Heating leads to liquid-crystal and crystalline order in a two-temperature active fluid of rods

TL;DR

This study demonstrates that heating a two-temperature active fluid of rods induces phase separation and promotes liquid-crystal and crystalline order in the colder regions, driven by activity-induced segregation and pressure effects.

Contribution

It reveals how scalar activity in a two-temperature system causes phase separation and order transitions in rod-like particles, a novel insight into active matter behavior.

Findings

Hot and cold particle segregation occurs due to activity.

Cold particles transition to nematic and crystalline phases at higher activity.

Hot particles become more disordered and occupy larger volume.

Abstract

We report phase separation and liquid-crystal ordering induced by scalar activity in a system of Soft Repulsive Spherocylinders (SRS) of aspect ratio $L/D = 5 $. Activity was introduced by increasing the temperature of half of the SRS (labeled \textit{`hot'}) while maintaining the temperature of the other half constant at a lower value (labeled \textit{`cold'}). The difference between the two temperatures scaled by the lower temperature provides a measure of the activity. Starting from different equilibrium initial phases, we find that activity leads to segregation of the hot and cold particles. Activity also drives the cold particles through a phase transition to a more ordered state and the hot particles to a state of less order compared to the initial equilibrium state. The cold components of a homogeneous isotropic (I) structure acquire nematic (N) and, at higher activity, crystalline (K) order. Similarly, the cold zone of a nematic initial state undergoes smectic (Sm) and crystal ordering above a critical value of activity while the hot component turns isotropic. We find that the hot particles occupy a larger volume and exert an extra kinetic pressure, confining, compressing and provoking an ordering transition of the cold-particle domains.