Mesoscopic clustering behavior of thermophoretic-type active particle suspension under quasi-one-dimensional...

We experimentally investigate the mesoscopic clustering behavior of thermophoretic-type active particle suspension under quasi-one-dimensional spatial confinement (high aspect ratio microchannel). The microchannel enhances the viscous dissipation to operate the system in subpropulsion regime. We find that, in the subpropulsion regime, the steady-state configuration of active particle suspension exhibits a transition from homogeneous state to sausagelike clustering bundle located at the channel center, quasiperiodic isolated clusters at the channel center, aperiodic isolated cluster deviated from channel center, and finally to the typical propulsion-induced accumulation around the channel boundary as increasing the excitation laser intensity. The formation of those patterns is under the interplay of outward-pointing mesoscopic scaled thermophoretic force and the applied spatial confinement. The finding of those special patterns can provide some further possibilities of particle manipulation at mesoscopic scale.