We have developed a technique of generating a micro-bubble inside an optical trap by using a material (Mo-based Soft Oxometalate (SOM) compound) that absorbs at the trapping laser wavelength. A high concentration aqueous dispersion of the SOMs is taken in a sample chamber, and the trapping laser is focused on SOMs adsorbed on one of the surfaces of the chamber, so as to create a hot spot due to which a microbubble is nucleated. Due to the temperature gradient on the bubble, a surface tension gradient results, which leads to Marangoni type flows around the bubble. The resultant Marangoni ow around the bubble causes self-assembly of material at its base, which undergoes a phase transition into a crystalline state when the laser spot is translated causing the bubble to follow due to convective effects.1 We have used this technique to pattern materials ranging from dyes to carbon nano-tubes to conducting polymers which co-assemble in a mixture with the SOMs. The method is rather universal and has been used to develop catalytic chips2 and solution processed printable electronics. The flow generated by the bubbles can be studied by mapping the trajectories of probe particles in the vicinity of the bubble. We show interesting self-assembly of the particles on the bubble surface, as well as manipulation of trajectories of the particles by multiple bubbles. The bubble can also be used to capture, transport, and release particles in a perfectly controlled manner.
Basudev Roy, Subhrokoli Ghosh, Soumyajit Roy, and Ayan Banerjee, "Interesting physics and applications using microbubbles in thermo-optic tweezers," Proc. SPIE 9548, Optical Trapping and Optical Micromanipulation XII, 95480R (Presented at SPIE Nanoscience + Engineering: August 10, 2015; Published: 25 August 2015); https://doi.org/10.1117/12.2191123.
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