Hydrodynamic effects on the liquid-hexatic transition of active colloids

We study numerically the role of hydrodynamics in the liquid-hexatic transition of active colloids at intermediate activity, where motility induced phase separation (MIPS) does not occur. We show that in the case of active Brownian particles (ABP), the critical density of the transition decreases upon increasing the particle's mass, enhancing ordering, while self-propulsion has the opposite effect in the activity regime considered. Active hydrodynamic particles (AHP), instead, undergo the liquid-hexatic transition at higher values of packing fraction phi than the corresponding ABP, suggesting that hydrodynamics have the net effect of disordering the system. At increasing densities, close to the hexatic-liquid transition, we found in the case of AHP the appearance of self-sustained organized motion with clusters of particles moving coherently.

Automated summary

In this study, we numerically investigate the role of hydrodynamics in the liquid-hexatic transition of active colloids under intermediate activity. We find that increasing the particle's mass enhances ordering, while self-propulsion has the opposite effect. Active hydrodynamic particles undergo the transition at higher packing fractions compared to active Brownian particles, indicating that hydrodynamics tend to disorder the system. At higher densities near the hexatic-liquid transition, organized motion with coherent particle clusters is observed in active hydrodynamic particles.