Microstructural Regulation And Performance Optimization Of Strain Sensor Based On Carbon Nanotubes Network

Carbon nanotube(CNT)has been widely used in the field of flexible electronics due to its excellent electrical conductivity and mechanical strength.Compared with traditional rigid materials,like silicon,metals,and metallic oxide,carbon materials offer promising applications for flexible,stretchable,and transparent electronics.Additionally,they have relatively low cost and numerous manufacturing technologies.For now,explaination of the machanisms on the relationship between the microstructure and the electrical-mechanical coupling performance is still not comletely for the carbon nanotubes network.Meanwhile,a common difficulty of the constructive design is that the development of two-dimension conductive network relies heavily on the quality of the despersion of nanoparticles.Besides,the other difficulty is that the preparation of these networks is always complicated.Moreover,to improve the sensitivity and effective strain range and to decrease the resistancestrain hysteresis simultaneously is a delimma when these conductive networks are applied as mechanical strain sensor,since there is scant research on the controlling of the microstructure of conductive networks.To solve the problems discussed above,this study focuses on the formation and regulation of carbon nanotubes conductive network,and applies it to flexible electrodes and strain sensors.By controlling the structure of carbon nanotube materials in micron scale,factors that affect the electrical and mechanical coupling properties of carbon nanotube materials were systematically studied.In addition,to figure out the mechanism of the electrical response of carbon nanotube network in this work,the mechanical properties of carbon nanotubes network under stress field were analyzed by using finite element simulation.Firstly,this study takes the advantage of the special structure of carbon nanotube sponge to combine the bottom-up and top-down method.In this study,an approach called ‘two-steps dry transfer’ were proposed for the first time.This approach makes it possible to overcome the complicated processing of the microstructure in sensor material,also to solve the problem of dispersion.By controlling the repeating times of transfer and the viscosity of transfer substrate,the thickness of the carbon nanotubes films can be regulated,as a result,the sheet resistance and transmittance of carbon nanotubes films can be regulated.The preparation strategy of carbon nanotube films can be applied to the patterning of flexible electrodes and stretchable sensors.To realize the fine control of carbon nanotubes network,a new strategy comes up by imitating copolymer-assembly structure and claudins in animal cells.It is the first time to modify the surface of carbon nanotubes film by using micron grade PU lattice,which enables the carbon nanotube networks with a composite structure modified by the lattice block.This microstructure can significantly improves the strain sensitivity,cycling stability and reduce the resistance hysteresis effect by controlling the size of the lattice in spots array and the size of PU spots.To explore the revolution of carbon nanotubes network in the stress field,finite element analysis simulation method was carried out here.Simulation results confirmed that the existence of the PU lattice can reduce the slide and the reorientation of the conductive network effectively.As a result,the cyclic stability is improved,and the resistance-strain hysteresis will be avoided to some extent.For another,a local cluster domain in carbon nanotubes network is formed by the influence of lattice structure during the process of tensile loading.Inhomogeneous revolution is conducted by the nonuniform distribution of stress.Sensitivity is then enhanced consequently.To find a balance between the sensitivity and stretchable range of the strain sensor,this study designed a three-dimension structure that combined cracks,tactile nano-hairs,and also,CNT/composites in one device.The structure contains two parts,where carbon nanotube sponge with cracks and nano-hairs alignment on the top layer,and the carbon nanotube /PDMS composites on the bottom.By adjusting the immersion thickness of CNT sponge in PDMS,the stretchable range is able to be improved.At the same time,cracks and the nano-hairs structure can improve the sensitivity of the sensor,which is controlled by the density of the CNT sponges.This work not only improves the tensile properties of CNT sponges,but also optimizes the sensitivity and reliability of the device.It provides a new idea for the design and development of sensors for human-computer interaction or internet of things medical treatment,and enriches the research on the mechanism of piezoresistive sensors based on the open and closed conductive network.