Second-virial theory for shape-persistent living polymers templated by discs

TL;DR

This paper develops a second-virial theoretical framework to understand how rigid colloidal discs influence the phase behavior of shape-persistent living polymers, revealing complex nematic and phase separation phenomena.

Contribution

It introduces a particle-based second-virial theory to predict how discotic additives control polymer phase behavior and induce novel coexistence states.

Findings

Small disc fractions promote polymer nematic phases.

Higher disc concentrations lead to anti-nematic polymer arrangements.

Discs induce liquid-liquid phase separation with coexistence of multiple nematic phases.

Abstract

Living polymers composed of non-covalently bonded building blocks with weak backbone flexibility may self-assemble into thermoresponsive lyotropic liquid crystals. We demonstrate that the reversible polymer assembly and phase behavior can be controlled by the addition of (non-adsorbing) rigid colloidal discs which act as an entropic reorienting ``template" onto the supramolecular polymers. Using a particle-based second-virial theory that correlates the various entropies associated with the polymers and discs, we demonstrate that small fractions of discotic additives promote the formation of a polymer nematic phase. At larger disc concentrations, however, the phase is disrupted by collective disc alignment in favor of a discotic nematic fluid in which the polymers are dispersed anti-nematically. We show that the anti-nematic arrangement of the polymers generates a non-exponential molecular-weight distribution and stimulates the formation of oligomeric species. At sufficient concentrations the discs facilitate a liquid-liquid phase separation which can be brought into simultaneously coexistence with the two fractionated nematic phases, providing evidence for a four-fluid coexistence in reversible shape-dissimilar hard-core mixtures without cohesive interparticle forces. We stipulate the conditions under which such a phenomenon could be found in experiment.