Surface and Bulk Properties of Dodecylbenzenesulphonate in Aqueous Medium: Role of the Nature of Counterions

Abstract

The lithium, potassium, and ammonium salts of dodecylbenzenesulphonic acid have been prepared from the pure sodium salt by applying ion-exchange technique. The critical micellization concentrations (CMC) of the surfactants with four different counterions have been determined in a temperature range of 10°C to 40°C using surface tension as well as electrical conductivity measurements. The counterion ionization constant, α, and various thermodynamic parameters of micellization viz, , , , along with the surface parameters (Γ _max, A_min) in aqueous media have been determined. The CMC value of dodecylbenzenesulphonate (DBS) having different counterions followed the order Na⁺ > Li⁺ >  > K⁺. While large negative free energy change and the positive entropy change favor the micellization process thermodynamically, nature of their variation with counterion supports the importance of hydrated counterion size factor in micellization process via a change in the hydrophilicity of surfactant head group along with the structure of branched chain of hydrocarbon tail.

Keywords:

• Counterion
• critical micelle concentration
• dodecylbenzenesulphonate
• thermodynamic parameters

Acknowledgments

Financial support from the University Grants Commission, New Delhi, India, under Special Assistance Program (SAP, No. F/540/6/DRS/2002) is gratefully acknowledged.

Notes

*The values in the parenthesis represent CMC determined from surface tension measurements.