Flipping water molecules at insulator/solution interface using an externally applied weak electric field

Abstract

Effects of an externally applied electric field on orientation polarization of the water molecules at an insulator–solution interface were studied using sum-frequency generation (SFG) spectroscopy. Orientation of water molecules that have a structure causing a signal at ∼3100 cm–1 in the SFG spectra are strongly affected by an applied electric field. Moreover, the water dipole flips when an electric field is applied in the opposite direction of the electric field generated from the surface charge of a solid insulator (calcium fluoride). The required electric field is extremely low compared to that expected by the zeta potential, implying that the structure of the SFG signal is formed not on the calcium fluoride surface, where the electric field is expected to be the strongest, but further from the interface.