Binding Mechanism Between Cellulose Nanofibers And Silver Nanomaterials And Their Application In Flexible Electronics

The rapid development of flexible electronics（such as folding mobile phones,curling TVs,FIRD labels,etc.）inevitably requires devices to withstand tens of thousands of bending,tearing,friction and other mechanical effects to maintain the performance of each functional layer.The substrate is the basis for subsequent functional material compounding and the key to ensuring high mechanical performance of the device.At present,the mainstream substrate materials are plastic polymer materials from petrochemical sources.Most of them have poor thermal stability and are not environmentally friendly.At the same time,the weak van der Waals force between the plastic substrate material and the conductive material during electrode preparation results in poor adhesion.So pre-processing or post-processing is required to improve this shortcoming.As an important derivative of green and natural cellulose,nanocellulose is used in template materials,optical materials,medical materials and other fields because of its excellent mechanical properties,controllable size,thermal stability and chemical modification.The flexible transparent nanopaper prepared from it has been proved to be a good substrate material.Here,inspired by the Ag-S bond theory,a novel cellulose nanopaper substrate is presented to improve the bond strength with the Agnanoparticle ink through a facile printing method.The substrate is fabricated using thiol-modified nanofibrillated cellulose and exhibits excellent optical properties（～85%@550 nm）,ultra-small surface roughness（3.47 nm）,and high thermal dimensional stability（up to at least 90°C）.Then print silver nanoparticle（AgNP）ink and silver nanowire（AgNW）ink on the surface respectively.The specific application of preparing electrode materials is as follows:（1）The AgNP ink was prepared by reducing silver nitrate with sodium borohydride.And it can be easily patterned on the surface of the NFC-HS substrate using a simple mask printing process.The NFC-HS substrate can attract Agnanoparticles initiatively and bind them firmly,which enable the conductive ink to be printed without using the ink binder and form a strong substrate-ink bonding and maintain a stable conductivity of 2×10^-4Ωcm even after extensive peeling and bending.This work may lead to exploring new opportunities to fabricate high-performance flexible electronics using the newly developed nanopaper substrate.（2）AgNO₃ was used as the silver source and reacted in ethylene glycol（EG）system to prepare the AgNW with a length of about 20μm and an average diameter of 38 nm.And then we dispersed the AgNW in ethanol to prepare a AgNW ink with good dispersibility.When the square resistance of the silver film prepared by spin coating is25Ω/sq,the light transmittance can reach 84.2%.The prepared NFS-HS-based AgNW conductive film can withstand even 60 times tears without obvious detachment,and the square resistance did not change significantly.It is proved that the NFC-HS nano-paper substrate has advantages over PET substrate due to its strong binding ability between sulfhydryl group and AgNW.