Alireza Foroozani Behbahani

Dynamic self-consistent field theory (DSCFT) provides an efficient continuum framework for studying structure formation in inhomogeneous polymer systems, but its predictive accuracy depends on the choice of nonlocal mobilities. Here, we construct mobility functions for moderately and strongly entangled homopolymer and diblock copolymer systems from the relaxation dynamics of single-chain structure factors, based on molecular dynamics (MD) simulations of the Kremer–Grest model and analytical reptation theory. Single-chain mobilities are combined such that the resulting DSCFT accounts for the dependence of fluxes on local chain densities. The theory is then applied to the spinodal decomposition of symmetric homopolymer blends and diblock copolymer melts following a quench into the (micro)phase-separation regime. Predictions of DSCFT are systematically compared with MD simulations. Mobility functions derived from single-chain dynamics are found to reproduce the kinetics of structure formation more accurately than conventional Debye-type mobilities. We additionally investigate the influence of adding stochastic currents (noise) that are correlated according to the fluctuation–dissipation relation. At low noise levels, they enable the generation of equilibrium initial states and facilitate defect annealing. At high noise levels, however, nonlinear effects lead to discrepancies between DSCFT and MD simulations.

Despite the widespread use of conductive composites with a binary blend matrix in electrical applications, computational studies examining the effects of conductive particle localization within individual phases and at their interface on conductance and the percolation threshold remain limited. To address this gap, we employ a simple cubic lattice model to simulate the localization of conductive sites within individual phases and at the interface between them. Our results show that exclusive localization of conductive sites within a single phase lowers the percolation threshold and enhances conductance, especially near the percolation threshold, whereas localization at the interface further reduces the threshold. When all conductive sites are exclusively localized in one phase, the percolation threshold can be expressed in two ways: first, as the fraction of conductive sites calculated relative to the total number of sites, denoted as Π; and second, as the fraction calculated relative to the available sites in that phase, denoted as Π _f . In this situation, the second phase effectively acts as an excluded volume, reducing the number of available sites. At a constant concentration of the excluded-volume phase, increasing the size of this phase causes the percolation threshold to first decrease and then converge to a constant value. The constant value corresponds to a state in which the structure of conductive sites within the available volume is similar to that of a homogeneous system. In this case, the percolation threshold expressed relative to the available sites is given by Π _f = Π _homogen , which equals 0.31 in the case of a simple cubic lattice; additionally, the percolation threshold relative to all sites is given by Π = (1 − φ _A )Π _homogen , where φ _A is the fraction of the excluded-volume phase. We also studied situations in which particles are distributed between the two phases with different probabilities. In such cases, the percolation threshold lies between the two extreme cases: a fully homogeneous system and a fully segregated system in which one phase acts as an excluded volume.

We analyze the displacements of the particles of a glass-forming molecular liquid perpendicular to a confining solid surface using extensive molecular dynamics simulations with atomistic models. In the vicinity of an attractive surface, the liquid molecules are trapped. Transient localization of liquid molecules near the surface introduces a relaxation process related to the escape of molecules from the surface into the dynamics of the interfacial liquid layer. To describe this process, we analyze several dynamical observables of the confined liquid. The self-intermediate scattering function and the mean-squared displacement of the particles located in the interfacial layer are dominated by the process of escaping from the surface. This relaxation process is also associated with a strong heterogeneity in the mobility of the interfacial particles. The studied model liquid is hydrogenated methyl methacrylate. For the confining wall, we consider different models, namely a periodic single layer of graphene and a frozen amorphous configuration of the bulk liquid (frozen wall). Near graphene, where the liquid molecules form a layered structure and adopt parallel-to-surface orientation, a clear separation between small-scale movements of the molecules near the surface and the process of escaping from the surface is observed. This is reflected in the three-step relaxation of the interfacial layer. However, near the frozen wall, where the liquid molecules do not have a preferential alignment, a clear three-step relaxation is not seen, even though the dynamical quantities are controlled by the process of escaping from the surface.

The authors wish to make the following corrections to this paper: