Thermoelectrical properties of graphene knife-coated cellulosic fabrics for defect monitoring in Joule-heated textiles

Knife-coating can confer new properties on different textile substrates efficiently by integrating various compounds into the coating paste. Graphene nanoplatelets (GNP) is one of the most used elements for the functionalization of fabrics in recent years, providing electrical and thermal conductivity to fabrics, later used to develop products such as sensors or heated garments. This paper reports thermoelectrically conductive textiles fabrication through knife-coating of cellulosic fabrics with a GNP load from 0.4 to 2 wt% within an acrylic coating paste. The fabric doped with the highest GNP content reaches a temperature increase of 100°C in few seconds. Besides, it is found out that the thermographic images obtained during the electrical voltage application provide maps of irregularities in the dispersion of conductive particles of the coating and defects produced throughout their useful life. Therefore, the application of a low voltage on the coated fabrics allows fast and effective heating by Joule’s effect, whose thermographic images, in turn, can be used as structural maps to check the quality of the GNP doped coating. The temperature values and the heating rate obtained make these fabrics suitable for heating devices, anti-ice and de-ice systems, and protective equipment, which would be of great interest for industrial applications.

Development of an Elastic, Electrically Conductive Coating for TPU Filaments

Electrically conductive filaments are used in a wide variety of applications, for example, in smart textiles and soft robotics. Filaments that conduct electricity are required for the transmission of energy and information, but up until now, most electrically conductive fibers, filaments and wires offer low mechanical elongation. Therefore, they are not well suited for the implementation into elastomeric composites and textiles that are worn close to the human body and have to follow a wide range of movements. In order to overcome this issue, the presented study aims at the development of electrically conductive and elastic filaments based on a coating process suited for multifilament yarns made of thermoplastic polyurethane (TPU). The coating solution contains TPU, carbon nanotubes (CNT) and N-Methyl-2-pyrrolidone (NMP) with varied concentrations of solids and electrically conductive particles. After applying the coating to TPU multifilament yarns, the mechanical and electrical properties are analyzed. A special focus is given to the electromechanical behavior of the coated yarns under mechanical strain loading. It is determined that the electrical conductivity is maintained even at elongations of up to 100%.

Study on the Electrical Conductivity of Inorganic Conductive Network in Sediments

The inorganic conductive network provides an essential channel for electron transport and supports the biogeochemical process in sediments, but the conductive mechanism of conductive network is not well understood. In this work, theory of circuit and electronics was applied to build a three-dimensional (3D) resistivity network simulation model for exploring the conductive mechanism and analysing the effect of the particle size on the conductive characteristic of inorganic conductive network. In order to simulate the real sediment environment, inorganic composites with silica (SiO2) particles as matrix using magnetite (Fe3O4) particles as fillers are constructed. The simulation results reveal that the electrical conductivity of these composites rises nonlinearly with the increasing volume fraction of conductive fillers, which is consistent with the percolation theory. Moreover, small-sized conductive particles or large-sized matrix particles are confirmed to exert a positive part in enhancing electrical conductivity of composites.

Influence of fabric structure on electrical resistance of graphene-coated textiles

Coating is a technique widely used in the textile industry for different purposes, mainly in coloring and functional finishes. Graphene is usually applied to fabrics using coating techniques to provide such fabrics with properties like thermal or electrical conductivity. All woven fabrics have peaks and valleys in their structure, generated by the warp and weft threads interlacing. When spreading the graphene coating, the paste is placed in the fabric’s interstices, and the connection between conductive particles is only produced when the height of the coating is sufficient to connect the different areas where it is deposited. This article analyzes three types of satin weave with three interlacing coefficients (ICs) (0.4, 0.25, 0.17) and two sets of weft yarns each (20 and 71.43 tex). For a blade gap of 1.5 mm, the electrical resistance of samples with weft yarn count of 20 tex and IC of 0.4 is 534.33 Ω, while for IC = 0.25 electrical resistance is 36.8% higher and for IC = 0.17 this parameter increases 249.3%. For samples with weft yarn count of 71.43, the sample with IC = 0.40 exhibits an electrical resistance of 1053 Ω, for IC = 0.25 this value rises to 33.9% and for IC = 0.17 the electrical resistance value increases a total of 78.9%. This finding can be of interest for coatings where continuity is crucial, and for the application of substances that need to be protected from external factors, for which fabrics with deep interstices can be designed to house said products.

SYNTHESIS OF FUNCTIONAL NANOPARTICLES FOR APPLICATION IN INKJET PRINTING

Ag nanoflakes were synthesized by chemical reduction method using cetyltrimethylammonium bromide (CTAB) as a surfactant. The results of transmission electron microscope (TEM) analysis, ultraviolet-visible spectroscopic (UV-Vis) analysis, X-ray diffraction (XRD) analysis showed that the obtained Ag nanoflakes had size of ~50 – 60 nm, thickness of 16 nm, with flake shape reached 96 %. The particles crystallized in cubic structure of Ag. The Ag nanoflakes synthesized with pH = 4 were dispersed stably after 60 days from synthesis. The properties of the obtained Ag nanoflakes were suitable for using them as conductive particles in fabrication of functional inks for electrohydrodynamic printing technique.

Transparent Electromagnetic Shielding Film Utilizing Imprinting-Based Micro Patterning Technology

Utilization of methods involving component integration has accelerated, owing to the growth of the smart mobile industry. However, this integration leads to interference issues between the components, thereby elucidating the importance of the electromagnetic interference (EMI) shielding technology to solve such issues. EMI shielding technology has been previously implemented via the reflection or absorption of electromagnetic waves by using conductive materials. Nevertheless, to tackle the recent changes in the industry, a transparent and flexible EMI shielding technology is necessitated. In this study, a transparent and flexible EMI shielding material was fabricated by filling a conductive binder in a film comprising an intaglio pattern; this was achieved by using the ultraviolet (UV) imprinting technology to realize mass production. Subsequently, changes in the aperture ratio and shielding characteristics were analyzed according to the structure of the pattern. Based on this analysis, a square pattern was designed and a film with an intaglio pattern was developed through a UV imprinting process. Furthermore, it was confirmed that the transmittance, conductivity, and EMI shielding rate of the film were altered while changing the coating thickness of the conductive particles in the intaglio pattern. The final film prepared in this study exhibited characteristics that satisfied the required EMI shielding performance for electric and electronic applications, while achieving flexible structural stability and transparency.

Enhanced Cementation of Co2+ and Ni2+ from Sulfate and Chloride Solutions Using Aluminum as an Electron Donor and Conductive Particles as an Electron Pathway

Cobalt and nickel have become important strategic resources because they are widely used for renewable energy technologies and rechargeable battery production. Cementation, an electrochemical deposition of noble metal ions using a less noble metal as an electron donor, is an important option to recover Co and Ni from dilute aqueous solutions of these metal ions. In this study, cementation experiments for recovering Co2+ and Ni2+ from sulfate and chloride solutions (pH = 4) were conducted at 298 K using Al powder as electron donor, and the effects of additives such as activated carbon (AC), TiO2, and SiO2 powders on the cementation efficiency were investigated. Without additives, cementation efficiencies of Co2+ and Ni2+ were almost zero in both sulfate and chloride solutions, mainly because of the presence of an aluminum oxide layer (Al2O3) on an Al surface, which inhibits electron transfer from Al to the metal ions. Addition of nonconductor (SiO2) did not affect the cementation efficiencies of Co2+ and Ni2+ using Al as electron donor, while addition of (semi)conductors such as AC or TiO2 enhanced the cementation efficiencies significantly. The results of surface analysis (Auger electron spectroscopy) for the cementation products when using TiO2/Al mixture showed that Co and Ni were deposited on TiO2 particles attached on the Al surface. This result suggests that conductors such as TiO2 act as an electron pathway from Al to Co2+ and Ni2+, even when an Al oxide layer covered on an Al surface.

Effect of Different Carbon Materials on the Conductivity of Epoxy Resin Conductive Coatings

In this work, the conductive coating was prepared by electrostatic spraying with graphene and Multi-walled carbon nanotube (MWCNTs) as conductive medium and epoxy resin powder as film-forming material, in order to solve the pro·blem of high content and uneven dispersity of conductive particles in conductive coatings prepared by brushing method. The resistance of the coating was measured by four probe method, the dispersity of conductive particles in the coating was analyzed by scanning electron microscope (SEM), and the conductive mechanism of the coating was analyzed by percolation theory model. The results show that the conductive particles can be dispersed evenly in the whole coating by electrostatic force. Meanwhile, the electrostatic force can also stretch the conductive particles in the coating along the direction of the thickness of that. The flake graphene is vertically arranged in the coating, and the curled MWCNTs forms the conductive network of "island-bridge" structure. The conductive particles laped each other to form a conductive path, which greatly reduced the content of conductive particles. The seepage threshold of graphene conductive coating was only 1.5 wt.%, which lower than that of the MWCNTs conductive coating, which is 3 wt.%. The resistance of epoxy coating containing with 0.5 wt.% graphene is 3397 Ω·m, and that of epoxy coating containing with 0.5 wt.% MWCNTs is 1049 Ω·m.