Crystallization and isothermal thickening of single crystals of C246H494 in dilute solution

Crystals of the uniform, long alkane C246H494 have been grown from dilute solution in extended chain and a number of integer folded forms, following our earlier work on solution crystallization and thickening of C294H590 and C198H398. Crystallization rates have been measured using DSC, and minima in growth rates found at both the transition between primary growth in the twice-folded (2F) and once-folded (1F) forms, and at the transition between primary growth in the 1F and extended (E) forms. Isothermal thickening has been followed both in the DSC and by TEM examination of the resultant crystal morphologies; allowing direct correlations to be made between the thickening kinetics and the changes in morphology. Different modes of thickening have been observed depending on the particular integer folded forms studied. Thickening between 2F and 1F crystals is accompanied by screw dislocation growth at crystal edges, and appears to occur largely through a solid state process resulting in a small scale roughness. Thickening between 1F and E crystals is likewise accompanied by screw dislocation growth at crystal edges but appears to proceed, at least partially, through a larger scale re-organization resulting in small, crystallographic, lozenge shaped, multiple twins. Differences between the thickening behaviour observed when samples are prepared in the DSC (using aluminium pans) or in oil baths (using glass tubes) are also discussed.