Tough Conductive Hydrogels And Devices Thereof

Conductive hydrogels,an excellent combination of biocompatibility and intrinsic flexibility,have recently emerged as promising materials in the fields of biosensors,flexible sensor,wearable devices,implantable sensors and electronic skin,etc.However,most hydrogels suffer from their poor mechanical properties,which is difficult to adapt themselves to the external loading in practical applications.In addition,sensors with high sensitivity requires a feasible and accurate sensing for the materials.To achieve them,a series of conductive hydrogels with high strength and sensitivity were fabricated through the elaborate regulation of polymer network.This thesis mainly consists of two chapters as follows:First,we propose a method to enhance the sensitivity of strain sensing.We prepared a novel kind of hydrogels consisting of a rigid network of polyaniline(PANI)and a flexible network of acrylamide and hydroxyethyl methyl acrylate copolymer(P(AAmco-HEMA)).Such two networks are held together by strong hydrogen bonding,resulting in conductive double network hydrogels with high strength and toughness.Under the action of minimal external strain,the hydrogel can deform simultaneously and recover in time,realizing high sensitivity and outstanding cycling stability.The mechanical properties,conductivity and sensing property of hydrogels were studied by adjusting the content of polyaniline in hydrogels.To investigate the mechanism of strain sensing,the microstructures of hydrogel network before and after strain with different contents of polyaniline were compared and analyzed.Furthermore,the hydrogels can detect many physiological signals of human body,including limb bending,pulse beating and vocal cord vibration.The ultra-sensitive array sensor made of the conductive hydrogels can also simulate the real-time perception of human skin.Second,we prepare a kind of self-adhesive conductive hydrogels.In most cases,the hydrogel strain sensor based on polyaniline often has a weak adhesion with the substrates,suppressing the accuracy and sensitivity of detection.To address this issue,we further prepare a new type of self-adhesive ionic conductive hydrogels containing a dynamic crosslinked polyzwitterionic network(PSBMA)and a physical crosslinked polyvinyl alcohol(PVA)network,exhibiting excellent mechanical properties,repeatable self-adhesion and linear high strain sensitivity.Among them,freeze-thaw treated polyvinyl alcohol endows the network with a framework for physical crosslinking of the gel,and self-crosslinked polyzwitterions form a functional network by virtue of their own electrostatic dipole action and hydrogen bond action.We further investigate the effect of PSBMA content on the mechanical properties,adhesion properties,conductivity and strain sensing properties of the hydrogels.The resulting hydrogels can be used as sensors to attach directly to human skin for monitoring the slight changes in human physiological signals.In this thesis,a reversible and energy dissipation mechanism was constructed by synergistically regulating the structure of the hydrogel network and the conductive network.Then,a conductive network that could make a quick response to the slight strain change was established.Tough conductive hydrogels with high strain sensitivity were thus obtained.The contributions of this thesis provide a new idea for the design and manufacture of flexible electronic devices based on conductive hydrogels.