Optothermal Microparticle Oscillator Induced by Marangoni and Thermal Convection

The light-fueled microparticle oscillator, exemplifying
sustained
driving in a static light source, potentially holds applications in
fundamental physics, cellular manipulation, fluid dynamics, and various
other soft-matter systems. The challenges of photodamage due to laser
focusing on particles and the control of the oscillation direction
have always been two major issues for microparticle oscillators. Here,
we present an optical–thermal method for achieving a 3D microparticle
oscillator with a fixed direction by employing laser heating of the
gold film surface. First, the microparticle oscillation without direction
limitation is studied. The photothermal conversion originates from
the laser heating of a gold film. The oscillation mechanism is the
coordination of the forces exerted on the particles, including the
thermal convective force, thermophoresis force, and gravity. Subsequently,
the additional Marangoni convection force, generated by the temperature
gradient on the surface of a microbubble, is utilized to control the
oscillation direction of the microparticle. Finally, a dual-channel
oscillation mode is achieved by utilizing two microbubbles. During
the oscillation process, the microparticle is influenced by flow field
forces and temperature gradient force, completely avoiding optical
damage to the oscillating microparticle.