Surface tension-mediated trapping and propulsion of small objects at liquid interfaces by using line-spot lasers

A new surface tension-mediated method of using line-spot lasers to trap and operate small objects at liquid interfaces is proposed for the first time. By forming closed halo rings, stable trapping can be achieved because of the potential barriers arising around the target object due to photothermal effects. Numerical analysis reveals that the surface tension differences generated for restraining objects can reach micro-Newton level, enabling safe and efficient millimeter-scale operations. Experiments on both a single-line spot and square halo rings demonstrate the good trapping and operation performance of the surface tension-mediated method. Effects of the object shape, size, material, line density of laser power, and halo ring size are quantitatively analyzed. The findings of this work might provide some insights for the development of interface-mediated manipulation techniques in future.