Reversible Swelling-Shrinking Behavior of Hydrogen-Bonded Free-Standing Thin Film Stabilized by Catechol Reaction

Dopamine-modified poly(acrylic acid) (PAA-dopa) and poly(vinylpyrrolidone) (PVPON), was layer-by-layer (LbL) assembled to prepare thin film based on hydrogen bonding. The carboxylic group of acrylic acid and the phenolic hydroxyl group of dopamine can both act as hydrogen bond donors. The critical assembly and the critical disintegration pH values of PVPON/PAA-dopa film are enhanced compared with PVPON/PAA. film. The hydrogen-bonded PVPON/PAA-dopa thin film can be dross-linked via catechol chemistry of dopamine. After truss-linking, the film can be exfoliated from the substrate in alkaline solution to get a freestanding film. Moreover, by tuning the pH value, deprotonation and protonation of PAA will make the hydrogen bond in the film break and reconstruct, which induces that the free-standing film has a reversible swelling-shrinking behavior.