Cyclic Thermoresistivity of Freestanding and Polymer Embedded Carbon Nanotube Yarns

Abstract

Carbon nanotube yarns (CNTYs) are hierarchical fibers with outstanding electrical properties, and understating the temperature‐dependence of their electrical resistance (thermoresistivity) is essential for sensing applications and development of self‐sensing polymer composites. The cyclic thermoresistive response of individual CNTYs and the effect of embedding the yarn into a polymer are experimentally investigated herein. The effect of confining the CNTY by a thermosetting polymer is addressed by studying the thermoresistive response of CNTY/vinyl ester single‐fiber composites. Heating–cooling cycles ranging from 25 (room temperature [RT]) to 100 °C and 25 to −30 °C are applied to individual CNTYs and to CNTYs embedded into a vinyl ester polymer, while their electrical resistance is simultaneously recorded. Both the CNTY and its single‐fiber composite show a negative dependence of electrical resistance with temperature. For both temperature ranges (above and below RT), the average temperature coefficient of resistance found for individual CNTYs is ≈−9.5 × 10−4 K−1, and its magnitude decreases about ≈30% when the yarn is embedded into the vinyl ester polymer. The hysteresis rendered by the different heating and cooling pathways is small for individual CNTYs, and largely increases when the CNTY is embedded into the polymer.

Effect of Polymer Viscosity and Polymerization Kinetics on the Electrical Response of Carbon Nanotube Yarn/Vinyl Ester Monofilament Composites

“…Therefore, the thermoresistivity of the CNTY itself is expected to be a negligible contributor to Δ R/R 0 . From a previous study, the normalized change in electrical resistance (Δ R/R 0 ) of a CNTY, embedded into a vinyl ester polymer was determined to be linearly proportional to the change in temperature (Δ T ) within a 25 to 100 °C temperature range [ 8 ]. The thermal coefficient of resistance ( β = (Δ R/R 0 )/Δ T ) of this embedded CNTY (the same kind as the one used herein) was also calculated in such a work as 6.53 × 10 −4 K −1 [ 8 ].…”

“…From a previous study, the normalized change in electrical resistance (Δ R/R 0 ) of a CNTY, embedded into a vinyl ester polymer was determined to be linearly proportional to the change in temperature (Δ T ) within a 25 to 100 °C temperature range [ 8 ]. The thermal coefficient of resistance ( β = (Δ R/R 0 )/Δ T ) of this embedded CNTY (the same kind as the one used herein) was also calculated in such a work as 6.53 × 10 −4 K −1 [ 8 ]. Using this temperature coefficient of resistance and a maximum change in temperature of 2.7 °C (~275 K), the decrease in Δ R/R 0 is estimated as ~−0.18%.…”

“…Regarding CNTYs dependence of electrical resistance with strain, the piezoresistive response of the yarn is driven by changes in its conductive network. This is a function of contact points and tunneling due to CNT and CNT bundles/fibrils proximities [ 7 , 8 ]. The dependence of mechanical, thermal, and chemical enviroments on the electrical response of CNTYs, combined with their tailorable structure, flexibility, and high surface area, makes them excellent candidates for sensory applications [ 3 , 9 , 10 , 11 ].…”

Monitoring of Curing and Cyclic Thermoresistive Response Using Monofilament Carbon Nanotube Yarn Silicone Composites

“…In addition, the high porosity of the CNTYs may promote infiltration of liquids between the CNT bundles affecting the stiffness, toughness, and electrical conductivity of the yarn by separating the adjacent CNT bundles and increasing the contact electrical resistance [3,[7][8][9]. It was observed that C 2021, 7, 60 2 of 14 the thermoresistive properties of the embedded CNTY strongly depend on the chemical structure of the polymeric matrix, temperature range, porosity, and capillary diffusion of polar liquids [3,8,[10][11][12][13][14][15]. Rodríguez-Uicab et al [10] investigated the effect of the curing kinetics of epoxy resins with different viscosities on the thermoresistive response of the CNTY monofilament composites at different curing temperatures.…”

“…The thermoresistive response of CNTYs embedded in thermosetting resins was also studied by a few authors. Balam et al [14] investigated the thermoresistive response of CNTY/vinyl ester composites and isolated CNTYs above RT. The electrical resistance per unit length of the isolated CNTY was~20 Ω mm −1 , and it increased by 37% during the curing process of the resin.…”