Growth of Gemini Surfactant Micelles Under the Influence of Additives: DLS Studies

Results are presented on the first extensive study on the influence of additives on the growth of gemini; alkanediyl alpha, omega-bis(dimethylcetylammonium bromide) surfactant micelles (16-s-16, with s = 5, 6); as measured by dynamic light scattering technique at 30 degrees C. The effect of adding n-butanol, n-pentanol, n-hexanol, and n-hexylamine in the absence or presence of general ionic salt potassium bromide on 0.03 M gemini solutions were observed. The tendency for micelles to grow from spherical to rodlike structures is decisively influenced by the spacer length s. At 30 degrees C, the micellar growth was more for s being 5, which has been interpreted in terms of short spacer having strong propensity for micellar growth. Addition of KBr plays a role in screening of the electrostatic interactions, thus promoting a change of morphology of the aggregates and giving rise to high hydrodynamic diameter (D-h) values. The micellar growth in presence of alcohols is interpreted in terms of the formation of the gemini-alcohol mixed micelles which followed the pattern C6OH>C5OH>C4OH. For equal chain length additives C6OH and C6NH2, the growth was more pronounced in case of alcohol. Also, in case of C6NH2, the value of D-h reached to almost constancy or decreased to some extent, which is discussed in terms of its partitioning in aqueous phase. A combined presence of KBr and n-alcohols or n-hexylamine produced favorable conditions for micellar growth due to synergistic effect.