DRYING OF GLASSY POLYMER VARNISHES - A QUARTZ RESONATOR STUDY

We report on desorption measurements on polymeric thin films coated on to quartz crystal resonators. Due to the high sensitivity of quartz cr ystal microbalances, the experiments can be performed on very thin fil ms: which have small diffusion time constants even in the glassy state . When drying is performed slowly enough, diffusion equilibrium can be maintained through the whole process of desorption, including the gla ssy domain. From these quasi-stationary pressure ramps, we derived the solvent chemical potential as a function of polymer volume fraction m u(phi) The results fit well to a model recently proposed by Leibler an d Sekimoto.(1) In addition, we have derived the mutual diffusion coeff icient D(phi) from pressure step experiments. We observe a strong decr ease of D(phi) for high polymer concentrations typical of hypodiffusiv e systems like polymers. We investigated the drying of an industrial v arnish that is a blend of 2 copolymers as well as the drying of its co mponents separately. Both the solvent chemical potential mu(phi) and t he mutual diffusion coefficient D(phi) of the blend interpolate betwee n the respective quantities of the components. (C) 1998 John Wiley & S ons, Inc.