Origin of Differences in Heats of Immersion of Silicas in Water

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 infrared spectra of hydroxyl groups. The contribution of interaction energy between 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 hydroxyl groups rather than on the interaction between dipole moments of water molecules and surface polarity. The hydrogen-bonded hydroxyl groups strongly interact with water molecules rather than the free hydroxyl groups and cause an increase in heat of immersion. Copyright 1998 Academic Press.