ATOMIC FORCE MICROSCOPY STUDIES ON MORPHOLOGY AND DISTRIBUTION OF SURFACE MODIFIED SILICA AND CLAY FILLERS IN AN ETHYLENE-OCTENE COPOLYMER RUBBER SUDIP RAY ,ANIL K. BHOWMICK* RUBBER TECHNOLOGY CENTRE,INDIAN INSTITUTE OF TECHNOLOGY KHARAGPUR 721302, INDIA S. BANDYOPADHYAY SCHOOL OF MATERIALS SCIENCE AND ENGINEERING,THE UNIVERSITY OF NEW SOUTH WALES SYDNEY 2052, AUSTRALIA ABSTRACT Topographic and phase imaging in tapping mode atomic force microscopy (TMAFM) has been performed to inves- tigate 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. INTRODUCTION Investigations during the past several years have established the role of particulate fillers in modifying the properties of various polymers. It is also well recognized that the reinforcing potential of a filler is primarily dependent on the filler surface characteristics and its distribution. 1 Amongst the non-black fillers, precipitated silica and clay fillers are used most extensively in the elastomeric applications. Both silica and clay fillers have a great disadvantage due to their poor reinforcing ability with the polymer. 2,3 In the case of silica filler, the presence of highly populat- ed surface silanol groups leads to an inherent tendency to form aggregated structures on a sub- micron scale and the presence of a large number of such undispersed agglomerates results in poor vulcanizates properties. On the other hand, due to the big particle size and low surface activity, clay filler has very poor reinforcing ability even compared to silica filler. In order to enhance the polymer-filler interaction, several attempts have been made in the past to reduce the filler-filler interaction, which in turn reduces such aggregate formation or filler networking and also improves the filler dispersion in the polymer matrix and the filler surface activity. 3-6 Thus, the study of the morphology and the microdispersion of filler particles on the polymer matrix play an important part in understanding the reinforcing behavior of a filler. These are usually determined by scanning electron microscopy (SEM) or transmission electron microscopy (TEM). However, these methods require special sample preparation techniques to make it amenable for assay with the system. New microscopic techniques like scanning tunneling microscopy (STM) and atomic force 1091 * Corresponding author. Ph: +91-3222-283180/282037; Fax: +91-3222-255303/277190; email: anilkb@rtc.iitkgp.ernet.in