Mathematical and experimental analysis of ultrasound velocity and refractive index in binary mixtures of pharmaceutically important polymer— PEG 600

Abstract

The estimation of ultrasonic velocity, refractive index and acoustical parameters are being increasingly used as tools for investigation of the properties of pure components and the nature of intermolecular interactions between the liquid mixture constituents. Polyethylene glycol (PEG) is a chemical that has a variety of applications in the world of medicine. It is used as a base to manufacture certain medicines, assist in drug delivery and is also used as an agent for some medical procedures. The present study proposes to estimate the viscosity of Polyethylene Glycol (Molar mass: 600) (PEG 600) at different concentrations (2, 4, 6, 8, 10, 12, 14, 16, 18 and 20 % w/v), in the temperature range from 303 to 318 K in steps of 5 K. The activation energy is determined and the impact of the solvent is studied from the experimental data. Density, ultrasonic velocity and refractive index have been estimated for aqueous solutions of PEG 600 at 303 K. The experimental ultrasound velocities are compared with theoretically calculated values obtained by using various mathematical methods like Vandeal Vangeal Relation, Nomotto’s Relation, Rao’s specific sound velocity and Impedance Relation. Similarly the experimental refractive index values are compared with theoretical values obtained from various mathematical methods like Lorentz-Lorentz relation, Newton relation, Heller relation, Arago-Biot relation, Gladstone-Dale equation and Eyring-John equation. The average percentage error (APE) is determined to identify the most suited method that agrees with the experimental values and discussions are made in the light of molecular interactions that occur in the binary liquid systems. Comparative study of estimated theoretical ultrasound velocities and refractive indices with experimental values helps to understand the nature of the interaction occurring among the component molecules in the mixtures. This kind of study is useful to identify and predict a comprehensive theoretical model for a specific liquid mixture. Also, various molecular interaction parameters like viscous relaxation time, inter-atomic free length, free volume, internal pressure, etc. are calculated and discussed in terms of polymer-solvent interactions.