The Preparation,Performances,and Applications Of PAM/SA Based Conductive Antifreezing Hydrogel

Hydrogels possess various properties such as transparency,biocompatibility,and ionic conductivity,which have broad application prospects in the fields of flexible electronics,biomonitoring,drug delivery,and ionic skin.However,their high water content brings many problems,such as easy freezing at low temperature,easy drying at room temperature,and poor mechanical properties caused by a loose cross-linked network,which seriously limit the practical application of hydrogels.Therefore,there is an urgent need to develop a high-strength conductive antifreezing hydrogel with environmental stability.Studies have shown that cryoprotectant（CPA）can improve the freezing resistance and drying resistance of hydrogels,adding ions can endow hydrogels with excellent ionic conductivity and general freezing resistance,which can also adjust the mechanical properties of hydrogels.Based on this,polyacrylamide-sodium alginate（PAM-SA）double network hydrogel with good flexibility and biocompatibility was selected in this paper,based on the salting-out effect of alkali metal ion salts and the CPA/water binary solvent system,through a simple one-pot solvent replacement method,a conductive antifreezing hydrogel with high transparency,long-term environmental stability and high strength was constructed by introducing multiple non-covalent bonds such as hydrogen bonds and hydrophobic association,and the application potential as a flexible sensor was explored.The preparation and performances of ionic organohydrogels based on PAM/SA.A series of ionic organohydrogels with conductive and antifreeze properties were prepared by soaking the PAM/SA double network hydrogel in a mixed solution of alkali metal ion salt solution/CPA.By adjusting the types and concentrations of CPA（glycerol,ethylene glycol,sorbitol）and alkali metal ion salts（KCl,Na Cl,Li Cl）in the replacement solution,the influence of displacement solution on performances of ionic organohydrogels was systematically explored.The results show that:under the same concentration,CPA enhanced the mechanical strength of ionic organohydrogels follows the order of Gly>EG>Sor;both Gly and EG can provide antifreezing performance of-20℃;under the same conditions,CPA regulated the conductivity of ionic organohydrogels in the order of Sor>EG>Gly,but the order was opposite at low temperature.Moreover,ionic salt enhanced ionic organohydrogels mechanical strength and ionic conductivity both follow the order of KCl>Na Cl>Li Cl.It is worth noting that under optimal conditions,the PAM/SA-Gly-KCl_1M hydrogel exhibits good mechanical properties（a tensile strain of up to 1465%,a tensile strength of 166 k Pa,a toughness of 1354 k J·m³）,high ionic conductivity（0.69 S/m）,excellent frost resistance（-100°C）,and long-term stability（70%of the weight can be kept for one month in an open environment）,making it an ideal material for the fabrication of flexible sensors.Low temperature-resistant,highly transparent stretchable strain sensor based on conductive antifreezing hydrogel.Based on the research on the performances of ionic organohydrogels,we selected PAM/SA-Gly-KCl_1M with the best comprehensive properties as the conductive antifreezing hydrogel,and fabricated a stretchable strain sensor that can operate at low temperature.The physicochemical properties,mechanical properties,electrical properties,long-term stability,and sensing properties were systematically explored.Studies have shown that the sensor has excellent self-recovery and fatigue resistance,and it can exhibit long-term stability（>7 days）in an open environment,and has the sensitivity and stability of strain sensing.In addition,the KCl solution/Gly binary solvent system endows the conductive antifreezing hydrogel with high transparency and excellent freezing-resistance,so that the sensor can maintain the sensitivity and stability of the sensing signal even at-20°C,it has broad application potential in health monitoring and ionic skin.