Ubiquitous nature of the three-layered structure formation in the asymmetric phase separation of the epoxy/thermoplastic blends

The reaction induced phase separation behavior was investigated in various epoxy/thermoplastic (TP) blends. Several morphological structures, including the sea-island, dual morphological (epoxy-rich particles may disperse in the TP-rich domains, while TP-rich particles can also have some dispersions in the epoxy-rich phase) or three-layered (TP-rich continuous domains mainly located in the middle part of the sample while outer layers are mostly composed of epoxy-rich matrix) and nodular structure, were observed with the increase of the TP concentrations. In the middle TP concentration ranges, when the TP with low glass transition temperature (Tg) was used, dual morphological structures were formed. While for the epoxy/TP blends with high Tg thermoplastics, three-layered structures were observed. High Tg and the large molecular weight of the TP was considered to cause the dynamic asymmetry, which dominated the phase separation mechanism and formed such an unusual structure. Through the in-situ investigation on time evolution of phase separation process, ubiquitous nature of this formation mechanism of the three-layered structure were discussed, which may have some important implications on the applications of the epoxy/TP blends.