MEASUREMENTS OF HYDROPHOBIC AND HYDROPHILIC SURFACE SITES BY FLOW MICROCALORIMETRY

Measurements of the surface areas of hydrophilic and hydrophobic sites in a variety of carbonaceous and mineral solids, which were known to be at least partly hydrophobic, have been carried out by flow adsorption microcalorimetry. The surface areas of the hydrophilic and hydrophobic sites were shown to be related to the integral heats of displacement of 1-butanol from n-heptane and water solutions, respectively. The concentrations of the solutions used for the determination of the heats of displacement were those for which the adsorbed 1-butanol formed closed packed monolayers at the solid/solution interface. For microporous solids the heats of adsorption of 1-butanol from both n-heptane and water solutions are enhanced and so is the constant relating the surface areas of solids to the heats of adsorption, resulting in the estimates of surface areas of polar and hydrophobic sites that are significantly higher than the surface areas measured by the BET gas adsorption method. It is considered, however, that the comparison of the heats of 1-butanol adsorption from n-heptane and water permits a more accurate evaluation of the relative hydrophobicity (or hydrophilicity) of the surface of the solids than the measurements of the heats of wetting or adsorptions of individual polar and nonpolar liquids or vapors.