Here we report the significant enhancement effect of mesoscopic fillers in viscoelastic phase separation of dynamic asymmetric polymer blends. Mesoscopic fillers with their size much larger than the dimensions of the polymer chains, from nanometres to microns, are preferentially immersed into the slow dynamic phase and phase interface due to the entanglement with polymer chains. For sufficiently high volume fraction and fine dispersion, mesoscopic fillers conduce to the pronounced slowing down of the phase separation process, and result in refined structures with sharply decreased characteristic length scales. The pinning of the phase separation is attributed to the dramatic increase of dynamic asymmetry from the entanglement of polymer chains with mesoscopic fillers. The principal difference between mesoscopic fillers in classic and viscoelastic phase separation is whether there exists a filler enforced elastic-force balance condition. This suggests a general physical scenario of entanglement selection of the polymer chains under stress.

In the present work, time-resolved attenuated total reflection Fourier transform infrared spectroscopy (ATR-IR), near-infrared (NIR) spectroscopy, and generalized two-dimensional (2D) correlation analysis were used to investigate water diffusion processes and the state of water molecules in six different epoxy resins. Positron annihilation lifetime spectroscopy (PALS) experimental results and IR results suggested that water diffusion is controlled by local chain reorientation and bond dissociation of water molecules from epoxy networks. Dynamic mechanical analysis (DMA) results of glass transition temperatures of epoxy resins after immersion in hot water correlated well with the PALS and IR results. In addition, four types of water molecules, termed nonbonded (S(0)), single bonded (S(1)), loosely double hydrogen bonded (S(2L)), and tightly double bonded (S(2T)), were detected. It was likewise found, as verified by rough estimation, that water molecules with double hydrogen bonds mostly accomplished diffusion.

Changes in the properties of epoxy prepregs during storage are of both industrial and theoretical interest. It would be very helpful to have a test, suitable for production use, to determine when a prepreg has aged beyond acceptable limits. In this article, different epoxy prepregs aged under various conditions were studied by near-infrared (NIR) and mid-infrared (MIR) Fourier transform spectroscopies, dynamic mechanical analysis (DMA), rheological analysis, time-resolved light scattering (TRLS), and optical microscopy (OM). A very good relationship between storage aging time and curing conversion was obtained by NIR measurements. Furthermore, the rheological study showed that both the viscosity and the gelation time changed with storage aging. Changes in the glass transition temperatures of epoxy prepregs can result from either curing or phase separation during storage aging. The TRLS and OM results showed that structural evolution might occur during storage for some prepregs.

In this article, an amphiphilic oligomeric silane (OS) was synthesized as a coupling agent to improve the interface bonding between resin matrix and glass fiber. The effect of the OS coupling agent on the interface of glass fiber/epoxy resin was studied by contact angle measurement, gravimetric measurements of water sorption, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and conductive anodic filament (CAF) resistance test. With the addition of the OS to the composites, the contact angle between epoxy resin and glass fiber decrease notably. Normalized water sorption by gravimetric measurements showed that the interfacial debonding time of composites with the OS can be prolonged significantly. CAF tests were also consistent with the water sorption results, which suggest that the gravimetric measurement of water sorption is a cost-effective method to assess the CAF resistance of materials.