The study of crystal growth with the electron microscope V. The crystal growth ofn-pentacontanol-1

Abstract

The crystal growth ofn-pentacontanol-1, C50H101OH, from a series of polar and non-polar solvents has been studied to obtain further information about the effect of molecular association on growth-step height. The solvents used were petroleum ether, benzene, xylene, amyl acetate, dioxan,n- andiso-propyl alcohols,n-butyl alcohol and amyl alcohol. In general, crystals grown from polar solvents showed monomolecular growth steps, and crystals grown from non-polar solvents showed a high proportion of bimolecular growth steps with some monomolecular growth steps. These results support the idea that step height is determined by the size of the associated group of molecules in solution. Alcohol solvents, although polar, gave results which did not conform to the general distribution of step heights for polar solvents. A suggested explanation is offered by the complex association possible when both solute and solvent are themselves alcohols. Twin growth occurs more extensively from non-polar solvents than from polar solvents. Habit modification was observed in crystallization from alcohols, and this was related to the residual water content of the solvent. In aqueous alcohols reproducible crystals showing modified growth habit could be obtained. Polytypism has been observed in one crystal out of the many hundreds examined. This crystal did not show cross-lacing of the growth-step pattern. Conversely, a crystal showing a cross-laced pattern was encountered which was not a polytype. These two results show that the detection of cross-laced growth steps cannot be taken as adequate proof of polytypism. In this investigation a unique crystal, composed of two independent helical monomolecular interleaving layers, has been encountered.