Investigations of Volumetric Properties and Estimation of the Molecular Radius of Poly(ethylene glycol) (PEG)-400 and Ionic Liquids/Alkyl Acrylates Mixtures

In the present work, volumetric properties, namely, partial molar volume, excess partial molar volume, partial molar volume at infinite dilution, and apparent molar volume, are determined for six binary mixtures of poly-(ethylene glycol) (PEG)-400 including three PEG-400 + ionic liquids (ILs), namely, [C₄mim] [Br], [C₆mim] [Br], and [C₈mim] [Br], and three PEG-400 + alkyl acrylates, namely, methyl acrylate (MA), ethyl acrylate (EA), and <i>n</i>-butyl acrylate (n-BA), at different concentrations and temperatures. These properties are further utilized to analyze the nature and strength of the solute-solvent interactions prevalent in these mixtures. Primarily, solute-solvent interactions mainly involve hydrogen bonding, ion-dipole interactions, and van der Waals forces in the case of PEG-400 and ILs systems. It has been observed that the strength of the solute-solvent (A-B) interaction between PEG-400 and ILs gradually increases with an increase in the concentration of PEG-400. An increase in the alkyl chain has a noticeable effect on these interactions. The limited change in <i>V̅</i> ₁ values across PEG-400 + MA, EA, and n-BA mixtures suggests that the interactions are mostly governed by nonspecific van der Waals and weak dipole-dipole forces. The molecular radius, which is an important property of liquids, has also been computed for these mixtures using six predictive methods: Schaaff's, Rao, Kittle, Eyring, CPFCC, and the refractive index method. Out of these, the Schaaff and Rao methods are found to be most suitable to determine the molecular radius.