INTERFACES BETWEEN A SATURATED AQUEOUS UREA SOLUTION AND CRYSTALLINE UREA - A MOLECULAR-DYNAMICS STUDY

Interfaces between a saturated urea solution and crystalline urea surfaces have been studied by means of molecular dynamics simulations. Mean densities of solute urea and water at both (001) and (110) interfaces show an enhanced adsorption probability for solute urea compared to water. Orientation distributions and positions in the horizontal plane have been calculated for urea molecules in the first adsorption layer. These indicate a ''preorganization'' for growth of a new crystal layer at the (001) interface. The adsorbed urea molecules at the (110) interface, on the other hand, are much more randomly distributed and oriented than at the (001) interface and even show a slight preference for wrong positions above the crystal surface. This indicates an increased interfacial entropy which may stabilize the (110) crystal surface.