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

Interfaces between a saturated urea solution and crystalline urea surf aces have been studied by means of molecular dynamics simulations. Mea n densities of solute urea and water at both (001) and (110) interface s 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 lay er at the (001) interface. The adsorbed urea molecules at the (110) in terface, on the other hand, are much more randomly distributed and ori ented than at the (001) interface and even show a slight preference fo r wrong positions above the crystal surface. This indicates an increas ed interfacial entropy which may stabilize the (110) crystal surface.