Interface Dynamics of Wet Active Systems.

Abstract

We study the roughening of interfaces in phase-separated active suspensions on substrates. At both large length and time scales, we show that the interfacial dynamics belongs to the |q|KPZ universality class discussed in Besse et al. [Phys. Rev. Lett. 130, 187102 (2023)PRLTAO0031-900710.1103/PhysRevLett.130.187102]. This holds despite the presence of long-ranged fluid flows. At early times, however, or for sufficiently small systems, the roughening exponents are the same as those in the presence of a momentum-conserving fluid. Surprisingly, when the effect of substrate friction can be ignored, the interface becomes random beyond a de Gennes-Taupin length scale that depends on the interfacial tension.