Cellulose-Multiwall Carbon Nanotube Fiber Actuator Behavior in Aqueous and Organic Electrolyte

Abstract

As both consumers and producers are shifting from fossil-derived materials to other, more sustainable approaches, there is a growing interest in bio-origin and biodegradable polymers. In search of bio-degradable electro-mechanically active materials, cellulose-multi wall carbon nanotube (Cell-CNT) composites are a focus for the development of actuators and sensors. In the current study, our aim was to fabricate Cell-CNT composite fibers and study their electro-mechanical response as linear actuators in aqueous and propylene carbonate-based electrolyte solutions. While the response was (expectedly) strongly solvent dependent, the different solvents also revealed unexpected phenomena. Cell-CNT fibers in propylene carbonate revealed a strong back-relaxation process at low frequencies, and also a frequency dependent response direction change (change of actuation direction). Cell-CNT fibers operated in aqueous electrolyte showed response typical to electrochemical capacitors including expansion at discharging with controllable actuation dependence on charge density. While the response was similarly stable in both electrolyte solution systems, the aqueous electrolytes were clearly favorable for Cell-CNT with 3.4 times higher conductivities, 4.3 times higher charge densities and 11 times higher strain.

Wider Potential Windows of Cellulose Multiwall Carbon Nanotube Fibers Leading to Qualitative Multifunctional Changes in an Organic Electrolyte

“…The choice of potential ranges covers limited negative charging (0.8 V to −0.3 V), limited positive charging (0.55 to −0.8 V), and increased positive charging at ranges 1.0 V to −0.8 V and 1.5 V to −0.8 V. EDX spectroscopy was performed from the cross-section of Cell-CNT fibers to establish the nature of the ions accompanying the positive and negative charging in each of the potential ranges. The characterization regarding FTIR was shown in previous research [22], and there was no difference whether 10 wt.% CNT was loaded or 50 wt.% as applied in this research.…”

“…As electromechanical transducers, Cell-CNT fibers can have potential applications in bending actuation [12] or linear actuation [22]. It has been observed recently that the electromechanical response of Cell-CNT fibers depends both quantitatively and qualitatively on the driving frequency as well as potential [22]. However, as in the present study the potential range was limited by the electrochemical window of water as the solvent, the full picture can be more complex.…”

“…The fiber image of the CNT-Cell (Figure 1a) shows a bulky, rough-surfaced shape, similar to what has been observed before [25], owing to the fact that on the surface mostly cellulose is found. The cross-section of Cell-CNT fibers (Figure 1b) with higher magnification of the inner section shown in Figure 1c revealed no visible CNT clusters, but a compact section likely representing CNT surrounded by cellulose concentrated in the inner core; this is in contrast to the 10 wt.% MWCNT loaded fibers studied before [22]. The conductivity of all Cell-CNT samples was found to be in the range of 1.15 to 1.2 ± 0.1 mS cm −1 , which is a nearly 6-fold improvement over the 10 wt.% CNT loading [22].…”

“…As electromechanical transducers, Cell-CNT fibers can have potential applications in bending actuation [12] or linear actuation [22]. It has been observed recently that the electromechanical response of Cell-CNT fibers depends both quantitatively and qualitatively on the driving frequency as well as potential [22].…”

“…To shed light on the processes and the overall electromechanical response of the composites as a function of driving potential and frequency, Cell-CNT fibers [22] are studied here in an organic electrolyte, to broaden the applicable potential window.…”