Oriented overgrowth (epitaxy) of macromolecular organic compounds

Willems, J.

doi:10.1007/bf02142147

Cited by 40 publications

(8 citation statements)

References 19 publications

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“…The [100] oriented crystals-i.e. the long chain c-axis was normal to the electron beam and parallel to the substrate-were obtained by the method of epitaxial crystallization (Willems 1959(Willems , 1967 1978; Wittmann et al 1983) by mixing the paraffin with a large excess of benzoic acid crystals, enclosing the mixture between two glass slides or freshly cleaved mica sheets. A flat aluminium bar with one end on a hotplate provided the temperature gradient, and the glass 'sandwich' was slid slowly up and down the bar causing the mixture to melt and then solidify.…”

Section: Methodsmentioning

confidence: 99%

High resolution electron microscopy of molecular crystals. IV. Paraffins and their solid solutions

Fryer

McConnell

Dorset

et al. 1997

Proc. R. Soc. Lond. A

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Lattice images of dislocations, growth boundaries and surface structure, of the nparaffin series have been obtained by high resolution electron microscopy. The crystals were grown so that the chain axes of the paraffin molecules were normal to the incident beam enabling distortion created by chain end interactions to be resolved. Solid solutions of paraffins within four carbon units in length, crystallized without eutectic segregation, irrespective of the even or odd numbers of carbon in the chains. However, for paraffins separated by only one or two carbon units there was lattice exfoliation at the crystal boundaries, which we have interpreted as evidence for an interblock structure with segregation of the minor component to the crystal boundaries.

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Section: Methodsmentioning

confidence: 99%

High resolution electron microscopy of molecular crystals. IV. Paraffins and their solid solutions

Fryer

McConnell

Dorset

et al. 1997

Proc. R. Soc. Lond. A

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“…However, epitaxial crystallization of polymers Onto various substrates is well known (13,14) and recently Wittmann and Lotz have undertaken a sys- tematic investigation of epitaxial crystallization of polyethylene onto organic and inorganic substrates (15) to check the possible relation between epitaxy and the nucleating efficiency of specific nucleants.…”

Section: Primary Nucleation and Epitaxymentioning

confidence: 99%

Nucleation in polymer crystallization: A physical or a chemical mechanism?

Mercier

1990

Polymer Engineering & Sci

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Primary nucleation is in general heterogeneous in polymer crystallization. In unseeded polymers, the crystallization originates from a very small concentration (<0.1 percent) of unknown submicroscopic heterogeneous nuclei. Only in three cases have the nucleation mechanisms been identified with precision. The first example is self‐nucleation, which relates to the nucleation of a polymer melt by fragments of its own crystals previously present in the melt. Another example of heterogeneous nucleation is represented by epitaxial nucleation of polymers on inorganic and organic substrates recently established by Lotz and Wittmann. More recently, it was discovered that finely divided organic salts added to reactive polymers do not behave as inert heterogeneous substrates but rather dissolve and cut molten macromolecules producing ionic chain ends which precipitate into the melt and form organized aggregates which are the true nucleating species. It is clearly shown that mechanisms of physical and chemical origin are involved in heterogeneous primary nucleation of polymer crystallization.

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“…It has been mentioned that it is also possible to crystallize long-chain compounds by epitaxy at the eutectic point. This technique has been studied extensively (Willems, 1955(Willems, , 1967Wittmann and Lotz, 1981;Wittmann et al, 1983). The conclusion from both the vacuum sublimation and the liquid-phase techniques is that most compound can be grown epitaxially if a suitable substrate can be found.…”

Section: Oriented Growthmentioning

confidence: 99%

“…This indicated that the specimen was either moving or oscillating about one axis. The first useful resolution of a paraffin stemmed from the work of Willems (1955Willems ( , 1967 and Wittmann and Manley (1978). They had shown that it was possible to crystallise linear long-chain molecules with the chain axis parallel to the substrate.…”

Section: Introductionmentioning

confidence: 99%

High‐resolution imaging of organic crystals

Fryer¹

1989

J. Elec. Microsc. Tech.

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The history of high-resolution imaging of organic crystals is summarized, followed by a discussion of radiation damage which reflects current thinking. Methods of specimen preparation and the experimental techniques for high-resolution imaging are described. The results show the application of these techniques to aromatic hydrocarbons, phthalocyanines, and linear-chain aliphatic molecules. Artefacts and image interpretation are also discussed.

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Oriented overgrowth (epitaxy) of macromolecular organic compounds

Cited by 40 publications

References 19 publications

High resolution electron microscopy of molecular crystals. IV. Paraffins and their solid solutions

High resolution electron microscopy of molecular crystals. IV. Paraffins and their solid solutions

Nucleation in polymer crystallization: A physical or a chemical mechanism?

High‐resolution imaging of organic crystals

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