Quantitative evaluation of evaporation rate during spin-coating of polymer blend films: Control of film structure through defined-atmosphere solvent-casting
Department of Physics and Astronomy, University of Sheffield, S3 7RH, Sheffield, UK
2 Department of Chemistry, Durham University, DH1 3LE, Durham, UK
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Accepted: 14 October 2010
Published online: 18 November 2010
Thin films of polymer mixtures made by spin-coating can phase separate in two ways: by forming lateral domains, or by separating into distinct layers. The latter situation (self-stratification or vertical phase separation) could be advantageous in a number of practical applications, such as polymer optoelectronics. We demonstrate that, by controlling the evaporation rate during the spin-coating process, we can obtain either self-stratification or lateral phase separation in the same system, and we relate this to a previously hypothesised mechanism for phase separation during spin-coating in thin films, according to which a transient wetting layer breaks up due to a Marangoni-type instability driven by a concentration gradient of solvent within the drying film. Our results show that rapid evaporation leads to a laterally phase-separated structure, while reducing the evaporation rate suppresses the interfacial instability and leads to a self-stratified final film.
© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg, 2010