USE OF INFRARED THERMOGRAPHY FOR TEMPERATURE-MEASUREMENT DURING EVAPORATIVE CASTING OF THIN POLYMERIC FILMS

In this paper we describe the development of a real-time, noninvasive technique using infrared (IR) thermography for measurement of the temperature of polymer solutions cast as thin films in which evaporation of a volatile solvent occurs. The technique requires the accurate determination of a single surface radiation property, the emittance, and its dependence on the casting solution composition, We report results obtained for the cellulose acetate (CA)-acetone system for which IR measurements indicate a relatively rapid and significant temperature decrease followed by a gradual temperature recovery toward the initial temperature, In general the thin film temperature response can be described by the parameters Delta T-max, the maximum degree of cooling; t(min), the time at which T-min is reached; and the recovery temperature, T-rec, at a time equal to 2 x t(min). For 155 and 258 mu m thick films evaporatively cast from a 15 wt% CA solution, IR thermography indicated maximum temperature decreases of 18 and 26 degrees C, respectively, The characteristics of the thin film temperature curves for these two cases compare favorably with those predicted by a first-principles model recently developed by the authors. Based upon these results, the general applicability of the infrared technique for the study of dense film- and membrane-formation processes is described, and the significance of thin film temperature measurements with respect to membrane morphology is discussed.