CHANGE OF MORPHOLOGY AND GROWTH-MECHANISM OF THIN N-PARAFFIN CRYSTALSINDUCED BY HOMOLOGOUS IMPURITIES

In situ optical and birefringence measurements were applied in observi ng the crystallisation of very thin (greater than or equal to 1.1 mu m ) n-paraffin crystals. Next, homologue impurities were found to reduce the crystal thickness even further to approximately 0.4 mu m. As such thin crystals are very sensitive to adsorption of (sub-) micron parti cles (e.g. dust particles) a new type of growth, i.e. ''particle-induc ed rough growth'', is induced. This growth is akin to the growth of st eps in the presence of immobile impurities adsorbed on the surface. Th e measured mean distance between the obstructing (sub-) micron particl es (12 mu m) is used to calculate the surface energy (36 mJ/m(2)) of t he top and bottom faces of the n-paraffin crystals. And it was shown t hat this is a reasonable value for the surface energy of {001} faces o f n-paraffin crystals. Further, it was shown that at fixed concentrati ons the saturation temperatures for thin crystals are different from t hose for thick crystals. These results can be explained in terms of a Gibbs-Thomson effect. (C) 1998 Elsevier Science B.V. All rights reserv ed.