Modification of ZnO and its effect on Rheological and Morphological Properties of PS/ZnO Nanocomposites Mehrnoosh Taghavi Mehr, Atefe Golbang, M.H.N Famili Polymer Engineering Group, Faculty of Chemical Engineering, Tarbiat Modares University, P.O. Box: 14115-143, Tehran, Iran Nano-sized ZnO, as one of the most studied semiconductors, is a good dispersant and its presence enhances dielectric and thermal properties of polymers. Homogeneous dispersion of nanoparticles in the polymer matrix is vital to achieve many of these properties. The possibility to modify and control the surface wettability of nanoparticles has attracted significant interest. Thus, the main purpose of this study was to evaluate the surface modification and dispersion of ZnO nanoparticles in polystyrene matrix using three different silane coupling agents; 3-Aminopropyltrimethoxysilne,Triethoxyoctylsilane and Vinyltriethoxysilne. The surface modified ZnO nanoparticles were characterized by Fourier Transform Infrared Microscopy (FTIR) in order to assess the efficiency of silane couplings. Then the effect of surface modification on the dispersion of nanoparticles was investigated through rheological tests on the obtained ZnO/PS nanocomposites. From the FTIR results it was confirmed that all the selected silanes were covalently bonded to the ZnO surface enabling better dispersibility and compatibility with the PS matrix as compared to the unmodified ZnO nanoparticles. The dispersion of ZnO particles in PS matrix was observed by SEM. It was found that the dispersion of surface-modified ZnO particles were better than unmodified one. Keywords: ZnO,Silane modification,PS.