Solvent Dependence of the Morphology of Spin-Coated Thin Films of Polydimethylsiloxane-Rich Polystyrene-block-Polydimethylsiloxane Copolymers
The as-spun, thin film morphologies of a series polydimethylsiloxane-rich cylinder and lamellar-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) copolymers with constant PDMS molecular weight and varying PS volume fraction were studied with a range of solvents of varying solubility parameter. It was found that PDMS occupies the surface of the thin films regardless of the choice of solvent used in spin-coating due to its extremely low surface tension. The morphology shifted from parallel cylinders to hexagonally perforated lamellar to parallel lamellar as the solvent was varied from PDMS to PS selective solvents (increasing solvent solubility parameter). The transition points between each morphology were also dependent on the volume fraction of the block copolymer where the transitions were observed at lower solubility parameter with increasing PS volume fraction of the polymer. The morphology variations are attributed to selective swelling effects of the individual blocks even under good solvent conditions. These results are discussed in the context of current theories of solvent evaporation induced ordering of block copolymer thin films.
Wadley, Maurice L.; Hsieh, I-Fan; Cavicchi, Kevin; and Cheng, Stephen Z. D., "Solvent Dependence of the Morphology of Spin-Coated Thin Films of Polydimethylsiloxane-Rich Polystyrene-block-Polydimethylsiloxane Copolymers" (2012). Polymer Engineering Faculty Research. 1381.