A flexible sandwich structure strain sensor based on silver nanowires and PDMS with excellent sensing capability

Abstract

Mechanical deformations can be responded by the strain sensors through the variation of electrical signals, such as resistance, capacitance or permittivity. However, conventional strain sensors typically have poor stretchability and sensitivity. With the increasing demand for flexible and wearable electronic devices, the flexible, stretchable and sensitive strain sensors are highly desired. Organic material based flexible strain sensors are not meant to replace silicon-based devices but rather to fill niches in next-generation portable and wearabile health care products. In this work, silver nanowires were used as a conductive component, and Polydimethylsiloxane (PDMS) was used as flexible polymer matrix. Silver nanowires have been synthesized using a polyol process. Then the silver nanowires were characterized by scanning electron microscopy (SEM), and $>20 \mu\mathrm{m}$ in length and <100 nm in diameter. Their surface was smooth and uniform in diameter, and length to diameter ratio was up to 200. After the morphology of the nanomaterials were demonstrated, the sensors composed of PDMS and AgNWs were prepared via a simple template method. The sandwich structure was formed by one conductive layer sandwiched between two insulating layers. Using the multimeter resistance strain curve and tensile testing machine work to characterize the strain sensor. As a result, the sensor exhibited excellent flexibility and can be bent freely without causing damage or negative effects on itself, which is unmatched by traditional inorganic rigid electronic materials. This kind of sensor could subject to a large tensile strain and revealed a high gauge factor, which was higher than other sensors reported previously. This feature also greatly expands the range of applications of flexible sensors, enabling them to be wearable. The flexible matrix is susceptible to deformation, increases designability, and is easily compounded with surfaces of various shapes. Moreover, cyclic strain on the sensor obtained repeatable resistive responses. As the deformation of the sensor increases, the resistance increases rapidly, and the deformation of the sensor decreases, and the resistance decreases, indicating that the sensor exhibits a highly strain sensitive characteristics of good linearity. The hysteresis of the sensor is affected by the tensile rate. Generally, as the tensile rate increases, the hysteresis increases slightly. Through the R/R0-strain curve drawn, it can be found that the hysteresis effect of the sensor has a negatively negligible negative impact on its performance. Under multiple cycles, the sensor still has the characteristics of sensitive response, negligible hysteresis and reliable performance. After multiple stretching, the resistance changes less than 3% after the fixed length is restored, indicating that the sensor exhibits excellent durability over hundreds of stretching-releasing cycles. Combining the easy-fabricated and low-cost features, the sensor may become promising candidate for highly-sensitive force detections, gesture controls, imaging of spatial pressure distributions, and find potential applications in advanced robotics, human-machine interfaces, next-generation prosthetics and healthcare monitoring devices. This paper has also done research and development on the application of flexible strain sensors, a polymer based flexible strain threshold adjustable alarm response was successfully prepared, the alarm sensor in flexible sensor based on flexible polymer matrix, with good quality, easy to carry, can be bent and folded flexible features, can achieve wear, not only that, the alarm provides a response threshold adjusting device, can satisfy more usage scenarios, expand the scope of application.