Flexible pressure sensor based on cigarette filter and highly conductive MXene sheets
Introduction
With the rapid development of electronics technologies, flexibility and wearability are targets for the next generation electronic devices. Owing to vast potential in portable healthcare diagnostic and electronic skin, piezoresistive pressure sensors have attracted much attention. Rational and ingenious structure designs, and various physical or chemical approaches have been used to fabricate innovative piezoresistive pressure sensors with fast frequency response and outstanding stability [[1], [2], [3], [4]]. Beyond, flexibility and low cost are also crucial for future commercial applications on piezoresistive pressure sensors.
To pursue the flexibility of piezoresistive sensors, commercial polymers, such as polydimethylsiloxane, ecoflex, polyurethane and poly(ethylene terephthalate) (PET) are widely studied as the flexible supporting substrates [[5], [6], [7], [8]]. Among the new materials for development of cost-efficient and sustainable sensors, cigarette filter (CF) is promising because it is composed of flexible cellulose acetate fibers [[9], [10], [11]]. Besides, due to the huge consumption of cigarettes in daily life, wasted CF can cause serious environmental pollution [12]. Hence, it is also worthy to explore the utilization of used CF to negate their damage to environment.
Until now, tremendous conducting fillers have been loaded to various substrates, which would endow the flexible substrates with favourable electrical conductivity. Carbon materials (e.g., carbon black, carbon nanotubes, and graphene), metal nanoparticles, and conducting polymers are chosen to prepare piezoresistive pressure sensors with excellent sensing properties [[13], [14], [15], [16], [17], [18]]. As a kind of both electrically conductive and hydrophilic nanomaterial, MXene is a satisfactory candidate for advanced piezoresistive sensors, which can be readily prepared by selectively etching the A-element from ternary transition metal carbides/nitrides materials (Mn+1AXn), where M represents an early transition metal, A is a group of XIII or XIV element, and X is C and/or N [19,20]. Due to the plenty of polar groups on its surface with its high electrical conductivity, MXene exhibits great potential in electromagnetic interference shielding materials [21], energy storage [22] and wearable smart devices [[23], [24], [25], [26], [27]].
Herein, MXene/CF (MCF) composites are fabricated by dip-coating CFs with aqueous dispersions of Ti3C2Tx MXene sheets for flexible and tactile piezoresistive sensors. The fabricated MCF sensor performs excellent cyclic stability (2500 cycles at 10% compressive strain) and exhibits different responses under different compressive strains in radial direction. Additionally, the MCF sensor is suitable for monitoring human physiological signals practically, demonstrating its great potential for sensitive and stable sensor applications.
Section snippets
Materials and preparation of MCF composites
Aqueous suspension of Ti3C2Tx MXene was purchased from Jilin 11 Technology Co. Ltd. (China). Cigarette filters were derived from a commercial product of Huanghelou cigarettes (China). Briefly, the commercial CFs were cut into cylinders with a length of 15 mm (d = 8 mm), then immersed into suspensions of MXene with different MXene contents ranging from 0.25 to 1 mg mL−1 under vacuum for 1 h. The MXene-decorated CFs were dried in a vacuum oven at 50 °C for 5 h. By repeating the immersion-drying
Results and discussion
Fig. 1a schematically illustrates the preparation of MCF composites by dip-coating approach. Original CFs are dipped in an aqueous dispersion of MXene with concentration of 1 mg mL−1 and then dried in an oven for 5 h at 50 °C. To fully coating CFs with MXene sheets, the MCF composites are dipped in the MXene dispersion again, leading to a conductive network. The resultant MCF composites are evaluated with their XRD spectra (Fig. 1b). The broad diffraction peaks at ~10° and ~20° are attributed
Conclusions
In summary, the MXene-cigarette filter piezoresistive sensors are successfully fabricated by dip-coating approach. MXene sheets can be deposited onto CF fibers. When MCF composite is compressed, MXene encapsulated CF fibers contact with each other, providing additional conductive paths. Therefore, the resultant MCF sensors exhibit fast response to compressive strains of 10%, 20% and 30%, and provide a good cyclic stability with 2500 pressing-releasing cycles at 10% compressive strain. Moreover,
CRediT authorship contribution statement
Ran Li: Investigation, Experiment, Writing-original draft. Xiaohan Tian: Investigation, Experiment, Data curation. Min Wei: Experiment, Data curation. Aijun Dong: Experiment, Data curation. Xi Pan: Investigation, Validation. Yunlu He: Investigation, Validation. Xuyan Song: Methodology, Supervision. Hongfei Li: Writing-review &editing, Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by China Tobacco Hubei Industrial Co., Ltd.
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