The Influence of Anionic and Nonionic Hydrotropes on the Phase Separation of Triton-X 100 and Polyethylene Glycol Mixtures: Assessment of Several Physico-Chemical Parameters

Abstract

The phase separation of triton X-100 (TX-100) and polyethylene glycol-400 (PEG-400) mixtures was investigated in aqueous and aqueous solutions of hydrotrope-containing systems (anionic: sodium benzoate (NaBenz), sodium salicylate (NaSal); nonionic: 4-aminobenzoic acid (4-ABA), resorcinol (benzene-1,3-diol (BDL)), and nicotinsaureamid (pyridine-3-carboxamide (PyC))) using the cloud point (CP) detection technique. The magnitudes of CP for the TX-100 and PEG-400 mixed solution were examined with TX-100 concentration significantly above its critical micelle concentration (CMC), and experienced changes upon the introduction of various hydrotropes (HDTs). The solubility of the PEG-400 and TX-100 mixture was notably impacted by the HDTs studied. As the HDTs concentration raised, the CP values showed an upsurge trend (indicating enhanced solubility) for anionic HDTs (NaBenz and NaSal) and an nonionic HDT (PyC). In contrast, CP values decreased (indicating reduced solubility) in solutions of remaining two nonionic HDTs (4-ABA and BDL). At CP, the changes in standard free energy (\({\Delta G}_{\text{c}}^{0}\)), enthalpy (\({\Delta H}_{\text{c}}^{0}\)), and entropy (\({\Delta S}_{\text{c}}^{0}\)) of the clouding were determined. The \({\Delta G}_{\text{c}}^{0}\) values for the clouding process were positive, indicating the process is not spontaneous. The negative \({\Delta H}_{\text{c}}^{0}\) of the clouding system in two nonionic HDTs, 4-ABA and BDL media, indicate exothermic clouding, whereas the other media was mostly endothermic in nature. The \({\Delta H}_{\text{c}}^{0}\) and \({\Delta S}_{\text{c}}^{0}\) values suggest that electrostatic (hydrogen bonding and dipole–dipole interactions) and hydrophobic forces dominate between TX-100 and PEG-400 during cloud formation. The thermodynamics properties of transfer (\({\Delta G}_{\text{c},\text{tr}}^{0}\), \({\Delta H}_{\text{c},\text{tr}}^{0}\), \({\Delta S}_{\text{c},\text{tr}}^{0}\)), compensation temperature (T_c), and intrinsic enthalpy gain (\({\Delta H}_{\text{c}}^{0,*}\)) were calculated and thoroughly analyzed to elucidate the system’s behavior and interaction forces.

Graphical Abstract