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

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.