The influence of electrostatic and H-bonding interactions on the optical storage of layer-by-layer films of an azopolymer

The optical storage properties of layer-by-layer (LBL) films of a copolymer of methacrylic acid and 4-[[2-(methacryloyloxy)-ethyl]ethylamino]-2′-chloro-4′-nitroazobenzene (MA-co-DR13) alternated with the cationic poly(allylamine hydrochloride) are reported. The writing process is considerably slower than in cast films due to electrostatic and H-bonding interactions that hinder molecular orientation. The speed of the writing process can be increased if the LBL film is immersed into pure water prior to the storage experiments, probably because entrapped water helps preventing intermolecular interactions. This is a reversible effect and cannot be attributed to mere water absorption of the polymer film, since cast films of the same components do not exhibit the ‘water effect’. It is also demonstrated that the films display sensing capabilities, with their optical storage properties being significantly affected by gushes of hot and humid air.