Phyllosilicate clays are layered structures with diverse nanoscale morphology depending on the composition. Size mismatch between the sheets can cause them to form nanoscrolls, a spiral structure with different inner and outer surface charges. The hydroxyls on the exposed surface of the nanoscrolls determine the adsorption properties and hydrophilicity of the surface. Vibrational sum frequency generation (VSFG) spectroscopy was applied to study the surface hydroxyls of nickel phyllosilicate (Ni3Si2O5(OH)4), revealing three distinct in-phase OH-stretch modes: 3642, 3645, and 3653 cm–1. The relative signs of the peaks allow their assignment as “outward” and “inward” pointing hydroxyls on the opposite sides of the scrolled sheet, consistent with the crystal structure. Orientational analysis of polarization-selected VSFG spectra is consistent with a broad (140–164°) step-function distribution of the OH-stretch tilt angles, which we attribute to the uncompensated portion of the scroll rolled more than a whole number of full turns.

Polarization-selected vibrational sum frequency generation (SFG) spectroscopy of D2O is used to obtain the orientation of the free OD bond at a monolayer graphene electrode. We modulate the interfacial field by varying the applied electrochemical potential, and we measure the resulting change in the orientation. A hyperpolarizability model is used for the orientational analysis, which assumes a quadratic free energy orienting potential in the absence of the field, whose minimum and curvature determine the average tilt angle and the Gaussian width of the orientational distribution. The average free OD tilt angle changes in an approximately linear fashion with the applied field, from 46° from normal at −0.9 V vs Ag/AgCl (E = −0.02 V/Å) to 32° at −3.9 V vs Ag/AgCl (E = −0.17 V/Å). Using this approach, we map the free energy profile for the molecular orientation of interfacial water by measuring the reversible response to an external perturbation, i.e., a torque applied by an electric field acting on the molecule’s permanent dipole moment. This allows us to extract the curvature of the free energy orienting potential of interfacial water, which is (4.0 ± 0.8) × 10–20 J/rad2 (or 0.25 ± 0.05 eV/rad2 ).