Mechanical properties of Al2O3/polymethylmethacrylate nanocomposites

Alumina/polymethyhnethacrylate (PMMA) nanocomposites were produced by incorporating alumina nanoparticles, synthesized using the forced gas condensation method, into methylmethacrylate. The particles were dispersed using sonication and the composites were polymerized using free radical polymerization. At an optimum weight percent, the resulting nanocomposites showed, on average, a 600% increase in the strain-to-failure and the appearance of a well-defined yield point when tested in uniaxial tension. Concurrently, the glass transition temperature (T-g) of the nanocomposites dropped by as much as 25degreesC, while the ultimate strength and the Young's modulus decreased by 20% and 15%, respectively. For comparison, composites containing micron size alumina particles were synthesized and displayed neither phenomenon. Solid-state deuterium NMR results showed enhanced chain mobility at room temperature in the nanocomposites and corroborate the observed T-g depression indicating considerable main chain motion at temperatures well below those observed in the neat polymer. A hypothesis is presented to relate the thermal and mechanical behavior observed in the composites to the higher chain mobility and T-g depression seen in recent ultrathin polymer film research.