A MICRODIELECTRIC ANALYSIS OF MOISTURE DIFFUSION IN THIN EPOXY/AMINE FILMS OF VARYING CURE STATE AND MIX RATIO

Recent work has shown that moisture diffusion coefficients can be measured in thin polymer films through monitoring changes in permittivity with microdielectric sensors. The sensor is constructed in silicon and consists of an interdigitated electrode and two depletion mode field effect transistors. When operated in conjunction with appropriate external circuitry, the sensor measures dielectric constant and loss factor of any material placed on the SiO2 insulator and aluminum electrodes. The dielectric properties are measured locally within the first 10 microns of the film in contact with the sensor. As a thin polymer film on the sensor is exposed to a high relative humidity, the dynamically measured dielectric constant can be used to determine exactly when the moisture arrives at the polymer-SiO2 interface and the rate at which the concentration increases. The magnitude of the change in permittivity after equilibration has also been related to total amount of moisture uptake. In this investigation, several epoxy/amine films of varying mix ratios and cure state are cured on microdielectric sensors. The films, approximately 100 microns thick, are alternately exposed to wet and dry environments. Diffusion coefficients for both absorption and desorption are determined from the dielectric data as a function of cure state and epoxy/amine mix ratio. In addition, relative changes in amount of moisture uptake after equilibration is monitored.