Study On Multi-Phase-Separation In An Epoxy Resin Modified With Polyethersulfone

The development of morphologies in Polyethersulfone (PES)-Epoxy (DGEBA)/4,4’-Methylene-bis(2,6-dimethylaniline) blends and these blends with inorganic rods were followed by Optical Microscope (OM), Scanning Electron Microscope (SEM) and Time-Resolved Light Scattering (TRLS). The effects during the phase separation process and the mechanism were discussed.The results show that, for the blends with composition in the near-critical region, the first phase separation begins with the micro-co-continuous morphologies. In the late-stage of the first phase separation, the fast-growth mode of the domains could be found. Comparing the continuously increasing quench depth, the fast hydrodynamic flow due to interface motion plays a great important role in the occurrence of secondary phase separation. The secondary Epoxy-rich particles in the primary PES-rich domains grow in the size and coalescence to each other by the increasing temperature. However, the secondary PES-rich particles in the primary Epoxy-rich domains change a little in the size.During the middle and late stage of the first phase separation in the blends with larger PES molecular weight cured at the higher temperature, the process of morphology evolution of primary domain shows the clear feature of viscoelastic phase separation:the micro-co-continuous morphologies at the beginning turn to inversed-phase structure, then to the co-continuous domains with larger size, and to the dispersed-phase in the end.For the off-symmetric cure reaction-induced phase separation system with multi-phase-separation, many complex nonlinear effect coupled with each other lead to change of the peak scattering vector (qm) versus time in complicated manner, and could not obey the scaling law. Contrast to the symmetric blends in which the primary domains grow in size due to the mutual diffusion, the diffusion of the fast dynamic component lead to but the slow dynamic component retard the primary domains growth in size in these asymmetric blends.For the blends with near critical component, in the primary slow dynamic component rich domains, the secondary phase separation due to the high hydrodynamic flow and multi phase separation triggered by the cure reaction would be observed. However the tertiary fast dynamic component rich particles could be found only in the secondary slow dynamic component rich domains in the primary phase, in the case of the phase separation could not be frozen by the gelation or vitrification.The processes of phase separation in the supercritical PES concentration blends with inorganic rods (ATT or CaSO4) are almost similar to that in the unfilled blends. In comparison with the networklike phase morphology in blends without inorganic rods, the less PES content blends with ATT or CaSO4rods show the final inversed-phase morphology. And the secondary phase separation could be restrained by the increasing of the inorganic rods content and temperature. It is very interesting that the PES-rich particles become to coalescence each other and coarsen in size along the axis of rods in the blends with CaSO4curing at140℃.2D TRLS correlation spectral analysis had been employed to study of the blends in which secondary phase separation occurs or not. The2D correlation spectral analysis results show that the sequential order of coarsening in size of the phase structure among the larger and smaller ones has been reversed between the diffusion regime and the hydrodynamic regime in the first phase separation. The results indicate that the hydrodynamic coarsening of the domain originated in the first phase separation still changes first after the secondary phase separation occurs for a quite long time. In the secondary phase separation, the size change of the new smaller domains takes earlier than that of the larger one. The results suggest that the system prefer to obey in the upper method to decrease the system energy quickly.