Micro-structural investigations on oppositely charged mixed surfactant gels

Dicarboxylic amino acid-based surfactants (N-dodecyl derivatives of -aminomalonate, -aspartate, and -glutamate) in combination with hexadecyltrimethylammonium bromide (HTAB) form a variety of aggregates. Composition and concentration-dependent mixtures exhibit liquid crystal, gel, precipitate, and clear isotropic phases. Liquid crystalline patterns, formed by surfactant mixtures, were identified by polarizing optical microscopy. FE-SEM studies reveal the existence of surface morphologies of different mixed aggregates. Phase transition and associated weight loss were found to depend on the composition where thermotropic behaviours were revealed through combined differential scanning calorimetry and thermogravimetric studies.

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Fig: (a) Chemical structure of C12Mal2– and HTA+; (b) truncated phase diagram of C12MalNa2 + HTAB + water mixed system at 25 °C. Phases: (A), gel; (B), viscous; (C), precipitate; and clear region indicate the formation of micelle. The dotted line in panel b corresponds to equimolar region. Panel (c), POM and (d), FE-SEM image of 5 wt% C12MalNa2 + HTAB (40:60, w/w) gel respectively. Scale bars (in μm) are mentioned in the microscopic images.

Systems comprising more than 60 mol% HTAB demonstrate shear-thinning behaviour. Gels cause insignificant toxicity to human peripheral lymphocytes and irritation to bare mouse skin; they do not display the symptoms of cutaneous irritation, neutrophilic invasion, and inflammation (erythema, edema, and skin thinning) as evidenced by cumulative irritancy index score. Gels also exhibit substantial antibacterial effects on Staphylococcus aureus, a potent causative agent of skin and soft tissue infections, suggesting its possible application as a vehicle for topical dermatological drug delivery.

Barai, M., Manna, E., Sultana, H. et al. Micro-structural investigations on oppositely charged mixed surfactant gels with potential dermal applications. Sci Rep 11, 15527 (2021). https://doi.org/10.1038/s41598-021-94777-2

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