Interfacial Structure Analysis for the Morphology Prediction of Adipic Acid Crystals from Aqueous Solution

In aqueous solution, adipic acid crystals have a hexagonal plate morphology with a dominant (100) face, where the hydrogen-bonding carboxylic acid groups are exposed. In the present work, the crystal morphology was investigated by interfacial structure. The key external habit-controlling factor turned out to be the concentration of effective growth units at the interface by molecular dynamics simulations at the crystal−solution interface. The differences of two factors from the interfacial structure analysis that determine the concentration of the effective growth units explained why faces of (002), (100), and (011) are experimentally observed and faces of (11-1), (10-2), and (20-2) are not. The observed faces were characterized by larger values of both the surface molecular orientation factor and scaling factor, high free energy barriers for reorientation on these faces and implying low anisotropic local concentrations at the interface, respectively. Furthermore, factors of spiral geometry were incorporated into the original approach which resulted in a close resemblance to the experimental morphology.