Influence of polyethylene glycol on the aggregation/clouding phenomena of cationic and non-ionic surfactants in attendance of electrolytes (NaCl & Na2SO4): An experimental and theoretical analysis

Abstract

Abstract Herein, multiple techniques were employed to gain an accurate and deep understanding for the interaction between synthetic polymer polyethylene glycol 400 (PEG 400) and surfactant (TTAB/Triton X-100 (TX-100)) in electrolytes or electrolytes free medium. Critical micelle concentration (cmc) and extent of counterion binding (β) over the 298.15 to 318.15 K temperature range were determined and thereby the degree of interaction between PEG 400 and TTAB has been estimated. The cmc of pure TTAB in H2O exhibits U-like variation with the escalation of temperature. Assessed cmc values of TTAB/TTAB + PEG 400 mixture in water as well as in NaCl solution enhance monotonically with temperature. The cmc values of TTAB + PEG 400 mixture in Na2SO4 solution exhibit reversed U-shaped variation with escalation of temperature. Estimated cmc values of TTAB + PEG 400 mixture in occurrence of NaCl/Na2SO4 were decreased in comparison to aqueous medium while at a fixed concentration of salts and particular temperature the magnitudes follow the order: cmcNaCl > cmcNa2SO4. The estimated values of Gibbs free energy (∆Gmo) & enthalpy (∆Hmo) of micellization were negative almost in each case. The values of ∆Hmo and ∆Smo indicate the presence of both hydrophobic & electrostatic interactions between PEG 400 and TTAB. Executed CP of TX-100 was reduced in the existence of PEG 400 almost in each case. The values of Gibbs free energy of clouding (∆Gco) were positive in all cases. The entropy-enthalpy compensation was observed both for aggregation of TTAB and clouding of TX-100. The atomic level interacting mechanism of PEG 400-surfactant system in salt and aqueous environment was disclosed by means of molecular dynamics simulation, which showed a good agreement with the experimental results.