Preparation And Strain Sensing Properties Study Of Chitosan Quaternary Ammonium Salt-based Liquid Metal Conductive Hydrogels

Conductive hydrogels combined the electrical properties of conductive materials and the flexibility of hydrogels have been extensively applied in soft sensor.Endowing conductive hydrogel-based sensors high sensitivity,excellent sensing stability,mechanical properties and multifunctional sensing performance is a hot research topic in the industry.Therefore,it is necessary to improve the sensing performance of conductive hydrogel-based sensors to meet higher application requirements through the structural design of conductive hydrogels.In this paper,by designing and optimizing the structure of the conductive hydrogel which based on both hydrogel matrix materials and conductive fillers two aspects to improve the mechanical properties and sensing performance of conductive hydrogels.Its application as a flexible strain sensor is also explored in detail.This also provides new ideas for the design,preparation and application of chitosan quaternary ammonium salt-based liquid metal conductive hydrogel.The contents and results of this paper are as follows:（1）The chitosan quaternary ammonium salt/liquid metal（CHACC-LM）composite hydrogel was prepared using biomass-based chitosan quaternary ammonium salt as the hydrogel matrix material and highly conductive liquid metal as the soft conductive filler.The cross-linked chitosan quaternary ammonium salt flexible backbone was produced using an organic combination of physico-chemical cross-linking techniques,and then the conductive hydrogel was constructed by synergistically responding with the liquid metal conductive network.LM toughen the hydrogel matrix（stress:1.11 MPa）and enhance the hydrogel extensibility（strain:233%）.The CHACC-LM hydrogel exhibits electrical self-healing property,conductivity(0.4 S m^-1),excellent antibacterial properties（>99%）and strain sensitivity（GF=1.6）.CHACC-LM hydrogel can be used as wearable flexible sensors,which has the ability to directly monitor human activities,handwriting recognition,and gesture recognition.Due to the presence of LM,it also shows sensitivity in the external environment such as low temperature,thermal response and aqueous solution response which offering the possibility of its application in harsh environments.Importantly,the CHACC-LM composite hydrogel has temperature-stress bimodal sensing properties which responds to different stress and temperature stimuli simultaneously.（2）The chitosan quaternary ammonium salt/sodium alginate/liquid metal（CHACC-SA-LM）double network hydrogel was prepared by using biomass-based chitosan quaternary ammonium salt as the matrix material and cleverly adding sodium alginate as a liquid metal modifier and a second network.The cross-linked chitosan quaternary ammonium salt obtained by physicochemical cross-linking in the above chapter is used as the first network of the hydrogel,and SA is used as the second network,both of which build a double network structure through hydrogen bonding and electrostatic forces between anions and cations,and then finally build a conductive double network hydrogel structure in concert with the LM conductive network modified by SA.The SA-modified LM is formed by complexation of-COO^-with Ga³⁺to form a core-shell structure.SA as a modifier of LM makes the stability of conductive filler solution better.The prepared CHACC-SA-LM hydrogel has electrical self-healing,better thermal stability,electrical conductivity(0.14 S m^-1),flexibility（strain:423%）and better strain sensing performance（GF up to 4.76）.In addition,CHACC-SA-LM hydrogel can be used as a flexible strain sensor which has the ability to directly monitor human activity and distinguish subtle motions（handwriting recognition）.Importantly,it can monitor more subtle movements of the human body.It also shows temperature sensitivity to the external environment,such as low temperature and thermal response.