What is it about?
The paper represents results from synchrotron high-energy X-ray diffraction (HEXRD) studies of multiwall carbon nanotubes (MWCNTs) heated and cooled in the temperature range of 298–450 K. Structural features of MWCNT powders have been studied by the real–space atomic pair distribution function (PDF) technique. XRD thermal study established that the MWCNTs are mainly of scroll type. The PDF structures on different length scales were used to study the interlayer spacing distribution in the carbon nanotube scrolls (CNSs). The method discovers that the pristine CNSs are described as left- or right-handed Fermat spiral (r = ±aθ1/2) with uneven interlayer distances, rather than the XRD crystallogra- phy equidistance Archimedean spiral (r = aθ). The increased interlayer spacings of the innermost layers are caused primarily by the high curvature and thus the high strains are caused by π–π coulombic repulsion between the curved layers. At larger diameters, the CNS layers are less deformed and extensively interact through the van der Waals force affecting interlayer spacing shrinkage. The irreg- ular interlayer spacing of the pristine CNS converses to a uniform spacing between layers at heating-cooling cycles within 298–450 K. The spatial changes in CNSs demonstrate the transformation of Fermat-type stroll in pristine nanotubes to more stable Archimedean spiral at heating-cooling processes.
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Why is it important?
The thermal behavior of the powder samples of MWCNT designates the scroll-type CNS model. The PDFgui length-scale refinements confirm a scroll-type structure for tubes, involving one single rolled-up graphene sheet. The PDF of CNS was simulated using a single-structure model of the ABAB... hexagonal graphite. The large interlayer spacings at a small r < 10 Å are linked to the large curvature/strains in the innermost part of the tube. It is found that the interlayer spacing of the pristine CNS decreases with increasing tube radius where bending curves, thus distortions are lesser (Fermat scroll; left-handed or right-handed branch). Upon the heating-cooling cycles of CNS, the low r-range interlayer spacings became lesser. It presents the tendency of transformation of the Fermat-type spiral to the more stable Archimedean spiral. Likely, thermal heating weakens interlayer stacking π–π bonding leading to partial transformation and relaxing of the layer distortions.
Perspectives
A variation of the interlayer spacing/coupling in MWCNT or CNS suggests significant changes in its functional parameters mainly controlled by interlayer π–π interactions. It is useful to explore the behavior of interlayer spacings in MWCNT or CNS at heating-cooling treatments. The knowledge of the thermal behavior of CNTs is of great interest for controlling the performance of nanotube devices as during fabrication and operation, the CNT-based devices may experience thermal manipulations.
Dr Bagautdin Bagautdinov
Read the Original
This page is a summary of: Pair Diffraction Function Analysis of Conversion of a Fermat Scroll to an Archimedean Scroll in Multiwalled Carbon Nanotubes, January 2024, Springer Science + Business Media,
DOI: 10.1007/978-981-97-1594-7_1.
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