(581g) Analyzing the Effects of the Solution Casting Process on Block Copolymer Microphase Separation Kinetics Using in-Situ x-Ray Scattering
Solution casting is a technique that is often utilized in the production of block copolymer films for diverse applications such as lithography and the production of proton exchange membranes. The rate of solvent removal during processing is known to have an effect on long-range ordering and morphology of the resulting films. However, the effect of the solvent removal rate on the kinetics of block copolymer self-assembly is not well understood. A method was developed for performing in-situ small-angle x-ray scattering experiments during the drying of thick (~100 micron) solution-cast block copolymer films consisting of poly(styrene-b-butadiene) in toluene. The film drying rate was varied over the course of several trials, and the volume fraction of ordered microstructure in the film was quantified. The film drying rate was measured gravimetrically and was controlled by running a sweep gas through the drying chamber to regulate the solvent vapor concentration in the chamber. Due to the geometry, ordering proceeded in a layer in the film where the solvent concentration was below the order-disorder transition, allowing microphase separation to proceed. This ordering layer eventually grew to encompass the entire film thickness as the solution dried. Solvent partitioning between the different microphase separated blocks in the ordering layer was estimated and used to calculate the volume fraction of ordered microstructure in the film. It was found that ordering rate with respect to time increased with increasing drying rate, likely because drying was not rapid enough to cause chain mobility effects to become more significant than the effects of quench depth on the ordering kinetics.