Design Of Two-Dimensional Titanium Carbide Based Functionalized Nanocomposite Films/Coatings And Investigation On Electromagnetic Interference Shielding Performance

The growing application of electronic devices across a broad fileld of military,industrial,commercial and consumer sectors has created a new form of pollution known as electromagnetic interference?EMI?that can cause interference or malfunctioning of equipment.Besides,It is also harmful to human health.Therefore,there is a greater need for the effective shielding of components from its adverse effects.The emergence of EMI shielding films or coatings are widely used to block the EM waves due to their light weight,easy processing,good flexibility and controllability.Especially,the fast-growing market of Wi-Fi devices have made the rapid popularity of portable and wearable smart electronics,which requires growing demand for multifunctional EMI shielding materials to fit different application background.Therefore,EMI shielding materials should not only reach enough EMI shielding performance,but also need to solve other practical problems.In particular,fire safety performance,durability performance,anti-fogging and anti-freezing performance are truly important for the long-term safe use of EMI shielding materials.Considering above issues,a special two-dimensional layered nanostructure,transition-metal carbide?Ti₃C₂T_x?,was adopted in this thesis as a promising EMI shielding filler due to their unique features such as metallic conductivity,light weight,excellent corrosion resistance and mechanical properties.In this paper,Ti₃C₂T_x was adopted as the EMI shielding filler,and then the influence of composition,proportion,configuration and structure on EMI shielding performance was explored deeply.Based on the results,with the help of different polymer substrates and methods,five different EMI shielding films and coating materials were prepared through specific adjustment and design of the overall structure and composition.Herein,the properties such as EMI shielding property,fire resistance,anti-fogging,frost-resistant,mechanical properties and durability were all well investigated to meet various requirements.The main contents of this thesis are shown as follows:1.A series of flexible cellulose based EMI shielding nacre-like films containing AgNWs and/or Ti₃C₂T_x nanosheets were prepared by a vacuum-assisted filtration self-assembly method.The EMI shielding performance was investigated for films containing different amounts of AgNWs and Ti₃C₂T_x alone.Though pure AgNWs possess the higher electrical conductivity than that of Ti₃C₂T_x,the comparison results show that the unique two-dimensional lamellar structure of Ti₃C₂T_x is more advantageous to form a conductive path at a lower addition?<15 wt%?than one-dimensional AgNWs.To investigate the structural interaction between one-dimensional AgNWs and two-dimensional Ti₃C₂T_x,we designed three different nacre structures such as mixed structure,double layered structure and multilayered structure.For comparison,we adopt 50 wt%content of AgNWs and Ti₃C₂T_x as the EMI shielding filler with different ratio as 4:1,2:1,1:1,1:2 and 1:4,where the thickness is about 20 nm.The EMI SE curves show that the mixed structure films with any ratios possess the lowest SET values than that of films containing 50 wt%of AgNWs?62.35 dB?or Ti₃C₂T_x?33.17 dB?,separately.SEM images indicate that AgNWs break the tight accumulation between Ti₃C₂T_x layers.And the enhancing interface resistance also has destructive effect on EMI performance.Particularly,the double layered structure film obtains the synergistic effect,which greatly enhances the EMI SE values.In addition,the multilayered structure lead to more impedance-mismatched interfaces,which will contribute to enhancing the EMI shielding performance under proper layer numbers.When the ratio of AgNWs to Ti₃C₂T_x is 1:1,the maximum SET value is obtained when the layer number is 6 in this work.Consequently,this work provides a detailed contrastive experimental process to fabricate optimal performance EMI shielding films by adjusting composition and architecture.2.Inspired by nacre and sandwich structure,herein,we firstly fabricate an electrical insulating sandwich structured film based on Ca ion cross-linked sodium alginate?SA?-montmorillonite?MMT?and Ti₃C₂T_x MXene through step-by-step vacuum-assisted filtration process.This novel design strategy not only maintains the inner EMI shielding network,but also can act as an excellent fire resistant barrier to protect the electron device once accidental fire happens.Compared with the pure Ti₃C₂T_x layer,such kind of sandwich film can effectively keep the EMI shielding performance?50.01 dB?,dramatically enhance the mechanical properties?84.4 MPa?and obtain excellent fire resistant performance.Especially,compared with the film by mixture,the EMI SE value is only 55%of sandwich films.Besides,it functions well under long-term heat aging test at 80?.Therefore,this unique design provides a novel EMI material strategy to facilitate its future application in flexible electronics.3.A flexible and transparent thin film has been fabricated by collaborating one-dimensional silver nanowire?AgNW?network and novel two-dimensional Ti₃C₂T_x nanosheets on PET film with external polymeric coating consisting of poly?vinyl alcohol??PVA?and poly?styrene sulfonate??PSS?.Especially,the combination of different dimensional nanomaterial networks exhibits obviously synergistic effect on EMI shielding performance,which is much superior than that of pure AgN W network or Ti₃C₂T_x network to some extent.By adjusting the AgNWs amount?0.05 mg/cm2?and Ti₃C₂T_x amount?0.01 mg/cm2?,we could obtain a high transmittance of 85%and a desirable EMI SE value as 30.5 dB.Besides,such film shows outstanding anti-fogging and frost-resistant performance due to the remarkable water-absorbing capacity of PVA and PSS in the external surface.At the same time,it can also play a protective role for the inner conductive network to endure continuous mechanical action.Considering its efficiency and simplicity,this kind of transparent conductive thin film has promising applications in flexible transparent electronic device and optics-related areas.4.A highly efficient flame retardant and EMI shielding coating on ramie fabric was fabricated by a simple layer-by-layer assembled technology and spin-coating method,which involved three layers of polyethyleneimine?PEI?,ammonium polyphosphate?APP?and Ti₃C₂T_x.Besides,Poly?caprolactone??PCL?with thermal-healing property was impregnated on the surface of modified ramie fabric to obtain self-healing property.When exposed directly to flame,the PEI/APP coating lead to a porous intumescent char residue resulting in self-extinguishing performance.In comparison with the pure ramie fabric,the pHRR value reduced about 62.8%for the modified ramie fabric that contains about 15 wt%of PEI/APP bilayer.Furthermore,the ramie fabric coated by increasing amount of Ti₃C₂T_x changed from insulating to conductive,thus gradually improving their EMI shielding performance.When the Ti₃C₂T_x sheets content was 1.2 mg/cm2,a high electrical conductivity of 925.4 S·m-1 and an outstanding EMI shielding effectiveness of 35.0 dB were also achieved over the frequency of 8.2-12.4 GHz with an absorption-dominated mechanism,which could escape above 99.9%of the electromagnetic waves.The outer PCL coating gives the fabric good thermal repair property.Once the fabric was accidentally cut,the broken parts would be healed at 60?with only 10 min,and the repaired parts has excellent mechanical strength.At the same time,the outer protective layer can effectively maintain the inner EMI shielding performance,which still functions well under long-term bending,friction or washing conditions.This simple and effective coating preparation technology enriches the research of flexible EMI shielding fabrics,which is beneficial to endow them with more practical functions.5.A highly EMI shielding coating on ramie fabric was fabricated by a simple impregnation/drying method,which made the Ti₃C₂T_x nanosheets evenly deposited on the surface of pure ramie fabric.Then the Ti2C2Tx-coated ramie fabric and the pure ramie fabrics were bonded together by the precured epoxy monomer via a hand lay-up method,where the precured epoxy monomer was mixed with 20 w%of APP as the flame retardant.The the composites were cured via oven vacuum bag manufacturing method at room temperature for 48 h.The results show that the Ti₃C₂T_x coating inside the composite material can still play a good EMI shielding effect.When the Ti₃C₂T_x sheets content was 1.2 mg/cm2,a high EMI SE value about 30 dB was also achieved over the frequency of 8.2-12.4 GHz with an absorption-dominated mechanism,which could escape above 99.9%of the electromagnetic waves.Besides,such Ti₃C₂T_x coating could also function well with APP during the combustion.It could obtain a very high LOI value as 40%and reach the V0 rating.One the other hand,the tensile strength could reach up to 51.2 MPa,which meets the needs for commercial use.This inner coating preparation technology enriches the research of fiber reinforced EMI shielding composite materials,which could guide the design of multifunctional fiber reinforced composite materials.