Determining the Surface Potential of Charged Aqueous Interfaces Using Nonlinear Optical Methods

Abstract

Second-order nonlinear optical techniques have recently been established as sensitive probes of charged interfaces through the nonlinear susceptibility of water and provide an attractive route to elucidate the surface potential. We discuss methods that have been proposed using electronic second-harmonic generation and vibrational sum-frequency generation. A detailed comparison is provided, using a unified notation and including a discussion of the assumptions that are either convenient or necessary in order to arrive at the surface potential. We then illustrate that, when using the full solution of the Poisson–Boltzmann equation that is applicable to a wide range of surface potentials, several benefits may be realized. The first is that, when using off-resonance phase measurements, the surface potential can be determined from the phase alone, without any additional information or calibrated intensity schemes. Next, we illustrate a scheme for surface potential measurement using intensity-only data off-resonance by changing the angle of incidence. Finally, we discuss the possibility of measurements that target the vibrational resonance with water and illustrate how the surface potential can be isolated from such data.

Influence of the Hydrogen-Bonding Environment on Vibrational Coupling in the Electrical Double Layer at the Silica/Aqueous Interface

“…The value of g 3 is determined from the interfacial potential, which we approximate by the ζ potential, and accounts for optical interference in the diffuse layer that occurs at low ionic strength. 49,50 This χ (3) g 3 term represents the contribution of H 2 O or HOD molecules aligned or polarized by the interfacial potential, which is analogous to the diffuse layer component of the EDL.…”

Sixty Years of Surface-Specific Spectroscopy

“…For example, Ma and Geiger employed the SHG phase and amplitude measurements through heterodyne-detected SHG to examine how ionic charge affects the structure and surface potential at SiO 2 interfaces (Figure ), and how dynamics differ in different regions of the double layer . The way the surface potential can be extracted from SHG experiments was also discussed by Hore and co-workers . Second-harmonic scattering (an incoherent version of SHG) was used to study ion adsorption at the surface of SiO 2 and TiO 2 particles .…”

“…16 The way the surface potential can be extracted from SHG experiments was also discussed by Hore and coworkers. 17 Second-harmonic scattering (an incoherent version of SHG) was used to study ion adsorption at the surface of SiO 2 and TiO 2 particles. 18 This technique was also used by Gonella and co-workers to investigate protein adsorption onto the surfaces of nanoparticles.…”

Influence of the Hydrogen Bonding Environment on Vibrational Coupling in the Electrical Double Layer at the Silica/Aqueous Interface

“…The value of 𝑔 3 is determined from the interfacial potential, which we approximate by the zeta potential, and accounts for optical interference in the diffuse layer that occurs at low ionic strength. 46,47 This 𝜒 (3) 𝑔 3 term represents the contribution of H2O or HOD molecules aligned or polarized by the interfacial potential, which is analogous to the diffuse layer component of the EDL.…”