Temperature as an external field for colloid-polymer mixtures : "quenching" by heating and "melting" by cooling

TL;DR

This study explores how temperature variations influence colloid-polymer mixtures, revealing that heating and cooling can induce gelation or melting, with the Asakura-Oosawa model accurately predicting these transitions and showing enhanced crystallization near criticality.

Contribution

The paper demonstrates that the Asakura-Oosawa model can quantitatively describe temperature-induced phase transitions in colloid-polymer mixtures, including gelation, melting, and crystallization enhancement.

Findings

Cooling reduces polymer-induced attractions, causing gel melting.

Heating effectively increases the system's temperature, leading to gel formation.

Crystallization rates are enhanced near the metastable critical point.

Abstract

We investigate the response to temperature of a well-known colloid-polymer mixture. At room temperature, the critical value of the second virial coefficient of the effective interaction for the Asakura-Oosawa model predicts the onset of gelation with remarkable accuracy. Upon cooling the system, the effective attractions between colloids induced by polymer depletion are reduced, because the polymer radius of gyration is decreases as the theta-temperature is approached. Paradoxically, this raises the effective temperature, leading to "melting" of colloidal gels. We find the Asakura-Oosawa model of effective colloid interactions with a simple description of the polymer temperature response provides a quantitative description of the fluid-gel transition. Further we present evidence for enhancement of crystallisation rates near the metastable critical point.