We use molecular dynamics simulations in 2D to study multi-component systems in the limiting case where all the particles are different (APD). The particles are assumed to interact via Lennard-Jones potentials, with identical size parameters but their pair interaction parameters are generated at random from a uniform or from a peaked distribution. We analyze both the global and the local properties of these systems at temperatures above the freezing transition and find that APD fluids relax into a non-random state characterized by clustering of particles according to the values of their pair interaction parameters (particle-identity ordering).

We study a minimal lattice model which describes bidirectional transport of "particles" driven along a one-dimensional track, as is observed in microtubule based, motor protein driven bidirectional transport of cargo vesicles, lipid bodies, and organelles such as mitochondria. This minimal model, a multispecies totally asymmetric exclusion process (TASEP) with directional switching, can provide a framework for understanding the interplay between the switching dynamics of individual particles and the collective movement of particles in one dimension. When switching is much faster than translocation, the steady-state density and current profiles of the particles are homogeneous in the bulk and are well described by mean-field (MF) theory, as determined by comparison to a Monte Carlo simulation. In this limit, we can map this model to the exactly solvable partially asymmetric exclusion-process (PASEP) model. Away from this fast switching regime the MF theory fails, although the average bulk density profile still remains homogeneous. We study the steady-state behavior as a function of the ratio of the translocation and net switching rates Q and find a unique first-order phase transition at a finite Q associated with a discontinuous change of the bulk density. When the switching rate is decreased further (keeping translocation rate fixed), the system approaches a jammed phase with a net current that tends to zero as J~1/Q. We numerically construct the phase diagram for finite Q.

We study the dynamics of particles in a multi-component 2d Lennard-Jones (LJ) fluid in the limiting case where all the particles are different (APD). The equilibrium properties of this APD system were studied in our earlier work [L. S. Shagolsem et al., J. Chem. Phys. 142, 051104 (2015).]. We use molecular dynamics simulations to investigate the statistical properties of particle trajectories in a temperature range covering both the fluid and the solid-fluid coexistence region. We calculate the mean-square displacement as well as displacement, angle, and waiting time distributions, and compare the results with those for one-component LJ fluid. As temperature is lowered, the dynamics of the APD system becomes increasingly complex, as the intrinsic difference between the particles is amplified by neighborhood identity ordering and by the inhomogeneous character of the solid-fluid coexistence region. The ramifications of our results for the analysis of protein tracking experiments in living cells are discussed.

We study a coarse grained model of cylinder forming diblock copolymers and nano‐particles (NPs) mixture confined between Lennard–Jones hard walls. Two models for non‐selective interactions between monomers and NPs are applied. In the case of purely repulsive interactions between NPs and monomers (athermal case) strong segregation of NPs at the film surfaces and the formation of droplets of particles inside the copolymer film can be observed. For weakly attractive interactions between NPs and monomers (thermal case) formation of droplets of particles disappears and segregation on the film surfaces depend on temperature. The uptake of NPs by the copolymer film in the thermal case displays a non‐monotonic dependence on temperature which can be qualitatively explained by a mean‐field model. In both cases of non‐selective interactions NPs are preferentially localized at the interface between the microphase domains.

By means of molecular dynamics simulations, we study AB diblock copolymer and nanoparticle mixtures confined between two identical walls in slit geometry. The nanoparticles are selective to the minority A-block, while the walls are neutral to both copolymer and nanoparticle. We obtained the various structures of the copolymer nanocomposites and are summarized in a phase diagram constructed in diblock composition and nanoparticle concentration space. In comparison to the phase diagram in bulk, we observe a much wider lamellar region with a broad class of lamellar structures, and the phase boundaries are shifted with increasing nanoparticle concentration. We find that both vertically and horizontally oriented lamellar structures are realized. The vertically oriented lamellae are formed by slightly asymmetric and symmetric diblock copolymers at low nanoparticle concentrations and have a very limited region of stability in the phase space, whereas the horizontally oriented lamellae are formed by asymmetric copolymer at large nanoparticle concentrations. In the vertically oriented lamellae, the segregated nanoparticles at the polymer−wall interfaces form nanoparticle monolayer above the A-domains and exclude A-monomers from this region. Consequently, the copolymer interface lines near walls are perturbed; also, the chains close to the walls are overstretched compared to the bulk. For horizontally oriented lamellae there is no overstretching of chains near the walls. The test of stability of the lamellar structures against the different thermodynamic pathways is also performed. Lastly, by considering the horizontal lamellae, we study the effect of nanoparticle concentration on the lamellar layer thickness.

The behavior of lamellae forming diblock-copolymer melts confined by two non-selective substrates under shear is studied by means of molecular dynamics simulations. Since the substrate/copolymer preferential interaction is absent, the vertically oriented lamellae (L) are formed. The response of L phase under transverse and perpendicular modes of shear is studied for a wide range of shear rates, γ̇. In particular, shear deformation and reorientation transition, flow behavior, and difference in the macroscopic response under the two modes of shear are discussed. We show that an inclined lamellae state observed for transverse shear below a critical shear rate γ̇ is stabilized by a cyclic motion of chains close to the substrates. The value of γ̇, at which lamellae dissolve and reorient along the flow field during transverse shear, coincides with the onset of shear-thinning. For γ̇<γ̇, the shear viscosity for transverse shear is much larger compared to that observed in perpendicular shear, while there is no difference for γ̇>γ̇.

No abstract

By means of molecular dynamics simulations we investigate the response of thin, symmetric diblock copolymer melts under shear in the limit of strong segregation with nonselective substrates, where vertically oriented lamellae form. Under small shear perpendicular to the lamellar orientation, we observe an inclination of the lamellar layers. At a critical shear rate, the lamellar layers become distorted and, for very large shear, recombine with a new orientation along the direction of shear. Our simulations are accompanied by a novel, easily understandable theoretical approach to predict the critical shear rate, at which the interfaces become distorted and shear-induced reorientation sets in. This allows one to calculate quantities such as the inclination angle or the pair interaction energy as a function of applied shear rate. Our results are relevant for many technical applications, where defect-free, long-range ordered structures are needed.