Unexpected Effect of Small Nanoparticles: New Horizon for Polymer Nanocomposites

The addition of nanoscale fillers with strong attraction to polymers causes significant changes to the polymers’ dynamics and mechanical properties. The challenge of polymer nanocomposite (PNC) research is to understand the critical microscopic parameters (e.g. chain rigidity, molecular weight, nanoparticle geometry) that control the emergent macroscopic properties of PNCs. In this work, we investigated the effects of adding very small (~1.8nm) POSS nanoparticles to a polymer (P2VP) melt. We found unexpectedly large increases in Tg (~35K) and fragility for the POSS-PNCs compared to PNCs with conventional 10-50nm filler. Further, the POSS-PNCs had unexpectedly small thermodynamic and viscoelastic changes from the neat polymer. This potential for easy processing overcomes a major challenge for polymer nanocomposites’ use in practical applications. Combining these results with theoretical calculations, we ascribe these unusual behaviors to two unique properties of PNCs with small nanoparticles: (i) fast mobility of small nanoparticles, and (ii) relatively short chain – nanoparticle desorption time. These features that are not accessible in conventional PNCs provide a new frontier for property enhancement in polymer composite materials.