The thickness dependence of elastic modulus of organosilane interphases

Abstract Series of organosilanes with varying molecular structure was deposited onto E glass. Solution coating and rf plasma enhanced Chemical Vapor Deposition (PE‐CVD) techniques were used. Thickness of the deposited layers varied from 30 nm to 10 ⁶ nm. Vibrational piezoelectric resonator technique and the speed of Rayleigh wave measurement were used to determine elastic modulus of the layers deposited on the glass substrate as a function of layer thickness. In all cases, increase of the Young modulus, E , of the organosilane layer with decreasing layer thickness was observed. Solution deposited layers exhibited always significantly lower elastic moduli compared to the layers deposited using PE‐CVD technique. Elastic moduli of deposited layers increased with increasing hydrocarbon chain rigidity at comparable chain length. Chlorosilane interlayers possessed always significantly greater elastic modulus compared to their ethoxy‐analogues. The observed increase of E with the decreasing layer thickness was ascribed to the reduction of the molecular mobility of chains near solid surface compared to their mobility in the bulk. It was shown that increasing the bond strength between the deposited layer and the solid E ‐glass substrate resulted in immobilized region with constraints imposed by the surface spanning into a distance from the surface. This was in agreement with current models of reinforcement mechanism in nanocomposites based on the idea of immobilized entanglements. It was shown that the deposition technique plays important role in controlling the structure and properties of the deposited interphase. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers