Morphology evolution of polysulfone nanofibrous membranes toughened epoxy resin during reaction-induced phase separation

The phase separation process and morphology evolution of 5 wt% polysulfone (PSF) nanofibrous membranes toughened epoxy resin at different temperatures were investigated by synchrotron radiation small angel X-ray scattering (SR-SAXS), phase contrast microscopy (PCM) and scanning electron microscopy (SEM). The onset time of phase separation obtained by different methods was basically identical. As the curing proceeded at constant temperature, the scattering peak corresponding to the maximum scattering intensity shifted to a smaller scattering vector (qm), and the average diameters of PSF spheres increased, which showed a phase separation pattern of nucleation and growth mechanism. PSF spheres exhibited random alignment in “sea-island” morphology, which was attributed to the in situ phase separation of PSF nanofibers. Also, the effects of phase separation kinetics on the phase morphology and fracture toughness of nanofibrous membranes toughened epoxy resin were investigated. Results showed that the phase separation process was faster than the curing reaction process, which implied that the diffusion coefficient of PSF in epoxy resin increased with increasing the curing temperature, resulting in the increase of PSF sphere size that in turn improved the fracture toughness at higher temperature.