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 < 0.16, adding a low volume fraction of HNPs (ϕ) disrupts the long range nematic order of the polymers, whereas adding HNPs in a moderately packed system (0.16 < ϕ < 0.32) facilitates polymer alignment due to the restricted polymer orientational degree of freedom. For dense packing (ϕ > 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). Furthermore, we found that INPs form a droplet-like fluid domain in dense nematic polymer systems.