Ultra-Stretchable and Self-Healing Anti-Freezing Strain Sensors Based on Hydrophobic Associated Polyacrylic Acid Hydrogels

Water-rich conductive hydrogels with excellent stretchability are promising in strain sensors due to their potential application in flexible electronics. However, the features of being water-rich also limit their working environment. Hydrogels must be frozen at subzero temperatures and dried out under ambient conditions, leading to a loss of mechanical and electric properties. Herein, we prepare HAGx hydrogels (a polyacrylic acid (HAPAA) hydrogel in a binary water–glycerol solution, where x is the mass ratio of water to glycerol), in which the water is replaced with water–glycerol mixed solutions. The as-prepared HAGx hydrogels show great anti-freezing properties at a range of −70 to 25 °C, as well as excellent moisture stability (the weight retention rate was as high as 93% after 14 days). With the increase of glycerol, HAGx hydrogels demonstrate a superior stretchable and self-healing ability, which could even be stretched to more than 6000% without breaking, and had a 100% self-healing efficiency. The HAGx hydrogels had good self-healing ability at subzero temperatures. In addition, HAGx hydrogels also had eye-catching adhesive properties and transparency, which is helpful when used as strain sensors.

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Highly viscoelastic, stretchable, conductive, and self-healing strain sensors based on cellulose nanofiber-reinforced polyacrylic acid hydrogel

Cellulose ◽

10.1007/s10570-021-03782-1 ◽

2021 ◽

Vol 28 (7) ◽

pp. 4295-4311

Author(s):

Yue Jiao ◽

Kaiyue Lu ◽

Ya Lu ◽

Yiying Yue ◽

Xinwu Xu ◽

...

Keyword(s):

Polyacrylic Acid ◽

Strain Sensors ◽

Cellulose Nanofiber ◽

Self Healing

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Dynamic Mussel-Inspired Chitin Nanocomposite Hydrogels for Wearable Strain Sensors

Polymers ◽

10.3390/polym12061416 ◽

2020 ◽

Vol 12 (6) ◽

pp. 1416 ◽

Cited By ~ 3

Author(s):

Pejman Heidarian ◽

Abbas Z. Kouzani ◽

Akif Kaynak ◽

Ali Zolfagharian ◽

Hossein Yousefi

Keyword(s):

Mechanical Properties ◽

Polyacrylic Acid ◽

Strain Sensors ◽

Self Healing ◽

Network Stability ◽

Ferric Ions ◽

Trade Off ◽

Nanocomposite Hydrogels ◽

Healing Efficiency ◽

Hydrogel Network

It is an ongoing challenge to fabricate an electroconductive and tough hydrogel with autonomous self-healing and self-recovery (SELF) for wearable strain sensors. Current electroconductive hydrogels often show a trade-off between static crosslinks for mechanical strength and dynamic crosslinks for SELF properties. In this work, a facile procedure was developed to synthesize a dynamic electroconductive hydrogel with excellent SELF and mechanical properties from starch/polyacrylic acid (St/PAA) by simply loading ferric ions (Fe3+) and tannic acid-coated chitin nanofibers (TA-ChNFs) into the hydrogel network. Based on our findings, the highest toughness was observed for the 1 wt.% TA-ChNF-reinforced hydrogel (1.43 MJ/m3), which is 10.5-fold higher than the unreinforced counterpart. Moreover, the 1 wt.% TA-ChNF-reinforced hydrogel showed the highest resistance against crack propagation and a 96.5% healing efficiency after 40 min. Therefore, it was chosen as the optimized hydrogel to pursue the remaining experiments. Due to its unique SELF performance, network stability, superior mechanical, and self-adhesiveness properties, this hydrogel demonstrates potential for applications in self-wearable strain sensors.

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Salt-mediated triple shape-memory ionic conductive polyampholyte hydrogel for wearable flexible electronics

Journal of Materials Chemistry A ◽

10.1039/d0ta08664a ◽

2021 ◽

Author(s):

Shanshan Wu ◽

Zijian Shao ◽

Hui Xie ◽

Tao Xiang ◽

Shaobing Zhou

Keyword(s):

Ionic Conductivity ◽

Shape Memory ◽

Human Health ◽

Shape Memory Effect ◽

Memory Effect ◽

Flexible Electronics ◽

Strain Sensors ◽

Self Healing ◽

Healing Property ◽

Triple Shape Memory

A type of supramolecular polyampholyte hydrogel with salt-mediated triple shape-memory effect, ionic conductivity, high stretchability and self-healing property was fabricated, which can be applied for strain sensors to monitor human health.

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Dynamic Optics with Transparency and Color Changes under Ambient Conditions

Polymers ◽

10.3390/polym11010103 ◽

2019 ◽

Vol 11 (1) ◽

pp. 103 ◽

Cited By ~ 6

Author(s):

Yejia Jiang ◽

Songshan Zeng ◽

Yu Yao ◽

Shiyu Xu ◽

Qiaonan Dong ◽

...

Keyword(s):

Hybrid Film ◽

Humanoid Robots ◽

Strain Sensors ◽

Working Environment ◽

Practical Implementation ◽

Ambient Conditions ◽

Widespread Application ◽

Smart Windows ◽

Color Changes ◽

Potential Applications

Mechanochromic materials have recently received tremendous attention because of their potential applications in humanoid robots, smart windows, strain sensors, anti-counterfeit tags, etc. However, improvements in device design are highly desired for practical implementation in a broader working environment with a high stability. In this article, a novel and robust mechanochromism was designed and fabricated via a facile method. Silica nanoparticles (NPs) that serve as a trigger of color switch were embedded in elastomer to form a bi-layer hybrid film. Upon stretching under ambient conditions, the hybrid film can change color as well as transparency. Furthermore, it demonstrates excellent reversibility and reproducibility and is promising for widespread application.

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Highly Viscoelastic, Stretchable, Conductive, and Self-Healing Strain Sensors based on Cellulose Nanofibers-Reinforced Polyacrylic Acid Hydrogel

10.21203/rs.3.rs-231511/v1 ◽

2021 ◽

Author(s):

Yue Jiao ◽

Kaiyue Lu ◽

Ya Lu ◽

Yiying Yue ◽

Xinwu Xu ◽

...

Keyword(s):

Polyacrylic Acid ◽

Cellulose Nanofibers ◽

Strain Sensors ◽

Self Healing ◽

Wearable Electronics ◽

Chemically Modified ◽

Mechanical And Electrical Properties ◽

Healing Efficiency ◽

Hydrogel Matrix ◽

External Stimuli

Abstract Conductive and self-healing hydrogels are among the emerging materials that mimic the human skin and are important due to their probable prospects in soft robots and wearable electronics. However, the mechanical properties of the hydrogel matrix limit their applications. In this study, we developed a physicochemically dual cross-linked chemically modified-cellulose nanofibers-carbon nanotubes/polyacrylic acid (TOCNF-CNTs/PAA) hydrogel. The TOCNFs acted both as a nanofiller and dispersant to increase the mechanical strength of the PAA matrix and break the agglomerates of the CNTs. The final self-healing and conductive TOCNF-CNTs/PAA-0.7 (mass ratio of CNTs to AA) hydrogel with a uniform texture exhibited highly intrinsic stretchability (breaking elongation to ca. 850%), enhanced tensile properties (ca. 59kPa), ideal conductivity (ca. 2.88S·m− 1) and pressure sensitivity. Besides, the composite hydrogels achieved up to approximately 98.36% and 99.99% self-healing efficiency for mechanical and electrical properties, respectively, without any external stimuli. Therefore, the as-designed multi-functional self-healing hydrogels, combined with stretching, sensitivity, and repeatability, possess the ability to monitor human activity and develop multifunctional, advanced, and commercial products such as wearable strain sensors, health monitors, and smart robots.

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A Skin-Inspired Stretchable, Self-Healing and Electro-Conductive Hydrogel with a Synergistic Triple Network for Wearable Strain Sensors Applied in Human-Motion Detection

Nanomaterials ◽

10.3390/nano9121737 ◽

2019 ◽

Vol 9 (12) ◽

pp. 1737 ◽

Cited By ~ 16

Author(s):

Yuanyuan Chen ◽

Kaiyue Lu ◽

Yuhan Song ◽

Jingquan Han ◽

Yiying Yue ◽

...

Keyword(s):

Polyacrylic Acid ◽

Cellulose Nanofibrils ◽

Human Motion ◽

Strain Sensors ◽

Current Response ◽

Oxidized Cellulose ◽

Self Healing ◽

Wearable Electronics ◽

Conductive Hydrogel ◽

Hydrogel Matrix

Hydrogel-based strain sensors inspired by nature have attracted tremendous attention for their promising applications in advanced wearable electronics. Nevertheless, achieving a skin-like stretchable conductive hydrogel with synergistic characteristics, such as ideal stretchability, excellent sensing performance and high self-healing efficiency, remains challenging. Herein, a highly stretchable, self-healing and electro-conductive hydrogel with a hierarchically triple-network structure was developed through a facile two-step preparation process. Firstly, 2, 2, 6, 6-tetrametylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils were homogeneously dispersed into polyacrylic acid hydrogel, with the presence of ferric ions as an ionic crosslinker to synthesize TEMPO-oxidized cellulose nanofibrils/polyacrylic acid hydrogel via a one-pot free radical polymerization. A polypyrrole conductive network was then incorporated into the synthetic hydrogel matrix as the third-level gel network by polymerizing pyrrole monomers. The hierarchical 3D network was mutually interlocked through hydrogen bonds, ionic coordination interactions and physical entanglements of polymer chains to achieve the target composite hydrogels with a homogeneous texture, enhanced mechanical stretchability (elongation at break of ~890%), high viscoelasticity (maximum storage modulus of ~27.1 kPa), intrinsic self-healing ability (electrical and mechanical healing efficiencies of ~99.4% and 98.3%) and ideal electro-conductibility (~3.9 S m−1). The strain sensor assembled by the hybrid hydrogel, with a desired gauge factor of ~7.3, exhibits a sensitive, fast and stable current response for monitoring small/large-scale human movements in real-time, demonstrating promising applications in damage-free wearable electronics.

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Dynamic Nanohybrid-Polysaccharide Hydrogels for Soft Wearable Strain Sensing

Sensors ◽

10.3390/s21113574 ◽

2021 ◽

Vol 21 (11) ◽

pp. 3574

Author(s):

Pejman Heidarian ◽

Hossein Yousefi ◽

Akif Kaynak ◽

Mariana Paulino ◽

Saleh Gharaie ◽

...

Keyword(s):

Mechanical Strength ◽

Strain Sensors ◽

Self Healing ◽

Nano Materials ◽

Strain Sensing ◽

Ferric Ions ◽

Research Activity ◽

Adhesion Properties ◽

High Mechanical Strength ◽

The Moment

Electroconductive hydrogels with stimuli-free self-healing and self-recovery (SELF) properties and high mechanical strength for wearable strain sensors is an area of intensive research activity at the moment. Most electroconductive hydrogels, however, consist of static bonds for mechanical strength and dynamic bonds for SELF performance, presenting a challenge to improve both properties into one single hydrogel. An alternative strategy to successfully incorporate both properties into one system is via the use of stiff or rigid, yet dynamic nano-materials. In this work, a nano-hybrid modifier derived from nano-chitin coated with ferric ions and tannic acid (TA/Fe@ChNFs) is blended into a starch/polyvinyl alcohol/polyacrylic acid (St/PVA/PAA) hydrogel. It is hypothesized that the TA/Fe@ChNFs nanohybrid imparts both mechanical strength and stimuli-free SELF properties to the hydrogel via dynamic catecholato-metal coordination bonds. Additionally, the catechol groups of TA provide mussel-inspired adhesion properties to the hydrogel. Due to its electroconductivity, toughness, stimuli-free SELF properties, and self-adhesiveness, a prototype soft wearable strain sensor is created using this hydrogel and subsequently tested.

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Rapid synchronized fabrication of vascularized thermosets and composites

Nature Communications ◽

10.1038/s41467-021-23054-7 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Mayank Garg ◽

Jia En Aw ◽

Xiang Zhang ◽

Polette J. Centellas ◽

Leon M. Dean ◽

...

Keyword(s):

Large Scale ◽

Capillary Flow ◽

External Heat ◽

Frontal Polymerization ◽

Self Healing ◽

Vascular Networks ◽

Ambient Conditions ◽

External Energy ◽

Imaging Phantoms ◽

Vascular Structures

AbstractBioinspired vascular networks transport heat and mass in hydrogels, microfluidic devices, self-healing and self-cooling structures, filters, and flow batteries. Lengthy, multistep fabrication processes involving solvents, external heat, and vacuum hinder large-scale application of vascular networks in structural materials. Here, we report the rapid (seconds to minutes), scalable, and synchronized fabrication of vascular thermosets and fiber-reinforced composites under ambient conditions. The exothermic frontal polymerization (FP) of a liquid or gelled resin facilitates coordinated depolymerization of an embedded sacrificial template to create host structures with high-fidelity interconnected microchannels. The chemical energy released during matrix polymerization eliminates the need for a sustained external heat source and greatly reduces external energy consumption for processing. Programming the rate of depolymerization of the sacrificial thermoplastic to match the kinetics of FP has the potential to significantly expedite the fabrication of vascular structures with extended lifetimes, microreactors, and imaging phantoms for understanding capillary flow in biological systems.

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Double-network hydrogel with adjustable surface morphology and multifunctional integration for flexible strain sensors

Soft Matter ◽

10.1039/d1sm00158b ◽

2021 ◽

Author(s):

Yang Yu ◽

Fengjin Xie ◽

Xinpei Gao ◽

Liqiang Zheng

Keyword(s):

Surface Morphology ◽

Flexible Electronics ◽

High Performance ◽

Strain Sensors ◽

Next Generation ◽

Double Network ◽

Conductive Hydrogels

The next generation of high-performance flexible electronics has put forward new demands to the development of ionic conductive hydrogels. In recent years, many efforts have been made toward developing double-network...

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Recyclable conductive nanoclay for direct in situ printing flexible electronics

Materials Horizons ◽

10.1039/d0mh02065f ◽

2021 ◽

Author(s):

Pengcheng Wu ◽

Zhenwei Wang ◽

Xinhua Yao ◽

Jianzhong Fu ◽

Yong He

Keyword(s):

Flexible Electronics ◽

Self Healing ◽

Stamping Process

A recyclable, self-healing conductive nanoclay and corresponding stamping process are developed for printing flexible electronics directly and quickly in situ.

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