Preparation And Properties Of Adhesive Hydrogels Based On Phenols

Hydrogel is a three-dimensional network structure polymer with high water content,flexibility,good mechanical strength and resilience.In recent years,multifunctional(such as self-healing,self-adhesive,shape memory,and response)hydrogels have been widely used in many fields.In particular,the research of adhesive hydrogels in the fields of drug carriers,antibacterial materials and wearable strain sensors has attracted the attention of a large number of researchers.Adhesive hydrogels can adhere to the surface of many materials without the need for additional adhesives to ensure safety and stability during their use.Self-adhesive gel adheres well to the interface.When used as a hydrogel-based strain sensor,it can ensure the stability and accuracy of the detection signal.Therefore,the preparation of multifunctional hydrogels with adhesive properties has certain application value in the field of gel-based strain sensors.Phenolic materials are widely known for their applications in inks,wood coatings and leather tanning.However,there recently has been a renewed interest in multifunctional advanced materials(hydrogels)constructed from phenols.Phenols have intrinsic properties such as metal chelation,hydrogen bonding,pH response and redox potential,making them unique structural units for the synthesis of functional materials.Materials prepared from phenolic compounds often retain many of these useful properties with synergistic effects in applications ranging from catalysis to biomedicine.Meanwhile,phenolic hydroxyl groups on phenols(such as dopamine,pyrogallic acid and tannic acid)can interact with different materials(such as hydrogen bond,coordination,cation-?,?-?stacking,etc.).For example,dopamine can adhere to various surfaces including inorganic and organic.In addition,catechol groups can also form high-strength reversible coordination interactions on inorganic surfaces,while oxidized to reactive catechol-quinones groups can be attached to organic surfaces by covalent crosslinking.Hence,based on the adhesion mechanism of phenols,two hydrogels with adhesive properties were prepared in this paper.The specific work is as follows:1)A multifunctional hydrogel(HAC-B-PAM)with adhesive,self-healing and conductive properties was prepared by dopamine grafted with hyaluronic acid(HAC),acrylamide and sodium tetraborate.HAC can balance with the PAM gel network through hydrogen bonding and covalent bonding,and endow hydrogels good self-repairing properties.Furthermore,catechol groups in HAC chains endowed the hydrogel with excellent self-adhesive properties,which can adhere to the surfaces of different materials(such as polytetrafluoroethylene,copper foil,and glass).In addition,the ion conductivity imparted to the gel by Na~+ions can be used as a strain sensor to detect the movement of human limbs.In the future,these hydrogel-based strain sensors may find potential applications in portable electronics,e-skin,and soft robotics.2)Considering that traditional adhesive hydrogels are all water based,they were extremely sensitive to the environment in practical applications.Long-term storage at low or high temperature and room temperature will cause severe dehydration,which will greatly reduce its performance and even make it unusable.In this chapter,an aqueous glycerol solution was used instead of pure water,and according to the adhesion mechanism of phenolic hydroxyl groups,small molecules with abundant phenolic hydroxyl groups-pyrogallic acid(PG)and acrylamide and(3-acrylamidopropyl)trimethylammonium chloride(ATC)were selected to prepare a moisturizing,antifreeze-adhesive hydrogel.Glycerol can form a large number of hydrogen bonds with water to lock water molecules in the gel network,so that the prepared hydrogel has excellent moisturizing and antifreeze performance.In addition,the phenolic hydroxyl groups on the PG endow the gel more excellent adhesion properties.The material is expected to be used in electronic sensors,smart drives and other fields in extreme environments.