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Synthesis and Interfacial Tensions of Sodium p-Dimethyl Dodecylbenzene Sulfonates

Abstract Six isomers of sodium para-dimethyl dodecylbenzene sulfonates (p-S12) were synthesized by a series of reactions. The surface tension of the isomers p-S12 in an aqueous NaCl solution (4000 mg/L) was measured. From the data the following parameters were calculated: critical micelle concentration (CMC), the surface tension at the CMC (γCMC), the surface excess concentration at surface saturation (Γmax) and the area per molecule at surface saturation (Asmin). The Asmin increased and the Γmax decreased when the aromatic nucleus moves to the center of long-chain alkyl group. The dynamic interfacial tensions (DIFT) between p-S12 in 4000 mg/L NaCl aqueous solution and five n-paraffins were measured by using a spinning drop technique. The DIFT of the p-S12 showed the characteristic that the interfacial tension (IFT) is low at the beginning, then increases, reaches a maximum value, and finally continues to decrease until it reaches a stable value. By the measurement of alkane carbon number for the minimum IFT, nmin, of the six isomers solutions, we found that the nmin firstly decreases and then increases when the aromatic nucleus moves to the long-chain alkyl group. This phenomenon is due to the differences of hydrophilic-lipophilic properties and the structure of the p-S12 isomers.