Exploration of the Impacts of Alcohols and Anionic Hydrotropes on the Phase Separation Behavior of Triton X-100 in the Presence of Indigo Carmine Dye

The present study has effectively investigated and evaluated the potential impacts of alcohols and hydrotropes (HyTs) on the phase separation behavior of triton X-100 (TX-100) and indigo carmine (IC) mixture by means of classical cloud point model. Indigo carmine has broader applications in the textile, food and cosmetic industries. The combined system containing all necessary components was studied at a fixed concentration of TX-100 (92.7 mmol·kg⁻¹), IC (0.05 mmol·kg⁻¹), and variable concentrations of alcohols and hydrotropes. Methanol (MeOH), ethanol (EtOH), 1-propanol (1-PrOH), and 1-butanol (1-BuOH) were used as alcohols as well as sodium benzoate (NaBenz) and sodium salicylate (NaSal) were utilized as HyTs in the studied system. The results revealed that hydrophilicity behavior of TX-100 significantly affected the clouding progression of TX-100 + IC mixture, and clouding process was found to be quite sensitive in the presence of alcohols and HyTs. The TX-100 + IC mixture experienced the reduction in the CP values with rising the alcohols and HyTs contents, where the magnitudes of CP followed the order: \({\text{CP}}_{\text{Aq}.\text{ NaSal}}>{\text{CP}}_{\text{Aq}.\text{ NaBenz}}>{\text{CP}}_{\text{Aq}.\text{ EtOH}}>{\text{CP}}_{\text{Aq}. 1-\text{PrOH}}\) \(\approx {\text{CP}}_{\text{Aq}.\text{ MeOH}}>{\text{CP}}_{\text{Aq}. 1-\text{BuOH}}\). The various energy parameters were observed to be solely dependent on the concentrations of IC dye, alcohols as well as HyTs in the micellar phase. In all circumstances, free energy change (\({\Delta G}_{c}^\text{o}\)) values were positive, stating the nonspontaneity nature of phase changes, whereas this nonspontaneity turned to the direction of spontaneous process (reduced + \({\Delta G}_{c}^\text{o}\) values) at the higher contents of alcohols and HyTs. The positive magnitudes of both \({\Delta H}_{c}^\text{o}\) and \({\Delta S}_{c}^\text{o}\) refer to the presence of hydrophobic interacting forces among the respective components, while the negative \({\Delta H}_{c}^\text{o}\) and \({\Delta S}_{c}^\text{o}\) values appeared from the consequences of electrostatic interactions of components. Evaluation of enthalpy-entropy compensation parameters showed the good analogy to the solutions of biological and small solute molecules. The significant findings of this investigation might be highly useful and beneficial for the purpose of drug storage, new drug development, drug transport, and better pharmaceutical formulations.

Graphical Abstract