Surface Tension, Activity of Counterion, and Conductivity of the Quaternary System Dodecyldimethylamine Oxide, TX‐100, HCl, and Water

We have investigated the mixing behavior of the mixtures of dodecyldimethylamine oxide (DDAO) and Triton X‐100 (TX‐100) at different ratios of the two surfactants and at different values of pH. From the equilibrium surface tension measurements, the critical micelle concentration (CMC) and surface tensions at CMC data were obtained as functions of the composition. For the binary mixtures of dodecyldimethylamine oxide and TX‐100 at different ratios in the natural values of pH, the behaviors of the mixtures deviate positively from ideal during micellization. The minimum of CMC of the mixtures of dodecyldimethylamine oxide and Triton X‐100 was observed in the range 4.0<pH<6.0. The bound fraction of counterion (Cl⁻) increased with the decrease of pH. At pH=4.99, the activities of the counterion decreased with the increase of the concentration of TX‐100 at a constant concentration of DDAO. At pH=1.96, the activities of the counterion increased with the increase of the concentration of TX‐100. However, the conductivities of the solution decreased with the increase of the concentration of TX‐100 at both pH=4.99 and pH=1.96. The experimental results show that the effect of TX‐100 on the activities of the counterion at pH=4.99 is different from that at pH=1.96.

Keywords:

• Dodecyldimethylamine oxide/TX‐100 mixture
• surface tension
• conductivity
• activity of Cl⁻ ion