Structural SAXS study of epoxy-acrylate interpenetrating polymer networks. Fractal geometry and spherical domain sizes

Five interpenetrating polymer network (IPN) epoxy-acrylate samples of the same composition synthesized with variable conditions - temperature and initiator rate - were studied by small-angle X-ray scattering (SAXS). The scattering curves, at first sight showing little detail, were meticulously analysed. The entire scattering curve of an IPN compound was analysed using new methods for background subtraction and desmearing. The treatment suggests a fractal behaviour of the internal surface, associated with this two-phase system, on a scale between 100 and 10 nm and, in the tail end of the SAXS curves, reveals maxima corresponding to those of two regular spheres with radii of the order of 7 and 14 nm. Analysis of the beginning of the curves yields one or two correlation lengths according to the conditions of the synthesis, close to 100 and 20 nm. These results are consistent with the general model of IPN structures as revealed by other physico-chemical techniques.