Polymer/surfactant interactions are well known to be important in emulsification, industrial, environmental, and biomedical applications. It has long been observed that combinations of polyelectrolytes and charged surfactants exhibit tunable synergy and enhanced interfacial behavior. What remain unknown are the molecular-level details of these interfacial macrostructures. Nonlinear spectroscopy can elucidate these details, but so far the technique has only been applied at the air/water interface, and on relatively few polymer/surfactant systems. The studies to be presented examine the interfacial molecular properties involved in the co-adsorption of deuterated cetrimonium bromide (CTAB) and poly(acrylic acid) (PAA) at an oil/water interface, with insights related to drug delivery and emulsion stability. Vibrational sum frequency spectroscopy is used to measure the vibrational features of the surfactant and polymer at the interface, complemented with additional surface tension, zeta potential, and dynamic light scattering studies.  The results show a complex interfacial structure which is highly dependent upon both the polymer concentration and surfactant/polymer ratio. At dilute concentrations, only the surfactant layer is highly structured, but as the polymer concentration increases, we first see an increase and then a decrease in total order. By isolating each component’s vibrational resonances, our studies have shed light on the specific environment for individual polymer and surfactant moieties.

New insights on interfacial structure of polymer/surfactant complexes

255th National Meeting (2018)

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