title: ATR-FTIR observations of water structure in colloidal silica: implications for the hydration force mechanism.
abstract: Attenuated total internal reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used to probe the change in water structure in silica colloids as a function of particle density. The absorption index (k) spectra were calculated from the ATR spectra using the subtractive Kramers-Kronig transform in order to avoid the effects of the density-dependent refractive index on the raw spectra and allow direct comparison of the different chemical environments. Normalized difference spectra were obtained by subtracting the k spectrum of bulk water from those of the silica colloids. At low particle densities, these difference spectra reveal the presence of a strongly hydrogen-bonded hydration layer at the surface of the colloidal particles. At higher particle densities, the hydrogen-bonding network is increasingly disrupted. The results provide direct experimental evidence of hydrogen-bond breaking as the mechanism for the hydration force, which provides the extraordinary stability of colloidal silica.
authors: Department of Chemistry, Bucknell University, Lewisburg, Pennsylvania 17837, USA.
authors: J Ryan
authors: JR
authors: Bailey
authors: Molly M
authors: MM
authors: McGuire