Microstructured MXene/polyurethane fibrous membrane for highly sensitive strain sensing with ultra-wide and tunable sensing range

doi:10.1016/j.coco.2020.100586

Composites Communications

Volume 23, February 2021, 100586

https://doi.org/10.1016/j.coco.2020.100586 Get rights and content

Highlights

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Conductive and highly stretchable microstructured MXene fibrous membrane was prepared.
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Micropatterns were constructed with assistance of a mechanically-driven approach.
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The mechanically weak points and strain-buffered microstructures significantly enhanced the sensing performance.
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Sensing properties can be tuned via adjusting the mechanically-driven deformation.

Abstract

Stretchable strain sensors have exhibited emerging prospects in bioelectronics due to the ubiquitous health-related strain in biosystems. However, most of the existing stretchable strain sensors are plagued by their sensitivity and sensing range trade-off. In this study, we designed a microstructured MXene/polyurethane fibrous membrane (m-MXene FM) with porous network structures and tunable micropatterns (including microcracks and microwrinkles), and demonstrated its superior strain sensing properties. The microcracks can serve as stable mechanical weak points to enhance the sensitivity, while the highly porous network as well as the microwrinkle patterns can cushion the strain loading on individual fibers under large deformations, thus offering wide sensing range. The as-prepared m-MXene FM is highly stretchable and conductive and shows extremely high gauge factor of 1000 and wide sensing range up to 120%. Furthermore, both the sensitivity and sensing range can be facilely tailored through adjusting the micropatterns. This work provides a scalable strategy to fabricate highly sensitive strain sensors with customizable sensing properties suitable for a range of applications in health monitoring.

Graphical abstract

Introduction

With the advent of Internet of Things, stretchable strain sensors have been intensively investigated due to their wide applications in terms of wearable electronics and personal healthcare systems [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]]. To satisfy the requirement for practical use, stretchable strain sensors need to be sensitive to low deformations and meanwhile applicable in a wide sensing range. Generally, strain sensors are constructed by two main parts: the sensitive conducting element and the flexible matrix [11,12]. Recent advances to achieve high-performance strain sensors have been focused on materials development and optimization. Various conductive nanomaterials including nanotubes [[13], [14], [15], [16]], nanowires [[17], [18], [19], [20], [21]] and nanosheets [3,[22], [23], [24], [25], [26], [27]] have been used as the active sensing elements to fabricate strain sensors. In general, one-dimensional (1D) nanomaterials such as carbon nanotubes, can offer wide sensing range owing to their high aspect ratio when serving as active materials. Various carbon nanotube based strain sensors have been explored for their sensing performance in the higher strain region (e.g. over 100% strain) [28,29]. However, due to the poor interface between the 1D material and the flexible substrate, the sensitivity and stability of these sensors are usually unsatisfactory [11]. In contrast, two-dimensional (2D) nanosheets can provide good interfacial adhesion [30,31], yet the relatively strong interaction (for example van der Waals forces and hydrogen bonding) between adjacent 2D sheets may hinder effective slippage, and lead to their assembled film rapidly splitting into cracks under deformations [32,33]. Vital physiological signals such as breath and pulse wave generate less than 1% strain [34]. Thereby, strain sensors sensitive for low deformations are highly desired for health-related signal detection. Generally, cracks are considered as defects to be avoided since they are detrimental to mechanical properties. Joint materials or lubricants have been commonly blended with 2D nanomaterials to promote the slippage of the adjacent nanosheets, and thus avoiding the formation of cracks [35]. However, stable and controllable cracks may also act as strain-sensitive active sites [36]. Inadequate strain sensitivity commonly originates from the strong structural integrity of the sensing element since tiny external strains cannot induce enough variation in the conductive network [37]. Cracks can serve as mechanically weak points where local strain would easily concentrate in, thus resulting in significant conductive pathway interruption in a heterogeneous conductive film and leading to a high sensitivity. However, penetrative cracks with gaps perpendicular to the strain direction would result in permanent conductive pathway cut-off. Therefore, how to introduce mechanically weak cracks into conductive films constructed from 2D nanosheets in a controllable manner is a great challenge.

Herein, we present a microstructured MXene/polyurethane (PU) fibrous membrane (m-MXene FM) comprising of highly stretchable PU fiber scaffold and highly conductive MXene nanocoatings, and demonstrate its superior and tunable strain sensing capbility with both high sensitivity and wide sensing range. Micropatterns including microcracks and microwrinkles are introduced into the MXene piezoresistive layer through a mechanically driven approach. The microcracks can serve as stable mechanical weak points which are highly sensitive to mechanical stimuli; while the highly porous network structure can buffer the strain loading on individual fibers, avoiding the totally conductive pathway interruption under large deformations. To further widen the strain senisng range, microwrinkles were developed on the m-MXene FM. The m-MXene FM based strain sensor exhibit excellent strain sensing performance characterized by a high gauge factor up to 1000, a wide and tunable sensing range from 0-120% to 0–270%, an ultralow limit of detection of 0.05% for tensile strain and 5 μm for tiny vibration, a superfast and stable sensing behavior, demonstrating great potential for health-related signal monitoring.

Section snippets

Preparation of MXene

Ti₃C₂T_x MXene was prepared according to the literature [38,39]. In brief, 2 g of LiF and 15 mL of HCl (12 M) were mixed with 20.5 mL of deionized water in a plastic vial. 2 g of Ti₃AlC₂ MAX (Fig. S1a) was gradually added into the above mixture under stirring (in course of 10 min). The reaction was allowed to proceed at 40 °C for 43 h under stirring. The product was washed with deionized water by centrifugation (5 min per cycle at 6000 rpm) to remove the excess acid and ions. After 8–10 cycles

Results and discussion

Ti₃C₂T_x MXene was selected as the building block unites for the fabrication of the piezoresistive layer due to its intrinsic metallic conductivity and good solution processability, which cannot be simultaneously achieved by other 2D materials (e.g. graphene) [40]. For instance, the conductivity of MXene used here has a high conductivity of 2900 S cm⁻¹ (measured by a four-point conductivity probe), which is over 1–2 magnitudes higher than the best value reported for reduced graphene oxide [[41],

Conclusions

In summary, highly stretchable and conductive m-MXene FM with porous network structure and micropatterns was fabricated through the combination of electrospinning and mechanically driven approach. The m-MXene FM with microcracks exhibited excellent sensing performance characterized by a high sensitivity with a gauge factor of 1000, an ultralow limit of detection (0.05% for tensile strain, 5 μm for vibration), a wide sensing range (0–120%) and a fast and stable sensing capability. To further

CRediT author statement

Xinxin Li: Investigation, Resources. Jinzheng Yang: Investigation, revision. Puguang Ji and Zhaobo Xu: Resources, Analysis. Shunan Shi, Xiaojing Han, and Weixiang Niu: Conceptualization. Wenjing Yuan: Conceptualization, Writing - review & editing, Supervision. Fuxing Yin: 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.

Acknowledgements

This work was supported by Natural Science Foundation of Hebei Province, China (E2018202179), Natural Science Foundation of China (51702084) and Key Research and Development Program of Hebei Province, China (17391001D).

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¹: Xinxin Li and Jinzheng Yang contributed equally.

View full text

Microstructured MXene/polyurethane fibrous membrane for highly sensitive strain sensing with ultra-wide and tunable sensing range

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of MXene

Results and discussion

Conclusions

CRediT author statement

Declaration of competing interest

Acknowledgements

Sens. Actuators A Phys.

Carbon

Carbon

Sensor. Actuator. B Chem.

Graphene-based smart materials

Nat. Rev. Mater.

Stretchable Ti3C2Tx MXene/carbon nanotube composite based strain sensor with ultrahigh sensitivity and tunable sensing range

ACS Nano

Epidermis microstructure inspired graphene pressure sensor with random distributed spinosum for high sensitivity and large linearity

ACS Nano

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ACS Nano

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Adv. Electron. Mater.

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Adv. Funct. Mater.

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ACS Appl. Mater. Interfaces

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Nano Lett.

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Nanoscale

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Science

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J. Mater. Chem.

Stretchable Ti₃C₂T_x MXene/carbon nanotube composite based strain sensor with ultrahigh sensitivity and tunable sensing range