Infrared dichroism of the band of valence vibrations of the C ? N bonds in polyacrylonitrile fibers

Litovchenko, G. D.

doi:10.1007/bf00614110

Cited by 2 publications

(5 citation statements)

References 3 publications

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“…Given this large angle between the nitrile group and the main chain, I HH should be stronger than I VV when preferred axial orientation of the main chain is present. A similar relationship between I ⊥ and I ∥ absorptions was observed in the past using FTIR dichroic ratio both in drawn films 39,45,47 and electrospun PAN NF bundles. 15 Raman examination of commercial conventional PAN microfiber, Dralon X250 (approximately 30 μm in diameter), also exhibited this expected relation between the intensities (see Figure 9c).…”

Section: Evaluation Of Polymer Chain Orientation Using Polarized Rama...supporting

confidence: 84%

“…The molecular conformation of PAN is that of an irregular helix . The angles between the nitrile groups and the axis of this helix are not constant, but several studies have estimated the average α angle to be in the vicinity of 70°. , As a result, if preferred chain orientation is present, the absorbance with the polarization parallel to the fiber is expected to be smaller than the one with polarization perpendicular to the fiber, resulting in dichroic ratios less than 1. However, because the α angle is significantly smaller than 90°, the dichroic ratio of the PAN nitrile band is not expected to be very small even in the presence of a significant degree of preferred backbone chain orientation ( R is approximately 0.32 for ⟨ P 2 ⟩ of 0.9).…”

Section: Methods Of Orientation Evaluation That Require Nanofiber Mat...mentioning

confidence: 99%

“…However, because the α angle is significantly smaller than 90°, the dichroic ratio of the PAN nitrile band is not expected to be very small even in the presence of a significant degree of preferred backbone chain orientation ( R is approximately 0.32 for ⟨ P 2 ⟩ of 0.9). Herman orientation factor was extracted in the past for uniaxially drawn PAN films. , Examination of oriented electrospun NF bundles was attempted as well (see discussion below) …”

Section: Methods Of Orientation Evaluation That Require Nanofiber Mat...mentioning

confidence: 99%

“…Herman orientation factor was extracted in the past for uniaxially drawn PAN films. 39,47 Examination of oriented electrospun NF bundles was attempted as well (see discussion below). 15 Oriented bundles of NFs with different average diameters were examined in this work by polarized FTIR in transmission (suspended fibers) and in transflection (fibers on an aluminum foil) modes.…”

Section: Methods Of Orientation Evaluation That Require Nanofiber Mat...mentioning

confidence: 99%

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Quantifying Polymer Chain Orientation in Strong and Tough Nanofibers with Low Crystallinity: Toward Next Generation Nanostructured Superfibers

et al. 2019

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Advanced fibers revolutionized structural materials in the second half of the 20 th Century.However, all high-strength fibers developed to date are brittle. Recently, pioneering simultaneous ultrahigh strength and toughness were discovered in fine (<250 nm) individual electrospun polymer nanofibers (NFs). This highly desirable combination of properties was attributed to high macromolecular chain alignment coupled with low crystallinity. Quantitative analysis of the degree of preferred chain orientation will be crucial for control of NF mechanical properties. However, quantification of supramolecular nanoarchitecture in NFs with low crystallinity in the ultrafine diameter range is highly challenging. Here, we discuss applicability of traditional as well as emerging methods for quantification of polymer chain orientation in nanoscale one-dimensional samples. Advantages and limitations of different techniques are critically evaluated on experimental examples. It is shown that straightforward application of some of the techniques to subwavelength-diameter NFs can lead to severe quantitative and even qualitative artifacts. Sources of such size-related artifacts, stemming from instrumental, materials, and geometric phenomena at the nanoscale, are analyzed on the example of polarized Raman method, but are relevant to other spectroscopic techniques. A proposed modified, artifact-free method is demonstrated. Outstanding issues and their proposed solutions are discussed. The results provide guidance for accurate nanofiber characterization to improve fundamental understanding and accelerate development of nanofibers and related nanostructured materials produced by electrospinning or other methods. We expect that the discussion in this review will also be useful to studies of many biological systems that exhibit nanofilamentary architectures and combinations of high strength and toughness.

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Section: Evaluation Of Polymer Chain Orientation Using Polarized Rama...supporting

confidence: 84%

Section: Methods Of Orientation Evaluation That Require Nanofiber Mat...mentioning

confidence: 99%

Section: Methods Of Orientation Evaluation That Require Nanofiber Mat...mentioning

confidence: 99%

Section: Methods Of Orientation Evaluation That Require Nanofiber Mat...mentioning

confidence: 99%

See 2 more Smart Citations

Quantifying Polymer Chain Orientation in Strong and Tough Nanofibers with Low Crystallinity: Toward Next Generation Nanostructured Superfibers

et al. 2019

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“…However, unexpectedly, the I VV intensity of the nitrile stretching mode was stronger than the I HH ( I VV / I HH > 1). The angle between the nitrile groups and the axis of the molecular helix in PAN is not constant, but several studies have estimated the average angle to be in the vicinity of 70°. , As a result, I VV / I HH should be smaller than 1 when the preferred axial orientation of the main chain is present. Several NFs with diameters below ∼500 nm were evaluated, producing qualitatively similar results.…”

Section: Resultsmentioning

confidence: 99%

Polarized Raman Analysis of Polymer Chain Orientation in Ultrafine Individual Nanofibers with Variable Low Crystallinity

Papkov¹,

Pellerin

Dzenis³

2018

Macromolecules

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Recent mechanical studies of ultrafine electrospun polymer nanofibers showed they can simultaneously possess high strength and toughness attributed to high degree of chain alignment coupled with low crystallinity. Quantitative analysis of macromolecular alignment in nanofibers is needed for better understanding of processing/structure/properties relationships and optimization. However, quantification of structural features in nanofibers with ultrafine diameters and low variable crystallinity is highly challenging. Here, we show that application of standard orientation analysis protocols developed for polarized Raman microscopy of bulk polymers and films can lead to severe errors in subwavelength-diameter samples. A modified polarized Raman method is proposed and implemented for study of size dependent orientation in individual nanofibers as small as 140nm. Macromolecular alignment improved significantly with the reduction of nanofiber diameter, correlating with nanofiber modulus increase. Applicability of the proposed method for quantitative comparative studies of nanofiber systems fabricated from solutions with different solvents is demonstrated.

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Infrared dichroism of the band of valence vibrations of the C ? N bonds in polyacrylonitrile fibers

Cited by 2 publications

References 3 publications

Quantifying Polymer Chain Orientation in Strong and Tough Nanofibers with Low Crystallinity: Toward Next Generation Nanostructured Superfibers

Quantifying Polymer Chain Orientation in Strong and Tough Nanofibers with Low Crystallinity: Toward Next Generation Nanostructured Superfibers

Polarized Raman Analysis of Polymer Chain Orientation in Ultrafine Individual Nanofibers with Variable Low Crystallinity

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