Preparation and characterization of polystyrene/TiO2 core-shell nanospheres via suspension technique

In the present work, at first, nano-TiO2 particles in anatase form were effectively surface modified via reacting with NCO groups of 4,4'-methylenediphenyl disocyanate (MDI). Secondly, a solution of azobisisobutyronitrile (AIBN) (0.1 g) in inhibitor-free styrene (10 g) was poured into a 150 mL flask containing poly (vinyl alcohol) (PVA) suspending agent (0.1 g) in deionized water (60 mL) under N-2 flow, while stirring. The reaction mixture was then heated to 80 degrees C, and stirred for another 1 h. Next, it was divided to two portions; one for the synthesis of pure PS, and the other for the synthesis of PS/TiO2 nanocomposites. Each aqueous portion was individually mixed with dichloromethane in a separating funnel. For PS/TiO2 nanocomposites, the organic phase was charged with nano-TiO2 particles (MDI-treated and/or untreated) (0.05 g), and then fully homogenized using ultrasonic homogenizer. Methanol non solvent was eventually used to precipitate the products. All samples involving pure PS, PS/surface modified TiO2 nanocomposite, and PS/surface unmodified TiO2 nanocomposite were thoroughly washed, filtered, and dried in vacuum at 50 degrees C for 12 h. From SEM images a core-shell relation could be clearly detected between the nano-TiO2 particles and PS matrix. Meanwhile, the surface modified TiO2 was dispersed into the PS matrix with better homogeneity compared to that of unmodified one. Undoubtedly, beside the surface modification factor, PVA suspending agent as an effective nanosized particle stabilizer, too, played a basic role in this high homogeneity. Also, FT-IR and XRD analyses led to promising results.