Thermodynamics of non-ionic surfactant Triton X-100-cationic surfactants mixtures at the cloud point

Abstract

This study investigates the effects of gemini and conventional cationic surfactants on the cloud point (CP) of the non-ionic surfactant Triton X-100 (TX-100) in aqueous solutions. Instead of visual observation, a spectrophotometer was used for measurement of the cloud point temperatures. The thermodynamic parameters of these mixtures were calculated at different cationic surfactant concentrations. The gemini surfactants of the alkanediyl-α-ω-bis (alkyldimethylammonium) dibromide type, on the one hand, with different alkyl groups containing m carbon atoms and an ethanediyl spacer, referred to as “ m-2- m” ( m = 10, 12, and 16) and, on the other hand, with –C 16 alkyl groups and different spacers containing s carbon atoms, referred to as “16- s-16” ( s = 6 and 10) were synthesized, purified and characterized. Additions of the cationic surfactants to the TX-100 solution increased the cloud point temperature of the TX-100 solution. It was accepted that the solubility of non-ionic surfactant containing polyoxyethylene (POE) hydrophilic chain was a maximum at the cloud point so that the thermodynamic parameters were calculated at this temperature. The results showed that the standard Gibbs free energy ( Δ G cp ∘ ) , the enthalpy ( Δ H cp ∘ ) and the entropy ( Δ S cp ∘ ) of the clouding phenomenon were found positive in all cases. The standard free energy ( Δ G cp ∘ ) increased with increasing hydrophobic alkyl chain for both gemini and conventional cationic surfactants; however, it decreased with increasing surfactant concentration.