Aspects of the density field in an active nematic

TL;DR

This paper investigates the behavior of active nematics, revealing that their growth from isotropic phases involves density clumping and that density domain growth exceeds typical conservation law expectations, with additional insights into fluctuation suppression.

Contribution

It demonstrates the necessity of density clumping during active nematic phase growth and analyzes the atypically fast density domain growth kinetics.

Findings

Density clumping occurs during phase growth.

Density domain growth is faster than 1/3-law.

Imposing an orienting field suppresses density fluctuations.

Abstract

Active nematics are conceptually the simplest orientationally ordered phase of self-driven particles, but have proved to be a perennial source of surprises. We show here through numerical solution of coarse-grained equations for order parameter and density that the growth of the active nematic phase from the isotropic phase is necessarily accompanied by a clumping of the density. The growth kinetics of the density domains is shown to be faster than the 1/3-law expected for variables governed by a conservation law. Other results presented include the suppression of density fluctuations in the stationary ordered nematic by the imposition of an orienting field. We close by posing some open questions.