  This paper presents a study of the polymer-filler interfacial effects on
filler dispersion and mechanical reinforcement in Polystyrene (PS) / silica
nanocomposites by direct comparison of two model systems: un-grafted and
PS-grafted silica dispersed in PS matrix. The structure of nanoparticles has
been investigated by combining Small Angle Neutron Scattering (SANS)
measurements and Transmission Electronic Microscopic (TEM) images. The
mechanical properties were studied over a wide range of deformation by
plate/plate rheology and uni-axial stretching. At low silica volume fraction,
the particles arrange, for both systems, in small finite size non-connected
aggregates and the materials exhibit a solid-like behavior independent of the
local polymer/fillers interactions suggesting that reinforcement is dominated
by additional long range effects. At high silica volume fraction, a continuous
connected network is created leading to a fast increase of reinforcement whose
amplitude is then directly dependent on the strength of the local
particle/particle interactions and lower with grafting likely due to
deformation of grafted polymer.
