Exotic fluids and crystals of soft polymeric colloids

TL;DR

This paper explores the unique behaviors of soft polymeric colloids, revealing their ultrasoft interactions, exotic phases, and complex phase diagrams, which differ significantly from traditional hard sphere models.

Contribution

It introduces a comprehensive description of ultrasoft interactions in various polymer architectures and demonstrates the existence of exotic crystal structures and complex phase behaviors.

Findings

Ultrasoft effective interactions remain finite or diverge slowly at zero separation.

Exotic crystal structures like diamond and A15 are stable at high concentrations.

Phase diagrams exhibit reentrant melting and clustering transitions.

Abstract

We discuss recent developments and present new findings in the colloidal description of soft polymeric macromolecular aggregates. For various macromolecular architectures, such as linear chains, star polymers, dendrimers and polyelectrolyte stars, the effective interactions between suitably chosen coordinates are shown to be ultrasoft, i.e., they either remain finite or diverge very slowly at zero separation. As a consequence, the fluid phases have unusual characteristics, including anomalous pair correlations and mean-field like thermodynamic behaviour. The solid phases can exhibit exotic, strongly anisotropic as well as open crystal structures. For example, the diamond and the A15-phase are shown to be stable at sufficiently high concentrations. Reentrant melting and clustering transitions are additional features displayed by such systems, resulting in phase diagrams with a very rich topology. We emphasise that many of these effects are fundamentally different from the usual archetypal hard sphere paradigm. Instead, we propose that these fluids fall into the class of mean-field fluids.