Effective management of thermal-fluids transport has become a critical challenge in many energy, water, and electronic applications due to the increasing power density and shrinking length scales. In this talk, I will first describe our effort to manipulate multi-phase fluid motion using light-responsive surfactants. Upon illuminating droplets and bubbles with light, the surfactants at the fluid-fluid interfaces go through photo-isomerization, which changes the local interfacial tension and introduces a Marangoni flow. The resulting interfacial shear stress generates a net force on the bubble or the droplets, causing them to depart or slide along the surface. We demonstrate real-time manipulation of multi-phase fluidic systems using low intensity light which can potentially enhance phase change heat transfer. I will also describe our effort to achieve passive salt-rejecting solar thermal desalination by thin-film condensation in microporous membrane which utilizes ample three-phase contact area, salt diffusion and a low vapor transport resistance. With our design, we demonstrate continuous desalination of seawater for 7-days in one Sun with no salt precipitation. These examples demonstrate the potential of combining fundamental thermo-fluid science and advanced micro/nano engineering approaches to address many of the pressing thermal challenges in energy and water systems. Series: "GRIT Talks" [Science] [Show ID: 39330]