Volumetric and Ultrasonic Studies of Molecular Interactions of PEG 400 and PEG 4000 in Aqueous Niacin Solutions at Different Temperatures

At multiple temperatures, 288.15-318.15 K, the density and speed of sound values for PEGs of molecular weights 400 and 4000 in aqueous niacin solutions were measured at concentrations of 0.07, 0.08, and 0.09 mol-kg(-1). Utilizing these experimental data, the apparent molar properties and partial molar properties were determined to analyze the interactions in aqueous niacin solutions with poly(ethylene glycol)s (400/4000). The volumetric parameters, such as apparent molar volume, V-phi, partial molar volume, V-phi(0) and partial molar volume of transfer, Delta V-phi(0) are obtained using experimental density values, while the acoustic parameters, i.e., apparent molar isentropic compression, K-phi,s(0), partial molar isentropic compression, K-phi,K-s, and partial molar isentropic compression of transfer, Delta K-phi,s(0), are determined with the speed of sound data. These positive volumetric apparent and partial molar properties suggest the presence of strong solute-solvent interactions. The partial molar expansibilities (E-phi(0)) along with their first derivative (partial derivative E-phi(0)/partial derivative T)(p) were calculated. Further, pair and triplet coefficients are obtained using partial molar isentropic compression and partial molar volume of the transfer, respectively.