The friction between a single silica glass sphere and a flat silica glass s
urface has been investigated using lateral force microscopy. Two types of s
ilica surface were investigated, one fully hydroxylated and the other parti
ally dehydroxlated. These samples have markedly different wetting propertie
s and are known as hydrophilic and hydrophobic silica, respectively. The la
teral friction force as a function of applied normal load has been collecte
d for five different-sized spheres for both surface types. Analysis of the
friction versus load data indicates that the hydrophilic surfaces have a mo
lecularly smooth contact. For the hydrophobic surfaces, it is not clear whe
ther the friction-load response is caused by a smooth or an asperity-domina
ted contact zone. (C) 2000 Academic Press.