Robustness of monolayers on the solids; comparative studies on thermal, solvent, pH, and mechanical resistance among 1-layer LB films of cadmium arachidate and alkylchlorosilanes

The resistance of Langmuir-Blodgett (LB) monolayers of n-alkylchlorosilane compounds against the external disturbances has been investigated. The sila ne compounds used as film materials are trichloro(octadecyl)silane (TCOS), dichloro(methyl)(octadecyl)silane (DCMOS), and chloro(dimethyl)(octadecyl)s ilane (CDMOS). Cadmium arachidate (CdA) monolayers are also employed for co mparison. FT-IR transmission and reflection absorption spectroscopic analys is of 5-layer LB films of the silanes indicates that the film molecules hav e residual silanol groups. The results reveal that the silane molecules can be fixed on the hydroxylic solid surfaces with covalent bonds after the mo nolayers are transferred on such substrates. Thermal stability and dissolut ion resistance of the LB monolayers on glass slides are investigated by the change of wavenumbers and intensities of CH, stretching bands in FT-IR tra nsmission spectra. It becomes clear that the TCOS monolayers are very stabl e against heating, organic solvents and acid, whereas the DCMOS and CDMOS m onolayers are very weak. The mechanical durability of the monolayers is inv estigated by following friction coefficient profiles. The results reveal th at the friction coefficients for the silane monolayers begin to increase af ter a few transits under high normal loads although those for the CdA monol ayers maintain lower values. These results can be interpreted from the view point of monolayer structures. (C) 2000 Elsevier Science B.V. All rights r eserved.