It is observed that light radiation can drive tangential micro/mili-scale flows in vicinity of the liquid-liquid interface between two immiscible liquids. Particle Image Velocimetry (PIV) study for these newly-reported phenomena shows that the strength of these light-driven flows strongly depends on the radiation power of the excitation light used, the inclination of the liquid-liquid interface, the thickness of the top-layer liquid, and the concentrations of the liquid involved. The effect occurs only in the case that the thickness of the top-layer liquid is sufficiently thin and positionally non-uniform. For a decane-water dual layer liquid system with a particular geometry, a Gaussian-type CW IR laser with a radiation power of several tens mili-watts can maintain a micro-scale flow with its maximum flow speed of several millimeter per second at the fastest point of the flow stream. The strength of the flows increases with inclination of the liquid-liquid interface but decreases with the thickness of the top-layer liquid. Adding another solute liquid into water in the decane-water system weakens the strength of the flows remarkably. For interpretation, Marangoni effect in association with an asymmetric deflection of the excitation light may be employed as a driving mechanism behind these phenomena. However, some characteristic behaviors of these flows revealed by PIV data also suggest that the recoil effects due to the abrupt change in the momenta of photons, which also occur associated with asymmetric light deflection at the inclined interfaces of liquid media, may also contribute significantly. In terms of application, these phenomena suggest a novel technological principle, based on which direct mechanical actuation and manipulation of liquids of extensive quantity using light beams may be accomplished.
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