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

Adipic acid crystals grown from aqueous solutions 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 analysis to obtain the relative growth rates for the spiral growth model. The concentration of effective growth units at the interface was found to be the key external habit-controlling factor by molecular dynamics simulations at the crystal-solution interface. The differences between the experimentally observed faces of (002), (100), and (011) and unobserved faces of (111), (102), and (202) were explained by two concepts from the interfacial structure analysis that determine the concentration of the effective growth units. The observed faces were characterized by larger values of both the surface scaling factor and molecular orientation factor, implying low anisotropic local concentrations at the interface and high free energy barriers for reorientation on these faces, respectively. Furthermore, the number of turns and the length of one complete spiral rotation and the number of unsaturated bonds were incorporated into the original approach. This consideration of the spiral geometry resulted in a close resemblance to the experimental morphology.