Girot A, Danné N, Würger A, Bickel T, Ren F, Loudet JC, Pouligny B. Motion of Optically Heated Spheres at the Water-Air Interface.
LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016;
32:2687-2697. [PMID:
26916053 DOI:
10.1021/acs.langmuir.6b00181]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
A micrometer-sized spherical particle classically equilibrates at the water-air interface in partial wetting configuration, causing about no deformation to the interface. In condition of thermal equilibrium, the particle just undergoes faint Brownian motion, well visible under a microscope. We report experimental observations when the particle is made of a light-absorbing material and is heated up by a vertical laser beam. We show that, at small laser power, the particle is trapped in on-axis configuration, similarly to 2-dimensional trapping of a transparent sphere by optical forces. Conversely, on-axis trapping becomes unstable at higher power. The particle escapes off the laser axis and starts orbiting around the axis. We show that the laser-heated particle behaves as a microswimmer with velocities on the order of several 100 μm/s with just a few milliwatts of laser power.
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