Spherulite morphology in thin films of natural rubber

1962 ◽  
Vol 270 (1341) ◽  
pp. 232-241 ◽  
Keyword(s):  
Thin Films ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Natural Rubber ◽  
Single Crystals ◽  
Growth Mechanism ◽  
Electron Irradiation ◽  
Electron Diffraction Data ◽  
Dilute Solution ◽  
Spherulite Morphology

Crystalline ‘spherulites’ grown in ultra-thin films of natural rubber at — 26 °C were examined in the electron microscope. The spherulites form hollow domes, like blisters in the film, which collapse under electron irradiation producing remarkable fibre-like patterns of folds and creases. Within the spherulite, crystalline and amorphous regions coexist and the former appear to grow to a preferred thickness of a few hundred Angstroms with the molecular chains oriented perpendicular to the film. The molecules are thus almost certainly folded as in polymer single crystals grown from dilute solution. Electron diffraction data suggest that relatively large regions of the spherulite correspond to single crystals. A growth mechanism for the spherulites is proposed.

Spherulite Morphology in Thin Films of Natural Rubber

1965 ◽  
Vol 38 (1) ◽  
pp. 33-44
Author(s):  
E. H. Andrews
Keyword(s):  
Thin Films ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Natural Rubber ◽  
Single Crystals ◽  
Growth Mechanism ◽  
Electron Irradiation ◽  
Electron Diffraction Data ◽  
Dilute Solution ◽  
Spherulite Morphology

Abstract Crystalline ‘spherulites’ grown in ultra-thin films of natural rubber at − 26° C were examined in the electron microscope. The spherulites form hollow domes, like blisters in the film, which collapse under electron irradiation producing remarkable fiber-like patterns of folds and creases. Within the spherulite, crystalline and amorphous regions coexist and the former appear to grow to a preferred thickness of a few hundred angstroms with the molecular chains oriented perpendicular to the film. The molecules are thus almost certainly folded as in polymer single crystals grown from dilute solution. Electron diffraction data suggest that relatively large regions of the spherulite correspond to single crystals. A growth mechanism for the spherulites is proposed.

Domains in single crystals of poly-4-methyl-pentene-1

1987 ◽  
Vol 45 ◽  
pp. 488-489
Author(s):  
P. Pradère ◽  
J.-F. Revol ◽  
R. St. John Manley
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Single Crystals ◽  
Solution Concentration ◽  
Dark Field ◽  
Dilute Solution ◽  
Contrast Imaging ◽  
Slow Cooling ◽  
Carbon Coated ◽  
Isothermal Crystallisation

Polymer single crystals are generally considered to be structurally homogeneous. In this paper it is shown that in a given single crystal of poly-4-methyl-pentene-1 (P4MP1) there exist narrowly delimited domains that give rise to different electron diffraction (ED) patterns. The shape and location of these domains is characterized by diffraction contrast imaging in the dark field (DF) mode.Monolayer single crystals of P4MP1 polymorphs I and III were prepared in dilute solution (concentration ranging from 0.01 to 0.05%). Form I was obtained by slow cooling of a hexadecane solution whereas form III was prepared by isothermal crystallisation in xylene at 60°C. Crystals were deposited on carbon coated grids and observed with a Philips EM 400 T electron microscope operated at 120 kV. The crystals are very radiation sensitive and the total end point dose, measured by the fading of the ED pattern is 27 C m-2.

Crystalline Morphology in Thin Films of Natural Rubber: Crystallization under Strain

1965 ◽  
Vol 38 (1) ◽  
pp. 45-57
Author(s):  
E. H. Andrews
Keyword(s):  
Thin Films ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Natural Rubber ◽  
Electron Diffraction Pattern ◽  
High Strain ◽  
Crystalline Morphology ◽  
Fibrillar Morphology ◽  
Strain Axis ◽  
Very High

Abstract The morphology of thin films of natural rubber crystallized under unidirectional strain has been examined in the electron microscope. As strain increases the spherulitic morphology of unstrained films gives way gradually to a fibrillar morphology with crystalline filaments (α filaments) measuring 60 by 250 A˚, growing perpendicular to the strain axis. The nucleation of these filaments is governed by the amount of strain but their rate of growth depends only on temperature and time. At very high strains (>300%) crystallization occurs rapidly allowing no time for filament growth, so that the resulting morphology consists of chains of nuclei (γ filaments) running in the direction of extension. The high strain transition from α to γ filaments is accompanied by no change in the electron diffraction pattern, but the earlier transition from spherulitic to filamentous growth reveals a rotation of the molecular axis into the direction of strain. This appears to correspond to a physical rotation of the α filaments about their direction of growth.

Crystalline morphology in thin films of natural rubber II. Crystallization under strain

1964 ◽  
Vol 277 (1371) ◽  
pp. 562-570 ◽  
Keyword(s):  
Thin Films ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Natural Rubber ◽  
Electron Diffraction Pattern ◽  
High Strain ◽  
Crystalline Morphology ◽  
Fibrillar Morphology ◽  
Strain Axis ◽  
Very High

The morphology of thin films of natural rubber crystallized under unidirectional strain has been examined in the electron microscope. As strain increases the spherulitic morphology of unstrained films gives way gradually to a fibrillar morphology with crystalline filaments (α filaments) measuring 60 by 250 Å, growing perpendicular to the strain axis. The nucleation of these filaments is governed by the amount of strain but their rate of growth depends only on temperature and time. At very high strains ( > 300 %) crystallization occurs rapidly allowing no time for filament growth, so that the resulting morphology consists of chains of nuclei (γ filaments) running in the direction of extension. The high strain transition from α to γ filaments is accompanied by no change in the electron diffraction pattern, but the earlier transition from spherulitic to filamentous growth reveals a rotation of the molecular axis into the direction of strain. This appears to correspond to a physical rotation of the α filaments about their direction of growth.

scholarly journals Donald William Pashley. 21 April 1927 — 16 May 2009

2010 ◽  
Vol 56 ◽  
pp. 317-340 ◽  
Author(s):  
Bruce A. Joyce ◽  
Michael J. Stowell
Keyword(s):  
Thin Films ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Film Growth ◽  
Epitaxial Thin Films ◽  
Disorder Effects ◽  
Transmission Electron ◽  
Innovative Materials ◽  
Low Dimensional

Donald William (Don) Pashley was one of the most innovative materials scientists of his generation. He was distinguished for his electron diffraction and transmission electron microscope studies of epitaxial thin films, especially for in situ investigations, work that contributed enormously to our understanding of film growth processes. He pioneered the use of moiré patterns to reveal dislocations and other defects. He also made important contributions to long-range disorder effects on semiconductor surfaces and to the structure of low-dimensional semiconductor systems.

The decomposition of magnesium hydroxide in an electron microscope

1958 ◽  
Vol 247 (1250) ◽  
pp. 346-352 ◽  
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Single Crystals ◽  
Magnesium Oxide ◽  
Magnesium Hydroxide ◽  
Basal Plane ◽  
Morphological Changes ◽  
Water Molecules ◽  
Two Stages

The beam of an electron microscope has been used to dehydrate single crystals of magnesium hydroxide to magnesium oxide. Electron diffraction photographs and electron micrographs were taken at various stages to follow the crystallographic and morphological changes which accompany decomposition. The decomposition may be considered to occur in two stages. First, there is a small shrinkage in the basal plane, and the resulting strain causes a maze of cracks in the crystal. This change is followed by a collapse of the planes down the original [0001] of magnesium hydroxide. The collapse is controlled by the migration of water molecules from between the planes to a surface where they can escape. The product is a highly oriented aggregate of micro-crystallites of magnesium oxide. More intense irradiation in the electron beam occasionally causes bulk movement of the solid.

Annealing Effects in Ten Films of Thoria

1968 ◽  
Vol 26 ◽  
pp. 392-393
Author(s):  
S. E. Bronisz ◽  
Dana L. Douglass
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Transmission Electron Microscopy ◽  
Electron Beam ◽  
Electron Microscope ◽  
Single Crystals ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Annealing Effects ◽  
Diffraction Effects

Thin films of thoria, either cleaved from air-fired material or vacuum deposited on polished copper substrates, were examined by transmission electron microscopy. As prepared, the two types of samples were considerably different, but after being heated in the electron microscope they were closely similar.The cleaved samples were obtained by means of extraction replication of fracture surfaces of polycrystalline thoria. The thin flakes ranged from about 0.1 to 20 μm in diameter. Most of them were single crystals exhibiting the diffraction effects expected of crystalline materials and containing many long dislocations. Upon heating with the unapertured electron beam the dislocations disappeared, the crystals became more electron transparent, and the striated microstructure shown in Fig. 1 developed. The orientations of most of the cleaved crystals were equally divided among ﹛110﹜, ﹛111﹜, and ﹛112﹜. The striae were usually parallel to <110> or <135>.

Direct Observation of the Surface Topography of Single Crystals in a Transmission Electron Microscope

1981 ◽  
Vol 39 ◽  
pp. 208-211
Author(s):  
G. Lehmpfuhl ◽  
Y. Uchida
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Surface Topography ◽  
Single Crystals ◽  
Dynamic Effect ◽  
Thickness Variation ◽  
Crystal Thickness ◽  
Kinematic Effect ◽  
Diffraction Patterns ◽  
Small Change

From the analysis of convergent-beam electron diffraction patterns it is well known that the intensity of some reflections may become most sensitive to the crystal thickness variation at special conditions for thickness and orientation. This can be understood as a dynamic effect as well as a kinematic effect of electron diffraction. Using such a diffracted beam for imaging, a small change in thickness of a single crystal can be observed in an electron microscope. At the beginning of the application of this technique only weak beams were used for imaging the surface topography of undistorted single crystals. Thickness differences down to the atomic level could be detected in darkfield micrographs of MgO and Au. However, the intensity of the weak beams was so low that long exposure times up to 2 minutes were necessary to record a micrograph at a magnification of 20,000. This magnification is the upper limit for the weak-beam darkfield technique for reasons of stability of the electron microscope. The thickness contrast can be explained already by the kinematical theory of electron diffraction.

Electron microscope studies on Nd2-xCexCuO4

1991 ◽  
Vol 49 ◽  
pp. 1100-1101
Author(s):  
H. Brigitte Krause
Keyword(s):  
Crystal Structure ◽  
Electron Microscope ◽  
High Resolution ◽  
Synchrotron Radiation ◽  
Electron Diffraction ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Neutron Powder Diffraction ◽  
Electron Diffraction Data ◽  
Tetragonal Unit Cell

The crystal structure of Nd2-xCexCuO4, as determined from neutron powder diffraction and high resolution synchrotron radiation, has been reported in the literature. The space group was found to be Immm. The ratio of the tetragonal unit cell was reported to vary as a function of the compositions with two separate branches resulting in two different ratios for each composition. In addition, commensurate superlattices have been observed and related to ordering, of atoms or vacancies. The present work deals with electron diffraction data on the same samples used for the neutron diffraction work at Argonne National Laboratory. The samples were kindly supplied by Dr. Bogdan Dabrowski.

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