Flexible Strain Sensor With Super-amphiphobic Function Based On Multilayer Structure

In the past two decades,smart fibers and fabrics with functions such as sensing,actuation,memory,display,etc.,are gradually entering the stage of history.Flexible wearable electronic products can monitor human physiological signals,motion information and environmental information in real time,serving smart medical care and personal health management.Compared with traditional rigid electronics,flexible electronics can be comfortably and compliantly integrated onto the soft and dynamically deforming human body.To achieve cross-application in multiple fields,flexible wearable strain sensors need to continuously optimize their mechanical properties,sensing performance,and stability in extreme environments.In this paper,based on the basic theory of solid surface wettability,we designed and fabricated two flexible superamphiphobic surfaces,and compared and analyzed their properties.On this basis,we further designed a flexible strain sensor(UDACF)with a multi-level hierarchical structure of polyurethane/polydopamine/silver nanoparticles/acid-treated carbon nanotubes/fluorinated carbon nanotubes(silica)(TPU/PDA/Ag NPs/ACNTs/F-CNTs(Si O₂)).By analyzing its micro-nano structure,mechanical properties,tolerance in extreme environments and electrical properties,we elucidate the mechanism of mechanical property enhancement,surface re-entrant structure mechanism and intrinsic mechanism of tensile sensing.The main contents of this paper are as follows:(1)Two flexible superamphiphobic surfaces were constructed.First,a cationic fluorinated emulsion(FV)with low surface energy was prepared by emulsion polymerization.After dipping and drying of the non-woven fabric,a flexible superamphiphobic surface was obtained(WCA=171.9°,OCA=150.8°);Second,1H,1H,2H,2H-perfluorodecyltriethoxysilane(PFDTES)was grafted onto multi-walled carbon nanotubes(CNTs)and silica(Si O₂)particles by utilizing the property of siloxane that could undergo hydrolysis and condensation reaction under the condition of ammonia water.After spraying and drying,a surface re-entrant structure was formed,and it had excellent superamphiphobic properties(WCA=171°,OCA=162°).(2)Silver nanoparticles(Ag NPs)were grown in situ on dopamine-modified polyurethane fibers and bridged with acid-treated carbon nanotubes(ACNTs)to construct flexible stretchable electrodes.Finally,fluorinated carbon nanotubes/silicon dioxide hybrid nanoparticles(F-CNTs/Si O₂)were uniformly sprayed on the electrode surface to construct a robust re-entrant structure.The electrode had excellent mechanical properties(tensile strength of 15.1 MPa),skin-like properties(Young's modulus of 1.65 MPa,good air permeability),and could be well suited for extreme environments(such as–60°C to 60°C,corrosion sexual liquids and non-polar liquids).we applied this electrode to a flexible strain sensor,which could detect both weak and large deformations,with ultra-high gauge factors(6.6×10~4),wide strain range(0.1-155%),fast response time(62 ms),good cycle durability(over 5000 cycles)and the ability to monitor high frequency movements.Furthermore,we further apply its design to human exercise health monitoring and cycling training.The sensor can monitor cycling training at different rates in real time.