WETTABILITY OF ORGANOSILICON AND ORGANOFLUOROSILICON MONOLAYERS COVALENTLY GRAFTED ON QUARTZ

Highly hydrophobic monolayers were obtained by covalent grafting of mo nofunctional alkyl silanes of the general formula (CH3)(2)NSi(CH3)(2)C nH2n+1 (n = 1, 4, 8, 16) and fluoroalkyl silanes of the general [GRAPH ICS] on quartz. Advancing and receding contact angles for water, dodec ane, pentadecane, and ethylene glycol on modified surfaces were measur ed by the capillary rise method. Significant wetting hysteresis was ob served for water. Additional silanization of the samples with an exces s of silanizing agents with small molecules (trimethyl- and butyldimet hyl silanes) has almost no influence on the wetting of the investigate d surfaces by water. When the surface is wetted by hydrocarbons, hyste resis is low. Grafted monolayers containing fluorocarbon groups are we tted much more poorly than grafted hydrocarbon monolayers. Correlation s between the structure of an organosilicon modifier and wetting of th e modified surfaces by water and hydrocarbons are obtained. The values of Zisman's critical surface tension were also determined for the mod ified surfaces.