Branched alkyldimethylamine oxide surfactants: An effective strategy for the design of high concentration/low viscosity surfactant formulations

Fabozzi A.

Member of the Collaboration Group

;Russo Krauss I.

Member of the Collaboration Group

;Vitiello R.

Member of the Collaboration Group

;Fornasier M.

Member of the Collaboration Group

;Sicignano L.

Member of the Collaboration Group

;King S.

Member of the Collaboration Group

;Guido S.

Member of the Collaboration Group

;Jones C.

Member of the Collaboration Group

;Paduano L.

Member of the Collaboration Group

;Murgia S.

Member of the Collaboration Group

;D'Errico G.

Last

Member of the Collaboration Group

2019-01-01

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Abstract

Hypothesis: The rational design of branched-tail surfactants is a suitable strategy to obtain low-viscosity surfactant-rich isotropic aqueous mixtures with negligible effects on biodegradability. This opens a way to the design of concentrated (“water-free”) surfactant formulations, highly attractive for their ecological and economic benefits. Experiments: The aggregation behaviour of N,N-dimethyl-2-propylheptan-1-amine oxide (C10DAO-branched) in aqueous mixtures is investigated across the entire composition range by polarized optical microscopy, small angle X-ray and neutron scattering, electron paramagnetic resonance, and pulse-gradient stimulated echo nuclear magnetic resonance. The humidity scanning quartz crystal microbalance with dissipation monitoring technique is validated as a tool for the fast screening of surfactants phase behaviour. Furthermore, the shear viscosities and viscoelastic moduli of the systems are determined by rheological measurements. Findings: With respect to the linear isomer, C10DAO-branched presents a much lower tendency to form lyotropic liquid crystalline phases. Except for a narrow composition and temperature range in which a lamellar structure is observed, C10DAO-branched aqueous mixtures are isotropic liquids whose microstructure changes, with increasing concentration, from micellar solutions to unstructured dispersions of hydrated surfactant molecules. Low-viscosity was found for all these mixtures, including the most concentrated ones. Thus, the introduction of a single short side-chain in the tail is demonstrated to be an effective approach to increase the active concentration in surfactant formulations.