Characterization and modeling of mechanical behavior of polymer/clay nanocomposites

Polymer/clay nanocomposites consisting of epoxy matrix filled with silicate clay particles were investigated. These particles consist of 1 nm thick platelets or layers with an aspect ratio in the range of 100-1000. Recent and ongoing research has shown that dramatic enhancements can be achieved in stiffness and thermal properties in these nanocomposites with small amounts of particle concentration. The resulting nanocomposite properties are intimately related to the microstructure achieved in processing these materials. The ideal situation of full exfoliation, dispersion and orientation is not usually achieved. A more common case is partial exfoliation and intercalation. The latter is a process whereby the polymer penetrates the interlayer spaces of the clay particles, causing an increase in layer spacing (d-spacing). A three-phase model, including the epoxy matrix, the exfoliated clay nanolayers and the nanolayer clusters was developed. The region consisting of matrix with exfoliated clay nanolayers or platelets was analyzed by assuming near uniform dispersion and random orientation. The properties of intercalated clusters of clay platelets were calculated by a rule of mixtures based on a parallel platelet system. The Mori-Tanaka method was applied to calculate the modulus of the nanocomposite as a function of various parameters, including the exfoliation ratio, clay layer and cluster aspect ratios, d-spacing, intragallery modulus, matrix modulus and matrix Poisson's ratio. With appropriate parameters obtained from experiments, model predictions were in good agreement with experimental results.