Partial disordering and crystal transitions in polytetrafluoroethylene*

Clark, Edward S.; Muus, L. T.

doi:10.1524/zkri.1962.117.2-3.119

Cited by 265 publications

(110 citation statements)

References 5 publications

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“…The chain bond angle C(l', 1,2) of 115.3 ° relieves F(2')-H(2) to 2.65 ,~; further noticeable distortions are found for the exocyclic bond angles C(1,2,3) and C(1,2,5) of 116.3 and 116.2 °. Similar values (114.6 and 115.6 ° ) have been calculated for Teflon (Clark & Muus, 1962). The C-C-F angles of the substituted cyclobutane ring average llS.1 ° (range 113.6-116.9°), at variance with the corresponding angles in the chain (av.…”

Section: Geometrical Parameters Of the Independent Unitsupporting

confidence: 80%

“…A planar zigzag carbon configuration as in (I) has also been found in perfluoro-n-pentane and perfluoro-n-hexane (Bastiansen & Hadler, 1952) but contrasts with the helical chain of poly(tetrafluoroethylene) (13 CF 2 units in six turns, r --163.5°; 15 CF 2 units in seven turns, r = 165.8 °) (Clark & Muus, 1962). The tendency towards a planar conformation of the chain is also present in Teflon at high temperatures (Clark & Muus, 1962). The configuration of the asymmetric carbon atoms C(2) and C(2') in tetrafluoro-l,2-bis(2,2,3,3-tetrafluorocyclobutyl)ethane is (RS) and therefore the compound has a meso configuration due to the crystallographic inversion centre.…”

Section: Geometrical Parameters Of the Independent Unitmentioning

confidence: 74%

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Structure of tetrafluoro-1,2-(RS)-bis(2,2,3,3-tetrafluorocyclobutyl)ethane

Bart¹,

Piccardi²,

Bassi³

1980

Acta Crystallogr Sect B

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Tetrafluoro-1,2-(R S)-bis(2,2,3,3-tetrafluorocyclobutyl)ethane, Ct0H6Faz, crystallizes in space group P2~/c with Z = 2 and cell parameters a = 5.154 (5), b = 10.010(7), c = 12.559(12) A and fl = 113°45 (10)'. The crystal structure has been determined by X-ray diffraction (763 observed reflexions; final R value 0.064). The conformation of the molecule is governed by the steric and electrostatic interactions of the substituents. Steric hindrance is minimized by the adoption of a staggered configuration by the carbon chain. By contrast, the cyclobutane ring is only slightly puckered (torsion angles of 4 °) with substituents in the eclipsed conformation.

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Section: Geometrical Parameters Of the Independent Unitsupporting

confidence: 80%

Section: Geometrical Parameters Of the Independent Unitmentioning

confidence: 74%

Structure of tetrafluoro-1,2-(RS)-bis(2,2,3,3-tetrafluorocyclobutyl)ethane

Bart¹,

Piccardi²,

Bassi³

1980

Acta Crystallogr Sect B

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“…Although a certain amount of caution must be exercised in interpre ting the present limited number of reflections (especially those with l= 15 since they are intrinsically weak [19]), some observations can be made. For example, for l= 15 (or 13 at low temperature) the reflections are governed by a zero-order Bessel function and therefore diffuseness would not result from rotational disorder about the chain axis but would result from disorder along the axis [17,19]. Longitudinal disorder would probably be the cause of diffuseness for l= 7 and 8 (or 6 and 7) but since these reflections are governed by a first-order Bessel function, diffuseness could result from rotational disorder.…”

Section: Resultsmentioning

confidence: 99%

Inclusion of perfluoromethyl groups in the crystals of copolymers of tetrafluoroethylene and hexafluoropropylene

Bolz¹,

Eby²

1965

J. RES. NATL. BUR. STAN. SECT. A.

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X-ray diffraction has bcen used to m easure the separation of the molecular axes as a function of temperature, lamella thickness, and comonomer concentration in copolymers of tet ra fluoro ethylene and h exafluoropropylene. These data show that the increase of separation with increasing concentration of p erfluoromethyl groups is a consequence of inclusion of the gr\lups in the crystals a~d not an artifact associated with la mella thickness or crystal tranSitIOn temperature. ThIS conclUSIOn lS supported by the fact t hat diffuseness of some of the x-ray refl ections in the copolyme rs indicates the presence of molecular di sorder which might be ex pected from inclusion of the p erfluoromethyl groups in the crystals. The la mellas in the copolymers are thinner than those in the typical homopolymer a nd this aspect of the s tructure is the primary cause of the lower density in the copolym ers. Analysis of the availa ble data indicates t hat this is a lso t he situation in ?opolymers of ethyle ne a nd propylene. For both copolym er sen es, the de nSity of the lamellas IS apparently increased by thc inclusion of the m ethyl gro ups in t he cry stals as defects.

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“…We would like to point out here that this formalism is equally relevant for describing the unsampled fiber pattern of polytetrafluoroethylene after the 292 and 303 K transitions. It has been understood for a considerable time from X-ray diffraction (Clark & Muus, 1962b) and NMR (Hyndman & Origlio, 1960) that individual chains in polytetrafluoroethylene crystals undergo torsional motions after the 293 K transition and that these motions appear to be of even greater magnitude after the 303 K transition. A previous treatment (Clark & Muus, 1962a)of the effect of this disorder dealt only with the crystal Bragg reflections (that is, the sampled intensities on layer lines).…”

Section: The Fourier Transform Of Actinmentioning

confidence: 99%

Structural studies onA-cation-deficient perovskite-related phases. II. Microdomain formation in ThNb₄O₁₂

Labeauu¹,

Grey²,

Joubert³

et al. 1982

Acta Cryst Sect A

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Electron diffraction/microscopy and X-ray diffraction techniques have been used to study the thorium/ vacancy ordering and microdomain structures of quenched and slow-cooled samples of the A-cationdeficient perovskite-related phase ThNb4Olz. In both types of samples, there is primary ordering of thorium atoms into the cuboctahedral sites in alternate (001)p layers. The quenched and slow-cooled samples have different secondary orderings of thorium atoms and vacancies in the occupied (001)p layers. In the quenched samples, the thorium atoms and vacancies are ordered in alternate rows parallel to [100]p and [010]p. Short segments (20-50A) of the two orientation variants are statistically distributed in a type of tweed pattern, separated by boundaries that are aligned predominantly parallel to (ll0)p and (ll0)p. In the slow-cooled samples, the ordering of columns of thorium atoms and vacancies parallel to [ll0]p or [1.10]p occurs in microdomains, with domain boundaries parallel to (100)p and (010)p and with average separations of 6ap, 6bp =-24 A. The domains corresponding to the two orientations of thorium columns form a checkerboard pattern of two interpenetrating sets of corner-shared squares. In either set, the ordering of columns is propagated along diagonal rows of corner-shared domains, but there is no correlation between adjacent rows. The NbO 6 octahedra are tilted about the [ll0]p and [ll0]p axes, parallel to the thorium-column orientations, and the domain boundaries act as mirror-twin planes for the octahedral tilt systems. This periodic change in the tilt-axis orientation * Permanent address: CSIRO Division of Mineral Chemistry, PO Box 124, Port Melbourne, Victoria 3207, Australia. 0567-7394/82/060753-09501.00gives rise to characteristic clusters of split superlattice spots in the diffraction patterns for ThNb40~2. Optical transform methods were used to check the validity of microdomain models for both the quenched and the slow-cooled samples. IntroductionIn part I (Alario-Franco, Grey, Joubert, Vincent & Labeau, 1982), we presented electron and X-ray diffraction results for samples of the A-cation-deficient perovskite-related phase Th0.25NbO 3 (i.e. ThNb40~2), which were slowly cooled from the melt. The diffraction patterns showed both strong, sharp reflections and groups of very weak, diffuse satellite reflections. The sharp reflections, which indexed with a tetragonal perovskite supercell (a t = ap, c t = 2Cp), resulted from long-range ordering of thorium atoms into alternate (001)p layers of cuboctahedral A-cation sites, as originally reported by Trunov & Kovba (1966). The diffuse satellite reflections were interpreted as resulting from short-range ordering of thorium atoms and vacancies within the (001)p layers. Splitting of certain groups of satellite reflections was observed, characteristic of a periodic two-dimensional array of domains, with domain boundaries oriented parallel to (100)p and (010)p. However, in order to simplify the interpretation of the diffraction patterns, we consid...

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Partial disordering and crystal transitions in polytetrafluoroethylene*

Cited by 265 publications

References 5 publications

Structure of tetrafluoro-1,2-(RS)-bis(2,2,3,3-tetrafluorocyclobutyl)ethane

Structure of tetrafluoro-1,2-(RS)-bis(2,2,3,3-tetrafluorocyclobutyl)ethane

Inclusion of perfluoromethyl groups in the crystals of copolymers of tetrafluoroethylene and hexafluoropropylene

Structural studies onA-cation-deficient perovskite-related phases. II. Microdomain formation in ThNb₄O₁₂

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Partial disordering and crystal transitions in polytetrafluoroethylene*

Cited by 265 publications

References 5 publications

Structure of tetrafluoro-1,2-(RS)-bis(2,2,3,3-tetrafluorocyclobutyl)ethane

Structure of tetrafluoro-1,2-(RS)-bis(2,2,3,3-tetrafluorocyclobutyl)ethane

Inclusion of perfluoromethyl groups in the crystals of copolymers of tetrafluoroethylene and hexafluoropropylene

Structural studies onA-cation-deficient perovskite-related phases. II. Microdomain formation in ThNb4O12

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Structural studies onA-cation-deficient perovskite-related phases. II. Microdomain formation in ThNb₄O₁₂