Hydration of urea and its derivatives – Volumetric and compressibility studies

• Urea and its alkyl derivatives in aqueous solutions were studied.
• The density and the speed of sound were measured for presented systems at different temperatures.
• The differences of hydrophobicity of solutes are observed in obtained data.
• The change of the solvent volume in hydration sphere depends on the shape of solute molecule.
• Bigger hydrophobic character of the solute results in bigger changes of calculated quantities with concentration.

The densities and sound velocities at T = (288.15, 293.15, 298.15, 303.15 and 308.15) K have been measured for aqueous solutions of urea, N,N-dimethylurea, N,N-diethylurea, N-propylurea, N-butylurea. From these data the apparent molar volumes, VΦ, the apparent molar isentropic compressions, KS,Φ, and the Passynski solvation numbers of solutes have been determined. The concentration dependencies of the calculated quantities, their limiting values and temperature characteristics are discussed in terms of (solute + solvent) and (solute + solute) interactions.