Magnetofluids-based Flexible Electronic Sensors Via Magnetic Printing And Photopolymerization Technique

Flexible-stretchable electronic sensors are a new kind of functional device which can be used to simulate human skin in recent years.Generally,flexiblestretchable electronic devices consist of flexible substrate materials and conductive sensitive materials,both of which are indispensable.The flexible substrate materials endow the sensor with basic mechanical properties,and play a role of supporting and protecting the whole sensor.However,the sensitive conductive materials endow the sensor with conductive property and play the role of signal transmission.Compared with other types of flexible electronic sensors,liquid conductors-based sensors have some advantages,such as liquid conductors intrinsically possess limitless and instantaneous deformability and endowing the final sensors better performance;more choice for flexible substrate materials and sensitive conductive materials and giving full play to their maximum roles;no safety problems caused by direct contact of conductive materials with skin and so on.But there are few reports about the preparation methods of liquid conductors-based sensors,and the existing methods are complex and timeconsuming.Therefore,it is necessary to develop new,efficient,green and environmental technology for the fabrication of liquid conductor-based flexible electronic sensors.In this study,patterned magnetofluids-based flexible sensors were fabricated by combining magnetic printing,ionic liquid-based magnetofluids(IL-MFs),oxygen inhibition of photopolymerization and in-situ encapsulation techniques.Among them,magnetic printing technique is the molding method/medium,IL-MFs is the conductive sensitive materials,oxygen inhibition effect can realize/promote the bonding of the upper and lower layers of materials,and the liquid photosensitive resins is the packaging materials(flexible substrate materials).Firstly,the IL-MFs were prepared and characterized by XRD,TEM,TGA and conductivity analyzer,and the stability of the magnetofluids are proved by quantitative observation of the sedimentation/stratification phenomenon of the magnetofluids with or without magnetic field.Then,the resin formula with good mechanical properties was obtained through screening liquid photosensitive resins,and used as the substrate materials and packaging materials.Then,the stability of resins and magnetofluids were studied through the compatibility of liquid photosensitive resins and ionic liquid,and the swelling properties of the cured resins and ionic liquid.Subsequently,the COMSOL Multiphysics software was used to characterize and simulate the NdFeB permanent magnet and magnetic printing technique,which proves the feasibility of patterning magnetofluids by magnetic printing.Finally,a series of magnetofluids-based electronic sensors with different line-width and patterns were fabricated,and their electro-mechanical properties were also studied.Specifically,the as-prepared magnetofluids-based sensors present wide monitoring range(at least 100%),good cycling stability and low degree of hysteresis(DH).And the sensitivity can be 11.7 for the linearsensor with 0.3 mm line-width(MFBL-0.3)and only be 1.9 for the sensor with three "S" curves(MFBS-3).In addition,we explored its potential application in health monitoring,such as pulse monitoring and finger bending.Besides,we also investigated its applications in the field of light,heat and magnetism monitoring due to the specific properties of ionic liquid-based magnetofluids.