Effect Of Organic Solvents On Halogen-bonded Layer-by-layer Assemblies And The Stability Of Multilayer Films In Organic Solvents

Layer-by-Layer (LbL) assembling technique has been rapidly developed for the past two decades. Scientists intended to obtain well-tuned thin films through controlling assembly conditions or by post-processing. We investigated the influence of the composition of mixed solvents of butanone/THF on halogen-bonded LbL assembly of PIPEMA and PPyPMA. We then used two methods to improve stability of the film assembled in butanone.We designed and synthesized poly(2-(4-iodo-2,3,5,6-tetrafluorophenoxy)ethyl methacrylate) (PIPEMA) and poly(3-(3pyridyl)propyl methacrylate) (PPyPMA). Using LbL technique, PIPEMA/PPyPMA multilayer films were prepared in butanone. QCM and AFM were used to monitor the growth of multilayer film and to characterize surface morphology of it, respectively.We first investigated the influence of the composition of mixed solvents of butanone/THF on LbL assembled films driven by halogen-bonding. We assembled LbL film in mixed solvents of butanone/THF. As THF content increased, polymers adsorbed on substrate decreased. Combined with Hansen Solubility Parameters distance between polymer and solvent we thought the decrease of polymers adsorbed on substrate are related to the conformation of polymers in solvents.We immersed the halogen-bonded multilayer films that were fabricated in butanone in THF, chloroform and pyridine to investigate desorption of multilayer films. It was found that the multilayer films desorbed from the substrate. Thus, we used two methods to improve the stability of the halogen-bonded film. (1) We crosslink the film with gaseous 1,3-dibromopropane, and then measured its desorption in THF. It was clear that after 120 min of crosslink the film loss in THF decreased to 6%. (2) We designed and synthesized a copolymer of halogen-bonded donor monomer and hydrogen-bonded donor monomer. By using this copolymer and PPyPMA to fabricate LbL film, we obtained a more stable multilayer film.