1741 Research Article Received: 9 June 2015 Revised: 27 July 2015 Accepted article published: 4 August 2015 Published online in Wiley Online Library: 21 August 2015 (wileyonlinelibrary.com) DOI 10.1002/pi.4974 Preparation and characterization of novel addition cured polydimethylsiloxane nanocomposites using nano-silica sol as reinforcing filler Dongzhi Chen, a* Fengxiang Chen, a,b Hongwei Zhang, a Xianze Yin, a Xin Liu a and Yingshan Zhou a Abstract A series of novel addition cured polydimethylsiloxane (PDMS) nanocomposites with various amounts of nano-silica sol were prepared via hydrosilylation for the first time. The influence of various amounts of nano-silica sol on the morphology, thermal behavior, mechanical and optical properties of these PDMS nanocomposites was studied in detail. It was found that with an increment in the amount of nano-silica sol the reinforcing effect of the nano-silica sol on the thermal and mechanical properties of the PDMS nanocomposites was very noticeable compared with the reference material. The prominent improvements in resistance to thermal degradation and mechanical properties can probably be attributed to the strong interaction of PDMS chains and uniformly dispersed particles resulting from the nano-silica sol. However, the transparency of the PDMS nanocomposites slightly decreased with an increment in weight fraction of nano-silica, compared with that of PDMS composite without nano-silica (Sol-0), which can probably be ascribed to an increasing size of the aggregated particles in the PDMS nanocomposites. The optimum amount of nano-silica sol for preparing novel addition curing PDMS nanocomposites was about 15 wt%. © 2015 Society of Chemical Industry Keywords: nano-silica sol; PDMS nanocomposites; thermal properties; mechanical properties; transmittance INTRODUCTION To date, polydimethylsiloxane (PDMS) has been widely applied in many fields (automotive field, construction industry, micro- electronics area, textile industry and gas separation processes) due to its unique properties, such as high transparency, unusually high gas permeability, good electrical insulation, low surface tension, 1 excellent weather resistance and low toxicity. 2 – 6 Although unfilled PDMS has good flexibility and good resistance to thermo-oxidative and thermal degradation in a broad temper- ature range from -100 ∘ C to 250 ∘ C, it still has weak mechanical properties due to an inherent weak interaction between PDMS molecular chains and cannot meet the service requirements in the rubber industry. 7 – 9 In order to improve the mechanical properties of PDMS composites, a variety of reinforcing fillers such as carbon black, 10 montmorillonite, 11 nano-CaCO 3 , 12 carbon fiber, 13 car- bon nanotubes, 14,15 fumed silica 16 – 18 and polyhedral oligomeric silsesquioxanes 19 – 24 have been introduced into the PDMS matrix by physical blending, solution mixing and chemical crosslinking. But most of these reinforcing fillers are incorporated into the PDMS matrix via ex situ methods, and so they are difficult to disperse in the PDMS matrix at a molecular level and agglomerations of fillers are usually unavoidable. The size of filler aggregations in the PDMS matrix becomes large enough to cause low transparency of the PDMS composites. Although great progress in reinforcing the mechanical properties of PDMS composites has been made, the enhancement in mechanical properties is fundamentally based on sacrificing their transparency and thermal stability. The decreasing transparency and thermal stability further limit applications of the PDMS composites in the field of electronic packaging, especially for addition curing PDMS composites. Therefore it is urgent for materials researchers to develop novel PDMS composites with high transparency, excellent thermal stability and good mechan- ical properties to meet increasing demands from fashionable electronic devices. In the past decade, nano-silica sol, as a new particle, has been widely applied in many fields to prepare a variety of functional materials such as ceramic coatings, 25 hydrophobic coatings, 26 – 28 nanoglue 29 and polymer nanocomposites. 30,31 Compared with precipitated silica and fumed silica, nano-silica sol should have more silanols on its surface and easily forms multiple hydrogen bonds between surface silanols of the silica sol and polymer ∗ Correspondence to: Dongzhi Chen, School of Materials Science and Engineering, Wuhan Textile University, Wuhan 430200, P. R. China. E-mail: chdozh_2008@163.com a School of Materials Science and Engineering, Wuhan Textile University, Wuhan 430200, P. R. China b Hubei Collaborative Innovation Center for Advanced Organic Chemical Materi- als, Hubei University, Wuhan 430062, P. R. China Polym Int 2015; 64: 1741–1746 www.soci.org © 2015 Society of Chemical Industry