In-situ neutron reflectometry probing competitive swelling and de-swelling of thin polystyrene films

The competitive penetration of toluene with respect to oxygen, nitrogen and carbon dioxide into a thin and initially dry film of deuterated polystyrene (dPS) is compared to the reverse process of de-swelling. In-situ neutron reflectometry is used to follow the swelling and de-swelling kinetics, allowing the determination of the total dPS thickness, roughness and solvent penetration. Swelling cannot be described in terms of case II diffusion due to the small film thickness and under-saturation results in a small swelling rate of 0.03 nm s^-1. Deswelling is slower by more than two orders in magnitude, thereby underlining the difficulty to remove once incorporated solvent molecules. A figure is presented. Schematic 3d presentation of the in-situ probed reflectivity during swelling and de-swelling.