Preparation Of Gradient Polyelectrolyte Hydrogels And Their Application In Self-powered Sensor

In modern society,various kinds of flexible wearable devices have become an indispensable part of people’s life,which plays an important role in numerous fields,such as human health detection,self-powered sensor parts,energy storage and conversion,etc.Based on the conductive ways(i.e.,electrons or ions),the flexible wearable sensors can be divided into electronic flexible sensors and ionic flexible sensors.Among them,the ionbased flexible sensors have drawn extensive attention from researchers due to their tissuelike mechanical properties and signal carriers,good biocompatibility and self-healability.Ion-based sensors can be divided into resistive and capacitive sensors according to their sensing mechanism,but these sensors need additional power supplies,which seriously affect the portability of wearable devices.In order to solve this problem,researchers have proposed the strategy to construct the self-powered sensors,which can rely on their own characteristics to harvest electrical energy from surrounding environments.The most typical self-powered sensors are piezoelectric and triboelectric sensors.However,these two kinds of sensors generally present the inefficient power density at low frequencies,and are not applicable for the construction of ion-based self-powred sensors.Although the new emrging ion diodes can be used to produce ion self-powered sensors,they have the risk of delamination.Herein,in order to solve the above problems existing in flexible sensors,we have designed a new self-powered ion multifunctional sensor and studied thier sensing mechanisms.(1)We used polyacrylamide hydrogel as containers of low-molecular-weight(LMW)polycation,high-molecular-weight(HMW)polyanion and LMW polycation as reaction raw materials,for the preparation of gradient polyelectrolyte hydrogel materials through a novel hydrogel-assisted reaction-diffusion method.the method has a stable reaction interface,the customized shapeand and good universality.The gradient polyelectrolyte hydrogel has high transparency(> 60 %),high mechanical properties(2.85 MPa)and the self-induced potential difference due to the presence of charge and pore size gradient structure that leads to directional movement of countervail ions.The gradient polyelectrolyte hydrogel lost the self-induced potential difference after freeze drying.The potential difference is gradually restored during water absorption.Therefore,we have prepared a humidity sensitive self-powered humidity sensor,which has the advantages of wide detection range(50-99 RH%),high sensitivity(2.05 m V/RH%)and no external power supply.(2)We first attempt to use gradient polyelectrolyte hydrogel as a self-powered sensor,which not only has multi-response self-induced potential similar to that of ion diodes,but also avoids the interface layering phenomenon of diodes.The flexible multifunctional selfpowered sensor has a wide pressure detection range(2 MPa),high pressure sensitivity(329.8 m V/MPa),good circulation stability(500 times),and can monitor a variety of human activities in real time,including walking,pulse and speech recognition.In addition,we also reveal the self-powered sensing mechanism of the self-powered sensor and achieve accurate sensing and coupling of multiple stimuli of pressure and temperature.This research can provide a general strategy and theoretical guidance for the development of high-performance and multifunctional self-powered ion-based sensor system.