We present a study of the effect of dimethyl sulfoxide (DMSO) on the interaction between poly(methacrylic) acid (PMAA) and polyvinylpyrrolidone (PVP) in aqueous solution at low pH and on its self-assembly in layer-by-layer (LbL) films. As a hydrogen bond acceptor, DMSO perturbs hydrogen-bonding network of water and hydrogen bonds to PMAA, competing with polymer-polymer binding in solution and strongly affecting assembly of PVP/PMAA LbL films. An increase in DMSO content in the mixed DMSO-aqueous solutions from 0 vol % to 60 vol % significantly weakened PVP-PMAA binding, leading to deposition of 2.5-fold thicker 20-bilayer films. Reversible inclusion of DMSO within the films was demonstrated by a combination of Fourier-transform infrared spectroscopy (FTIR) and ellipsometric measurements. Neutron reflectometry (NR) studies which involved deuterated PMAA showed strong effect of DMSO present in the deposition solution on polymer chain intermixing within LbL films. Isothermal titration calorimetry (ITC) revealed that binding between PVP and PMAA switched from endothermic to exothermic as content of DMSO in the mixed solvent increased, reflecting a   transition from polymer-polymer binding dominated by release of water from polymer solvation shell to the one controlled by interpolymer hydrogen-bonding.<br/>

Controlling assembly of layer-by-layer films via a small hydrogen-bonding molecule

2019 Fall National Meeting

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