![Author ORCID: We display the ORCID iD icon alongside authors names on our website to acknowledge that the ORCiD has been authenticated when entered by the user. To view the users ORCiD record click the icon. [opens in a new tab]](https://chemrxiv.org/engage/assets/public/chemrxiv/images/logos/orcid.png)
Abstract
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.
Supplementary materials
Title
Movie S1
Description
Assembly of oil droplets and pattern formation under UV illumination for 180 s. This movie was 4 times faster than the real time observation.
Actions
Title
Movie S2
Description
Disassembly of oil droplets and pattern disappearance under subsequent Vis illumination for 180 s. This movie was 4 times faster than the real time observation.
Actions
Title
Movie S3
Description
Observation of induced flows at the interface between 50 mM AzoTAB/DTAB (50/50 mol%) solution and HBA in a glass vial when the specimen was illuminated with UV from the right side. This movie was 16 times faster than
the real time observation.
Actions
Title
Movie S4
Description
Motion of fluorescent beads which moved radially from a droplets’ cluster and were accumulated in line with circular patterns under UV illumination. This movie was 8 times faster than the real time observation.
Actions
Title
Movie S5
Description
Motion of fluorescent beads which circulated around droplets’ clusters under UV illumination. The bead surrounded by a yellow circle represents the one which we traced. We kept on focusing the microscope on the bead constantly. Estimated by the degree of rotation of an adjustment knob, the bead rose to the upper cover slip near a droplets’ cluster and went down at the area where the circular pattern generated repeatedly. This movie was 8 times faster than the real time observation.
Actions
Title
Movie S6
Description
Motion of fluorescent beads which circulated around droplets’ clusters under Vis illumination. The bead surrounded by a yellow circle represents the one which we traced. We kept on focusing the microscope on the bead constantly. Estimated by the degree of rotation of an adjustment knob, the bead rose to the upper and went down repeatedly. This movie was 8 times faster than the
real time observation.
Actions
Title
Movie S7
Description
Motion of fluorescent beads which did not circulate around droplets’ clusters under Vis illumination. The bead surrounded by a yellow circle represents the one which we traced. We kept on focusing the microscope on the bead constantly. Estimated by the degree of rotation of an adjustment knob, the bead gradually rose to the upper. This movie was 8 times faster than the real time observation.
Actions
Title
Supporting Information
Description
Supporting Information includes experimental methods, microscope images of droplets, image analytical data of droplet motion, time-course of the isomerization ratio of azonbenzene-containing surfactants, and mathematical simulation.
Actions
