Fibrication Of Ionic Gel With Choline Chloride Based-deep Eutectic Solvents And Its Application In Sensor

Ionic conductor is an important part of flexible electronic devices,which can be used as the interface between human body and external devices to transmit electrical signals.Although hydrogel and ionic liquid ionic gel are considered as candidate materials for ionic conductor,hydrogels are easy to freeze at low temperature and volatile at high temperature.The development of ionic liquid ionic gel is restricted by its high cost and toxicity.Deep eutectic solvent（DES）is a kind of green ionic liquid,which not only makes up for the shortcomings of hydrogel and ionic liquid ionic gel,but also has the excellent characteristics of non-flammability,low vapor pressure,non-toxic,biodegradable and good electrical conductivity.In this paper,taking advantage of the DES,a series of ionic gels with different properties were designed and assembled as flexible strain sensors.Excellent ionic gels were obtained by comparing frost resistance,electrical conductivity,sensitivity,chemical stability and mechanical properties.The research results provide a new idea for the process and design of green electronic products such as flexible sensors.The main contents are as follows:（1）Using choline chloride（ChCl）as hydrogen bond acceptor,ethylene glycol（EG）and glycerin（Gly）as hydrogen bond donors,choline chloride DES was synthesized.At the same time,three monomers of acrylic acid（AA）,acrylamide（AM）and itaconic acid（IA）were selected to prepare DES ionic gel under the action of crosslinking agent and initiator.Studies showed that ChCl-EG DES was unstable at room temperature and was not suitable for ionic conductors.The mechanical properties and electrical conductivity of PAM-ChCl-Gly ionic gel were the best.Free radical polymerization of AM occurs in the hydrogen bond network of DES and the cross-linking network of poly acrylamide（PAM）was formed.It greatly promoted ion conduction and had good frost resistance and environmental stability.In addition,the gauge factor（GF）of the sensor assembled by PAM-ChCl-Gly ionic gel was 0.52,showing good cyclic stability to tensile,compression and torsion.Finger,wrist bending movement can be monitored.However,its tensile strength was low,at only 12 k Pa.（2）In order to improve the tensile strength of PAM-ChCl-Gly ionic gel,natural polymer starch is introduced as the supporting material.Starch was directly dispersed in ChCL-Gly DES,and the conductive gel was prepared by free radical polymerization of AM.The effects of starch type and dosage on the properties of PAM-ChCl-Gly ionic gel were investigated.Compared with high amylose corn starch（HACS）and high branched corn starch（HAm CS）,common corn starch（CS）was more easily dispersed in DES and had certain molecular entanglement.At the same time,hydrogen bond was formed between hydroxyl group and amide group of PAM,and the tensile strength was significantly improved.The CS4-PAM ionic gel with 4%CS had the best mechanical properties,up to 90 k Pa,and had better adhesion,conductivity,frost resistance and stability.The sensor assembled by CS4-PAM has a GF=0.55,which can monitor finger bending,but its light transmittance is only 37%.（3）In order to improve the light transmittance of the ionic gel,a Ca Cl₂comediated double-network ionic gel was designed.HACS was dissolved in Ca Cl₂solution to form a starch-calcium homogeneous complex as a physical cross-linking network,and PAM as chemical cross-linking network.HACS/Ca-PAM ionic gel was formed through double network cross-linking.The results show that when the amount of HACS was 4%,the concentration of Ca Cl₂solution was 41%,and the amount of Ca Cl₂solution was 2.00 g,he light transmittance of HACS4/41Ca2-PAM was significantly increased to～80%,the elongation at break was 512%,and the tensile strength was increased to 109 k Pa.At the same time,t,it also shows good frost resistance and adhesion advantages.Its assembled sensor（GF=1.38）,showed good monitoring stability for stretching,compression,finger and wrist bending and other movements.（4）Itaconic acid（IA）is insoluble in DES due to the large steric hindrance caused by stable C=C and-COOH.However,the existing methods need a large number of initiators and the obtained ionic gel has the problem of high brittleness.In this chapter,IA and ChCl were blended to prepare polymerable DES as a soft segment,and AM was added to DES to form hard segment of PAM.The interaction between soft segment and hard segment further promoted the formation of P（IA-co-AM）ionic gel.The results show that when IA:AM=1:1.1,the elongation at break of the ionic gel is about 1250%,and the thermal stability is high,and the light transmittance is 83%and so on.The GF of the sensor assembled by the ionic gel is 1.82,showing a good ability to monitor the movement of stretching and compression fingers and wrist bending.