Investigation of Optical and Thermally Stimulated Properties of SiO 2 Nanoparticles-Filled Polycarbonate Bhupendra Singh Rathore, 1,2 Mulayam Singh Gaur, 1 Kripa Shanker Singh 2 1 Department of Physics, Hindustan College of Science & Technology, Farah, Mathura (U.P.)-281122, India 2 Department of Physics, R.B.S. College, Agra (U.P.)-282002, India Received 19 January 2011; accepted 13 February 2012 DOI 10.1002/app.37004 Published online in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: Polycarbonate nanocomposite containing silicon oxide nanoparticles average size of 5 nm at differ- ent weight ratio has been prepared by solution mixing method. The dispersion of nanoparticles in polymer matrix was studied by transmission electron microscopy (TEM). The optical and thermally stimulated behavior of nano- composites were analyzed by energy dispersive X-ray spectra (EDX), X-ray diffraction pattern (XRD), UV–vis spectroscopy, differential scanning calorimetry (DSC), and thermally stimulated discharge current (TSDC). TEM images show the dispersion and size of the nanoparticles, however, EDX indicate the presence of SiO 2 on the surface of the nanocomposite film. An XRD result reveals that the crystallinity increases with increase in concentration of SiO 2 nanoparticles in polymer matrix. The direct and indi- rect optical energy band gaps decreased and number of carbon atom increased with concentration of SiO 2 nano- particles. We have observed that the increase of SiO 2 nano- particles in PC significantly reduces the refractive index. DSC and TSDC show that glass transition temperature increases according to SiO 2 weight ratio. The TSDC of nanocomposites samples could be understand in terms of non-Debye theory of charge relaxation and co-tunneling mechanism of charge transport. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 000: 000–000, 2012 Key words: TSDC; nanocomposite; activation energy; relaxation time; co-tunneling INTRODUCTION The electret state in insulating materials arises from the induced polarization owing to the frozen in phe- nomenon of electric charges. The study of electret state in insulating polymers using thermally stimu- lated discharge current (TSDC) technique reveals the nature of various relaxation processes. TSDC is the study of charge decay by heating the electret at con- stant rate. These decay processes are investigated as a function of temperature. The application of poly- mer nanocomposites as an electret is the promising area of research. 1–3 Electrets can store the charge for long time and will especially apply as a supercapaci- tor, piezosensor, pyro sensor, etc. 4–10 The SiO 2 thin film electret is a promising electret for energy har- vesting. It can be used to realize vibration-based capacitive energy harvester systems using CMOS- compatible processes. 11 Organic–inorganic nanocomposite materials are increasingly important because of their outstanding properties arises from synergism between the prop- erties of the components. There are several routes to these materials, but probably the most prominent one is the incorporation of inorganic fillers in or- ganic polymers. These materials have gained much interest because of their excellent mechanical, 12 elec- trical, 13 thermal, 14–18 and magnetic 19 properties when compared with pristine organic polymers. There are many similarities in PC and SiO 2 nano- particles. PC and SiO 2 both are amorphous, trans- parent, light weight, high stability and wide band gap materials. 20–22 Therefore, the combinations of PC and SiO 2 have been chosen in this study. The issues of dispersion of SiO 2 in composite sys- tem, as a result of poor interactions at nanofiller polymer interface, are very important. Because uni- form dispersion of nanofiller could able to achieve the desired properties. Zheng et al. 23 recently applied the ultrasound waves for dispersion of nanoparticles in polymers and achieved uniform dis- persion of silica nanoparticles in epoxy resin. A dra- matic increase in interfacial area between fillers and polymer can significantly improve the properties of pristine polymers. 24 The well-dispersed nanopar- ticles can effectively enhance the comprehensive properties of nanocomposites, which are unique and different from any other composites. 25 In experimental point of view, the relaxation kinetics in the amorphous-glassy state can be charac- terized by means of thermally stimulated depolariza- tion current (TSDC) whereas the relaxation kinetics Correspondence to: B. S. Rathore (bsrathorephy@gmail. com) or M. S. Gaur (mulayamgaur@rediffmail.com). Journal of Applied Polymer Science, Vol. 000, 000–000 (2012) V C 2012 Wiley Periodicals, Inc.