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

AMER CHEMICAL SOC

Año: 2019 vol. 52 p. 7786 - 7797

0024-9297

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.