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While the concept of interfacial tension synergism in surfactant mixtures is well established, little attention has been paid to the possibility of synergistic effects on the interfacial rheology of mixed surfactant systems. Furthermore, interfacial tension synergism is most often investigated for mixtures of surfactants residing in a single phase. Here, we define dilatational modulus synergism and report a study of interfacial tension isotherms and complex dilatational moduli for a binary surfactant system with the two surfactants accessing the oil/water interface from opposite sides. Using an oil-soluble fatty acid surfactant (palmitic acid, PA) that may be ionized at the oil/water interface and a quaternary ammonium water-soluble cationic surfactant (tetradecyltrimethylammonium bromide, TTAB), the binary interfacial interaction was tuned by the aqueous phase pH. Interfacial tensions and dilatational moduli were measured by the pendant drop method for the binary surfactant system as well as the corresponding single-surfactant systems to identify synergistic effects. The possible occurrence of dilatational modulus synergism was probed from two perspectives: one for a fixed total surfactant concentration and the other for a fixed interfacial tension. The aqueous pH was found to have a controlling effect on both interfacial tension synergism and the dilatational modulus synergism. The conditions for interfacial tension synergism coincided with those for the storage modulus synergism: both tension and storage modulus synergisms were observed under all conditions tested at pH 7 where PA was mostly deprotonated, for both perspectives examined, but not for any conditions tested at pH 3 where PA is mostly protonated. The loss modulus synergism exhibited more complex behaviors, such as frequency and interfacial tension dependences, but again was only observed at pH 7. The tension and modulus synergism at pH 7 were attributed to the increased attraction between ionized PA and cationic TTAB and the formation of catanionic complexes at the oil/water interface.

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In this paper, an effective approach is demonstrated for the fabrication of IrO 2 -decorated polystyrene@functionalized polypyrrole (core@shell; PS@PPyNH 2 ) microspheres. The synthesis begins with the preparation of monodispersive PS microspheres with a diameter of 490 nm, by a process of emulsifier-free emulsion polymerization, followed by a copolymerization process involving pyrrole and PyNH 2 monomers in a PS microsphere aqueous suspension, to produce uniform PS@PPyNH 2 microspheres with a diameter of 536 nm. The loading of 2 nm IrO 2 nanoparticles onto the PS@PPyNH 2 microspheres can be easily adjusted by tuning the pH value of the IrO 2 colloidal solution and the PS@PPyNH 2 suspension. At pH 4, we successfully obtain IrO 2 -decorated PS@PPyNH 2 microspheres via electrostatic attraction and hydrogen bonding simultaneously between the negatively-charged IrO 2 nanoparticles and the positively-charged PS@PPyNH 2 microspheres. These IrO 2 -decorated PS@PPyNH 2 microspheres exhibit a characteristic cyclic voltammetric profile, similar to that of an IrO 2 thin film. The charge storage capacity is 5.19 mA cm −2 , a value almost five times greater than that of PS@PPyNH 2 microspheres. In addition, these IrO 2 -decorated PS@PPyNH 2 microspheres exhibit excellent cell viability and biocompatibility.