TY - JOUR

T1 - Polyacrylonitrile (PAN) based electrospun carbon nanofibers (ECNFs)

T2 - Probing the synergistic effects of creep assisted stabilization and CNTs addition on graphitization and low dimensional electrical transport

AU - Ali, Ahmad B.

AU - Slawig, Diana

AU - Schlosser, Anja

AU - Koch, Julian

AU - Bigall, Nadja-Carola

AU - Renz, Franz

AU - Tegenkamp, Christoph

AU - Sindelar, Ralf

N1 - Funding Information: To reveal an atomistic insight regarding the alignment of carbon planes, TEM was performed both on creep stress stabilized (PAN and PAN/CNT) and non-creep stress stabilized (PAN and PAN/CNT) nanofibers, carbonized at 1700 ?C. It is can be seen that the graphitic domains for non-creep stress stabilized (PAN - 1700 ?C) reveal no preferred alignment and the graphene layers are majorly curved resembling fragments of fullerene related structures (Fig. 7a). More apparent in the skeletonized image (Fig. 7b), the curvature in carbon planes and ripples of graphene like layers are observed. Compared to PAN, the graphitic domains in PAN/CNT are comparatively well aligned and no ring like fullerenic segmented motifs were observed [Fig. 7 (c. d)]. For creep stress stabilized PAN (PAN - T), the size of graphitic zone increases, they are highly aligned along the nanofiber axis [Fig. 7 (e, f)]. The tortuosity in graphene layers is prevented by the application of creep stress during the stabilization process and rather more continuous domains are observed. However, for PAN/CNT - T, the graphitic domains appear to be slightly fragmented/discontinuous and their alignment is reduced compared to PAN/CNT and PAN - T [Fig. 7 (g, h)]. The directional analysis and distribution of orientation is also performed on TEM images to have additional insight, using Orientation J plug-in of Image J software (Fig. S2) [35]. To further have a holistic insight of orientation of graphene planes, the polarized Raman was performed with polarization of incident light parallel and perpendicular to fiber axis. The G-band is sensitive to the laser polarization, hence by evaluating the difference in intensity of G-band for both cases, the orientation is evaluated. The results from polarized Raman supported the TEM findings, the factor ?IG /?? (intensity ratio of G-band obtained for polarization of laser parallel and perpendicular to fiber axis) showed increased values specifically for PAN - T and PAN/CNT samples, indicating improved alignment of graphitic domains (Fig. S3).The authors are grateful to Hannover School for Nanotechnology (HSN) and Deutsche Forschungsgemeinschaft (DFG) for their financial support (grant number: 21-78904-63-7/16) provided by Nieders?chsisches Ministerium f?r Wissenschaft und Kultur (Ministry of Science and Culture of Lower Saxony/Germany). N. C. B. would also like to acknowledge the DFG (Cluster of Excellence PhoenixD (EXC 2122, Project ID 390833453) and grant agreement BI 1708/4?1) and the European Research Council (European Union's Horizon 2020 research and innovation program, grant agreement 714429) for funding.

PY - 2021/2

Y1 - 2021/2

N2 - We report on the fabrication of Polyacrylonitrile (PAN) based electrospun carbon nanofiber (ECNF) reinforced with multi-walled carbon nanotubes (MWCNTs) and characterization of the graphitic structure as well as electrical transport properties for four different ECNF systems. The different systems were obtained by the combination of two different ways of cyclization for pristine PAN and PAN with CNTs addition (PAN/CNT), typically by the application of constant creep stress and a constraint fixing. The addition of CNTs improved the graphitic structure of PAN. For the detailed analysis of different systems, carbonization was performed at 1700 °C and the graphitic structures were characterized. The CNTs improve the alignment of graphitic domains even for non-creep cyclized systems. The application of creep stress during cyclization results in highly aligned graphene planes. However, the creep stress cyclized PAN/CNT system exhibited a reduction in the alignment of graphene planes coming along with the observation of discontinuous, randomly orientated domains and a reduced conductivity. The electrical anisotropy increased for creep cyclized PAN and PAN/CNT compared to non-creep stress cyclized system. Our findings reveal that electrical transport in carbon nanofibers need to be considered as a cumulative effect of hopping and band transport along chemically and structurally inhomogeneous ECNFs.

AB - We report on the fabrication of Polyacrylonitrile (PAN) based electrospun carbon nanofiber (ECNF) reinforced with multi-walled carbon nanotubes (MWCNTs) and characterization of the graphitic structure as well as electrical transport properties for four different ECNF systems. The different systems were obtained by the combination of two different ways of cyclization for pristine PAN and PAN with CNTs addition (PAN/CNT), typically by the application of constant creep stress and a constraint fixing. The addition of CNTs improved the graphitic structure of PAN. For the detailed analysis of different systems, carbonization was performed at 1700 °C and the graphitic structures were characterized. The CNTs improve the alignment of graphitic domains even for non-creep cyclized systems. The application of creep stress during cyclization results in highly aligned graphene planes. However, the creep stress cyclized PAN/CNT system exhibited a reduction in the alignment of graphene planes coming along with the observation of discontinuous, randomly orientated domains and a reduced conductivity. The electrical anisotropy increased for creep cyclized PAN and PAN/CNT compared to non-creep stress cyclized system. Our findings reveal that electrical transport in carbon nanofibers need to be considered as a cumulative effect of hopping and band transport along chemically and structurally inhomogeneous ECNFs.

KW - Aligned graphitic domains

KW - Anisotropic conductivity

KW - Carbon nanofibers

KW - Creep stress assisted cyclization

KW - Graphitization

UR - http://www.scopus.com/inward/record.url?scp=85092714882&partnerID=8YFLogxK

U2 - 10.1016/j.carbon.2020.10.033

DO - 10.1016/j.carbon.2020.10.033

M3 - Article

AN - SCOPUS:85092714882

VL - 172

SP - 283

EP - 295

JO - Carbon

JF - Carbon

SN - 0008-6223

ER -