Investigation of nematic to smectic phase transition and dynamical properties of strongly confined semiflexible polymers using Langevin dynamics

Rich phase transitions in strongly confined polymer-nanoparticle mixtures: Nematic ordering, crystallization, and liquid-liquid phase separation

We investigate the rich phase behavior of strongly confined semi-flexible (SFC) polymer-nanoparticle (NP) systems using the graphics processing unit accelerated Langevin dynamics simulation. Hard nanoparticles (HNP) that repel each other and ideal nanoparticles (INP) that do not interact with the same species are used as model additives to a strongly confined semiflexible polymer fluid. Both types of NPs exclude the monomer beads in the same way, but they have qualitatively different effects on the SFC isotropic-nematic (I-N) transition. For the total volume fraction ϕ_tot < 0.16, adding a low volume fraction of HNPs (ϕ_p) disrupts the long range nematic order of the polymers, whereas adding HNPs in a moderately packed system (0.16 < ϕ_tot < 0.32) facilitates polymer alignment due to the restricted polymer orientational degree of freedom. For dense packing (ϕ_tot > 0.32), polymers and NPs separate into layers along the slit height and the NPs form crystalline microdomains. In contrast, INP additives always promote inter-polymer alignment for low to moderate monomer volume fractions (ϕ_m). Furthermore, we found that INPs form a droplet-like fluid domain in dense nematic polymer systems.

Entropy-induced Separation of Binary Semiflexible Ring Polymer Mixtures in Spherical Confinement

Coarse-grained molecular dynamics simulations are used to investigate the conformations of binary semiflexible ring polymers (SRPs) of two different lengths confined in a hard sphere. Segregated structures of SRPs in binary mixtures are strongly dependent upon the number density of system (ρ), the bending energy of long SRPs (Kb, long), and the chain length ratio of long to short SRPs (α). With a low ρ or a weak Kb, long at a small ratio α, long SRPs are immersed randomly in the matrix of short SRPs. As ρ and bending energy of long SRPs (Kb, long) are increased up to a certain value for a large ratio α, a nearly complete segregation between long and short SRPs is observed, which can be further characterized by the ratio of tangential and radial components of long SRPs velocity. These explicit segregated structures of the two components in spherical confinement are induced by a delicate competition between the entropic excluded volume (depletion) effects and bending contributions.