Effects of shape and size disparity of nanofillers on percolation and thermal properties of polymers.

摘要

Powdered materials of sizes ranging from nanometers to microns are widely used in materials science and are carefully selected to enhance the performance of a matrix. Fillers have been used in order to improve, among the others, mechanical, rheological, electrical, magnetic and thermal properties of the host material.; Changes in the shape and size of the filler particles can magnify such enhancement. This effect is usually associated with an increased probability of formation of a percolating cluster of filler particles in the matrix.; Previous model calculations of percolation in polymeric systems generally did not take the possible difference between the size and shape of monomers and filler particles into account and usually neglected interactions or accounted for them in a crude fashion.; In our approach the original lattice is replaced by a recursive structure like a Husimi tree or a Bethe lattice on which calculations are done exactly and interactions as well as size and shape disparities can be easily taken into account.; Here we study the possible percolation of filler particles of different sizes and shapes in the system in various phases including metastable states. In order to validate this approach, we have applied the method first to simpler systems made of particles of different sizes and shapes. The approach has then been extended to take into account the presence of a polymer matrix in which particles of different sizes and shapes are embedded.; The approach appears to be extremely successful since it is able to capture most of the important features observed in experiments. In particular, we are able to observe how the percolation threshold increases with the size of the filler particles and how the presence of size disparity between the filler particles decreases such threshold.; The approach that has been developed represents a new method to deal with nanoscales and it shows promise for future implementations.