Morphology-Controlled Kinetics of Solvent Uptake by Block Copolymer Films in Nonselective Solvent Vapors

We compare the swelling behavior of a compositionally symmetric diblock copolymer in films with nonbulk micellar morphology and with vertically oriented lamellae. The morphologies preformed by spin-coating from selective/nonselective solvents differ in shape and total area of the AB interfaces between incompatible units. Experimental measurements and dissipative particle dynamics (DPD) simulations demonstrate that AB interfaces dominate as the diffusion pathways of nonselective solvent molecules in strongly segregated films. In experiments, the lamellar films swell about 20× faster as compared to densely packed micellar structures, while the degrees of swelling at saturation are equal for the two types of morphologies. The difference in the kinetics of solvent uptake vanishes as soon as the solvent plasticizing effect allows for micelles-to-lamellae transition. DPD simulations confirm the inhomogeneous distribution of the solvent inside the film, with the higher fraction of the solvent localized at the AB interface and reveal morphology-dependent kinetics of the solvent uptake. The effect of dissimilar abilities of the nanodomains and of AB interface to serve as diffusion pathways for small molecules may find potential in designing nanosensors and heterogeneous barrier layers.