Crystal Habits and Morphology of n-Tetranonacontane (n-C94H190)

Abstract

The electron microscope has been used to study (i) the growth habits of orthorhombic (a=7.4Å, b=4.95 Å, c=122 Å) crystals of n‐tetranonacontane grown by cooling hot dilute solutions of this n‐alkane in xylene to room temperature and (ii) to examine by means of a replicating technique the surface morphology of monoclinic (a=9.0 Å, b=4.95 Å, c=122 Å, β=123°) n‐tetranonacontane crystallized from the melt in polycrystalline form. The general habit characteristics of orthorhombic solution grownsingle crystals, {110} twinned crystals, multiple {110} twins, as well as {310} twinned crystals are described. In addition, the observed dependence of the habit of {110} twinned crystals on screw dislocations situated within the constituent twin lattices as well as the twin boundary in such crystals, is considered in some detail. Polycrystalline monoclinic n‐tetranonacontane is shown to possess a distinctly stepped surface structure. The steps are of the order of 100 Å in thickness. It is deduced that the interstep surfaces are {001} faces of the constituent molecular layers and that these layers are bound peripherally by {hko} faces. Although no distinct spiral growth patterns associated with screw dislocations have been observed, the apparent presence of such dislocations in these polycrystalline samples is indicated.