External Fields Response Performances Of Flexible Biomimetic Fibers With Designed Porous Structure

Recently,exciting progress has been made in the field of flexible electronics,and it will definitely bring a revolution to people’s lives and manufacture in the future.However,due to the poor sustainability of active materials in complex stress environments,new requirements are imposed on the construction of flexible devices.By studying natural selection,a variety of environmentally-adapted structures and layered architectures of natural materials can be used as a guide to solve the limitations of materials and engineering technology.In this thesis,inspired by the unique hollow-porous structure of polar bear hair,in order to prepare a fiber-based flexible fabric that can be used for human motion monitoring and self-warmth,we prepared thermoplastic polyurethane by solution spinning,ultrasonic dispersion and in-situ chemical reduction(TPU)/carbon nanotubes(CNTs),pure TPU fibers with different diameters and silver nanoparticles(Ag NPs)/polydopamine(PDA)/CNTs/TPU-TPU flexible conductive polymer composite fibers,their external field response behavior was studied,brief experimental results are as follows:Preparation of CNTs/TPU conductive composite fiber and its external field response behavior:(1)We used N-N dimethylformamide(DMF)to dissolve TPU particles,and prepared ultra-fine pure TPU elastic fibers by uniaxial solution spinning.Ultrasonic method was used to fix CNTs on the surface of TPU fiber.Then CNTs/TPU conductive composite fiber was obtained.(2)Analysis of the micro-morphology of the surface and cross-section of pure TPU fibers and CNTs/TPU fibers shows that there is a microporous structure inside the fiber with a pore size distribution between 0.83-1.64μm and an average diameter of about 1.16μm.CNTs are randomly and uniformly dispersed on the fiber surface,forming a good conductive network.(3)The CNTs/TPU fiber is integrated into a tensile strain sensor.It is found in the tensile sensitive response test that it has a high response factor(GF,102 at 300%strain)and a very large testable range(300%Strain),the exponential response in the entire strain range,showing excellent durability and stability in 10,000 cycles of testing,small response time(200 ms)and low density(0.85 g/cm~3),showing Good strain-sensitive performance and wearability.(4)The CNTs/TPU fiber strain sensor is insensitive to buckling,torsion,temperature and humidity external field stimuli,and exhibits excellent resistance to external interference.(5)The CNTs/TPU fiber-shaped strain sensor is directly attached to the skin or embedded in clothing,which can monitor a series of joint movements such as fingers,wrists,elbows flexion,walking.2.Research on bionic TPU fiber with hollow-porous structure and its wearable thermal insulation performance:(1)The coaxial solution spinning method is used to adjust the diameter of the syringe needle to prepare different diameter TPU fibers with hollow porous diameters.(2)The diameters of TPU fibers are 1.2,1.6,1.9,and 2.1 mm,respectively,and their elongation at break and breaking strength have reached 807%,175%,1387%,1468%,and 3.76,0.81,1.52,and 1.92 MPa,respectively.TPU fibers of different diameters all show excellent flexibility.(3)TPU fibers with different diameters have obvious porous structures,and TPU fibers with diameters of 1.6,1.9,and 2.1 also have obvious hollow structures.The densities of the four different diameter fibers are 0.41,0.40,0.35,and 0.30 g/cm~3,and the porosity is 62.8%,63.7%,68.2%,and 72.8%.Fibers of different diameters have smaller density and larger porosity.(4)Four kinds of fibers with different diameters are woven into the fabric using the orthogonal weaving method.The thermal insulation effect of a layer of fiber-based fabrics with diameters of 1.2,1.6,1.9,and 2.1 mm measured at 75oC and 115oC is measured.Reached 23.3,26.1,27.5,30.1,40.6,44.7,49.0 and 52.1oC.The corresponding two-layer fiber-based fabrics have thermal insulation effects of 32.7,33.0,34.4,36.9oC,55.2,61.2,62.4 and 78.6oC,showing excellent thermal insulation properties.(5)The thermal insulation mechanism of fiber fabrics is explained in detail.(6)The fabric can be used as gloves,wristbands,clothes with warmth and protection.3.Research on the bionic TPU conductive composite fiber with hollow-porous structure and its multifunctional external field response behavior(1)We first used a biaxial wet spinning method to prepare hollow-porous CNTs-TPU/TPU conductive fibers with a core-shell structure.Dopamine(PDA).Finally,an in-situ reduction method was used to form a silver nanoparticle(Ag NPs)layer on the surface of the fiber to obtain the final Ag NPs/PDA/CNTs-TPU/TPU conductive composite fiber,here referred to as APTTF fiber.(2)Detailed micro-morphology and elemental analysis of APTTF fiber surface show that Ag NPs are evenly distributed on the fiber surface,forming a good conductive network.The micro-morphology of APTTF fiber cross section shows that it has a hollow-porous structure.Infrared analysis showed that TPU,CNTs,PDA,and Ag NPs had good binding power,indicating that the components were well bonded.(3)As a flexible electric heating device,APTTF fiber can be heated to 40oC in 18seconds under a small voltage of 2V,showing excellent electrical heating performance.(4)As a flexible strain sensor,APTTF fiber has ultra-high response(6.5×10~7)and very large strain response range(250%),and the minimum detection limit can reach0.5%.The crack-bridge structure was used to analyze the excellent strain sensing performance of APTTF fibers.(5)In addition,the sensor can monitor temperatures from 30 to 90oC after assembly.Furthermore,APTTF fiber can be integrated into a capacitive pressure sensor,showing excellent sensing performance under a force of 1 to 25 N,and can be integrated into a two-dimensional matrix to detect pressure and falling points.(6)APTTF fiber can be fixed at the joints of the throat,fingers,wrists,knees and other joints to monitor a series of human movements.In addition,APTTF fibers can also be used for temperature alarms,pressure monitoring,and physical assisted heat to treat joint pain,showing great wearable application potential.