Dielectric investigation of interphase formation in composite materials. I. Ionic conductivity and permittivity exploration

The aim of this study was to demonstrate the application of dielectric spec troscopy to composite material characterization during processing. Therefor e, the microdroplet pullout test was used to follow the mechanical interfac ial properties during processing. The results showed that interfacial shear stress strongly depends on the pressure, temperature, and process time at resin deposition. These observations were understood with dielectric spectr oscopy. Literature data were first applied to our system. Results based on the ionic conductivity signal showed the existence of a mutual diffusion me chanism at the interface The mechanism rate constant depends strongly on th e temperature, pressure, and process time. In a second part, we developed a way to follow the penetration depth with the permittivity signal. This app roach is based on electric field line exploitation. The results highlighted the same observations. In conclusion, it appears that the adhesion of matr ix-fiber is increased by composite processing at the monomeric state of the resin. Moreover, this study shows that this improvement is a consequence o f a mutual diffusion mechanism at the interface. (C) 2000 John Wiley & Sons , Inc.