Ultrasonic and Thermo-Acoustic Investigation of Ethylbenzoate + 2-Butanol Binary Mixtures at Variable Temperatures

Ultrasonic velocity (U), density (ρ), and viscosity (η) of binary mixtures of ethylbenzoate (X₁) and 2-butanol (X₂) were measured over the entire mole fraction range at temperatures 303.15, 308.15, 313.15, and 318.15 K to investigate molecular interactions and thermodynamic behavior. From the experimental data, several derived acoustic parameters such as molar volume (V), adiabatic compressibility (βₐd), intermolecular free length (L_f), internal pressure (π), acoustic impedance (Z), and molar enthalpy (H) were evaluated using standard theoretical relations. Ultrasonic velocity and density were observed to increase with increasing mole fraction of ethylbenzoate, while viscosity showed a decreasing trend with temperature, consistent with enhanced molecular mobility and reduced internal friction. The decrease in adiabatic compressibility and intermolecular free length with composition indicates stronger molecular associations arising from dipole– dipole interactions and hydrogen bonding between ethylbenzoate and 2-butanol molecules. Excess thermoacoustic parameters exhibited significant deviations from ideality, confirming the presence of specific interactions, which weaken at higher temperatures due to thermal agitation. The systematic composition- and temperature-dependent variations of acoustic parameters demonstrate that ultrasonic techniques are powerful tools for probing intermolecular interactions in organic liquid mixtures. The present study provides reliable thermophysical data useful for industrial solvent formulation, process modelling, and theoretical validation of liquid-state interaction models.