With the rapid development of studies involving droplet microfluidics, drug delivery, cell detection, and microparticle synthesis, several models have been proposed to study the flow of fluid-filled bodies.

Depending on the type and strength of disorder, the presence of obstacles in a medium can either enhance or hinder the diffusive transport of active particles.

Motivated by results for the propagation of active–passive interfaces of bacterial Serratia marcescens swarms [Nat. Commun., 2018, 9, 5373], we used a hydrodynamic multiphase model to investigate the propagation of interfaces of active nematics on substrates. We characterized the active nematic phase of the model through the calculation of the spatial and temporal auto correlation functions and the energy spectrum and discussed its description of the statistical dynamics of the swarms reported in the experiment. We then studied the propagation of circular and flat active–passive interfaces. We found that the closing time of the circular passive domain decays quadratically with the activity and that the structure factor of the flat interface is similar to that reported for the swarms, with an activity dependent exponent. Finally, the effect of the substrate friction was investigated. We found an activity dependent threshold, above which the turbulent active nematic forms isolated islands that shrink until the system becomes isotropic and below which the active nematic expands, with a well defined propagating interface. We also found that the interface becomes static in the presence of a friction gradient.

Kinetic Monte Carlo simulations of an active lattice gas model indicate that the wetting film diverges in the whole range of activities considered, i.e. that the solid surface is always wet at the MIPS phase boundary.

The hydrodynamic behavior of the interface between nematic (N) and isotropic (I) phases of a confined active liquid crystal is investigated using numerical simulations.

Self-propelled active particles are inherently out of equilibrium as they collect energy from their surroundings and transform it into directed motion. A recent theoretical study suggests that binary mixtures of active particles with distinct effective diffusion coefficients exhibit dynamical demixing when their diffusion coefficients differ by more than one order of magnitude. Here, we show that this difference may be reduced drastically in the presence of external fields even when the response to the field is the same for both species. We investigate this demixing as a function of the ratio of the diffusion coefficients and discuss the implications of the results for active systems.