| Fillers with characteristic sizes on the nanometer scale and aspect ratios near unity are investigated for their potential to enhance the mechanical properties of a linear amorphous polymer, polystyrene. Four types of nanoparticles with different sizes, structures, and interactions with the matrix have been investigated to better understand the particle-polymer interaction and its significance for mechanical property enhancement. Generally, the particle inclusion increases polymer mobility and free volume. This is observed through decreases in the glass transition temperature, bulk modulus, and internal pressure, as well as increases in the free energy anharmonicity, and strain-to-failure for a sample in tension. The particles behave in a manner similar to a good solvent, swelling the polymer and increasing chain mobility and sample ductility, an observation confirmed by neutron scattering. The details of the particle size, loading, and chemistry introduce other nuances to the polymer-particle behavior. Bulk modulus increases have been observed for many systems, and a general increase in the energy dissipation for a sample in tension is observed with nanoparticle addition. The role of the particles in the orientation of the matrix during uniaxial hot-drawing is studied. In many cases, it is found that equivalent tensile property enhancement can be achieved under more moderate processing conditions by the addition of nanoparticles. |
