Preparation And Properties Of Nanostructured Silver Films Deposited On Nonwovens

Silver nanoparticles possess the opto-electrical,photocatalitic,anti-bacterial and electromagnetic shielding properties,which common silver materials don't have,due to quantum effect,surface effect and quantum tunneling effect.The construction of nanostructure silver films from silver nanoparticles is the key step in the applications of this material.In this research,low temperature magnetron sputter coating was employed to deposit nanostructured silver films on the surface of nonwovens to functionalize the textile materials.The use of magnetron sputter coating not only overcomed the problems of aggregation of nanoparticles as filling particles,but also shortened the production processes and eliminated the water pollution.The use of magnetron sputter coating,on the other hand,could reduce the processing cost.This research focused on the formation principle of the nanostructured silver,preparation techniques and properties of the nanostructured silver deposited on the surface of nonwovens to meet the demands of the markets for functional textiles.This work will provide the theoretical and practical guidance for the development of functional textiles based on its advanced and practical findings.The antibacterial silver films were deposited on polypropylene(PP) and PLA nonwovens and the silver films with the properties of conductive,electro-magnetic shielding and anti-ultraviolet radiation were deposited on polyester(PET) in this project.The effects of sputtering parameters and argon plasma pretreatment for nonwovens on the properties of the samples were investigated.The surface morphology was observed with scanning electron microscopy(SEM) and atomic force microscopy(AFM).Surface chemical compositions were examined employing X-ray energy dispensive spectrometer(EDX).The crystal structures of silver films were observed using X-ray diffraction(XRD).Electrical resistances of silver films were measured by four-probe tester.Electro-magnetic shielding properties of nonwovens coated with silver films were assessed according to ASTM D4935-99 test standard.The antibacterial performance was tested using shake flask test.The test results indicated that deposition time and argon plasma pretreatment were the two key factors affecting antibacterial properties of the coated materials, while sputtering power,gas pressure and gas flow had a slight influence on antibacterial properties.Both the reduction percentage of Staphylococcus aureus and Escherichia coli bacteria reached 100%for PP nonwovens,when the silver film thickness was above 3nm.Both the reduction percentage got to 100%for PLA nonwovens,as the coating thickness exceeded 2nm.Under the same processing conditions,the coated samples with argon plasma pretreatment showed the better antibacterial performance.The reduction percentage of both the bacteria tested reached 100%for the pretreated PP and PLA nonwovens,when the film thickness got to 2nm and 0.5nm respectively.Sputtering parameters also affected the electrical, electromagnetic and ultra-violet transmission properties of the coated materials.Electrical conductivity was improved as the film thickness increased.With the same film thickness,the electrical conductivity was decreased as the sputtering power increased,while the electrical conductivity was first decreased and then improved as the pressure of argon increased.Electromagnetic shielding effect(SE) was increased as the film thickness increased.As the film thickness got to 100nm,the value of SE was above 26dB(shielding effect was over 99.7%).The nanostructured silver films also exhibited great ultraviolet and visible light shielding effect.The transmittance is below 6%in the wavelength range between 250 and 600nm when the film thickness was above 50nm, Multiple antibacterial mechanism of nanostructured silver films deposited on nonwovens were first provided in this paper.The silver ions released from the nanostructured silver films and the active action of the released silver ions,on one hand,led to the antibacterial effect and the adhension free energy between bacteria and the coated silver films,on the other hand,converted from negative to positive after argon plasma pretreatment and silver sputter coating,indicating that act of adhension could hardly take place. The adhension was reversible even if it happened.Thus,the antibacterial mechanism was well explained from the viewpoint of energy.The mechanism of the interfacial adhension between silver and polymer substrate was examined and discussed.The effec of argon plasma pretreatment on interfacial adhension strength was analyzed,and the adhension strength between silver films and substrate was characterized by abrasion test and peel-off test. The fractal characteristic of the silver films sputtered on nonwovens was analyzed for the first time.Fractal dimensions could well describe the surface topography of the sputtered films on the nonwoven substrates. The larger fractal dimension indicated the better surface topography.Fractal dimension was closely related to the electrical conductivity,the grain size and the electromagnetic shielding properties of the sputtered films.The growth mechanism of nanostructured silver films and the microstructure of films were investigated and explained.The growth model could be considered as layer growth when the silver film was less than 5nm.This was because the roughness of the sputtered film did not show any significant change. The growth model was regarded as nucleus growth or island growth as the film thickness was between 30nm and 40nm.It was related to the surface state of the substrate,the temperature of the substrate and the sputtering conditions.The study revealed that the crystal structure of silver films with different thicknesses on nonwovens substrate was face centered cubic.The increased film thickness led to larger average grain size of the silver crystals.