Highly Sensitive, Stretchable Strain Sensor Based on Ag@COOH‐Functionalized CNTs for Stroke and Pronunciation Recognition

Abstract

piezoelectricity, [21,22] and turboelectricity. [23,24] Among them, the resistivetype soft sensor is particularly prominent for its flexibility, stretchability, and simple support system. [1,[16][17][18] Resistive-type soft sensors normally consist of a conductive sensor film and a soft substrate. [1] Polydimethylsiloxane (PDMS) has become prevalent in using as flexible and stretchable substrate owing to its remarkable elasticity, simple processing, high thermal stability, and chemical inertness. [1][2][3]7,12,25] The most essential issue of strain sensor is the choice of sensitive material. Carbon nanotube (CNT) has been broadly used in strain sensors due to its excellent mechanical properties, chemical inertness, and low cost, [1,2,5,6,10] whose stretchability could reached 280% [7] or even 500%. [11] In order to make up some defects that carbon base materials often suffered, like low conductivity (sheet resistance of ≈4 kΩ sq −1 [5] ) and the relatively low sensitivity, [9,11] researchers has mixed CNT with metal materials. Takei and some researchers have mixed CNT with silver particles physically, [13] while Zhang and others using chemical methods produced AgNP modified CNTs. [26] Metal materials have good electrical properties [1,2,7,8,15] and high sensitivity (GF is easily achieved twice or even more times than CNTs [7,12] ), and can effectively supplement the shortage of CNT. Based on our previous researches, Ag@CNT synthesized by chemical reduction is a good material that combines the both advantages of CNTs and silver nanoparticles. [25] However, there are still some drawbacks here: pristine CNTs are insoluble in water or organic solvents and easily agglomerate; the bond between CNT and metal nanoparticle is not as tight and strong. On this basis, how to further improve the performance of Ag@CNT is an important and meaningful research direction. Researches on this aspect have not been reported as far as we know.In this study, we fabricated a stretchable and flexible strain sensor using Ag@COOH functionalized CNT. To get a better performance, three different CNTs were chosen for comparison: pristine CNT, COOH functionalized CNT, and OH functionalized CNT. In order to deeply compare the mechanism of binding energy and charge transfer ability, different Combining metal and carbon nanomaterials is an effective way to significantly enhance the performance of soft strain sensors. The role of carbon nanotubes (CNTs) functionalized with different chemical groups in improving the properties of nanosilver-coated carbon nanotubes (Ag@CNT) is investigated. The functionalized CNTs are first calculated with different chemical groups combined with the silver atoms. Ag@COOH-functionalized CNTs exhibit greater binding energy and a smaller bandgap, which leads to better hydrophilicity, stability, and stronger bonding. Ag@CNTs are then synthesized using pristine CNT, OH-functionalized CNT, and COOHfunctionalized CNT. Strain sensors are fabricated by wrapping the sensing material with polydimethylsiloxane (PDMS) to form a s...

A Flexible Strain Sensor Based on the Porous Structure of a Carbon Black/Carbon Nanotube Conducting Network for Human Motion Detection

“…At present, to satisfy the aforementioned characteristics, researchers have designed strain sensors with different sensing mechanisms, among which the resistance sensor has gradually become the mainstream design method of strain sensors due to its simplicity and low cost. According to the response principle of resistance sensors, conductive carbon fillers and mental nanowires (such as carbon black [16,17], carbon nanotubes [18,19], graphene [20,21], and Ag nanowires [22,23]) can be combined with flexible substrates (such as polydimethylsiloxane (PDMS) [24,25], polyurethane (PU) [26,27], silicone rubber (SR) [28,29], elastic fabrics [30,31], and elastic bands [32]) to make a flexible piezoresistive sensor with a high sensitivity and a large stretch range by a certain preparation method. Therefore, these studies reveal that composites made of a conductive material and polymer can meet the performance requirement of strain sensors.…”

1D Nanomaterial‐Based Highly Stretchable Strain Sensors for Human Movement Monitoring and Human–Robotic Interactive Systems

“…Innovative fabrication approaches have been experimented to develop highly sensitive resistive sensors employing NC materials with pre‐stretching, [ 59 ] 3D printing, [ 60 ] direct ink writing, [ 61 ] and microfluidic techniques. [ 27,62 ] For instance, Muth et al., used 3D printing to fabricate sensitive strain sensors with conductive carbon grease materials to obtain a high stretchability of 400%. [ 60 ] It is challenging to design a high sensitivity strain sensor with improved stretchability.…”

Stretchable Strain Sensors for Human Movement Monitoring

“…Innovative device fabrication approaches have been experimented to develop highly sensitive stretchable strain sensors such as pre-stretching [7], 3D printing [8], direct ink writing [9] and microfluidic techniques [10]. For instance, exploiting 3D printing method [8] fabricate sensitive strain sensors with conductive carbon grease materials to obtain a high stretchability of 400%.…”

“…More recently, microfluidic based approach was used to fabricate high performance strain sensor. In this fabrication approach, networks of 1D materials, such as carbon nanotubes (CNTs) or silver (Ag) nanowires (NWs), on top of a stretchable substrate are realized in a micro/macro channels, which offers an alternative way to realize stretchable strain sensors with high gauge factor (GF) [1], [10]. Using this fabrication strategy, Han et al [1], created a NW-based strain sensor by hybridizing brittle metal nanowires (Ag NWs, Copper NWs, or CNTs) and a conductive organic solution with poly(3,4ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS).…”