ABSTRACT
The subdivision of surfaces into hydrophilic and hydrophobic is an important consideration of classical and modem colloid science. Clean surfaces of polar inorganic materials such as the basal plane of mica (and clays) or hydroxylated quartz (silica glass, sand) are completely wetted by water with a zero value of the contact angle. On nonpolar hydrocarbon and fluorocarbon substrates (paraffin wax, Teflon), water forms contact angles in excess of 90°. Other solids according to the chemical nature of their surfaces cover the entire spectrum between these extremes. For example, talc, graphite or molybdenum disulfide are at the hydrophobic end.
