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Order–Order Phase Transitions Induced by Supercritical Carbon Dioxide in Triblock Copolymer Thin Films

Abate, Anabella A.; Vu, Giang Thi; Piqueras, Cristian M.; del Barrio, María Cecilia; Gómez, Leopoldo R.; Catalini, Gabriel; Schmid, Friederike; Vega, Daniel A.

Macromolecules, 2019, vol 52, 20, pp. 7786-7797



We study the influence of supercritical carbon dioxide (scCO2) on the phase behavior of a cylinder-forming polystyrene-block-polybutadiene-b-polystyrene triblock copolymer thin film. Solvent annealing with scCO2 can produce patterns with long-range order but these structures become unstable for thin films with small thicknesses. These results are in good agreement with self-consistent mean field calculations, which indicate that a drying transition occurs for thicknesses below the radius of gyration of the molecule. After decompression and solvent extraction, the initially swollen polymer nanostructure suffers a strong reduction in the average domain spacing, which has a deleterious effect on the degree of order in the resulting pattern. Both, experiments and Cahn–Hilliard simulations suggest that during decompression the pattern suffers an order–order instability where the collapse of the lattice constant leads to uncommon patterns with long-range orientational order but structural distortions at small-length scales.

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