Shear Modulation Force Microscopy Studies on Cross-linked Elastomer Thin Films

ABSTRACTThe atomic force microscope in the shear force modulation microscopy (SMFM) mode has been used to characterize the surface modulus and cross-link density of elastomer thin films, where standard rheological methods cannot be applied. Brominated poly(isobutylene-co-4-methylstyrene) (BIMS) is a synthetic terpolymer which can be stoichiometrically cross-linked by N, N'-dicinnamylidene-1,6-hexanediamine. The results on several types of BIMS elastomers with different bromide content are reported. The cross-linking reaction at the surface is found to be significantly faster than that of bulk. The estimated shear moduli of the thin films were found to be proportional to the cross-link density, as expected from the rubber elasticity theory for bulk materials.