Preparation Of Super-stretched Ionic Hydrogel And Its Application In Flexible Sensors

In the past a few decades,wearable flexible electronic devices have received growing interests due to their great potentials in electronic skin,personalized health-monitoring,implantable devices,human-machine interfaces and so on.As the key components,flexible sensors play a significant impact on the performance of flexible electronic devices.And hydrogel is one of the most developed flexible sensors with promising high-performance.Though traditional hydrogels bio-mimic natural structures and functions,they are exhibiting more and more limitations versus the growing requirements for biomedical applications,mainly facing the following challenges:i)Traditional hydrogels possess relatively poor mechanical strength comparing with natural tissues.ii)Hydrogels are pursued of self-healing to extend their working lifetime and maintain stable performance.iii)The optimization of comprehensive capability remains challenging to well integrate strength,high stretchability,elasticity,and high sensitivity.Herein,to address aforementioned points,double-network hydrogels are designed in this thesis to achieve improved mechanical properties,self-healing and good comprehensive properties.As flexible sensors,a series of research work has been carried out as follows:1.By adding NaCl into the sodium alginate(SA)solutions,the semi-rigid polymer chain of SA was transferred into a supramolecular nanofiber network with multiple hydrogen bondings.The supramolecular nanofiber network was regarded as the energy dissipation network in hydrogel.Besides,a chemically cross-linked PAM network could provide strong elastic support,while NaCl and SA carried a large amount of ionic conductors and drastically increased the conductivity of hydrogels.The double network hydrogel thus realized good comprehensive properties through the synergistic contribution from the mechanical network and the conductive network.Based on this,the hydrogel can mimic the composition and structure of human skin(collagen fiber,inorganic salt and elastic fiber).The prepared hydrogel exhibited excellent performance such as high transparency(99.6%),high tensile strength(0.75 MPa),compression resistance(rebounding immediately after rolling),high stretchability(3120%),high toughness(4.77MJ/m~3)and fast recovery from large deformations.Furthermore,the ionic hydrogel sensor exhibited remarkable sensitivity,an extremely broad strain working window(0.3-1800%),excellent adhesion,good stability,and a low applied voltage(down to 0.04 V).This sensor can also quickly and accurately monitor both large(limb motions)and tiny(speaking,wrist pulses)motions of human body.2.By adding ethanol into the SA solutions,a physical network of nanofibers was created in the hydrogels.Combining with PAM network,a double network hydrogels were fabricated.The obtained hydrogels showed excellent mechanical properties,such as high tensile strength(0.92 MPa),high tensile strain(3230%),high toughness(9.39 MJ/m~3),and good elasticity.The hydrogel also exhibited good self-healing and adhesion properties.The hydrogel sensor possessed high sensitivity(GF=8.6),excellent stability,and could monitor the real-time movement of different parts of the human body.