STABILITY OF HYDROXYL AND METHOXY SURFACE GROUPS ON SILICA AEROGELS

Silica aerogels were prepared by the hydrolysis of tetramethyl orthosi licate in methanol. Surface group stability was characterized by infra red spectroscopy. Results showed OH, H2O, and OCH3 surface groups pres ent after supercritical drying. H2O groups are easily removed under a vacuum at ambient conditions; however, the OCH3 groups are strongly he ld and remained even at 600 degrees C. If air is admitted during heati ng, the OCH, groups disappear rapidly and surface OH groups are formed . The resultant surfaces were found to be quite hydrophilic, easily ad sorbing water at room temperature. D2O vapor exposure showed an extrem ely active surface, with nearly 1/2 of the OH groups exchanged in 30 m in at room temperature. Exposure to CCl4 vapor eliminated surface OH g roups and the surface was found to be more hydrophobic after long term exposure to H2O.