Study On The Synthesis And Properties Of Aramid Nanofiber/carbon Nanotubes Composites

As one of the most characteristic of one-dimensional nanomaterials,carbon nanotubes(CNTs)has been outstanding at the forefront of scientific research since found for their special electrical,strong mechanical properties and large lengthdiameter ratio.As the star in the field of composite materials,carbon nanotube reinforced polymer matrix composites have been proved with superiority especially in mechanical properties and electrical charactistics than mostly traditional materials.Especially in aerospace and aeronautics field,CNTs reinforced polymer matrix composites have shown great potential in electromagnetic shielding coating,microwave absorption stealth,antistatic engineering plastic composite material,environment gas detection device,spacecraft hydrogen storage carrier and high energy density energy storage electrode.However,due to the flaws of itself agglomeration and bad interface,the mechanical properties of CNTs reinforced polymer matrix composites are still far behind the theoretical estimate.Therefore,the research of preparing carbon nanotube polymer matrix composite materials with more powerful,multipied functions,lower price and better aerospace environment bearig ability are always proposed as the goal from beginning to end.Due to its high specific strength,temperature resistance,flame retardant,the synthetic aramid fiber has been widely used in the field of armor protection,space environment protection and aircraft structural components.However,in the past few decades,the research direction of aramid fiber has been foucused on the preparation and application of macroscopic fiber composites.Aramid fiber(ANFs),which can be regarded as a "miniaturized version" of nanostructured Kevlar? fiber,was first developed and discovered from Kotov group through deprotonization proceress.ANFs not only inherits the well crystal structure and construction of the Kevlar? macro fiber,but also endowing itself with better wettability and fruitful terminals.In some ways,the research of Kevlar? fiber has enrolled into a new field of nano version.As a new member of one-dimensional material,ANFs has inherbited the large specific surface area of nanomaterials together with polymers viscous flow characteristics,which are condemmed as rendency in expanding the application scope of Kevlar? fiber,especially in the aerospace field.It can be hypothesised the merits of high mechanical strength and temperature resistance of ANFs must candaciate itself as a new solution for the wide application of CNTs polymer matrix composites in the furure.To satisfy the requirements for high strength fiber wet spinning,the ANFs/SWCNTs coaxial composite fibers are fabricated by using ANFs as sheath and single-walled carbon nanotubes(SWCNTs)as inner layer.The alignment of ANFs orientation are observed through electron microscopic demonstrating the significant role of ANFs for the improvement of fiber tensile strength and Young's modulus.By adjusting the spinning parameters,series of coaxial fiber with different core sheath proportions were obtained.When the ratio of core sheath reached 1:20,the mechanical properties of the coaxial fiber reached an optimal value with an ultimate strength up to 818.4 MPa,and Young's modulus up to 43.4 GPa.What's intrigued,the gap between core and sheath layer provided a smooth channel for the doping.Based on that,an improved electrical conductivity up to 115 S/cm can be archived after iodine vapor modification.Therefore,a combination of high strength and high conductivity facilitated the manufacture of SWCNTs fiber easily and low cost,which is highly deemed as promising for its broad application on light weight energy transporting fabrics and energy transmission.Inspired by the structure of “steel and concrete”,an ANFs/Carbon nanotube fibers(CNTF)flexible solid capacitors is assembled by utilizing CNTF as electrode and ANFs incorporated PVA as gel electrolyte.It' glad to observed the addition of ANFs not only greatly improves the mechanical properties,but also impact negligibly on its storage characteristics.Hence,such solid capacitors are identified with great promising for providing personnel with high efficient,safety and portable energy storage.To fully manifesting the strong mechanical properties of ANFs and multi-walled Carbon nanotubes(MWCNTs),a ANFs/MWCNTs composite film is prepared by vacuum filtration method.The improvement of MWCNTs on films mechanical properties is proved from tensile testaments.However,the excessive of MWCNTs may also arouse agglomeration and defects,bringing negative effect on its mechanical properties.To conquer such dilemma,a vacuum assisted LBL method was innovatively proposed to future improve the mechanical properties of films.When the content of MWCNTs reach 5wt%,the ANFs/MWCNTs composite film reach a record high among all CNTs composite polymer film with an ultimate strength of 383 MPa and Young's modulus of 35.6 GPa.Multiple characterizations are utilized showing the attribution of such prominent mechanical properties on the existing of hydrogen bonds and ?-?* stack.Meanwhile,such films also show excellent electrical and thermal properties.A combination of high strength,low expansion coefficient,low dielectric equips our films with great promising in applications such as aerospace electronic device packaging and aerospace protecting device.Based on the unique characteristic of ANFs,series of ANFs hydrogel with honeycomb structure are prepared by ice template method.By controlling the content of methanol addition,ANFs hydrogels with different mechanical properties are adjusted by controlling the degree of reprotonation.When the degree of reprotonation reach 15%,ANFs hydrogel show optimized compressive cycling response,together with a compression strength up to 5.1Mpa and young's modulus 20.6Mpa.This is the first time that aramid based materials are reported with elastic characteristics.Whereafter,ANFs/MWCNTs composite hydrogels are future prepared by soaking ANFs hydrogel into MWCNTs dispersion.It's excited to observe that MWCNTs could effectively adsorb on ANFs honeycomb laminas forming an independent conductive network with electrical conductivity up to 1.88s/m.The ANFs/MWCNTs composite hydrogels are tested with optimum in all CNTs elastic and conductive hydrogels.Subsequently,based on the characteristics of good compressive cycling and strong deformation resistance,ANFs/MWCNTs composite hydrogels are proved with efficiency in high loading strain sensor devices and solid-state supercapacitor electrode materials.