Thermodynamic Behavior of Commercial Paracetamol Suspension under Aqueous Dilution
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Paracetamol, Suspension, Density, Viscosity, Surface tension, Redlich–Kister model, Non-ideal mixtures
Abstract
This study examines the thermophysical and excess thermodynamic behavior of paracetamol Suspension upon dilution with water to form binary mixtures (paracetamol-water) at room temperature over a concentration range of 1 mg/mL – 10 mg/mL. Experimental measurements of density, viscosity and surface tension were used to calculate derived parameters including molar volume (Vm), excess molar volume (VE), excess viscosity (ηᴱ), and excess surface tension (γᴱ). The results showed that density decreased from 1.0152 g/mL to 0.998 g/mL with decreasing paracetamol concentration; additionally, the viscosity decreased from 1.1746 to 0.8903 mPa·s upon the dilution process. Surface tension initially increased, peaking at 75.64 mN/m at 5 mg/mL, before decreasing at lower concentrations. The minimum excess molar volume was −0.177 cm³/mol, indicating volume contraction and strong molecular interactions. Maximum excess viscosity and surface tension were observed at mole fractions around 0.12, with ηᴱ = 0.284 mPa·s and γᴱ = −7.52 mN/m. The Redlich–Kister polynomial model provided an excellent fit for all excess properties with R² values above 0.98. These findings highlight the significant non-ideality and strong solute–solvent interactions in the system, offering valuable insight for pharmaceutical formulation and solubility optimization.
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