Through compilation and analysis of literature reports and our own research, we have developed a semi-empirical correlation between the binding strength of surfactants to polyelectrolytes in salt-free mixtures as a function of the polyion linear charge density and surfactant hydrophobicity [1,2]. We find that the cooperative binding strength increases as the quadratic of the polyelectrolyte's linear charge density and in proportion to the surfactant's hydrophobicity, such that a quantitative relationship holds across a broad range of polyelectrolytes. This engineering relationship aids in the rational design of oppositely charged polyelectrolyte-surfactant formulations for consumer products and biomedicines by enabling prediction of binding strengths in polyelectrolyte-surfactant mixtures based on mesoscale parameters determined from the chemical composition.  To study coacervate phase behavior and mechanical properties, we combine a wide range of experimental techniques, ranging from thermodynamic measurements (microcalorimetry and phase behavior), to microstructure characterization techniques (microscopy and scattering), and coacervate rheology at different structural levels (Bulk rheology and Nano-indentation atomic force microscopy (AFM)). A systematic variation of model mixtures has been investigated, to assess the significance of polymer charge density and surfactant hydrophobicity. Modeling of the molecular interaction enthalpic isotherms using a statistic thermodynamic theory enables a semi-empirical quantification of the polymer/surfactant association behavior [2,3]. Coacervation is tied to charge equivalence at low surfactant concentrations, while resolubilization is shown to be related to the colloidal stability of surfactant-polyelectrolyte complexes. The effects of binding strength on phase behavior, coacervate nanostructure, and shear and elastic moduli are examined and a systematic correlation with polyelectrolyte and surfactant properties observed through the binding strength. [1] Li, D.; Wagner, N. J., Journal of the American Chemical Society 2013 .[2] Li, D.; Kelkar, M. S.; Wagner, N. J., Langmuir 2012,  28, (28), 10348-10362.[3] Chiappisi, L.; Li, D.; Wagner, N. J.;  Journal of Chemical Thermodynamics 2014,  68, 48-52.

Coacervates of alkyl surfactants with oppositely charged polyelectrolytes

248th National Meeting (2014)

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