Collective
motion is ubiquitous in living systems. Although various biomimetic artificial
systems have been constructed, there have been few studies reported on
collective motion induced by the coupling of chemical reactions, diffusion and
convection in a far-from-equilibrium state. In this study, we report an
artificial system of oil droplets in a surfactant solution wherein the
collective motion of multiple droplets and pattern formation occurred
concurrently. Using photo-responsive surfactants with an azobenzene moiety, the
assembly of droplets and the formation of circular patterns around the formed droplet
clusters occurred under UV illumination, whereas the disassembly of droplets
and disappearance of the patterns occurred under subsequent visible light
illumination. The observed dynamics were induced by Marangoni flows based on
the reversible photoisomerisation of azobenzene-containing surfactants. The
phenomena were considered analogous to the bioconvection of microorganisms. These
findings could be useful for understanding the mechanism of motion of life in
terms of physicochemical aspects.<br>
Photoinduced Collective Motion of Oil Droplets and Concurrent Pattern Formation in Surfactant Solution
