Comparing the morphology of β-n.n.n with β'-n.n+2.n and β'-n.n.n-2 triacylglycerol crystals

The morphology of β-16.16.16, β‘-10.12.10, and β‘-16.16.14 fat crystals is explained on the basis of a connected net analysis taking into account the edge energies of a 2D nucleation growth mechanism. It is shown that the conventional prediction of the morphology on the basis of attachment energies is not capable of explaining the very different morphologies of these fat crystals. The morphology of the three fats ranges from long needles in spherulitic growth forms to lozenge shaped single crystals. It is shown that the elongated growth habit of β‘-10.12.10 fat crystals having fast growing top faces is a result of a very small edge free energy of 2D nuclei on these faces. The bonding topology and its high structural symmetry explain these small edge energies. In contrast, for the β‘-16.16.14 crystals, having a lower symmetry, the corresponding edge energies are much higher, resulting in lozenge shaped crystals.