This paper describes the design and performance of a new instrument to track temporal changes in physical parameters during the drying behavior of solutions, as well as curing of monomers. This real-time instrument follows in-plane and out-of-plane birefringence, weight, thickness, and surface temperature during the course of solidification of coatings and films through solvent evaporation and thermal or photocuring in a controlled atmosphere. It is specifically designed to simulate behavior of polymer solutions inside an industrial size, continuous roll-to-roll solution casting line and other coating operations where resins are subjected to ultraviolet (UV) curing from monomer precursors. Controlled processing parameters include air speed, temperature, initial cast thickness, and solute concentration, while measured parameters are thickness, weight, film temperature, in-plane and out-of-plane birefringence. In this paper, we illustrate the utility of this instrument with solution cast and dried poly (amide-imide)∕DMAc (Dimethylacetamide) solution, water based black paint, and organo-modified clay∕NMP (N-Methylpyrrolidone) solution. In addition, the physical changes that take place during UV photo polymerization of a monomer are tracked. This instrument is designed to be generic and it can be used for tracking any drying∕swelling∕solidification systems including paper, foodstuffs such as; grains, milk as well as pharmaceutical thin paste and slurries.

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The development of optical anisotropy gradient as a result of solvent evaporation for poly(amide–imide) (PAI) solution in dimethylacetamide (DMAc) was investigated for the first time. Experiments were carried out using real-time optical measurement with spectral birefringence technique coupled with off-line optical techniques such as the Abbe refractometer and optical compensator method. We have shown that drying process induces temporal evolution of nonuniform out-of-plane birefringence profile through the thickness direction while in-plane birefringence remained zero. The highest birefringence was observed at the substrate–solution interface at early stages of drying. Beyond a critical time, the formation of highly oriented layer was observed at the air–solution interface. This oriented layer progresses through the thickness direction as the solvent concentration is disproportionately reduced in these regions. Abbe refractometer results confirmed the anisotropy is preserved at longer drying times, the air–solution interface birefringence becoming higher compared to the substrate–solution interface. Overall, observations obtained by real-time measurement system agreed with off-line measurements.

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