“Micro-structure–macro-response” relationship in swollen block copolymer films

Abstract

We demonstrate the effect of confinement on the thickness-dependent swelling behavior of poly(styrene)-b-poly(2-vinylpyridine) diblock copolymer films as revealed by in situspectroscopic ellipsometry. “Microscopic” molecular confinement to the dimension smaller than the characteristic lamella spacing, as well as to the non-equilibrium microstructures limits the solvent up-take by the polymer film. The maximum degree of swelling (“macroscopic response”) is achieved for films with a starting thickness in a dry state h_dr in the range of ∼one–two characteristic lamella dimension in bulk L₀ and drops down according to ∼h_dr^−0.1 as the film thickness increases up to ∼μm scale (∼tens of L₀). These findings bring novel fundamental insights into the stimuli-responsive behavior of confined soft matter.