The effect of temperature on urea–urea interactions in water: a molecular dynamics simulation

Abstract

We investigate the temperature effect on the structural and dynamical properties (translation, rotation) of an urea/water system at 0.20 mole fraction of urea. We report the radial distribution functions of like and unlike molecules and conclude that, even at large distances, these molecules are spatially correlated (with respect to their centers of mass). This behavior is interpreted as an indication that urea molecules are not uniformly distributed at a microscopic level. However, the orientational distribution shows that, at long distances, the urea molecules are not orientationally correlated. A strong correlation between urea molecules is observed within the first-shells of neighboring molecules. In view of these results, it is postulated that urea behaves slightly like a nonpolar molecule. The dynamical properties were analyzed using the velocity (translation) and angular velocity (rotation) time autocorrelation functions, as well as their Fourier transforms. The results indicate a significant hydrogen bonding between urea and other molecules in the solution.