Volumetric and Viscosity Properties for the Dilute Solution of [Bmim][OAc] in NMP and the Solute–Solvent Interaction from 288.15 to 318.15 K

The binary system of [Bmim][OAc] (1-butyl-3-methylimidazolium acetate) with NMP (N-methylpyrrolidone) is a potential effective cellulose solvent, and its physicochemical properties and solute–solvent interaction are important to design and understand its application. The physicochemical properties can infer the solute–solvent interaction of a system, especially for an infinite dilution; so, in this work, over the molality range 0.0–2.1 mol·kg⁻¹ and temperature range 288.15–318.15 K, the density and absolute viscosity for the dilute solution of [Bmim][OAc] in NMP were measured and correlated. The apparent molar volume and the relative viscosity were calculated and correlated by Redlich–Rosenfeld–Meyer equation (including parameters \(V_{\Phi}^0\), A_v, B_v) and Jones–Dole equation (including parameters D, F), respectively. Then, the structure behavior of [Bmim][OAc] on solution and the [Bmim][OAc]–NMP interaction were discussed based on the parameters \(V_{\Phi}^0\), A_v, B_v, D, F, and the volume ratio r, limiting apparent molar expansibility \(E_{\Phi}^0\) and the solvation number n_s. The results show that [Bmim][OAc] acts as a structure-maker for the solution, the [Bmim][OAc]–NMP interaction is weaker than the interactions of cation–anion and NMP–NMP, and such effect becomes more and more obvious with increasing temperature. Finally, based on the interactions and the widely accepted solvation hypothesis, the possible better temperature to dissolve cellulose was discussed for the potential cellulose solvent.