The alignment of polymers during the solvent-coating process

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Abstract
The solvent-casting process preferentially aligns polymeric chains in the plane of the film. This paper proposes that the mechanism responsible for this behavior is the competition between the relaxation times of the concentrating solution and the time scales associated with the physical collapse of the film. The orientation of molecules has been determined as a function of the coating conditions (film thickness, polymer molecular weight, plasticizer content, casting solvent, and substrate temperature) by measuring the optical anisotropy of the coating with a single-prism film coupler. This orientation is shown to reflect both the stresses supported by the entanglement network and the alignment of localized segments and to be a function of the difference between the casting temperature and the Tg of the film.