Effect of a Competitive Solvent on Growth and Chain Intermixing in Hydrogen-Bonded Multilayers

The role of a competitive solvent - dimethyl sulfoxide (DMSO) - on growth and internal structure of hydrogen-bonded layer-by-layer (HB-LbL) films was explored. 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, promoting non-linear film growth and chain intermixing. The internal structure of HB-LbL films was monitored with neutron reflectometry using deuterated PMAA chains, while growth profiles of a multilayers were studied with spectroscopic ellipsometry. Films assembled with short-chain PMAA were less stratified and were more prone to further DMSO-induced film intermixing as compared to films of long-chain PMAA. Moreover, while the presence of DMSO in aqueous assembly solutions had resulted in dramatic weakening of polymer-polymer binding leading to non-linear film growth, addition of the same concentrations of DMSO post-assembly caused only slight changes in the penetration of deuterated material into neighboring layers. The effects of a competitive solvent explored in this work can potentially be extended to other polymer assemblies that employ hydrogen-bonding interactions.