Self-healing PVA-based Sensing Comoosite Reinforced By Multi-branched Cellulose Nanocrvstals

E-skins were electronic devices that mimic the flexibility and sensing properties of human skin by converting various external stimuli into electrical signals.Due to their potential applications in smart clothing,biomedical prosthetics,robots,etc.,they were receiving more and more attention.This study aimed to prepare an electronic skin that had good immediate monitoring performance for human motion.Polyvinyl alcohol(PVA)was widely used in the field of electronic skin because of its excellent biocompatibility,environmental stability,ease of processing and non-toxicity.In this study,two kinds of multi-branched carboxylate cellulose nanocrystals(Multi CNC)as the reinforcement material for PVA matrix were designed for the electronic skin field.The effects of Multi CNC on the thermal stability mechanical properties,self-healing properties and sensing properties of PVA composites film were investigated and the sensing mechanisms were clarified.(?)Preparation and characterization of high sensitivity multi-branched cellulose nanocrystalline ion composite films.Multi CNC,potassium chloride and PVA were used to design a self-healing Multi CNC/PVA ion composite films with a hydrogen bond network structure.The introduced Multi CNC with its own hydrogen bonding not only enhanced the PVA,but also formed a hydrogen bond network structure with PVA,causing higher mechanical properties and self-healing properties for Multi CNC/PVA ion composite films.With the increase of Multi CNC content,the thermal degradation temperature and tensile strength of Multi CNC/PVA ion composite film materials increased,showing excellent thermal stability and mechanical properties.In particular,the mechanical strength of 0.8wt%Multi CNC/PVA reached 50.03 MPa,which was 1.80 times than that of pure PVA membrane material.In addition,Multi CNC/PVA ion composite films exhibited good self-healing properties.The self-healing efficiency after self-healing in water vapor environment reached 69.54%during 20min,and the recovered strength was 1.31 times than that of pure PVA.Multi CNC/PVA ion composite films had excellent strain sensitivity and pressure sensitivity,which could monitor different movement changes of the human body and the relative resistance changes of different pressures(5.60KPa and 8.72KPa)timely and accurately,and the minimum relative change in resistance during the movement of small insects(4.50mm small insects)could be monitored.At the same time,the Multi CNC/PVA ion composite films also exhibited excellent long-term stability and repeatability(repetitive application of pressure of 15.00KPa at 1000 times).(?)Preparation and characterization of self-healing multi-branched cellulose nanocrystalline composite conductive hydrogels.By using Multi CNC as the reinforcing phase and as a dispersion template for PANI to construct conductive polymer hydrogel with a continuous conductive skeleton,hydrogen bonding and an intrinsic 3D network structure,which could provide an electrically and mechanically stable sensing system.The morphology,structure,thermal stability,moldability,mechanical properties,self-healing properties,self-adhesive properties,conductivity and strain sensing of Multi CNC-PANI/PVA conductive hydrogels with different multi-branched cellulose nanocrystals-polyaniline(Multi CNC-PANI)contents were studied.And the feasibility of Multi CNC-PANI/PVA conductive hydrogels for human motion health monitoring was analyzed.Hydrogels exhibited ultra-high stretchability(over 1500%)and stress self-healing efficiency(99.56%)due to the inclusion of dynamic borate and hydrogen bonds in the Multi CNC-PANI/PVA conductive hydrogel.With the increase of the content of Multi CNC-PANI,the mechanical properties of conductive hydrogel had been greatly improved.When the content of Multi CNC-PANI was 5wt%,the fracture strength of hydrogel reached 171.52KPa and the elongation is 1085%.5wt%Multi CNC-PANI/PVA conductive hydrogel had a self-healing efficiency of 99.56%in 120s without external stimulation.The 5wt%Multi CNC-PANI/PVA conductive hydrogel which self-healed for 120s was manually stretched,it did not break even its deformation more than 1500%occurred,demonstrating the excellent self-healing properties of this hydrogel.The resistance strain sensitivity(which could be further evaluated by the gauge factor(GF))of the hydrogel reached 18.79 at 550-700%strain,indicating that the Multi CNC-PANI/PVA conductive hydrogel had high sensitivity.This hydrogel could accurately and timely monitor and distinguish human large movements and small movements,which had high sensitivity for the movement on the human body.In addition,compared to unbroken hydrogels,the healed hydrogels were also kept highly sensitive,the healed hydrogels had a slightly reduced sensitivity to human activity,but still had an excellent sensing property.It had great potential in the fields of human motion detection,electronic skin clothing and personalized health monitoring.