Hydrogen-bonding-directed layer-by-layer multilayer assembly: Reconformation yielding microporous films

The influence of a basic aqueous solution on a hydrogen-bonding-directed layer-by-layer (LbL) self-assembled film, based on poly(acrylic acid) (PAA) and poly(4-vinylpyridine) (PVP), was investigated. The composition change of a multilayer film in a NaOH solution was monitored by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy,and W-vis spectroscopy.. The morphology variation was observed. by atomic force microscopy. A two-step variation was observed: the. first step is the dissolution of PAA from the film into the basic solution; the second is the gradual reconformation of PVP polymer chains remaining on the substrate, which produces a microporous film. The evidence for the reconformation of the polymer chains was further provided by single molecule force spectroscopy. Both the release of PAA and the formation of the microporous film are attributed to the properties of the LbL film based on hydrogen bonding. This interesting. and novel way to fabricate microporous films is envisaged to have potential applications in areas ranging from pharmaceutics to materials science.