Abstract:

Objective Flexible sensors have shown broad development prospects in fields such as electronic skin, human-computer interaction, soft robots, human motion monitoring, and smart wearables due to their characteristics of light weight, bendability, wearability, low cost, implantability, and high sensitivity. The emergence of nanomaterials has created conditions for the development of flexible sensors. Research shows that combining flexible polymer substrates with emerging conductive fillers is a common strategy for preparing flexible smart electronic fiber devices. The sensor proposed is composed of high aspect ratio AgNWs combined with a highly elastic and stretchable TPU substrate, forming a perfect conductive network. Their electrical conductivity, sensitivity and cycling stability were studied.

Method Silver nanowires are prepared by one-step polyol method. Factors affecting the morphology of silver nanowires are analyzed. The appearance morphology, chemical structure, crystallization properties and other properties of AgNWs synthesized under the optimal conditions are tested. Through electrospinning, TPU nanofiber membrane is prepared. The TPU film is fixed in a vessel. The prepared AgNWs are coated on one side of the TPU film by dipping method. After the ethanol solution volatilizes, a transparent conductive film with a silver nanowire network structure is formed on the surface of the TPU film. Two TPU films are attached and encapsulated face to face to obtain a flexible film sensor with a ″sandwich″ structure. The performance of the developed sensor was evaluated.

Results The solution reacts at 150 ℃ for 7 h, and the silver nitrate solution is dropped into the solution at a speed of 1.5 mL/min and stirred for 7 h to reach the optimal morphology and aspect ratio of the generated silver nanowires. Their length is 60-150 μm, the diameter is 60-120 nm, and the average aspect ratio exceeds 1 000 with the maximum reaching 1 921. The TPU/AgNWs/TPU sensor is a flexible strain resistance sensor with low initial resistance (36.1 Ω), high strain range (ε=0%-130%), high sensitivity (ε=0%-10%, G_F=180; ε=10%-110%, G_F=610; ε=115%-130%, G_F=1 270), and a fast response time of 220 ms). At the same tensile speed and different strains (25%, 50%, 75%, 100%), the resistance change remains highly consistent, and the resistance is proportional to the strain size, indicating that the sensor has the accuracy and repeatability of sensing under different strains. When the strain is the same (50%) and the tensile speed is different, the resistance change is highly consistent, and the resistance changes slightly under different speeds, indicating that the resistance response has good independence from the stretching speed. In the strain range of 0%-10%, after 3 000 tension cycles, the resistance change rate is between 0%-2%, indicating good cyclic stability and strain sensitivity.

Conclusion Through the research on the process parameters during the growth of silver nanowires (AgNWs) using the polyol method, silver nanowires with excellent performance were successfully prepared. A flexible sensor was fabricated by combining a polyurethane (TPU) film prepared via electrospinning technology with AgNWs, which significantly enhanced the flexibility, adhesiveness, and wear resistance of the material. Thanks to the structural design of TPU/AgNWs/TPU, the sensor effectively addresses problems with the conventional sensors, such as significant performance differences under different strains, obvious interference from the stretching rate, or substantial performance degradation after cyclic use.

Key words: flexible sensor, silver nanowire, polyurethane nanofiber membrane, sensitivity, smart textiles