New insights into rubber-clay nanocomposites by AFM imaging

In the present study, topographic and phase imaging in tapping mode atomic force microscopy was performed to investigate the size of clay platelets, the polymer-filler interface, pull-off and contact forces between the sample and the tip, power spectral density, fractal dimension and spatial distribution of the nanoclays [unmodified (Cloisite NA) and modified clay (Cloisite 20A)] in the terpolymer of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene (fluoroelastomer). The phase images of the above nanocomposites elucidated that the width of clay particles was lower in the case of the unmodified clay filled system. Interestingly, the polymer was able to exfoliate both the unmodified and modified clays. This phenomenon was supported by transmission electron microscopy and X-ray diffraction studies. The results obtained from the section analysis and the histogram of the filler distribution further supported the above findings. The surface roughness was less in the case of the unmodified clay based nanocomposite, as determined from roughness, power spectral density and fractal analysis. The study also indicated an improved particle distribution in the case of the unmodified clay filled samples. The results were explained with the help of thermodynamics and soft-hard acid base theory. (c) 2006 Elsevier Ltd. All rights reserved.