Entropic phase separation of linked beads

TL;DR

This paper presents a theoretical model showing that a system of microemulsion droplets connected by polymers can undergo a first-order phase separation driven purely by entropy, independent of specific interactions.

Contribution

It introduces a novel entropic phase separation model for linked beads, applicable to various polymer-linked particle systems, explaining experimental observations.

Findings

Phase separation occurs at high polymer-to-drop ratios.

The transition is first order and driven by entropy.

The mechanism is robust across different physical realizations.

Abstract

We study theoretically a model system of a transient network of microemulsion droplets connected by telechelic polymers and explain recent experimental findings. Despite the absence of any specific interactions between either the droplets or polymer chains, we predict that as the number of polymers per drop is increased, the system undergoes a first order phase separation into a dense, highly connected phase, in equilibrium with dilute droplets, decorated by polymer loops. The phase transition is purely entropic and is driven by the interplay between the translational entropy of the drops and the configurational entropy of the polymer connections between them. Because it is dominated by entropic effects, the phase separation mechanism of the system is extremely robust and does not depend on the particlular physical realization of the network. The discussed model applies as well to other polymer linked particle aggregates, such as nano-particles connected with short DNA linkers.