The influence of the micellar pseudophase of the double-chained cationic surfactant di-n-tetradecyldimethylammonium bromide on the absorption spectra and protolytic equilibrium of indicator dyes

• Ditetradecyldimethylammonium bromide in water forms large-sized colloidal species.
• The growth of the ionic strength increases the zeta-potential of the vesicles.
• The Reichardt's dye spectrum is sensitive to the CTAB additives to the vesicles.
• The behavior of acid-base indicators in vesicles resembles that in CTAB micelles.

The absorption spectra and protolytic equilibrium of a set of acid–base indicators and solvatochromic dyes have been studied in aqueous solutions of the cationic surfactants possessing two long hydrocarbon tails. In water, the double-chained surfactant di-n-tetradecyldimethylammonium bromide, DTDAB, forms large-sized anisometric self-assembled aggregates or bilayer (vesicle) type. The anionic dyes are readily bound to the DTDAB pseudophase, which results in the pronounced shifts of their absorption bands and alterations of the pKas. The results have been compared with those obtained earlier in CTAB and gemini 16-4-16 cationic surfactants.

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