Deciphering Molecular Association in PG–HG Aqueous Tetrasodium EDTA Solutions through Physicochemical and Thermodynamic Approaches

Understanding molecular interactions in aqueous co-solvent systems is important for pharmaceutical and physicochemical applications. In this work, the density and speed of sound of aqueous mixtures containing propylene glycol (PG), hexylene glycol (HG), and tetrasodium EDTA were measured over the temperature range 288.15–318.15 K at 0.1 M P a and concentrations from 0.07 to 0.09 m o l · k g − 1 . Various compressibility and physicochemical parameters were evaluated from the experimental data to examine intermolecular interactions in the studied systems. The obtained experimental density and speed of sound values are used to calculate apparent molar properties (e.g., V ϕ ; K ϕ , s ), partial molar properties (e.g., V ϕ ∘ ; K ϕ , s ∘ ), partial molar transfer properties (e.g., Δ V ϕ ∘ ; Δ K ϕ , s ∘ ), and the partial molar expansibility ( E ϕ 0 ), along with its first derivative ( ∂ E ϕ 0 ∂ T ) P . The calculated interaction coefficients revealed the presence of dipole–dipole, solute–solvent, ion–hydrophilic, and hydrophilic–hydrophilic interactions. FTIR analysis further supported hydrogen bonding within the mixtures. The study provides valuable insight into the thermodynamic and molecular interaction behavior of aqueous tetrasodium EDTA–glycol systems.