The electro-structural behaviour of yarn-like carbon nanotube fibres immersed in organic liquids

Abstract

Yarn-like carbon nanotube (CNT) fibres are a hierarchically-structured material with a variety of promising applications such as high performance composites, sensors and actuators, smart textiles, and energy storage and transmission. However, in order to fully realize these possibilities, a more detailed understanding of their interactions with the environment is required. In this work, we describe a simplified representation of the hierarchical structure of the fibres from which several mathematical models are constructed to explain electro-structural interactions of fibres with organic liquids. A balance between the elastic and surface energies of the CNT bundle network in different media allows the determination of the maximum lengths that open junctions can sustain before collapsing to minimize the surface energy. This characteristic length correlates well with the increase of fibre resistance upon immersion in organic liquids. We also study the effect of charge accumulation in open interbundle junctions and derive expressions to describe experimental data on the non-ohmic electrical behaviour of fibres immersed in polar liquids. Our analyses suggest that the non-ohmic behaviour is caused by progressively shorter junctions collapsing as the voltage is increased. Since our models are not based on any property unique to carbon nanotubes, they should also be useful to describe other hierarchical structures.

Enhanced ordering reduces electric susceptibility of liquids confined to graphene slit pores

“…Our interest in this configuration, in which a thin film of liquid is “sandwiched” between graphitic walls, arises from its resemblance to an immersed junction between two bundles of carbon nanotubes (CNT), which is described in detail in the methods section. Interbundle junctions play a significant role in determining the electrical properties of macroscopic assemblies of CNTs 6 and the results of the current study, which show that liquids organise spontaneously into ordered layers parallel to the confining surfaces, help to understand better a series of electro-structural phenomena recently discovered in CNT fibres immersed in organic liquids 7 8 9 . Furthermore, the recent possible discovery by Algara-Siller et al of “square-ice” (a new two-dimensional solid-like phase of water), stable at ambient conditions inside graphene slit pores, adds further interest to this configuration, since other organic liquids may also present previously unknown 2D solid-like structures 10 .…”

“…In previous work 7 8 9 , we experimentally studied the interactions between direct-spun CNT fibres 27 , and organic liquids. We found that liquids with surface tensions ≲50 mN m −1 infiltrate the fibres, readily filling the pores in between CNT bundles.…”

“…where the bundles are not in contact) and the ease with which carriers can tunnel through them 7 . Furthermore, fibres immersed in polar liquids were found to exhibit a “non-Ohmic” behaviour in which their conductivity is modulated by an applied electric field 8 9 . We attributed this effect to the electrostatic force due to the accumulation of charge at junctions bringing the bundles closer together, thus improving the electrical conductivity.…”

Influence of Capillary Effects on Electric Response of Well-Ordered Carbon Nanotube Film

“…Many studies have compared the effects of different liquids and succeeded in increasing the mechanical strength of CNT assemblies. For example, Windle and co-workers found that the electrical behavior of CNT-based fibers is also influenced by liquid medium, including ethanol, toluene, acetone, cyclohexanone, and N -methylpyrrolidone (NMP). − However, there are few reports focused on the electrical transport behavior of CNT assemblies aside from their mechanical properties during the liquid infiltration and evaporation process. In particular, the change mechanism of the electrical transport behavior throughout the process is unclear.…”

Development of multifunctional flexible and structural supercapacitors based on carbon nanotube fibers

“…Linear regression on the multi-point BET in the relative pressure range 0.1 to 0.3 shows the correlation coefficient R 2 of 0.9998 indicating high accuracy of obtained values(Figure 4.4b). It is noteworthy, that the literature values of SSA for CNT fibers are scarce, possibly due to the difficulties in producing the ∼1-10 km uniform fiber required for typical BET measurement, but they range from 75 to 500 m 2 g −1 [53,[218][219][220][221][222]. Such variation in specific 4.1 Textural, structural and mechanical properties of CNT fibers…”