Physicochemical Properties and Molecular Interactions of Long-Chain 1-Alkanols and <i>N</i>-Dodecyl-2-pyrrolidone: Density, Viscosity, Thermodynamics, Spectroscopy, and Theoretical Calculations

Long-chain 1-alkanols and N-dodecyl-2-pyrrolidone (NDP) exhibit significant potential in the field of solvent extraction. Investigating their physicochemical properties is valuable for understanding mass transfer, heat transfer, and the fluid transport process. In this study, we investigated the effect of the alkyl chain length of 1-alkanols (C4/C6/C8/C10) on NDP organic liquid mixtures. The densities and viscosities were measured at temperatures ranging from 303.15 to 323.15 K and atmospheric pressure. Excess properties, including excess molar volume (VmE), viscosity deviation (Δη), and the excess Gibbs free energy of activation of viscous flow (ΔG*E), were calculated and correlated by Redlich–Kister equation to identify the differences between real and ideal solutions. It was found that the steric hindrance increased with the alkyl chain length increasing from C4 to C10 for 1-alkanols, leading to weaker molecular interactions in the mixtures. Furthermore, the Fourier transform infrared spectroscopy (FT-IR) and UV–vis spectra confirmed the presence of intermolecular hydrogen bond interactions between the −OH group of 1-alkanols and the –C═O group of NDP. Finally, the conductor-like screening model for realistic solvation (COSMO-RS) and Gaussian spectra further proved the hydrogen bond interactions. Overall, this study reported a range of physicochemical properties from both experimental and theoretical perspectives, which can be used to guide industrial production.