The origin of differences in immersional heats of various silicas in water
has been investigated by measurements of water vapor adsorption isotherms,
strength of electrostatic fields of surfaces, and concentration and infrare
d spectra of hydroxyl groups. The contribution of interaction energy betwee
n dipole moments of water molecules and the electrostatic fields of silica
surfaces to immersional heat was 30-40% of the total heat of immersion. The
differences in immersional heats of silicas in water significantly depend
on the interaction of hydrogen bonds between water molecules and surface hy
droxyl groups rather than on the interaction between dipole moments of wate
r molecules and surface polarity. The hydrogen-bonded hydroxyl groups stron
gly interact with water molecules rather than the free hydroxyl groups and
cause an increase in heat of immersion. (C) 1998 Academic Press.