Influences of freeze-drying and UV-irradiation on the microstructured morphology and on the wetting properties of PS41–PAA271 coating

Influences of freeze-drying process and of UV-irradiation are studied on morphology, surface composition and wetting properties of polystyrene–b-poly(acrylic acid) (PS41–PAA271) diblock copolymers (dip-coated on the substrate made of stainless steel). Observations by scanning electron microscopy (SEM) and measurements of static water contact angles highlight that morphology of non-UV-irradiated PS41–PAA271 is re-organised after steps of immersion/emersion in water and freeze-drying. These both processes modify PS41–PAA271 surface in a microstructured layer of polymer that covers a part of the stainless-steel substrate. Moreover, analyses by X-ray photoelectron spectroscopy (XPS) and measurements of dynamic wetting angles with the Wilhelmy plate method demonstrate that stimuli-responsive properties of PS41–PAA271, whose wetting properties depend on the environment, are enhanced after using a step of UV-irradiation for 20 min. This process influences the composition of the coating in order to stabilise the smart material. Consequently, repeated cycles of immersion/emersion in water showed that a maximum gap of 20–25° is obtained between the hydrophobic state (after drying at air for 90 min) and the hydrophilic state (after immersion in water).