Glass Transitions in PS-TiO₂ Nanocomposites

Atactic polystyrene is considered a fully amorphous polymer. Homogeneous solutions of atactic polystyrene in chloroform were obtained by adding the two components and stirring the mixture for 4 hours. After homogenization, the polystyrene-chloroform solutions were moved in a larger beaker and sonicated for about 1 hour. Then, deionized water was suddenly added to the polymer solution, without interrupting the sonication process. The added volume of water was typical twice the volume of the polymer solution. The sonication was stopped after 15 minutes and the polymer was collected and then dried in an oven at 90 ^oC, for about 12 h. Full water evaporation was confirmed by TGA. Nanocomposites of PS-TiO₂, containing various amounts of TiO₂, have been obtained by using this procedure. It was expected that the rapid collapse of the polymeric chain (as the nonsolvent was added) would trap the nanofiller within the polymeric matrix.
The as-obtained nanocomposites were investigated by using a TA Instruments Q 50 DSC at various heating and cooling cycles ranging between 5 ^oC/min to 30 ^oC/min. The research is focused on the effect of heating/cooling rates (ranging between 5 ^oC/min to 30^oC/min) and of the concentration of TiO₂ on the glass transition temperature of PS-TiO₂ nanocomposites.