Structure and sum-frequency generation spectra of water on uncharged Q₄ silica surfaces: a molecular dynamics study

Abstract

Molecular dynamics simulations shed light on the relationship between the structure and sum-frequency generation vibrational spectrum of water on uncharged Q4 surfaces of different affinity for water.

Role of Ions on the Surface-Bound Water Structure at the Silica/Water Interface: Identifying the Spectral Signature of Stability

“…Therefore we assign this positive 3100 cm -1 mode to the waters which donate a hydrogen bond to the charged siloxides in agreement with the work of Urashima et al 23 Additionally, the trends in imaginary surface spectra evolution with increasing surface charge density are consistent with recent MD simulations of hydrophobic and hydrophilic silica in contact with water. 75 In those simulations, the calculated imaginary nonlinear susceptibility was negative at low wavenumber and positive at high wavenumber for a hydrophobic silica surface.…”

“…The SFG spectra derived from MD simulations of an uncharged, hydrophobic silica/water interface also exhibited these two modes of opposite phase originating from waters close to the surface. 75 The similarity in surface water structure at low ionic strength, where the silica has a negative zeta potential ( ≈ -110 mV), and the neutral silica surface at pH 2 is not obvious from a direct comparison of the intensity spectra owing to the significance of the (3) 3 contribution to the total complex spectra for the former.…”

The Role of Ions on the Surface-Bound Water Structure at the Silica/Water Interface: Identifying the Spectral Signature of Stability

“…Therefore we assign this positive 3100 cm -1 mode to the waters which donate a hydrogen bond to the charged siloxides in agreement with the work of Urashima et al 23 Additionally, the trends in imaginary surface spectra evolution with increasing surface charge density are consistent with recent MD simulations of hydrophobic and hydrophilic silica in contact with water. 75 In those simulations, the calculated imaginary nonlinear susceptibility was negative at low wavenumber and positive at high wavenumber for a hydrophobic silica surface.…”

“…The SFG spectra derived from MD simulations of an uncharged, hydrophobic silica/water interface also exhibited these two modes of opposite phase originating from waters close to the surface. 75 The similarity in surface water structure at low ionic strength, where the silica has a negative zeta potential ( ≈ -110 mV), and the neutral silica surface at pH 2 is not obvious from a direct comparison of the intensity spectra owing to the significance of the (3) 3 contribution to the total complex spectra for the former.…”

Structure and sum-frequency generation spectra of water on neutral hydroxylated silica surfaces

“…A number of modeling works on silica/water interfaces attempted to relate their structure of to the nonlinear spectra. 17,21,29,[31][32][33][34][35][36][37][38] As at normal pH conditions, silica surface possesses a negative charge due to a partial deprotonation of surface OH groups, the computational works considered charged surfaces, 21,29,31,[33][34][35]37 addressed the effect of concentration and nature of charge-balancing ions on the spectra. 21,31,33 An attention has also been paid to a contribution of the third-order susceptibility and of surface electric field to the SFG signal.…”