Studies on spread monolayers and LB films of long-chain alkylchlorosilanes by Brewster angle microscopy and x-ray photoelectron spectroscopy

Long-chain alkylchlorosilanes (trichloro(octadecyl)silane; TCOS, dichloro(methyl)(octadecyl)silane; DCMOS, and chloro(dimethyl)(octadecyl)silane; CDMOS) form stable spread monolayers on water surfaces. From the experimental fact that X-ray photoelectron spectra of the LB films showed no chlorine peak, it is estimated that chlorosilyl residues were hydrolyzed rapidly just after spreading on the water surface. Brewster angle microscopic observation of the monolayers gave information on the molecular tilt and phase transitions in these monolayers with compression. It is expected that dimerization or polymerizations of resultant hydroxysilane residues could proceed by condensation among the hydroxyl groups in monolayers. However, condensation reactions were very slow in neutral conditions and the film molecules exist mainly as monomeric or dimeric hydroxysilanes and not in polymeric forms, based on the comparison of the atomic ratios of Si to O estimated from the X-ray photoelectron spectroscopy measurements of LB films of the three compounds and those of the polymers of TCOS and DCMOS, and the dimer of CDMOS.