Preparation Of Ion-crosslinking Polyacrylamide Composite Hydrogels And Study On Their Sensing Properties

In recent years,with the development of wearable intelligent sensing devices,a variety of respiratory,heart rate monitoring devices and sports bracelets as well as other sensing products have emerged as the times demand.Hydrogels are considered as ideal materials for wearable sensors because of their good biocompatibility,softness and elasticity.However,traditional hydrogels lack the necessary energy dissipation mechanism,and often do not have good conductivity and stability,thus limiting the application of hydrogels in the area of flexible sensors.In order to obtain hydrogels with high strength,good conductivity and stable performance,a series of composite hydrogels based on ion cross-linking were prepared,in which acrylamide was used as the monomer and cellulose materials were used as the composite objects,their physical and chemical properties as well as sensing properties were tested,and the application of these hydrogels as wearable strain sensors in human activities was explored.Firstly,the polyacrylamide hydrogels were prepared by one-pot method based on the enhancement of density of the cross-linking network by ions.At the same time,different ions were introduced to successfully prepare the polyacrylamide ionic hydrogels.The influence of ion types on the properties of hydrogels was explored.The physical and chemical properties test showed that the density of the hydrogel network was significantly enhanced after the introduction of ions,and the mechanical properties test showed that the prepared hydrogels had excellent toughness.Ions also give the hydrogel conductivity,so the conductivity and conductivity of the hydrogel were tested.The hydrogel has high strain sensitivity（GF=8.77）in the strain range of 700%,and can be used as a wearable sensor to monitor human activities such as breathing and wrist movement.Secondly,high strength double network（PAM–CMC）/Ca hydrogel was prepared by introducing sodium carboxymethyl cellulose on the basis of the above network based on the fact that carboxyl group can coordinate with Ca²⁺.This kind of hydrogel has strong adhesion because of its abundant active groups.In addition,compared with polyacrylamide ion composite hydrogels（PAM–CMC）/Ca hydrogels,the mechanical properties are significantly improved,indicating that the physical crosslinking network can effectively dissipate energy.It is found that the sensor based on hydrogel can monitor the tiny physiological activities of the throat by testing the sensing performance of hydrogel.Finally,water-soluble hydroxypropyl methyl cellulose is compounded with polyacrylamide,and then,a kind of antifreeze high-strength conductive hydrogel is prepared by doping lithium chloride with good water retention as a conductive material.Through testing,it is found that the hydrogel still does not undergo phase transition at-50°C,and still has elasticity and conductivity at-20°C.These results indicate that the hydrogel has excellent frost resistance.It can still be used as a sensor to transmit human motion signals.