Preparation And Properties Of Carbon Quantum Dot/Chitosan Quaternary Ammonium Salt-based Multi-responsive Hydrogels

Multi-responsive hydrogel combines multi-responsiveness and flexibility of hydrogel,which is widely used in the field of smart wearable sensors.High sensitivity,sensing stability,extensibility and multi-responsivity of hydrogel-based sensors are the focus of current research.At present,more research is still some single-responsive hydrogels with poor performance and single application.Therefore,it is quite necessary to improve the performance of multi-responsive hydrogel-based sensors by designing the structure of multi-responsive hydrogels to meet higher application requirements.The purpose of this paper is to design and optimize the structure of multi-responsive hydrogels,focusing on the selection of hydrogel matrix materials and functional fillers,with the aim of improving the mechanical and sensing properties of hydrogels and exploring their applications in the field of flexible wearable sensors,providing a new approach for the design and preparation of carbon quantum dot/chitosan quaternary ammonium salt-based multi-responsive hydrogels.The contents and results of this paper are as follows:(1)By using biomass-based chitosan quaternary ammonium salt(HACC)as the first network of the hydrogel,carboxymethyl cellulose(CMC)as the second network of the hydrogel,and nitrogen-doped carbon quantum dots(CQDs)with good biocompatibility,stable fluorescence performance and unique p H responsiveness as the functional filler,carbon quantum dots/chitosan quaternary ammonium salt/carboxymethyl cellulose double network hydrogels(CCCDs)were prepared.Cross-linked chitosan quaternary ammonium salt(CHACC)was prepared by combining physical crosslinking with chemical crosslinking,a double network hydrogel is prepared by cross-linking the CMC with the first network as a second network through an ionic bond,and the carbon quantum dots were uniformly dispersed in the hydrogel matrix through hydrogen bonding to build the multi-responsive hydrogel synergistically.CQDs increase the strength of the hydrogel(stress:0.67 MPa)and improve the toughness of the hydrogel(strain:404%),and also impart photoresponsiveness,force responsiveness,and p H responsiveness to the dual-network hydrogel.CCCDs hydrogels have good fluorescence properties,strain sensitivity(GF=9.88),and linearity(R~2=0.97).(2)By using biomass-based chitosan quaternary ammonium salt(HACC)as the first network,polyvinyl alcohol(PVA)as the aqueous second network,and nitrogen-doped carbon quantum dots(CQDs)as the functional filler in the previous chapter,carbon quantum dots/chitosan quaternary ammonium salt/polyvinyl alcohol double network hydrogels(CPCDs)were prepared.Cross-linked chitosan quaternary ammonium salt(CHACC)was prepared by combining chemical crosslinking with physical crosslinking,as a second network,the polyvinyl alcohol was cross-linked with the quaternary ammonium salt network of cross-linked chitosan via hydrogen bonds to form a double-network hydrogel,synergistic effect in the construction of multi-responsive hydrogels.CPCDs hydrogels have good fluorescence properties,strain sensitivity(GF=10.89)and linearity(R~2=0.93).Compared with CCCDs hydrogels,CPCDs hydrogels have more outstanding mechanical properties and strain sensitivity,and poorer fluorescence properties.Both can be used as wearable flexible sensors with the capability of gesture recognition,direct monitoring of human activity and monitoring of human sweat lactate levels to measure health status.