The phenomenon of “partial isobaric compression” of urea as a solute in tertiary butanol: Comparison with a similar effect in the (methanol + urea) system

Abstract

The densities of urea (U) solutions in tert-butanol (t-BuOH) with the solute molality from (0.01 to 0.33) mol∙(kg solvent)-1 were measured at T = (299.15, 303.15, 308.15, 313.15, 318.15, 323.15, and 328.15) K and p = 0.1 MPa. The uncertainty in density measurements was estimated to be 0.03 kg m−3. The standard (at infinite dilution) molar volumes and expansibilities of U were calculated. Similar to the solution of water in t-BuOH, the phenomenon of negative partial expansibility or partial isobaric compression of a solute (PICS) was discovered for U solvated in the alkanol in question. The local structural aggregates or solvation complexes formed by U in t-BuOH becomes increasingly compact with increasing temperature due to that the solute – solvent affinity prevails over the affinity of the solvent molecules to each other.