Effects of temperature and surfactant structure on the solubilisation of 4-chlorobenzoic acid by various surfactants

• The solubilisation constants (Ks) of 4-chlorobenzoic acid in aqueous solutions of various surfactants are determined by the UV–Vis spectrophotometric method.
• The effects of head- and tail-groups on the solubilisation of 4-chlorobenzoic acid have been studied.
• A synergistic effect is happened at the solubilisation of 4-chlorobenzoic acid by LSB/nonionic mixed systems.
• The iso-structural temperatures are increased with the increase of the alkyl chain-length of surfactant for each system but not severely depending on the head groups of surfactants.

The solubilisation constants (Ks) of 4-chlorobenzoic acid in aqueous solutions of various pure and mixed surfactants are determined by the UV–Vis spectrophotometric method. And the dependence of the Ks values on temperature has been measured and thermodynamic parameters are calculated to analyse the effects of head- and tail-groups on the solubilisation of 4-chlorobenzoic acid by various surfactants. The results show that the ΔGo values for all the surfactants are negative and decrease with the increase of temperature. On the other hand, the values of ΔHo and ΔSo are all positive within the measured temperature range and those values increase together with the increase of temperature. These thermodynamic parameters are depending severely on a chain length of alkyl-group as much as on a head-group of surfactant.

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