We explore the role of a competitive solvent - dimethyl sulfoxide (DMSO) - on growth and internal structure of hydrogen-bonded layer-by-layer (HB-LbL) films. The films were constructed at acidic pH using poly(methacrylic acid) (PMAA) and polyvinylpyrrolidone (PVPON). Like salt in the case of electrostatically assembled films, DMSO disrupts interpolymer PMAA/PVPON bonds and promotes chain intermixing. Spectroscopic ellipsometry was used to study film growth, and neutron reflectometry was employed to probe the internal structure of films containing deuterated PMAA. We compared the effect of DMSO on film growth and chain intermixing when the competitive solvent was used during film construction or post-assembly. First, the presence of 10-40% DMSO in aqueous assembly solutions triggered non-linear film growth, resulting in significant chain intermixing. Second, DMSO also induced significant layer intermixing within HB-LbL films when added after film construction, but the effect of solvent was weaker in this case. In both cases, the degree of intermixing was strongly dependent on PMAA molecular weight, with fast DMSO-induced penetration of a shorter polyacid in the neighboring layers, and diffusion of longer PMAA being less affected by the presence of a competitive solvent. This work allows one to quantitatively compare the dynamics of PMAA chains assembled within HB-LbL films with that previously explored for electrostatically assembled systems.

Effect of competitive solvent on chain dynamics within hydrogen-bonded polyelectrolyte multilayers

254th National Meeting (2017)

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