMAM CG model describes correctly the conformational behavior of the dendrimers, and the DMPC CG model can properly give the surface tension of the amphiphilic membrane. A series of systematic simulations is performed to investigate the binding structures of the dendrimers on membranes with varied length of the hydrophobic tails of amphiphiles. The permeability of dendrimers across membranes is enhanced upon increasing the dendrimer size (generation). The length of the hydrophobic tails of amphiphiles in turn affects the dendrimer conformation, as well as the binding structure of the dendrimer-membrane complexes. The negative curvature of the membrane formed in the dendrimer-membrane complexes is related to dendrimer concentration. Higher dendrimer concentration together with increased dendrimer generation is observed to enhance the permeability of dendrimers across the amphiphilic membranes.

  • 12.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Jilin University.
    Lyubartsev, Alexander
    Lu, Zhong-Yuan
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Multiscale coarse-grained simulations of ionic liquids: comparison of three approaches to derive effectivepotentials2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 20, p. 7701-7712Article in journal (Refereed)
    Abstract [en]

    A coarse-grained model, with three sets of effective pair potentials for 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) ionic liquid, is introduced and used to study the structural and dynamical properties over extended length and time scales. Three sets of effective pair potentials between coarse-grained beads are obtained using the Newton Inversion and the Iterative Boltzmann Inversion methods, respectively, with different treatment of electrostatic interactions. The coarse-grained simulation results are compared systematically with corresponding atomistic simulation results on several thermodynamical and structural quantities together with charge density distributions. In addition, the scattering and dynamical properties are also calculated and compared to both atomistic simulation results and experimental measurements. While all three sets of the effective potentials provide perfect agreement with the atomistic simulation for radial distribution functions, our analysis shows that in coarse-grained simulations, the long-range electrostatic interactions between ionic groups are important and should be treated explicitly to improve the reliability of other simulation results. With explicit incorporation of electrostatic interactions derived from the Newton Inversion, the coarse-grained potentials provide the most consistent description of thermodynamical, scattering and dynamical properties including their temperature dependence as compared to atomistic simulations. We conclude also that the current atomistic force field should be further improved to meet specific requirements for studying the dynamical properties of the [Bmim][PF6] system over a large temperature range.

  • 13.
    Wang, Yong-Lei
    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).
    Gavatskth, Sergei
    Antzutkin, Oleg N.
    Rutland, Mark W.
    Laaksonen, Aatto
    Atomistic Insight into Tetraalkylphosphonium-Bis(oxalato)borate Ionic Liquid/Water Mixtures. I. Local Microscopic Structure2015In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 16, p. 5251-5264Article in journal (Refereed)
    Abstract [en]

    Atomistic simulations have been performed to investigate the microscopic structural organization of aqueous solutions of trihexyltetradecylphosphonium bis(oxalato)borate ([P-6,P-6,P-6,P-14] [BOB]) ionic liquid (IL). The evolution of the microscopic liquid structure and the local ionic organization of IL/water mixtures as a function of the water concentration is visualized and systematically analyzed via radial and spatial distribution functions, coordination numbers, hydrogen bond network, and water clustering analysis. The microscopic liquid structure in neat IL is characterized by a connected apolar network composed of the alkyl chains of [P-6,P-6,P-6,P-14] cations and isolated polar domains consisting of the central segments of [P-6,P-6,P-6,P-14] cations and [BOB] anions, and the corresponding local ionic environment is described by direct contact ion pairs. In IL/water mixtures with lower water mole fractions, the added water molecules are dispersed and embedded in cavities between neighboring ionic species and the local ionic structure is characterized by solvent-shared ion pairs through cation-water-anion triple complexes. With a gradual increase in the water concentration in IL/water mixtures, the added water molecules tend to aggregate and form small clusters, intermediate chain-like structures, large aggregates, and eventually a water network in water concentrated simulation systems. A further progressive dilution of IL/water mixtures leads to the formation of self-organized micelle-like aggregates characterized by a hydrophobic core and hydrophilic shell consisting of the central polar segments in [P-6,P-6,P-6,P-14] cations and [BOB] anions in a highly branched water network. The striking structural evolution of the [P-6,P-6,P-6,P-14] [BOB] IL/water mixtures is rationalized by the competition between favorable hydrogen bonded interactions and strong electrostatic interactions between the polar segments in ionic species and the dispersion interactions between the hydrophobic alkyl chains in [P-6,P-6,P-6,P-14] cations.

  • 14.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shah, Faiz Ullah
    Glavatskih, Sergei
    Antzutkin, Oleg N.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stellenbosch University, South Africa.
    Atomistic Insight into Orthoborate-Based Ionic Liquids: Force Field Development and Evaluation2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 29, p. 8711-8723Article in journal (Refereed)
    Abstract [en]

    We have developed an all-atomistic force field for a new class of halogen-free chelated orthoborate-phosphonium ionic liquids. The force field is based on an AMBER framework with determination of force field parameters for phosphorus and boron atoms, as well as refinement of several available parameters. The bond and angle force constants were adjusted to fit vibration frequency data derived from both experimental measurements and ab initio calculations. The force field parameters for several dihedral angles were obtained by fitting torsion energy profiles deduced from ab initio calculations. To validate the proposed force field parameters, atomistic simulations were performed for 12 ionic liquids consisting of tetraalkylphosphonium cations and chelated orthoborate anions. The predicted densities for neat ionic liquids and the [P-6,P-6,P-6,P-14][BOB] sample, with a water content of approximately 2.3-2.5 wt %, are in excellent agreement with available experimental data. The potential energy components of 12 ionic liquids were discussed in detail. The radial distribution functions and spatial distribution functions were analyzed and visualized to probe the microscopic ionic structures of these ionic liquids. There are mainly four high-probability regions of chelated orthoborate anions distributed around tetraalkylphosphonium cations in the first solvation shell, and such probability distribution functions are strongly influenced by the size of anions.

  • 15.
    Zhang, Weiyi
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Huazhong University of Science and Technology, China; Clarkson University, United States.
    Wei, Shen
    Wu, Yongneng
    Wang, Yong-Lei
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhang, Miao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Roy, Dipankar
    Wang, Hong
    Yuan, Jiayin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Clarkson University, United States.
    Zhao, Qiang
    Poly(Ionic Liquid)-Derived Graphitic Nanoporous Carbon Membrane Enables Superior Supercapacitive Energy Storage2019In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 13, no 9, p. 10261-10271Article in journal (Refereed)
    Abstract [en]

    High energy/power density, capacitance, and long-life cycles are urgently demanded for energy storage electrodes. Porous carbons as benchmark commercial electrode materials are underscored by their (electro)chemical stability and wide accessibility, yet are often constrained by moderate performances associated with their powdery status. Here via controlled vacuum pyrolysis of a poly(ionic liquid) membrane template, advantageous features including good conductivity (132 S cm(-1) at 298 K), interconnected hierarchical pores, large specific surface area (1501 m(2) g(-1)), and heteroatom doping are realized in a single carbon membrane electrode. The structure synergy at multiple length scales enables large areal capacitances both for a basic aqueous electrolyte (3.1 F cm(-2)) and for a symmetric all-solid-state supercapacitor (1.0 F cm(-2)), together with superior energy densities (1.72 and 0.14 mW h cm(-2), respectively) without employing a current collector. In addition, theoretical calculations verify a synergistic heteroatom co-doping effect beneficial to the supercapacitive performance. This membrane electrode is scalable and compatible for device fabrication, highlighting the great promise of a poly(ionic liquid) for designing graphitic nanoporous carbon membranes in advanced energy storage.

  • 16. Zhou, Fang
    et al.
    Sultanbawa, Yasmina
    Feng, Huan
    Wang, Yong-Lei
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Meng, Qingtao
    Wang, Yue
    Zhang, Zhigiang
    Zhang, Run
    A New Red-Emitting Fluorescence Probe for Rapid and Effective Visualization of Bisulfite in Food Samples and Live Animals2019In: Journal of Agricultural and Food Chemistry, ISSN 0021-8561, E-ISSN 1520-5118, Vol. 67, no 15, p. 4375-4383Article in journal (Refereed)
    Abstract [en]

    The development of new methods for rapid and effective detection of bisulfite (HSO3-) in food samples and imaging of HSO3- intake in animals is of significant importance due to the key roles of HSO3- in food quality assurance and community health. In this work, a new responsive fluorescence probe, EQC, is reported for the quantitative detection of HSO3- in food samples and visualization of HSO3- intake in animals. Upon addition of HSO3-, the UV-vis absorption and red emission of EQC were significantly decreased within 120 s. The changes in absorption and emission spectra of EQC were rationalized by theoretical computations. The proposed reaction mechanism of EQC with HSO3- was confirmed by high-resolution mass spectrometry (HRMS) and spectroscopic titration measurements. EQC has the advantages of high sensitivity, selectivity (a detection limit of 18.1 nM), and fast response toward HSO3-, which enable rapid and effective HSO3- detection in buffer solution. The practical applications of EQC were demonstrated by the detection of HSO3- in food samples and the imaging of HSO3- intake in live animals.

1 - 16 of 16
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf