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Orientational order in naphthalene crystal-solution interfaces

1987; Elsevier BV; Volume: 83; Issue: 3 Linguagem: Inglês

10.1016/0022-0248(87)90290-9

1873-5002

M. Elwenspoek, P. Bennema, J.P. van der Eerden,

Surfactants and Colloidal Systems

We present experimental studies of growth forms of naphthalene crystals growing from various solutions under the condition that the classical α-factor of Jackson (i.e. the ratio of the heat of dissolution to the temperature) is essentially constant for all cases studied. If the molecules of the solvent contain phenyl rings or similar rings (in particular: pyridine), the side faces of the crystals become round at moderate supersaturations, indicating small step free energies. If the molecules of the solvent do not contain phenyl rings, but are of elongated or roughy spherical shape, the crystals stay faceted at all accessible supersaturations, indicating a much higher step free energy on the side faces. The analysis shows that these results are not compatible with the Jackson interface model. We suggest that in the first case there exists orientational order (a quasi smectic layer) in the liquid adjacent to the crystal faces. In the latter case the order is disturbed by the molecules of spherical or elongated shape, penetrating the ordered layers.