Surface properties of linear alkyl benzene sulfonates in hard river water

Abstract

Abstract Surface properties of a series of highly purified linear alkyl benzene sulfonates were extensively studied in hard river water. The effects of water hardness, alkyl chain length and position of the phenyl sulfonate group in the molecule on such surface properties as pC 20 , critical micelle concentration (CMC), γ CMC , CMC/C 20 ratio, and minimum area per molecule at the interface are discussed in detail. The position of phenyl sulfonate group in the molecule was found to have a pronounced effect on the CMC, γ CMC value, CMC/C 20 ratio, and, to the contrary, a relatively small effect on the pC 20 value. The linear relationship between pC 20 or‐log CMC, and m , the number of carbon atoms in the alkyl chain, was found for surfactants with the phenyl sulfonate group either at the terminal position or at the more central position in the molecule. γ CMC decreases but the CMC value increases, when the position of phenyl sulfonate group moves from the terminal toward a more central position of the molecule, reflecting the “Hartley Effect” resulting from the branched alkyl chain.