Nature of water at the rutile/organic liquid interface

The nature of trace water on rutile surface has been investigated by means of adsorption, electrophoresis and infrared analysis as a prelude to the study of the affects of trace water on dispersibility. The isosteric heats of adsorption of water on rutile revealed the presence of two types of water on the rutile surface. The isosteric heat was found to increase from 11 to 27 kcal/mole at a fractional water coverage of 0.1. Further‐more, this increase was observed only at temperatures above 120°C. Further support for this theory was evidenced by the electrophoretic mobility of rutile in heptanol which first increased and then decreased with increasing water coverage. Infrared analysis of water adsorbed on rutile revealed the presence of isolated OH groups on the surface. Based on the relative intensities of the infrared CH2 and OH bending bands, the adsorption of heptanol, n‐hexylamine and n‐heptanoic acid was at a maximum at a water coverage of 0.08. Average aggregate size produced by ultrasonic dispersion in a closed system as revealed by ultramicroscope examination, was also at a minimum at a coverage of 0.08. An important factor affecting dispersibility was concluded to be the Rehbinder effect as well as the double layer repulsion.