High-Performance Resistive Pressure Sensor Based on Elastic Composite Hydrogel of Silver Nanowires and Poly(ethylene glycol).

Youngsang Ko,Goomin Kwon,Dabum Kim,Jungmok You

doi:10.3390/mi9090438

Abstract

Improved pressure sensing is of great interest to enable the next-generation of bioelectronics systems. This paper describes the development of a transparent, flexible, highly sensitive pressure sensor, having a composite sandwich structure of elastic silver nanowires (AgNWs) and poly(ethylene glycol) (PEG). A simple PEG photolithography was employed to construct elastic AgNW-PEG composite patterns on flexible polyethylene terephthalate (PET) film. A porous PEG hydrogel structure enabled the use of conductive AgNW patterns while maintaining the elasticity of the composite material, features that are both essential for high-performance pressure sensing. The transparency and electrical properties of AgNW-PEG composite could be precisely controlled by varying the AgNW concentration. An elastic AgNW-PEG composite hydrogel with 0.6 wt % AgNW concentration exhibited high transmittance including T550nm of around 86%, low sheet resistance of 22.69 Ω·sq−1, and excellent bending durability (only 5.8% resistance increase under bending to 10 mm radius). A flexible resistive pressure sensor based on our highly transparent AgNW-PEG composite showed stable and reproducible response, high sensitivity (69.7 kPa−1), low sensing threshold (~2 kPa), and fast response time (20–40 ms), demonstrating the effectiveness of the AgNW-PEG composite material as an elastic conductor.

Highlights

Flexible electronic devices capable of transducing physical phenomena, such as pressure, strain, and temperature, into electrical signals have received considerable attention for use in next-generation wearable electronics for health monitoring [1–8]
Our experiments showed that this piezoresistive pressure sensor based on the silver nanowires and poly(ethylene glycol) (AgNW-PEG) sandwich structure exhibited good electrical properties, excellent flexibility, good transparency, high sensitivity, and fast response time
Poly(ethylene glycol) diacrylate (PEG-DA; MW 575) and polyethylene terephthalate (PET; film thickness 0.175 mm) were purchased from Aldrich Chemicals (Gillingham, UK) and used without further purification. 4-(2-Hydroxyethoxy) phenyl-(2-hydroxy-2-propyl) ketone (Irgacure 2959) was purchased from BASF (Ludwigshafen, Germany). 3-Acryloxy-propyl trichlorosilane was obtained from Gelest, Inc. (Morrisville, PA, USA)

Summary

Introduction

Flexible electronic devices capable of transducing physical phenomena, such as pressure, strain, and temperature, into electrical signals have received considerable attention for use in next-generation wearable electronics for health monitoring [1–8]. A number of research groups have been pursuing the development of high-performance pressure sensors with high flexibility, optical transparency, and ultrahigh sensitivity, because of their wide range of potential applications in robotics and medicine, and applications to specific devices including smart phones, touch screen devices, and electronic skin [9–17]. We focus on the piezoresistive transducing type (which has a number of advantages over the piezoelectric), capacitance, and triboelectric types (including low cost, convenient readout, faster response time, lower power consumption, small temperature dependence, and simple device structure) [18–21]. Most piezoresistive pressure sensors have simple sandwich structures in which conductive materials are embedded into insulated elastomeric polymer matrices. The elastic material is an essential component of such devices to accomplish high sensitivity and stable contact in the ultralow pressure region [22–24]. It is reasonable to expect that properties of the elastic matrix play an important role in the performance of pressure sensors

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