Atomic Force Microscopy Studies on Morphology and Distribution of Surface Modified Silica and Clay Fillers in an Ethylene-Octene Copolymer Rubber

Topographic and phase imaging in tapping mode atomic force microscopy (TMAFM) has been performed to investigate the effect of surface modification of silica and clay fillers on the morphology and the microdispersion of the filler particles in the rubber matrix. The above fillers have been modified by using surface coating agents like an acrylate monomer (trimethylolpropane triacrylate, TMPTA) or a silane coupling agent (triethoxy vinylsilane, TEVS) followed by electron beam modification at room temperature. Both unmodified and surface modified fillers have been incorporated in an ethylene-octene copolymer rubber. The phase images of the above composites elucidate the reduction in aggregate size due to the filler surface modification, which is more pronounced in the case of silane modification. The results obtained from the section analysis and the histogram of the filler distribution further corroborate the above findings. The corresponding topographic images are characterized by various statistical quantities like roughness parameters and two-dimensional power spectral density (2-D PSD). As compared to the control silica and clay filled rubbers, a noticeable reduction in the surface roughness is observed in the case of modified filled composites. Thus, the whole study based on AFM suggests that the surface modification of the above fillers significantly reduces the filler-filler interaction, which in turn reduces the filler aggregate size and helps in improving the filler dispersion.