Effects of nanoparticles SiO 2 on the performance of nanocomposites Yaping Zheng a , Ying Zheng b, * , Rongchang Ning a a Department of Chemical Engineering, Northwestern Polytechnical University, Xian 710072, China b Department of Chemical Engineering, University of New Brunswick, 15 Dineen Drive, P.O. 4400, Fredericton, N.B., Canada E3B 5A3 Received 28 September 2002; accepted 28 October 2002 Abstract New developments in the synthesis of nanoparticles SiO 2 have enabled the processing of exciting new nanoparticle/epoxy composites. Ultrasonic and mechanical methods were used to disperse the nanoparticles in epoxy resin. The nanocomposites were characterized by tensile and impact testing as well as TEM studies. Additionally, the effects of nanometer-sized SiO 2 particles on free volume of nanocomposites were studied using positron annihilation lifetime spectroscopy. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Nanocomposites; Epoxy resin; Positron annihilation 1. Introduction Epoxy resins are used in a variety of applications since their properties, such as thermal stability, mechanical response, low density and electrical resist- ance, can be varied considerably. The important factors influencing their performance are the molecular archi- tecture, curing conditions and the ratio of the epoxy resin and the curing agent(s). The use of an additional phase (e.g. inorganic fillers) to strengthen the proper- ties of epoxy resins has been a common practice. Developments in the synthesis of nanometer-sized particles have made it possible to process nanocompo- sites. Nanoparticles can fill up the weak microregions of resins to boost the interaction forces at the polymer – filler interfaces. A dramatic increase in the interfacial area between fillers and polymer can significantly improve the properties of the polymer [1]. The rein- forcement efficiency is reported to show strong dependence on dispersion of nanoparticles. Well-dis- persed nanoparticles can effectively enhance the com- prehensive properties of nanocomposites, which are unique and different from any other current composites with typical filler amounts of less than 5 wt.% [2,3]. Both macroscopic and microscopic measurements are normally performed for a newly synthesized com- posite to achieve an overall understanding. The posi- tron annihilation lifetime spectroscopy (PALS) technique has been widely used in the study of poly- meric systems at the molecular level in the recent years. This technique utilizes the interactions between the positrons and the electrons from the host material. Although there has been an observed increase of the number of papers concerning PLAS applications in the 0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(02)01401-5 * Corresponding author. Fax: +1-506-453-3591. E-mail address: yzheng@unb.ca (Y. Zheng). www.elsevier.com/locate/matlet Materials Letters 57 (2003) 2940 – 2944 Downloaded from http://www.elearnica.ir