Preparation Of Multifunctional Viscous Hydrogels And The Research On Their Flexible Sensing Performance

Flexible sensors have attracted much attention for their flexibility,portability,and comfort,showing great potential in the fields of health management,electronic skin,and human computer interactive interfaces.Hydrogel is a polymer material with high hydrophilicity,flexibility,and tissue similarity,which shows unique advantages in the field of flexible sensing and is an ideal material for the new generation of wearable sensing devices.Great progress has been made in the design and development of hydrogel-based flexible sensors so far,but a series of problems still need to be solved,such as weak interface adhesion,poor temperature resistance,poor swelling resistance,poor skin compliance,poor air permeability,and single application scenarios.To solve the above problems,this paper prepared a variety of adhesive hydrogels based on the interaction of hydrogen bonding,hydrophobic association,and electrostatic adsorption,and started from the design of the network structure.A series of studies have been carried out to improve the adhesion,temperature resistance,and environmental adaptability of hydrogels,which have been applied in the field of flexible sensing.The main research contents are as follows:1.To solve the problems of poor temperature resistance and weak interfacial adhesion of traditional hydrogels,organogels with strong adhesion and temperature resistance were synthesized by using a mixture of ethylene glycol and water as binary solvent,acrylamide and polyvinyl alcohol as substrate,and introducing tannic acid containing polyphenol groups as adhesion factor.The effect of tannic acid addition on the internal crosslinking density and interfacial interaction force are analyzed by testing the mechanics and viscosity of different components of organogels.The effect of binary solvent components on the hydrogen bonding interactions within the organogels is analyzed by DSC and water retention test.The experimental results show that the prepared organogels have high elongation at breaking(1800%),tensile strength(320 k Pa)and toughness(3.02 MJ/m3).The organogels can bond firmly to various material surfaces and exhibit excellent repeatability.Meanwhile,the binary solvent consisting of ethylene glycol and water enables the organogels to adapt to different environment and maintain good flexibility,adhesion,and electrical conductivity from-40°C to 40°C.Based on the above properties,the organogels are applied to the flexible stress sensors,which can monitor human movement and pronunciation accurately at different temperature.2.To solve the problems of poor wet adhesion and easy swelling of hydrogels,we have synthesized an organogel with good wet adhesion and swelling resistance by using hydrophobic acrylate and hydrophilic acrylic acid as monomers and adding choline-based bioionic liquid and tannic acid.The influence of hydrophobic aggregation caused by solvent exchange on the water resistance of the organogels is analyzed by testing the mechanics,adhesion,electricity and swelling properties of different component organogels in the underwater environment.The prepared organogels show strong wet adhesion to a variety of substrates and achieve long-term underwater adhesion.Hydrophobic aggregation imparts good water resistance to the organogels.They still have the low swelling rate(7%),good mechanical properties(elongation at breaking 1500% and tensile strength 436 k Pa),and electrical conductivity(ionic conductivity of 0.00421 S/cm)even after immersion in water for 15 days.The organogels are used for underwater bioelectrodes,which exhibit extremely low interfacial impedance(<15 Ω),minimal noise(19 μV)at physiologically relevant frequencies,and can effectively reduce the effect of motion artifacts to obtain high-quality ECG and EMG signals in the underwater environment.3.To solve the problem that hydrogels can only have adhesion in the single air or underwater environment and to extend their range of use,the biogels with good skin compliance and wet/dry adhesion were prepared by using ethanol to dynamically adjust the hydrogen bond between polyvinyl alcohol and tannic acid,a method of coating and molding directly on the body surface.The effect of the direct molding strategy by solvent volatilization on the skin compliance of the biogels is analyzed through adhesion and interfacial impedance tests.The effect of hydrogen bonding crosslinking density on the water resistance of the gels is analyzed by testing the mechanics,adhesion,electricity,and swelling properties of biogels in the underwater environment.The experimental results show that the prepared biogels have good conformal contact,skin compliance and low interface impedance(13.2 Ω).At the same time,the biogels show high mechanical properties,strong adhesion,and stable electrical conductivity in the both dry and wet environment.The biogel ink is coated on the surface of cotton to make a fabric electrode,which can obtain high-fidelity ECG signals in the wet and dry environment.In addition,the biogel ink can be combined with cotton to make a multi-channel fabric electrode,which can real-time monitor ECG signals in multiple channels to obtain a full range of bioelectric signals and reduce the risk of misdiagnosis.4.To solve the problems of poor air permeability,poor responsiveness,and difficulty in the continuous preparation of conventional bulk hydrogels,thermally responsive hydrogel composite fibers with a skin-core structure were prepared by adhering thermal responsive hydrogels to the surface of commercial fibers.By constructing specific anchoring groups,the problem of weak interfacial bonding between commercial fibers and hydrogel sheaths is solved,and the solid coating of hydrogel sheaths on the surface of commercial fibers is achieved.The continuous and large-scale preparation of thermally responsive hydrogel composite fibers is achieved by a homemade spinning device.Through mechanical,rheological,and thermal conductivity tests,the synergistic effects of hydrophobic action and ionic bonding on the thermal responsiveness and insulation of hydrogel sheaths are analyzed.The experimental results show that the three-point bending strength of the composite fibers increases instantaneously and dramatically(from 0.26 GPa to 2.58 GPa)when the temperature rises from room temperature to 70℃,exhibiting good impact resistance.At the same time,the composite fibers have good heat insulation performance,which can reduce the surface contact temperature by about 18℃ and effectively prevent thermal burns.In addition,the composite fibers exhibit good wear resistance without significant breakage after 1000 wear cycles.The composite fibers are made into fabric electrodes,which are capable of high-quality monitoring of ECG and EMG signals at room temperature.Under high temperature,they can be used as high temperature protective clothing,which can effectively protect the human body from external impact and thermal burns.