Study For Preparation And Properties Of Conductive Polymer Composites Based On Aligned Fiber Network

As an important subfield of wearable electronic devices,flexible strain sensors can convert the mechanical stimuli of various environments into electrical signals and generate corresponding response behaviors,which have received extensive attention according to the application in the fields of human motion detection,healthcare,phonation recognition,soft robotics and so on.In recent years,conductive polymer composites(CPCs)?which are composed of single or multi-phase conductive fillers dispersed in polymer matrix,are often used as strain sensing materials owing to the advantages of light weight,low cost and good processability.In this paper,aligned thermoplastic polyurethane(TPU)fibrous mats were prepared by electrospinning.Strain sensing composites with different microstructures were prepared by adjusting the conductive network.The response behavior of the materials to different external stimuli was explored,and the relationship between the microstructures and performance of conductive network was analyzed.The details are as follows:(1)Preparation and performance of carbon nanotubes(CNTs)/TPU conductive composite fibrous matsIn this chapter,CNTs are decorated on aligned TPU fibers by ultrasonication,and CNTs/TPU conductive composite fibrous mats at parallel and vertical direction were prepared,respectively.Microscopic morphology observation showed that TPU fibers were highly oriented and wavy,and there were joint structures and gaps between TPU fibers.When stretched along the vertical direction of the TPU fibers,the CNTs/TPU conductive composite fibrous mats had higher elongation at break due to joints and some non-directional fibers.The stress-strain and strain-resistance responses of CNTs/TPU conductive composite fibrous mats based on parallel and vertical direction were compared and studied.The CNTs/TPU conductive composite fibrous mats in vertical direction had superior strain range.The hysteresis phenomena of CNTs/TPU conductive composite fibrous mats in vertical direction under different strains was investigated.It was found that the hysteresis phenomena increased gradually with the increase of the strain.The mechanism of CNTs/TPU conductive composite fibrous mats under strain was analyzed,which was consistent with the tunnel theory.The CNTs/TPU conductive composite fibrous mats based on vertical direction had fast response time(70 ms),high sensitivity(20),good durability(100,000 cycles of 200%strain),and large strain range(<900%),which met the application requirements of a flexible wearable strain sensor.We had assembled the corresponding strain sensor using CNTs/TPU conductive composite fibrous mats based on vertical direction.The material can not only monitor the motions of human joints,but also be used to detect large strain range,such as the brightness of light emitting diode(LED)indicating the strain change in circuit,and detection of the deformation of balloon,etc.The above research indicates that the conductive composite material as a flexible strain sensor has good application prospects in artificial intelligence,human motion detection,etc.(2)Preparation and performance of MXene-CNTs/TPU/Ecoflex conductive compositesWe used the method of vacuum filtration to filter the prepared CNTs dispersion and MXene dispersion onto the aligned TPU fibrous mats successively,and then the MXene-CNTs/TPU/Ecoflex conductive composites were prepared by casting.It was investigated that the structure of MXene flake with wrinkles on the surface was complete by observing the micro-morphology of single MXene flake.It was observed that MXene and CNTs were evenly distributed on TPU fibrous mats.For the cross section,it can be seen that Ecoflex immersed into the conductive network and constituted a stable "sandwich" structure.MXene-CNTs/TPU/Ecoflex conductive composites are more sensitive than MXene/TPU/Ecoflex conductive composites due to their complete "bridge" conductive network.The strain sensitivity of MXene-CNTs/TPU/Ecoflex conductive composites was investigated,and it was found that the responsivity of them was independent of the tension frequency.MXene-CNTs/TPU/Ecoflex conductive composites had low strain limitation(0.1%),weak mechanical and electrical hysteresis,the fast response(50 ms),excellent repeatability,and good durability,providing a reference for the development of flexible strain sensors.(3)Preparation and performance of CB/TPU/Ecoflex Conductive CompositesCB/TPU/Ecoflex conductive composites were prepared by using CB that is a zero-dimensional conductive filler,with the methods of electrospinning technology,ultrasonication and casting.Microscopic morphology observation showed that CB was uniformly decorated on aligned TPU fibers,forming a perfect conductive network.Obvious”sandwich"structure can be observed from the cross section of CB/TPU/Ecoflex conductive composites,in which Ecoflex has a certain immersion for the conductive network.The stress-strain and strain-resistance responses of CB/TPU conductive composites before and after encapsulation with Ecoflex were compared,which showed that CB/TPU/Ecoflex conductive composites had wider sensing range and higher sensitivity.During the tensile test,the responsivity of CB/TPU/Ecoflex conductive composites had no relation to the tensile rate.Moreover,CB/TPU/Ecoflex conductive composites that is insensitive to external humidity and temperature changes,had a wide strain range(<225%),good stability and repeatability(5000 cycles under 40%strain).It can be used in various forms of human motion detection,such as finger,elbow,knee joint movement,etc.which indicates the prefect application prospect in flexible strain sensors.