When a nanoporous silica gel surface modified by silyl groups is decomposition-treated at a relatively low temperature, while the network is stable, the organic surface layers can be deactivated. As a result, the degree of hydrophobicity, which can be measured by the liquid infiltration pressure, is lowered. The infiltration and defiltration behaviors of liquid are dependent on the controlled decomposition-treatment time, the liquid composition, as well as the testing temperature. By adding electrolyte or using higher testing temperature, the infiltration pressure can be increased and the defiltration can be promoted. (C) 2008 Elsevier B.V. All rights reserved.