Research On Preparation And Performance Evaluation Of Wood-based Intelligent Stress Sensors

Inspired from the natural hierarchical structure of wood,two kinds of wood-based polyelectrolyte hydrogels and a simple wood sheet active separator were developed,and the feasibility of serving as a multifunctional dielectric layer for capacitive stress sensors was investigated.Additionally,tactile sensors of electric double-layer capacitive configuration were assembled with electrodes and dielectric layers of different micromorphology.Sensors with highly sensitive and wide pressure range were finally developed.The main contents are as follows:(1)Wood/polyacrylic acid(PAA)hydrogels were developed by introducing chemically and ionically cross-linked as polyelectrolyte network into the abundant pores of delignified wood as skeleton and separator.The tangential slices had a high compressive strength of 1.73 MPa and a maximum strain at fracture of 69.4%,while those of the radial slices were 0.6 MPa and 47.0%.The capacitive pressure sensor with a tangential slice as electrolyte and reduced graphene oxide(r GO)as wrinkled electrode displayed the most desired,gradient sensitivity values in the whole stress range.(2)The wood/poly(ionic liquid)integrated the anisotropic mechanical strength,electronic insulation of wood fiber,and the flexibility,ion conductivity of polyionic liquid.The influences of the wood texture and cross-linker(BIS)content on the mechanical and sensing performances of the hydrogels were investigated.The results showed that the tangential hydrogel slice with a 1.0 mol%BIS content(tan 1.0)displayed the most significant improvement in compressive stress(1.65 MPa)and deformation(73.3%)at fracture,suggesting the best compressibility.Electrodes also played a significant role in the sensitivity and stability of the sensor devices.While tan1.0 with r GO electrodes displayed the largest sensitivities(1.13–19.70 MPa^-1),tan1.0 with Ni foams possessed much more stable ionic signals within the whole stress range with sensitivities of 0.33–9.67 MPa^-1.(3)A simple and green strategy to fabricate biomass-based ultra-highly sensitive flexible tactile sensors was developed.Capacitive sensing devices were constructed by stacking conductive micropatterned PDMS electrodes with different texture wood slice/ionic liquid(IL@wood)dielectric layers.After IL impregnation,the sensor made of wood cross slice and a lotus-leaf-like PDMS film had a maximum capacitance value in the order of 100?F·cm^-2 under 80 k Pa compression,thereby exhibiting outstanding signal-to-noise ratio and responsive stability of the device.Its sensitivity reached 2.09 k Pa^-1 without obvious attenuation after 500 cycles.