Crystallization of polyacrylonitrile: Growth mechanisms for various growth features

Gohil, R. M.; Patel, K. C.; Patel, R. D.

doi:10.1007/bf01775410

Cited by 14 publications

(9 citation statements)

References 19 publications

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“…In other words, increasing the crystallization temperature, causes a coarsening of the spherulites. A similar observation was also noted by the author for spherulites of polyacrylonitrile grown at a variety of temperatures (2). As may be seen from Figure 12 (a) and the region marked with ~' in Figure 1, the formation of Sshaped lamellae is common in the samples crystallized under large undercooling.…”

Section: Type-jvsupporting

confidence: 59%

“…These structures are similar to sheaves of spherulites commonly noted in polymers [2]. Sometimes, these sheaves fan out and give a spherulitic type appearance.…”

Section: Type-iimentioning

confidence: 90%

“…It is relatively easy to characterize the morphology in thin fdms with electron diffraction, surface replication, phase contrast and darkfield electron microscopic techniques [1][2][3][4]. Several other methods have been developed to increase the contrast of an amorphous phase in thin fdms of polymers [5,6].…”

Section: Introductionmentioning

confidence: 99%

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Etching and the morphology of branched and cross-linked polyethylene

Gohil

1986

Colloid & Polymer Sci

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A permanganic acid etching technique was used to characterize the genuine morphologies of bulk crystallized samples of linear, branched, and crosslinked polyethylene. Four different kinds of artifacts as large as 15-20 p~a were detected. It was also noted that artifact density could be drastically reduced by proper selection of etching conditions. The morphologies of artifacts were independent of specimen crystallinity and the orientation of lamellar crystals; however, their rate of production was susceptible to the crystallinity of samples. The formation of a fresh surface involved the preferential etching of edge-on and secondary lamellae. As the growth features of cross-linked polyethylene were less than 6 paxa and were mainly sheaf-like structures, growth features could be readily distinguished from the artifacts by transmission electron microscopy. Another type of artifact (globules morphology) produced at angstrom scale was found to depend on the crystallinity and the surface structure of lamellar crystals. It is demonstrated that the fine lamellar details of branched and cross-linked polyethylene can be observed using transmission electron microscopy. Increasing the number of cross-links in polyethylene, modifies the size and nature of supermolecular structures, the periodic twisting of lamellar crystals, and the nature of the nucleation process. The study of a blend of branched and cross-linked polyethylene showed that the structurally dissimilar molecules co-crystallized at low crystallization temperatures, while there is a tendency for molecular fractionation at higher crystallization temperatures.

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Section: Type-jvsupporting

confidence: 59%

“…These structures are similar to sheaves of spherulites commonly noted in polymers [2]. Sometimes, these sheaves fan out and give a spherulitic type appearance.…”

Section: Type-iimentioning

confidence: 90%

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Etching and the morphology of branched and cross-linked polyethylene

Gohil

1986

Colloid & Polymer Sci

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“…18 Previous works have shown that twinning plays an important role in the development of complex structure of PAN. 4,8,9,13,40 Because of the stability of these polyhedral crystals, the rare observation of twinning in a polymer crystal is able to be documented by electron microscopy in this work.…”

Section: Resultsmentioning

confidence: 94%

Characterization and Structural Analysis of Solution-Grown Polyacrylonitrile-co-Methacrylic Acid (PAN-co-MAA) Single Crystals

Zhang

Minus

2014

Macromolecules

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To date studies regarding the growth and characterization of polyacrylonitrile (PAN)-based polymer single crystals have been limited. Polyacrylonitrile-co-methacrylic acid (PAN-co-MAA) was used in this work, which outlines the conditions for three major types of solution-grown crystals. Electron microscopy and diffraction are used to provide a comprehensive study for chain arrangement and growth characteristics for all crystal morphologies. The three major morphological types included polyhedral and polygonal (i.e., parallelogram and elongated rhombus) crystals. Lower crystallization temperatures (65 °C) resulted in more even growth along all facets, while crystals formed at both intermediate (75 °C) and higher (85–95 °C) temperatures exhibited preferential growth along a specific growth plane. Overall crystal size also increased with elevated crystallization temperature (T c ). On the basis of the experimental d-spacing measured by electron diffraction for the (h00) and (0k0) planes, the crystal unit cell lattice constants along a and b axes are found to be a o = 1.023 ± 0.003 nm and b o = 0.612 ± 0.003 nm. This study also examines irradiation sensitivity as it pertains to lattice imaging for these single crystals.

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“…Though PAN and DMSO2 are crystallisable components, [32][33][34] both are unable to construct spherulites by themselves (see Fig. S1 of the ESI 3 ).…”

Section: Morphology Of the Giant Spherulitesmentioning

confidence: 99%

Centimeter-scale giant spherulites in mixtures of polar polymers and crystallizable diluents: Morphology, structure, formation and application

Wan

2013

RSC Adv.

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A series of giant spherulites at centimetre scale were effectively constructed from the mixtures of polyacrylonitrile (PAN)/dimethyl sulfone (DMSO2), although neither PAN nor DMSO2 itself forms spherical morphology during crystallization. A detailed investigation was carried out on the morphology, microstructure, and formation mechanism by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray diffraction, polarized FTIR spectroscopy, and differential scanning calorimetry. These giant spherulites constituted of PAN phase and DMSO2 crystals alternately distributed in divergent patterns. The fast crystallization of DMSO2 dominates the large growth rate and the macroscopic size, while PAN composes the skeleton of the giant spherulites. The cooperative deposition of PAN beside DMSO2 crystals originates from dipole-dipole interaction between the nitrile groups of PAN and the sulfone groups of DMSO2, accounting for the branching and splaying in the giant spherulites. These macroscopic morphologies were universally observed in other mixtures of PAN/dimethyl sulfoxide, PAN/ maleic anhydride, poly(vinylidene fluoride)/DMSO2, and cellulose acetate/DMSO2. We propose that the giant spherulites can be formed by introducing suitable diluent crystallization and appropriate polymerdiluent interaction. Furthermore, this spherulitic pattern has been used as a template to direct the oriented growth of calcium carbonate based on the molecular orientation in the giant spherulite.

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Crystallization of polyacrylonitrile: Growth mechanisms for various growth features

Cited by 14 publications

References 19 publications

Etching and the morphology of branched and cross-linked polyethylene

Etching and the morphology of branched and cross-linked polyethylene

Characterization and Structural Analysis of Solution-Grown Polyacrylonitrile-co-Methacrylic Acid (PAN-co-MAA) Single Crystals

Centimeter-scale giant spherulites in mixtures of polar polymers and crystallizable diluents: Morphology, structure, formation and application

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