(708c) Real-Time Monitoring of the Ordering Process in Solution-Cast Block Copolymer Films Using Small Angle X-Ray Scattering

The manner in which solvent is removed during the solution-casting of block copolymer films has a significant influence on the polymer morphology in the final film, which in turn governs film properties. It is, therefore, desirable to understand the mechanism by which the various morphologies develop during the drying process. A majority of the studies concerning ordering kinetics of block copolymers, whether in the melt or in solution, focus on phase separation following temperature quenches. Among the work examining the effect of processing conditions on film properties of solution-cast block copolymer films, most only consider final film morphologies after drying or rely on imaging of films using microscopy at discrete concentrations during the drying process by cryogenically locking in the structures. Thus, information concerning real-time formation of ordered domains during isothermal drying is limited, thereby hindering the ability to gain a full understanding of the ordering kinetics.

In order to better understand the mechanism by which the ordered structures develop and progress through both order-disorder transitions and order-order transitions during the drying cycle, in-situ small angle x-ray scattering measurements are made using a sample cell capable of heating samples, monitoring film weight changes and allowing for grazing-incident scattering images to be obtained simultaneously. In addition to measuring the real-time response of the ordering kinetics to changes in concentration at the film surface, films are probed at various depths to unveil the effect of concentration gradients on phase separation and homogeneity in film morphology. Microscopy is being used to confirm the ordered structures present during drying, while constant-concentration rheological measurements are being used to track the ordered domain growth a various concentrations to gain further quantitative information regarding the ordering process. Poly(styrene-b-butadiene) and poly(styrene-b-butadiene-b-styrene) are being dried in various solvents at a number of different temperatures to study the influence of copolymer structure, solvent selectivity, and drying temperature and rate.