Langmuir, Vol.10, No.10, 3765-3773, 1994
The Structural Microscopic Hydrophilicity of Talc
Talc, Mg3Si4O10(OH)(2) is a trioctahedral phyllosilicate with no layer charge. It is macroscopically hydrophobic as it floats naturally. However, water immersion calorimetry measurements reveal that, once outgassed at medium temperatures (100-400 degrees C), it exhibits a strong affinity towards water molecules. Controlled rate thermal analysis measurements coupled with mass spectrometric analyses show that, upon outgassing, different surface species (water, nitrogen, carbon dioxide, and organic molecules) are released from the talc surface. The behavior of the talc surface toward nitrogen, argon, and water as a function of the outgassing temperature was then studied in detail. The surface presents highly energetic sites for nitrogen and water molecules. These sites are assigned to the hydroxyl groups pointing toward the basal surface of talc through the hexagonal cavity formed by the silica tetrahedra. The adsorption of water and nitrogen on a synthetic fluorinated talc confirms this assignment as the substitution of OH groups by fluorine atoms suppresses the specific interactions. On outgassed talc, the presence of highly hydrophilic sites isolated on a hydrophobic surface controls the adsorption of water which seems to occur through the growth of hydrogen-bonded clusters anchored on the OH groups.