The Construction Of Conductive Fibrous Network And Their Response Behaviors To External Stimuli

In recent years,conductive polymer composites(CPCs)based functionalized polymer composites have been highly regarded by researchers.Combining the excellent advantage of polymer matrix and conductive fillers,CPCs are lightweight,low-cost,flexible,and multifunctional,which can be widely applied to many fields,such as food inspection,chemical engineering as well as the fabrication of novel smart sensors.The electrical property and the performance in practical application of CPCs are influenced by their conductive network.Actually,the conductive network is tunable by many factors,including the variety of the filler,dispersion method and the microstructure of polymer matrix.Therefore,the exploration about the design of conductive network in CPCs and their effect on the electrical property and practical performance is of great significance for harvesting sensors with effective conductive network and superior response behavior.CPCs containing electrospun fibrous network are prepared in this paper,on the basis of their novel characteristics including flexibility,high surface area and nice design capability.The construction mechanisms of the conductive network constructed by diverse fillers and the humidity sensing characteristics of the CPCs are analyzed.Moreover,the strain sensing capacities of the CPCs with different microstructure of polymer matrix are studied.All exploration is aimed at paving the theoretical foundation for the design of CPCs applied in sensing materials.The main research results are as follows:1.The fabrication and sensing properties of carbon black(CB)/nylon 6(PA6)and carbon nanotubes(CNTs)/PA6 conductive nanofibrous composites1)CB/PA6 and CNTs/PA6 conductive composites with zero-dimension and one-dimension fillers decorated on the surface of electrospun PA6 nanofibers have been fabricated by ultrasonication.The distribution of the fillers is controlled and sustained by the fibrous network.2)Scanning electron microscopy(SEM)images and the current-voltage(I-V)curves indicate that the two composites have different conductive network and conductive mechanism,determined by their geometry difference.3)The two CPCs both showed rapid response,large-scale sensing range and exponentially increasing responsivity with ascending relative humidity in humidity sensing behavior.CB/PA6 membranes display higher responsivity,yet CNTs/PA6 membranes show more stable response.Importantly,pretreatment can improve the sensing stability.4)Vapor-sensing test shows that both of the two samples exhibit almost linear and rapid response to formic acid vapor,coupled with good repeatability.CB/PA6 is more sensitive to tiny concentration change,while the response of the latter is more stable.5)The flexible membranes show stable response and non-linear change of resistance in bending test.CB/PA6 has a higher responsivity and is more sensitive to microdeformation,which is similar to humidity sensing result.2.The fabrication and mechanism of aligned PA6 fibers1)PA6 aligned fibers are prepared from the complexation of calcium chloride(CaCl2).SEM images show the porous structure on the aligned fibers.The differential scanning calorimetry(DSC),thermal gravimetric analysis(TGA)together with the Fourier transform infrared(FTIR)spectra results demonstrate the shield of PA6 hydrogen bonding and the removal of CaCl2.2)The PA6 aligned fiber membrane shows obviously improved tensile strength and elongation at break than PA6 nonwoven.3.The anisotropism of CNTs/PA6 aligned fiber membrane in strain sensing behavior and its detection for ultralow deformation1)CNTs/PA6 membranes with fillers decorated on the surface of PA6 aligned fibers are fabricated by ultrasonication.The distribution of CNTs is controlled by the aligned structures of the fibers.2)The anisotropism: the membrane based on paralleled direction shows obviously higher tensile strength and elongation at break,yet a lower gauge factor;while the membrane based on perpendicular direction shows a much higher sensitivity due to the weak interaction between neighboring fibers,and can even detect ultralow strain(0.2%).3)The membrane based on perpendicular direction displays a fast response(< 100 ms).Larger strain rate or pretreatment can be used to improve the sensing stability.The membrane is flexible and wearable,showing good sensing repeatability and potential applications in detecting human small-scale motion such as pulse,sound signal,expression,and so on.