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 temp erature of polymer solutions cast as thin films in which evaporation o f a volatile solvent occurs. The technique requires the accurate deter mination of a single surface radiation property, the emittance, and it s dependence on the casting solution composition, We report results ob tained for the cellulose acetate (CA)-acetone system for which IR meas urements indicate a relatively rapid and significant temperature decre ase followed by a gradual temperature recovery toward the initial temp erature, In general the thin film temperature response can be describe d 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 e vaporatively cast from a 15 wt% CA solution, IR thermography indicated maximum temperature decreases of 18 and 26 degrees C, respectively, T he characteristics of the thin film temperature curves for these two c ases compare favorably with those predicted by a first-principles mode l recently developed by the authors. Based upon these results, the gen eral applicability of the infrared technique for the study of dense fi lm- and membrane-formation processes is described, and the significanc e of thin film temperature measurements with respect to membrane morph ology is discussed.