Solvent effects on the surface composition of poly(dimethylsiloxane)-co-polystyrene/polystyrene blends

The effects of mixed solvents used for casting films of diblock copolymer/homopolymer blends of poly(dimethylsiloxane)-co-polystyrene/polystyrene have been studied in detail at the surface of the films. The surface composition was determined over a wide range of detection depths using data from various spectroscopic techniques, including X-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR) FTIR, and time-of-flight secondary ion mass spectrometry (ToF SIMS). After surveying a range of solvents, the surface segregation dependence on the solvent composition was investigated for two binary solvent mixtures, namely, toluene/chloroform and cyclohexanone/chloroform. One hundred percent surface poly(dimethylsiloxane) (PDMS) coverage has been observed for the polymer blends containing 2% PDMS in bulk using the optimized cyclohexanone/chloroform mixture as solvent. Detectable amounts of polystyrene (PS) residue can be observed on surfaces for samples cast from other solvents. The PDMS-enriched surface region is much thicker for samples cast from cyclohexanone/chloroform solvent mixtures. ToF SIMS analysis results suggest that casting solvents also alter the surface morphology of sample films. The effects of solvent on the surface composition, depth gradient, and surface molecular structure of solution-cast films are discussed in terms of the polymer-solvent interaction parameters and polarity of solvents.