Structural transition of bifunctional surfactants

Abstract  The effect of primary alcohols (butanol to hexanol) and n-hexylamine on the micellar properties of solutions of alkanediyl-α,ω-bis(dimethylcetylammonium bromide) (16-s-16, with s = 5, 6) in the absence and presence of KBr was investigated by viscometric studies at 30 ± 0.1°C. The viscosities were determined using an Ubbelohde viscometer. The viscosity values exhibit the order s = 5 > 6, i.e., the gemini with short spacer produces the more viscous solution with hexanol > pentanol > butanol. The high viscosities observed in these systems are interpreted in terms of a micellar sphere to rod transition that takes place over a certain range of concentration of the surfactants with added salt or organic additives or both. Micellar growth was higher in case of C₆H₁₃OH when compared to C₆H₁₃NH₂. In the presence of C₆H₁₃NH₂, the relative viscosity becomes almost constant when the concentration of the additive is increased, which has also been discussed in terms of electrostatic and hydrophobic forces operating in the solution. The positive synergistic effects of additives also confirm pronounced micellar growth. Graphical abstract