Solvent vapor mediated polymer adsorption in thin films

Abstract

The effectiveness of a "solvent annealing" process was investigated for thin (similar to150 nm) polystyrene films, in which the diffusion and reorganization of polymer chains were mediated by the controlled absorption of cyclohexane vapor. Results were compared with conventional "thermal annealing" of films under vacuum above the glass transition temperature. Elastic recoil detection analysis (ERDA) was used to determine the surface excesses of fluorocarbon end-capped polystyrene (hPSF) and poly(styrene-b-dimethylsiloxane) (hPS-PDMS) in deuterated polystyrene (dPS) films. Both annealing methods enabled diffusion of the surface-active polymers; however, only thermal annealing gave rise to a surface excess in hPSF/dPS films. The inhibition of hPSF adsorption under solvent annealing was due to the low surface tension of cyclohexane. In contrast, hPS-PDMS, having a larger surface-active group than that of hPSF, was found in excess at the air surface under solvent annealing, and surface excesses were consistent with the formation of saturated monolayers in blended films. The mixing of hPS-PDMS with dPS was inhibited by the unfavorable interaction between the PDMS block of the copolymer and the homopolymer. The slow interdiffusion of hPS-PDMS in dPS is consistent with the formation of micelles, and the formation of an excess layer at the air surface may be kinetically inhibited by the rate of dissociation of hPS-PDMS micelles.