Optothermophoretic Manipulation of Colloidal Particles in Nonionic Liquids

The response of colloidal particles to a light-controlled external temperature field can be harnessed for optothermophoretic manipulation of the particles. The thermoelectric effect is regarded as the driving force for thermophoretic trapping of particles at the light-irradiated hot region, which is thus limited to ionic liquids. Herein, we achieve optothermophoretic manipulation of colloidal particles in various nonionic liquids, including water, ethanol, isopropyl alcohol, and 1-butanol, and establish the physical mechanism of the manipulation at the molecular level. We reveal that the nonionic driving force originates from a layered structure of solvent molecules at the particle-solvent interface, which is supported by molecular dynamics simulations. Furthermore, the effects of hydrophilicity, solvent type, and ionic strength on the layered interfacial structures and thus the trapping stability of particles are investigated, providing molecular-level insight into thermophoresis and guidance on interfacial engineering for optothermal manipulation.