Strong Dependence of Mechanical Properties on Fiber Diameter for Polymer−Nanotube Composite Fibers: Differentiating Defect from Orientation Effects

Abstract

We have prepared polyvinylalcohol-SWNT fibers with diameters from ∼1 to 15 μm by coagulation spinning. When normalized to nanotube volume fraction, V(f), both fiber modulus, Y, and strength, σ(B), scale strongly with fiber diameter, D: Y/V(f) ∝ D(-1.55) and σ(B)/V(f) ∝ D(-1.75). We show that much of this dependence is attributable to correlation between V(f) and D due to details of the spinning process: V(f) ∝ D(0.93). However, by carrying out Weibull failure analysis and measuring the orientation distribution of the nanotubes, we show that the rest of the diameter dependence is due to a combination of defect and orientation effects. For a given nanotube volume fraction, the fiber strength scales as σ(B) ∝ D(-0.29)D(-0.64), with the first and second terms representing the defect and orientation contributions, respectively. The orientation term is present and dominates for fibers of diameter between 4 and 50 μm. By preparing fibers with low diameter (1-2 μm), we have obtained mean mechanical properties as high as Y = 244 GPa and σ(B) = 2.9 GPa.

Exploiting high quality PEDOT:PSS–SWNT composite formulations for wet-spinning multifunctional fibers

“…15,16,[44][45][46] For fibers obtained here, alignment of the SWNT was observed. As can be seen from Fig.…”

“…This has been reported previously for PVA-SWNT based fibers and is opposite to the behaviour typically observed in classic composites. 15,44,47 Filling of a ductile polymer by rigid fillers usually improves the strength, but adversely affects ductility because rigid fillers (or large bundles of SWNT) act as stress concentration points where failure is initiated. In contrast, individually dispersed oriented flexible SWNT in the polymer matrix (as confirmed by the SEM images and Raman spectroscopy) serve as reinforcing fillers and provide strengthening effect without the loss of ductility.…”

“…The outstanding electrical conductivity of these fibers places them among the most conducting SWNT-based composite fibers and 14,22,38,39,52 comparable with the most successful SWNT-reinforced composites reported to date. 7,[13][14][15][16]38,[53][54][55][56][57][58][59] …”

3D RVE Models Able to Capture and Quantify the Dispersion, Agglomeration, and Orientation State of CNT in CNT/PP Nanocomposites

“…In these studies, random distribution of CNT characteristics within the polymer is considered, which is due to the difficulty in experimentally quantifying their distribution within the polymer. Efforts to experimentally determine the distribution of CNT characteristics have been made (Yokozeki et al, 2010;Young et al, 2010;Blighe et al, 2011); however, only qualitative information was provided. Image analysis techniques of electron microscopy have been used to quantitatively characterize CNT dispersion, distribution, and orientation state in polymer (Gommes et al, 2003;Thostenson and Chou, 2003;Sarkar and Banerjee, 2004;Fan and Advani, 2005;Wang et al, 2006).…”

With great structure comes great functionality: Understanding and emulating spider silk

“…111 Diameter-dependence of mechanical properties had previously been demonstrated for fibers formed from another protein-based material, the recombinant Drosophila melanogaster transcription factor Ultrabithorax, 112 as well as for other materials like glass, 77 polyethylene, 113,114 polydiacetylene, 115 and other polymers 116 and composites. [117][118][119] Simulations using a coarse-grained mesoscopic computational model for spider silk fibers revealed similar behavior, showing that failure stresses and strains increased with decreasing fiber diameter, finally reaching the limit of a defect-free fiber at a diameter of 50 6 30 nm. 45 Porter et al note that toughness is dependent on the internal structure of spider silk, in particular its hydrogen bonds, which are critical for its high cohesive energy density.…”