Slit confinement effects on the Isotropic-Nematic-Smectic transition for semiflexible polymers: Structure, dynamics, and criticality

Strong quasi-two dimensional confinement on semi-flexible polymer increases the polymer bending rigidity. In this study, we explored how confinement-induced change in the bending rigidity affects the phase transition of semi-flexible polymer solutions. We investigated the density induced isotropic to nematic to smectic phase transition for slit heights (H) comparable and smaller than the chain persistence length (P).

In unconfined systems (H >> P), we found the dependence of the isotropic-nematic transition volume fraction (f_IN) follows Onsager theory. For strongly confined polymer solutions, f_IN decreases as H decreases due to the increased segmental correlation length, and enhanced segmental alignment is found throughout the solution. For the isotropic to nematic transition, diffusion along the nematic director increased as the density increased while lateral diffusion decreased. Further increase in volume fraction leads to smectic transition. The transition volume fraction (f_NS) systematically shifts higher for more flexible polymers. Upon transition into the smectic phase, polymer diffusivity decreases sharply by two order of magnitude. For both I-N and N-S transitions, we found evidence of universal critical exponents near the transition density.