Research On Silicone Rubber-based Stretchable Nanocomposites And Their Patterning And Application Of Strain Sensors

Stretchable electronic devices are an important part of artificial intelligence equipment,and have broad application prospects in wearable electronics,implantable medical devices and other fields.Stretchable electronics requires all kinds of components to have good stretchability,so as to meet the needs of fitting curved surfaces and adapting to stretching deformation.At present,stretchable electronic materials face problems such as low stretchability,high structural rigidity of inorganic materials,poor cyclic stability,and low sensitivity.In view of the above problems,this dissertation focus on silicone rubber-based nanocomposites and their patterning preparation methods.The stretchable silicone rubber is used as the matrix of the composite,which can avoid the problem of excessive rigidity of the inorganic nanomaterial structure.Silicone rubber-based nanocomposites can be used as stencil printing pastes to pattern-print on silicone rubber substrates,which can improve the stretchability,cycling stability,and sensitivity of the device.The main contents of this sissertation are as follows:The silicone rubber-based conductive nanocomposite is composed of silicone rubber matrix and inorganic nanofillers.The fillers are silver nanoparticles（Ag NPs）and multi-walled carbon nanotubes（MWNT）.The conductive nanocomposite based on polydimethylsiloxane（PDMS）exhibits good electrical conductivity,stretchability and cyclic stability,with a tensile strain of 150%and a sheet resistance as low as 0.5Ωsq^-1.In order to further improve the stretchability,the conductive nanocomposite with Ecoflex as the elastic matrix was prepared here.On the other hand,the dielectric nanocomposite exhibits good dielectric properties（k=35）and insulating state,and its dielectric constant decreases with the increase of tensile strain and stretching cycles.This thesis reveals the state transition law of silicone rubber-based nanocomposites.Under tensile strain,the nanocomposite conductive material will undergo a transition of"conducting state-mixing state-insulating state"or"conducting state-insulating state".State transitions are reversible and cyclic.The dielectric constant of this insulating state at 1000 Hz reaches 70.The mechanism of the composite material is analyzed and calculated through various percolation models and tensile strain SEM images.Tensile deformation of the silicone rubber matrix of the nanocomposite,rearrangement of nanofillers,and the initiation of microcracks lead to the failure and reconstruction of the percolation network,resulting in a reversible,cyclable state transition.Based on this transition,a combined resistance-capacitance strain sensor is invented,and its sensing type is resistive in the 0-68%strain range and capacitive in the strain range greater than 68%.The maximum tensile strain corresponding to the conducting state in the state transition is lower.In order to optimize the stretchability of nanocomposites,this dissertation uses advanced laser marking equipment to fabricate patterned templates,and then the silicone rubber-based conductive nanocomposite is pattern-printed on a flat silicone rubber substrate.The stretchability of the patterned PDMS-based conductive nanocomposite was improved to 320%and did not fail after 100000 cycles of stretching.The finite element simulation results of the patterned structure show that the nanocomposite remains within the strain range of the conductive state when stretched.The effect of the type of pattern on the resistance change during the tensile process was further studied.The rhombus mesh pattern makes the resistance change slightly,while the straight line,triangle,ellipse,and serpentine make the resistance increase rapidly.In addition,a patterned capacitor with a stretchability of 200%was prepared by combining the silicone rubber-based conductive nanocomposite with the dielectric nanocomposite by patterning.The Ecoflex-based composite conductive material is patterned and printed on a flat Ecoflex substrate,and its overall performance is worse.In order to improve the stretchability of Ecoflex-based composites and avoid the constraints of the substrate on the patterned composite conductive materials,a multi-layer patterned structure with a patterned strain coordination layer（PSCL）as the intermediate layer was invented here.The ANSYS simulation results show that the multi-layer patterned structure contributes to the deformation of the pattern,so that the conductive nanocomposite is always kept in the strain range of the conductive state.A high-strain sensor with PSCL and Ginkgo biloba-like pattern has been developed,and its stretchability reaches 800%,the resistance change rate reaches 10⁴,the resolution is as low as 10%,and the resistance shows a logarithmic linear increase trend with the increase of tensile strain.The overall performance of this high-strain sensor is better than that of sensors in recent studies.The patterned silicone rubber-based nanocomposites in this dissertation will be possiblely applied in wearable and stretchable electronics.