Laser-induced strong Marangoni effect in deformation and manipulation of ferrofluid

Optical manipulation of fluid or droplet has long been investigated for applications in microfluidics. The light-induced thermocapillary effect is one of the strategies in optical control of liquid. We demonstrate the laser-induced deformation of ferrofluid surfaces with ultra-violet to infra-red lasers. The surface deformation reaches the bottom and breaks the liquid, achieving the highest liquid rupture thickness for over 1000 μm. The deformation process and rupture are related to strong Marangoni effect, high laser absorption and low viscosity of ferrofluid. As applications of the laser-controlled ferrofluid, we show that a ferrofluid droplet in the capillary can be easily moved horizontally and vertically by the illumination of a laser beam. We also demonstrate that letters and patterns can be written on the black surface of ferrofluid thin film with a laser beam even with a common laser pointer. Laser manipulation of ferrofluid also makes it a controlling vehicle for varieties of liquid or droplets.