Wettability of organically coated tridymite surface - Molecular dynamics study

Abstract

Classical molecular dynamics (MD) study was performed in order to explain a different wettability of silanized silica-glass surfaces prepared by using two different precursors - dichlorodimethylsilane (DCDMS) and dimethyldiethoxysilane (DMDES), respectively. Whereas the modified surface prepared by DCDMS becomes hydrophobic (contact angle (CA) of water >90 ), DMDES-modified surface stays partially hydrophilic (CA ∼39 ). In order to explain the observed discrepancy, several models of surfaces of trydimite with different coating by (CH3)2-Si= units were constructed and treated by water nanodroplets in the MD simulations. The models of surfaces differ by a different degree of surface coverage and/or oligomerized (CH3)2-Si= units in a lateral dimension. The simulations showed that incomplete coverage leads to a decrease of the computed CA, whereas upon lateral oligomerization the CA increases. This variation of the CA is directly related to the accessible amount of the hydroxyl groups on the surfaces and can be a possible explanation of the difference in wettability between DCDMS- and DMDES-treated glass surfaces.