FORMATION OF THE INTERPHASE IN ORGANIC-MATRIX COMPOSITES

This paper addresses attempts made to determine the mechanical and chemical properties of material within a micrometre of the surface of a single carbon fibre in an epoxy/amine matrix. Work reported earlier has shown that deformation data near a fibre can be interpreted as showing that the modulus of this material could be lower than that of the bulk matrix for a distance of about 0.5 mum from the fibre. Spectral evidence suggests that the material in this region is chemically different from material remote from the interface. Analysis of the variation of fibre debond forces in a composite as a function of the fibre content also suggests that the matrix is softer near the fibre. The present paper addresses studies done to determine a mechanism for the variation of mechanical and chemical properties over such a distance. Possibilities considered include modification of resin stoichiometry in the region by preferential absorption of active species, formation of a zone of incomplete polymerization caused by entropic effects related to the two-dimensional nature of the interface, and modification of the resin solidification mechanism in the region of the fibre.