Interfacial acidities, charge densities, potentials, and energies of carboxylic acid-functionalized silica/water interfaces determined by second harmonic generation

Second-harmonic studies were carried out to determine the interfacial acidity, the potential, and the interfacial energy density of an acid-functionalized silica/water interface between pH 2 and 12. The interfacial potential changes over 3 orders of magnitude, from 10-2 mV to several tens of millivolts, and the interfacial energy density changes by 7 orders of magnitude, from less than 10-7 mJ/m2 to several millijoules per square meter. The methodology presented in this study provides quantitative thermodynamic information necessary for understanding and predicting how solvated species interact with functionalized organic adlayers at liquid/solid interfaces over a wide pH range. Copyright © 2003 American Chemical Society.