Thermo Acoustical Analysis of Polyethylene Glycol and Ethanol: Insights into Molecular Interactions

Introduction: The purpose of this work is to investigate the molecular interactions in binary mixtures of polyethylene glycol (PEG) and ethanol at different temperatures (25°C, 35°C, 45°C, and 55°C) and concentrations (5%, 10%, and 15%). The goal is to comprehend how these factors affect important physicochemical and thermoacoustic characteristics that are pertinent to coatings, drug delivery systems, and material formulation. Methods: At a steady frequency of 4 MHz, the ultrasonic velocity, density, and viscosity of PEG-ethanol solutions were measured. Internal pressure, free volume, available volume, Rao's constant, Wada's constant, molar volume, and surface tension were among the thermodynamic and acoustic parameters that were computed from these measurements. To guarantee accuracy, calibrated instruments and standard procedures (ASTM) were used. Results: The findings showed that while free volume and molar volume increased with temperature, ultrasonic velocity and density decreased. Rao's and Wada's constants, as well as internal pressure, exhibited a declining trend as the temperature rose, suggesting that intermolecular interactions were becoming weaker. On the other hand, higher PEG concentrations improved hydrogen bonding, which raised the interaction constants, surface tension, and ultrasonic velocity. All of these patterns point to a significant reorganisation of the molecular structure in the PEG-ethanol system that is dependent on temperature and concentration. Discussion: Internal pressure in PEG-ethanol mixtures rises with temperature as molecular vibrations intensify, but falls with increasing PEG concentration because PEG disrupts the hydrogen-bond network in ethanol. On the other hand, increased molecular spacing due to polymer addition and thermal expansion is indicated by the rise in free volume, available volume, and molar volume with concentration and temperature. Rao's and Wada's constants also rise in both scenarios, indicating variations in density, sound speed, and molecular packing that affect the mixture's thermodynamic and acoustic properties. Conclusion: The study demonstrates that molecular interactions in PEG-ethanol mixtures can be successfully revealed by thermoacoustic and ultrasonic analysis. The trends demonstrate how PEG can form hydrogen bonds, which have a significant impact on the behavior of solutions. These results provide important new information for designing and optimising the stability of polymer-based solutions in material science and pharmaceutical applications.