Critical behavior of a cationic surfactant in an aqueous salt solution

The critical behavior of a cationic surfactant, butyl-tetradecyldimethylammonium bromide, in an aqueous 4M–NaBr solution was investigated concerning the isothermal osmotic compressibility and long-range correlation length by means of light scattering, coexistence curve, and turbidity. The critical exponents were obtained as γ′=1.39±0.04 and ν′=0.70±0.03 together with ξ0=(2.48±0.06) nm, and β′=0.375±0.01. The temperature dependence of turbidity showed a good accordance with the result of light scattering measurement. Negative α′ was obtained from the scaling relation. The critical exponents are in good agreement with the Fisher-renormalization prediction for the ternary system (almost fully renormalized Ising exponents).