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 (T-g) was used, dual morphological structures were formed. While for the epoxy/TP blends with high T-g thermoplastics, three-layered structures were observed. High T-g 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. (C) 2011 Elsevier Ltd. All rights reserved.