  The structure of a polystyrene matrix filled with tightly cross-linked
polystyrene nanoparticles, forming an athermal nanocomposite system, is
investigated by means of a Monte Carlo sampling formalism. The polymer chains
are represented as random walks and the system is described through a coarse
grained Hamiltonian. This approach is related to self-consistent-field theory
but does not invoke a saddle point approximation and is suitable for treating
large three-dimensional systems. The local structure of the polymer matrix in
the vicinity of the nanoparticles is found to be different in many ways from
that of the corresponding bulk, both at the segment and the chain level. The
local polymer density profile near to the particle displays a maximum and the
bonds develop considerable orientation parallel to the nanoparticle surface.
The depletion layer thickness is also analyzed. The chains orient with their
longest dimension parallel to the surface of the particles. Their intrinsic
shape, as characterized by spans and principal moments of inertia, is found to
be a strong function of position relative to the interface. The dispersion of
many nanoparticles in the polymeric matrix leads to extension of the chains
when their size is similar to the radius of the dispersed particles.
