Polar swimmers induce several phases in active nematics

TL;DR

This study introduces a minimal model showing how polar swimmers induce multiple phases in active nematics, revealing phase transitions and large-scale structure formation, with implications for detection and control of active matter systems.

Contribution

It presents a new minimal model for polar particles in active nematics, demonstrating phase transitions and structure formation at low polar particle densities.

Findings

Active nematics are highly sensitive to polar particles.

Two phase transitions occur with increasing polar particle density.

Large, aligned polar clusters sweep the system, inducing local order.

Abstract

Swimming bacteria in passive nematics in the form of lyotropic liquid crystals are defined as a new class of active matter known as living liquid crystals in recent studies. It has also been shown that liquid crystal solutions are promising candidates for trapping and detecting bacteria. We ask the question, can a similar class of matter be designed for background nematics which are also active? Hence, we developed a minimal model for the mixture of polar particles in active nematics. It is found that the active nematics in such a mixture are highly sensitive to the presence of polar particles, and show the formation of large scale higher order structures for a relatively low polar particle density. Upon increasing the density of polar particles, different phases of active nematics are found and it is observed that the system shows two phase transitions. The first phase transition is a first order transition from quasi-long ranged ordered active nematics to disordered active nematics with larger scale structures. On further increasing density of polar particles, the system transitions to a third phase, where polar particles form large, mutually aligned clusters. These clusters sweep the whole system and enforce local order in the nematics. The current study can be helpful for detecting the presence of very low densities of polar swimmers in active nematics and can be used to design and control different structures in active nematics.