MEASUREMENT OF DIFFUSIVITY OF A LIQUID DIAMINE IN SOLID EPOXIES USINGATTENUATED TOTAL REFLECTANCE INFRARED-SPECTROSCOPY (FTIR-ATR)

A number of studies on thermosetting polymeric composite materials hav e indicated the existence of a three dimensional region of the matrix in the vicinity of the fiber, which exhibits distinct properties. A ke y factor in the interphase formation of epoxy-diamine mixtures is the diffusivity of the diamine relative to the epoxy prepolymer. A techniq ue for measuring diffusion coefficients of a liquid through solid poly meric thin layers is described. Infrared attenuated total reflectance (ATR) spectroscopy is used to analyze diffusion couples with infrared distinguishable bands. A cylindrical germanium crystal, coated with th e polymeric layer of interest, is immersed in a boat cell filled with the diffusant, and infrared spectra of the system are taken in real ti me. By those means, only the region close to the solid surface is scan ned without interferences from the bulk. The temperature dependence of diffusivity can also be evaluated by the use of a heated cell. Diffus ivities that are evaluated in this way can be used to predict stoichio metric gradients during the curing reaction of the system and, therefo re, the structure and property gradients of the material around the fi ber. (C) 1994 John Wiley & Sons, Inc.