Detecting interphases using micro-interferometric measurements

A scanning micro-interferometer is utilized to detect differences in the thermal displacements caused by applying a thin coating to a fiber surface. Measurements are made on samples containing single pitch based carbon fibers embedded in an epoxy matrix. Two different interphase conditions are investigated. In the first type of sample, the fiber is coated with a resin which when cured has a lower glass transition temperature than the matrix. In the second type of sample, the fibers are untreated (no coating). Displacement gradients near the fiber/matrix interface are significantly larger for the coated fiber. Comparison of the experimental profiles measured for both types of samples with theoretical displacement predictions, indicate that the value of the matrix properties near the fiber surface differ appreciably from the value in the neat resin. The data provides evidence consistant with previous research findings of a depressed glass transition temperature in the interphase.