Still Playing with Sticks: Patterning Compressible Active Nematics with Light

Motivated by experiments in light-responsive active fluids, we develop and study a continuum theory for compressible active nematics, i.e., active fluids of “sticks’’ whose average orientation is invariant under rotations of π. Turbulent flows and density variations arise from extensile, density-dependent deviatoric stresses and active pressure. For spatially patterned sinusoidal activity of increasing wavelength, we observe several new effects. Filaments accumulate in passive regions, with the density contrast between high- and low-activity areas growing rapidly before saturating. The density profiles also become increasingly asymmetric. Using a minimal analytically solvable 1D model, we show that this asymmetry is driven mainly by active pressure, while the sharp increase and crossover are controlled by deviatoric stresses. Above a critical active pressure, the interplay between the two drives yields a dynamical state of interfacial vortices trapped at the high/low-activity interface.