Adiabatic limit collapse and local interaction effects in non-linear active microrheology molecular simulations of two-dimensional fluids.

Nonlinear active microrheology molecular dynamics simulations of high-density two-dimensional fluids show that the presence of strong confining forces and an external pulling force induces a correlation between the velocity and position dynamics of the tracer particle. This correlation manifests in the form of an effective temperature and an effective mobility of the tracer particle, which is responsible for the breaking of the equilibrium fluctuation-dissipation theorem. This fact is shown by measuring the tracer particle's temperature and mobility directly from the first two moments of the velocity distribution of a tracer particle and by formulating a diffusion theory in which effective thermal and transport properties are decoupled from the velocity dynamics.

The generalized continuous multiple step (GCMS) potential: model systems and benchmarks.

The generalized continuous multiple step (GCMS) potential is presented in this work. Its flexible form allows forand/orcontributions to be encoded through adjustable energy and length scales. The GCMS interaction provides a continuous representation of square-well, square-shoulder potentials and their variants for implementation in computer simulations.

Defect-mediated colloidal interactions in a nematic-phase discotic solvent.

Interactions between colloidal inclusions dispersed in a nematic discotic liquid-crystalline solvent were investigated for different solute-solvent coupling conditions. The solvent was treated at the level of Gay-Berne discogens. Colloidal inclusions were coupled to the solvent with a generalized sphere-ellipsoid interaction potential.

Specific inter-domain interactions stabilize a compact HIV-1 Gag conformation.

HIV-1 Gag is a large multidomain poly-protein with flexible unstructured linkers connecting its globular subdomains. It is compact when in solution but assumes an extended conformation when assembled within the immature HIV-1 virion. Here, we use molecular dynamics (MD) simulations to quantitatively characterize the intra-domain interactions of HIV-1 Gag.

Anomalous dynamic arrest of non-interacting spheres ("polymer") diluted in a hard-sphere ("colloid") liquid.

Upon compression, the equilibrium hard-sphere liquid [pair potential u(r)] freezes at a packing fraction ϕ = 0.494 or, if crystallization is prevented, becomes metastable up to its glass transition at ϕ ≈ 0.58.

Influence of anchoring in the phase behaviour of discotic liquid crystals.

Molecular dynamics simulations were performed for a Gay-Berne discotic fluid confined in a slab geometry for two different anchorings: homeotropic (face-on) and planar (edge-on), and for two different confinement lengths. Our results show that the behaviour of the more confined system in the temperature region of the isotropic-nematic transition is critically influenced by the presence of the walls: the growth of the solid-liquid crystal interface spans over the entire width of the cell, and the character of the transition is changed from first order to continuous. For all the confined systems studied, we observe a higher nematic-columnar transition temperature and a smaller nematic phase region in the phase diagram, as compared with the behaviour of the infinite system.

Separating the effects of repulsive and attractive forces on the phase diagram, interfacial, and critical properties of simple fluids.

Molecular simulations in the canonical and isothermal-isobaric ensembles were performed to study the effect of varying the shape of the intermolecular potential on the phase diagram, critical, and interfacial properties of model fluids. The molecular interactions were modeled by the Approximate Non-Conformal (ANC) theory potentials. Unlike the Lennard-Jones or Morse potentials, the ANC interactions incorporate parameters (called softnesses) that modulate the steepness of the potential in their repulsive and attractive parts independently.

Induced stabilization of columnar phases in binary mixtures of discotic liquid crystals.

Three discotic liquid-crystalline binary mixtures, characterized by their extent of bidispersity in molecular thickness, were investigated with molecular dynamics simulations. Each equimolar mixture contained A-type (thin) and B-type (thick) discogens. The temperature-dependence of the orientational order parameter reveals that A-type liquid samples produce ordered phases more readily, with the (hexagonal) columnar phase being the most structured variant.

Phase equilibria, fluid structure, and diffusivity of a discotic liquid crystal.

Molecular Dynamics simulations were performed for the Gay-Berne discotic fluid parameterized by GB(0.345, 0.2, 1.

Analytical equation of state with three-body forces: application to noble gases.

We developed an explicit equation of state (EOS) for small non polar molecules by means of an effective two-body potential. The average effect of three-body forces was incorporated as a perturbation, which results in rescaled values for the parameters of the two-body potential. These values replace the original ones in the EOS corresponding to the two-body interaction.

Thermodynamic scaling and corresponding states for the self-diffusion coefficient of non-conformal soft-sphere fluids.

In this work, we explore transport properties of a special type of repulsive spheres that exhibit remarkable scaling of their thermodynamic properties. In order to accomplish that we propose a new way to derive and express effective hard-sphere diameters for transport properties of simple fluids. The procedure relies on mapping the system's transport properties, in the low density limit, to the hard-sphere fluid.

Isotropic-nematic phase transition in the Lebwohl-Lasher model from density of states simulations.

Density of states Monte Carlo simulations have been performed to study the isotropic-nematic (IN) transition of the Lebwohl-Lasher model for liquid crystals. The IN transition temperature was calculated as a function of system size using expanded ensemble density of states simulations with histogram reweighting. The IN temperature for infinite system size was obtained by extrapolation of three independent measures.

Liquid-crystal-mediated self-assembly at nanodroplet interfaces.

Technological applications of liquid crystals have generally relied on control of molecular orientation at a surface or an interface. Such control has been achieved through topography, chemistry and the adsorption of monolayers or surfactants. The role of the substrate or interface has been to impart order over visible length scales and to confine the liquid crystal in a device.

Modeling flows of confined nematic liquid crystals.

The flow of nematic liquid crystals in tightly confined systems was simulated using a molecular theory and an unsymmetric radial basis function collocation approach. When a nematic liquid crystal is subjected to a cavity flow, we find that moderate flows facilitate the relaxation of the system to the stable defect configuration observed in the absence of flow. Under more extreme flow conditions, e.

Single nanoparticle tracking reveals influence of chemical functionality of nanoparticles on local ordering of liquid crystals and nanoparticle diffusion coefficients.

This letter reports that darkfield microscopy can be used to track the trajectories of chemically functionalized gold nanoparticles in nematic liquid crystals (LCs), thus leading to measurements of the diffusion coefficients of the nanoparticles in the LCs. These measurements reveal that the diffusion coefficients of the nanoparticles dispersed in the LC are strongly dependent on the surface chemistry of the nanoparticles. Because the changes in surface chemistry are measured to have negligible influence on the diffusion coefficients of the same nanoparticles dispersed in isotropic solvents, we conclude that surface chemistry-induced changes in the local order of LCs underlie the behavior of the diffusion coefficients of the nanoparticles in the LC.

Fractionation in Gay-Berne liquid crystal mixtures.

We present a constant-pressure molecular dynamics simulation study of the phase behavior of binary (50:50) Gay-Berne liquid crystal mixtures consisting of elongated particles with different lengths (LA>LB) and equal diameters. We focus on systems at dense liquid-state conditions. Considering three mixtures characterized by different values of LA(B) and different length ratios q=LB/LA<1, we find complex fluid-fluid phase behavior resulting from the interplay between nematic, smectic-A-type, or smectic-B-type orientational ordering, on the one hand, and demixing into two phases of different composition (fractionation), on the other hand.

Phase and interfacial behavior of partially miscible symmetric Lennard-Jones binary mixtures.

We have carried out extensive equilibrium molecular-dynamics simulations to study quantitatively the topology of the temperature versus density phase diagrams and related interfacial phenomena in a partially miscible symmetric Lennard-Jones binary mixture. The topological features are studied as a function of miscibility parameter, alpha = epsilonAB/epsilonAA. Here epsilonAA = epsilonBB and epsilonAB stand for the parameters related to the attractive part of the intermolecular interactions for similar and dissimilar particles, respectively.

Wetting phenomenon in the liquid-vapor phase coexistence of a partially miscible Lennard-Jones binary mixture.

We have carried out extensive equilibrium molecular dynamics simulations to study the structure and the interfacial properties in the liquid-vapor phase coexistence of partially miscible binary Lennard-Jones mixtures. By analyzing the structural properties as a function of the miscibility parameter, alpha, we found that at relatively low temperatures the system separates forming a liquid A-liquid B interface in coexistence with the vapor phase. At higher temperatures and, 0< alpha < or =0.

Metastable liquid lamellar structures in binary and ternary mixtures of Lennard-Jones fluids.

We have carried out extensive equilibrium molecular dynamics simulations to investigate the liquid-vapor coexistence in partially miscible binary and ternary mixtures of Lennard-Jones fluids. We have studied in detail the time evolution of the density profiles and the interfacial properties in a temperature region of the phase diagram where the condensed phase is demixed. The composition of the mixtures is fixed, 50% for the binary mixture and 33.