TRANSPORT AND DIELECTRIC-PROPERTIES OF POLY(ETHYLENE-TEREPHTHALATE) AS DETERMINED VIA ELECTROCHEMICAL TECHNIQUES

The electrochemical impedance spectroscopy (EIS) technique was used to evaluate the water transport (diffusion and equilibrium water uptake) and the dielectric properties of free-standing poly (ethylene terepht halate) (PET) membranes at 40-degrees-C. Permeability and diffusion co efficients were also obtained using the Payne cup method and the MacBa in quartz spring balance to assess the reliability of the EIS method w hen compared to other techniques. In addition, an electromigration (dc ) technique was used to estimate the NaCl diffusion coefficient across PET films. Results obtained indicate that PET is highly permeable to water and much less permeable to salt. The water diffusion coefficient , D, varies from 2.11 X 10(-9) to 9.97 X 10(-9) cm2 s-1 for thicknesse s between 22 and 205 mum, whereas the equilibrium water uptake, W, var ies from 0.54 to 0.95 wt % for the same given range of thicknesses. Th e average calculated dielectric constant of the free-standing PET film s is 3.6. An estimate of the NaCl diffusion coefficient, D(s), is 9.34 X 10(-14) CM2 s-1. Transport properties results obtained via the elec trochemical technique are in reasonable agreement with those obtained with the classical gravimetric method.