Calculation of X-ray Density of Amorphous–Crystalline Polymer Taking into Account Degree of Ordering of Amorphous Phase

Kalistratova, L. F.; Mashkov, Yu. K.; Egorova, V. A.

doi:10.1134/s2075113318040147

Cited by 6 publications

(21 citation statements)

References 6 publications

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“…This conclusion is confirmed by the data presented in Table 1: the dominance of equatorial reflections (l = 0) in the range of diffraction angles 2θ = 30°-70° on the diffraction patterns of the initial polymer and TRM-PTFE can be attributed to disordering along the hexagonal axis of the PTFE unit cell (space group P6mm) [19]. It is known that the crystal structure of PTFE is based on the close packing of spiral polymer molecules along the hexagonal axis [18][19][20]. However, in the course of crystallization, the CF 2 groups that form the PTFE unit cell can be disordered with respect to the rotation angle around the hexagonal axis and the monomer units of the polymer chains that form the PTFE unit cell can be shifted with respect to each other.…”

Section: Characterization Of X-ray Diffraction Patterns Registered For Initial and Thermal-radiation Modified Polytetrafluoroethylenesupporting

confidence: 71%

“…The diffraction patterns of the initial and TRM-PTFE were indexed by the method described in [14][15][16], taking into account the reference data (protocol JCPDS No. 47-2217 [17]) and the results previously obtained in [18][19][20]. The procedure for determining the degree of crystallinity X c of polymers was described earlier [11].…”

Section: Characterization Of X-ray Diffraction Patterns Registered For Initial and Thermal-radiation Modified Polytetrafluoroethylenementioning

confidence: 96%

“…It is usually considered that PTFE crystals at room temperature belong to the hexagonal system with the unit cell containing 15 CF 2 groups packed into a spiral with 7 turns around the hexagonal axis [14][15][16][17][18][19][20]. Gamma-irradiation of PTFE up to 173 kGy with simultaneous exposure to temperatures in the range of 327-350°С leads to the shift of almost all diffraction maxima towards smaller diffraction angles (Table 1).…”

Section: Characterization Of X-ray Diffraction Patterns Registered For Initial and Thermal-radiation Modified Polytetrafluoroethylenementioning

confidence: 99%

“…The origin of halo II can be attributed to intramolecular scattering from disordered polymer chains with a conformation close to that of PTFE crystals, but not included in the crystalline phase; presumably, these macromolecules are included in the smectic phase of the polymer [18,20]. The spectral shape of halo II can be approximated by two Gaussians (Table 3, Figure 4, a, b), which suggests the existence of two independent non-crystalline components in the smectic phase of PTFE, the first of which includes partially ordered PTFE macromolecules, and the second, disordered layers of specific structural formations, so-called hexagons [18].…”

Section: Characterization Of X-ray Diffraction Patterns Registered For Initial and Thermal-radiation Modified Polytetrafluoroethylenementioning

confidence: 99%

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Structure of polytetrafluoroethylene modified by the combined action of γ-radiation and high temperatures

Smolyanskiĭ¹,

Политова²,

Koshkina³

et al. 2021

Preprint

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By means of X-ray computed microtomography (XCMT) the existence of a developed microporous structure having an average pore diameter of ~3.5 μm and pore content of ~1.1 vol.% has been revealed in unirradiated polytetrafluoroethylene (PTFE). It has been found that the combined action of gamma radiation (absorbed dose per PTFE of ~170 kGy) and high temperatures (327-350 °C) leads to the disappearance of the microporous structure and the formation of several large pores with sizes from 30 to 50 μm in the bulk of thermal-radiation modified PTFE (TRM-PTFE). It has been established by X-ray diffraction (XRD) analysis that the thermal-radiation modification of PTFE leads to an increase in the interplanar spacings, the degree of crystallinity and volume of the unit cell, as well as to a decrease in the size of crystals and the X-ray density of the crystalline phase in comparison with the initial polymer. It is assumed that the previously established effect of improving the deformation-strength and tribological properties of the TRM-PTFE can be due not only to the radiation cross-linking of polymer chains but also to the disappearance of the micropore system and to the ordering of the crystalline phase of PTFE.

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Section: Characterization Of X-ray Diffraction Patterns Registered For Initial and Thermal-radiation Modified Polytetrafluoroethylenesupporting

confidence: 71%

Section: Characterization Of X-ray Diffraction Patterns Registered For Initial and Thermal-radiation Modified Polytetrafluoroethylenementioning

confidence: 96%

Section: Characterization Of X-ray Diffraction Patterns Registered For Initial and Thermal-radiation Modified Polytetrafluoroethylenementioning

confidence: 99%

Section: Characterization Of X-ray Diffraction Patterns Registered For Initial and Thermal-radiation Modified Polytetrafluoroethylenementioning

confidence: 99%

See 2 more Smart Citations

Structure of polytetrafluoroethylene modified by the combined action of γ-radiation and high temperatures

Smolyanskiĭ¹,

Политова²,

Koshkina³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…The density of the initial PTFE was 2.16 g/cm 3 , with a degree of crystallinity of 63%. The difference between the theoretical and experimental density of PTFE and PCM was calculated using the following equation [17]:ρadd=1normalK(1−φ)ρc+(1−normalK)·(1−φ)ρa+φρf where ρ f is the filler density, ρ c is the extrapolated density of the crystalline phase (~2.30 g/cm 3 ), ρ a is the extrapolated density of the amorphous phase (~2.04 g/cm 3 ), K is the degree of crystallinity (%) determined by XRD, and φ is the filler weight content (wt %) [17]. Table 1 shows that the addition of the combined fillers resulted in an increase in the degree of crystallinity from 63% for the initial PTFE to 74% for PCM, regardless of the layered filler type.…”

Section: Resultsmentioning

confidence: 99%

Mechanical and Tribological Properties of Polytetrafluoroethylene Composites with Carbon Fiber and Layered Silicate Fillers

et al. 2019

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Mixtures of layered silicates (vermiculite and kaolinite) and carbon fibers were investigated as filler materials for polytetrafluoroethylene. The supramolecular structure and the tribological and mechanical properties of the resulting polymer composite materials were evaluated. The yield strength and compressive strength of the polymer increased by 55% and 60%, respectively, when a mixed filler was used, which was attributed to supramolecular reinforcement of the composites. In addition, the wear resistance increased by 850 times when using vermiculite/kaolinite fillers, which was due to protection of the surface by the formation of hard tribofilms.

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First-Principles-Based Machine-Learning Molecular Dynamics for Crystalline Polymers with van der Waals Interactions

Chun

Lee

Kim

et al. 2021

J. Phys. Chem. Lett.

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Machine-learning (ML) techniques have drawn an ever-increasing focus as they enable high-throughput screening and multiscale prediction of material properties. Especially, ML force fields (FFs) of quantum mechanical accuracy are expected to play a central role for the purpose. The construction of ML-FFs for polymers is, however, still in its infancy due to the formidable configurational space of its composing atoms. Here, we demonstrate the effective development of ML-FFs using kernel functions and a Gaussian process for an organic polymer, polytetrafluoroethylene (PTFE), with a data set acquired by first-principles calculations and ab initio molecular dynamics (AIMD) simulations. Even though the training data set is sampled only with short PTFE chains, structures of longer chains optimized by our ML-FF show an excellent consistency with density functional theory calculations. Furthermore, when integrated with molecular dynamics simulations, the ML-FF successfully describes various physical properties of a PTFE bundle, such as a density, melting temperature, coefficient of thermal expansion, and Young's modulus.

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Calculation of X-ray Density of Amorphous–Crystalline Polymer Taking into Account Degree of Ordering of Amorphous Phase

Cited by 6 publications

References 6 publications

Structure of polytetrafluoroethylene modified by the combined action of γ-radiation and high temperatures

Structure of polytetrafluoroethylene modified by the combined action of γ-radiation and high temperatures

Mechanical and Tribological Properties of Polytetrafluoroethylene Composites with Carbon Fiber and Layered Silicate Fillers

First-Principles-Based Machine-Learning Molecular Dynamics for Crystalline Polymers with van der Waals Interactions

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