Preparation Of Adhesive Hydrogels And Their Application In Flexible Strain Sensors

As a new type of functional material,adhesive hydrogels have attracted wide attention due to their excellent adhesion and ion transport capacity,and are one of the ideal candidate materials for the flexible electronic devices.However,the preparation of adhesive hydrogels is still complicated and expensive.Photografting is a fast and green surface modification method,which is easy to operate and can endow new surface properties of materials without changing the properties of the material itself.This study is based on the Type ? photoinitiator initiation mechanism,that is,the photoinitiator takes away the hydrogen from the hydrogen donor,making the hydrogen donor a free radical initiation center,but the initiator does not have the initiation function,so that the polymer chain can eventually be grafted and grown from the hydrogen donor.Therefore,by introducing a polymer network containing hydrogen donors into the hydrogel matrix,the target polymer can be grafted onto the surface of the hydrogel,thus giving the desired performance of the hydrogel.Since compounds containing amine groups are one of the good hydrogen donors,this study used hydrogels containing amino functional groups as bulk hydrogels,then the Type ?photoinitiation mechanism was used to graft onto the surface of the hydrogel and introduce an adhesive layer.This study selects hydrogels prepared from 2-(dimethylamino)ethyl methacrylate(DMAEMA)and acrylamide(Am)as examples.Firstly,hydrogels with rich amino groups were synthesized by free radical photopolymerization.Then,isooctyl acrylate(2-EHA)and butyl acrylate(BA)were grafted on the surface of hydrogels respectively according to the mechanism of Hydrogen abstraction photoinitiator.Since the light penetration ability is poor,the initiator contained in the graft layer absorbs the light,and the Type ? initiator is insoluble in water and will not enter the hydrogel,all of those ensure that grafting only occurs on the surface of the material.Through this principle and preparation method,we grafted the traditional adhesive materials polyisooctyl acrylate and polybutyl acrylate to the surface of the hydrogel,endowing the hydrogel better self-adhesive properties and water retention properties.The surface-modified hydrogels in this experiment were studied,and the results showed that the hydrogels had higher tensile strength(0.28 MPa)and elongation at break(800%).With the addition of sodium chloride(NaCl),the hydrogel showed high conductivity,its conductivity was 0.028 S/cm;After photo-grafting,the hydrophilicity and hydrophobicity of the surface of the hydrogel changed significantly.For the hydrogel grafted 2-EHA,the contact angle was 120 degrees.For the hydrogel grafted BA,the contact angle of the gel also reached 112 degrees,and the grafted hydrogel could be stably placed in the air without large loss of mass.In addition,the grafted hydrogels showed adhesion to various substrates.The hydrogel exhibited good electromechanical properties.At low strain(100%),the guage factor(GF)of hydrogel strain sensor was 1.92,with the increase of strain,the GF of the sensor increases gradually,and the GF value at the maximum strain was 4.0.In addition,the hydrogel strain sensor also had a fast response time(180 ms),with only 3.58%hysteresis at 300%strain stretching,and in the 20%strain repeated tensile unloading experiment,it showed high repeatability and good stability.When the hydrogel was used as a flexible strain sensor,it could instantly monitor human movements such as fingers and wrists.