A versatile crystal-growth simulation program, based on the Monte Carlo algorithm, is introduced. It enables the handling of any crystallographic orientation. The crystal is modeled by a set of molecular interactions, which are obtained from molecular mechanics calculations. The motherphase is parametrized by its bulk thermodynamic properties. As an example, the program was used to simulate the growth of various fat crystals. The results show the importance of the details of the crystal structure, its energetics, and the actual growth conditions upon the crystal morphology. The model intends to fill the gap which exists by the fact that supersaturation, temperature, concentration, and dissolution free energy are not taken into account by the established morphology prediction models.

We present a surface x-ray diffraction study on the KDP-water interface in which the structure of both the crystalline and liquid part of the interface has been measured. We have been able to determine the ordering components in the liquid in both the perpendicular and parallel directions. We find interface-induced ordering in the first four layers of water molecules. The first two layers behave icelike and are strongly bound to the surface. The next two layers are more diffuse and show only minor lateral and perpendicular ordering. Subsequent layers are found to behave similar to a bulk liquid.

The crystal morphology of n.n.n TAGs, still the only triacylglycerol series of which the crystallographic structures have been elucidated, is predicted using a revised version of the Hartman-Perdok theory. In an earlier publication by Bennema et al. 1 the morphology was predicted on the basis of attachment energy. The platelike shape of the crystals was predicted well, but the indices for the top faces failed. Second, the experimentally observed crystals are much more elongated. In the present approach, the morphology is not only predicted using the attachment energy but also use is made of roughening temperatures. For faces that grow below the roughening temperature at low supersaturation, the rate-limiting step is the formation of steps on the surface. Therefore, under these growth conditions, the roughening temperatures of the faces determine the morphology rather than the attachment of new growth units to the surfaces. The roughening temperature of a flat face {hkl} can be estimated by the Ising temperatures, which are calculated from substitute nets constructed from all possible step energies found from the connected nets. In some cases, depending on the topology of the connected net, exceptionally low Ising temperatures can be found. In these cases, it is shown that the roughening temperature is not directly determined by the slice energy. If this concept is used for the prediction of the morphology of TAG crystals, a good agreement with the experimentally observed faces is obtained. Moreover, the dependence of the morphology for the various TAGs on the chain length n is explained. Using this concept, however, the presence of the {31l} faces on the morphology cannot be explained. It is shown that this face is probably an F-face that is stabilized by solvent molecules.

The crystal structure of the beta polymorph of tripalmitin (1,2,3-trihexadecanoylglycerol, beta-PPP) has been determined by single-crystal X-ray diffraction. The molecules crystallize in space group P1; in an asymmetric tuning-fork conformation. This structure and the already-known crystal structures of beta-tricaprin (beta-CCC) and beta-trilaurin (beta-LLL) could be matched in an overlap model. Apart from a difference in chain length, the three structures are almost identical. The overlap model can be used to predict the crystal structure of the other members of the C(n)C(n)C(n)-type (n = even) TAG series reasonably accurately. This is demonstrated by predicting the crystal structure for beta-trimyristin (beta-MMM) and successively comparing the experimental and calculated X-ray powder diagrams.

The crystal structures of the beta' phase of CLC (1, 3-didecanoyl-2-dodecanoylglycerol) and MPM (1, 3-ditetradecanoyl-2-hexadecanoylglycerol) have been determined from single-crystal X-ray diffraction and high-resolution X-ray powder diffraction data, respectively. Both these crystals are orthorhombic with space group Iba2 and Z = 8. The unit-cell parameters of beta'-CLC are a = 57.368 (6), b = 22.783 (2) and c = 5.6945 (6) A and the final R value is 0.175. The unit-cell parameters of beta'-MPM are a = 76.21 (4), b = 22.63 (1) and c = 5.673 (2) A and the final R(p) value is 0.057. Both the beta'-CLC and beta'-MPM molecules are crystallized in a chair conformation, having a bend at the glycerol moiety. The zigzag planes of the acyl chains are orthogonally packed, as is typical for a beta' phase. Furthermore, unit-cell parameters of some other members of the C(n)C(n+2)C(n)-type triacylglycerol series have been refined on their high-resolution X-ray powder diffraction pattern. Finally, the crystal structures are compared with the currently known structures and models of triacylglycerols.