Nematic transition and liquid-liquid phase separation in semiflexible polymers – nanoparticle mixtures

Adding nanoparticles (NPs) to a polymer matrix may significantly modify its glass transition temperature, dielectric constant, istropic-nematic phase transition behavior, etc. In the present study, we used GPU-accelerated Langevin dynamics simulation to explore how polymer-NP interaction affect the isotropic-nematic (I-N) transition and microstructural modifications of a matrix of semi-flexible polymers with persistence length P=20 and contour length L=25. The mixture is confined under slit. Polymers are modeled as semi-flexible chains with beads of diameter σ_m=1, and NPs are spheres with σ_p =2.5.
Two limits of NP-polymer interactions - hard NPs that repel, and ideal NPs do not interact with other NPs are explored. Adding low volume fraction Φ_p of hard NPs disperse the NPs in the polymer matrix, which disrupt the polymer nematic ordering and upshifts the I-N transition. In contrast, ideal NP additives induce depletion attraction between polymers, which enhances polymer alignment and downshifts the I-N transition. For moderate or high Φ_p, hard NPs would crystalize and discrete nematic polymer micro-domains are formed. On the other hand, ideal NPs forms a liquid micro-domain that decreases in size as the monomer volume fraction Φ_m increases.