Equilibrium properties of highly asymmetric star-polymer mixtures

TL;DR

This paper investigates how adding small star polymers affects the structure and phase behavior of large star polymer solutions, revealing a depletion-induced melting of the crystalline phase.

Contribution

It introduces a generalized depletion mechanism for asymmetric star-polymer mixtures and validates it through theoretical analysis and computer simulations.

Findings

Addition of small stars weakens large star repulsions

Small stars induce melting of the large star crystal

Effective one-component models reliably describe the mixture

Abstract

We employ effective interaction potentials to study the equilibrium structure and phase behavior of highly asymmetric mixtures of star polymers. We consider in particular the influence of the addition of a component with a small number of arms and a small size on a concentrated solution of large stars with a high functionality. By employing liquid integral equation theories we examine the evolution of the correlation functions of the big stars upon addition of the small ones, finding a loss of structure that can be attributed to a weakening of the repulsions between the large stars due to the presence of the small ones. We analyze this phenomenon be means of a generalized depletion mechanism which is supported by computer simulations. By applying thermodynamic perturbation theory we draw the phase diagram of the asymmetric mixture, finding that the addition of small stars melts the crystal formed by the big ones. A systematic comparison between the two- and effective one-component descriptions of the mixture that corroborates the reliability of the generalized depletion picture is also carried out.