Metallisation of Textiles and Protection of Conductive Layers: An Overview of Application Techniques

Terahertz conductivity mapping of thin films on smart textiles

Smart textiles that promise to become sensors and actuators for multiple applications are an active area of research. Conductive textiles formed by coating a fabric with a conductive film will play a key role in such applications. Here we present contactless mapping of the terahertz (THz) conductivity of thin conductive films deposited on textiles. These conductivity maps enable non-destructive assessment of the conductivity of such layers and therefore the identification and localization of non-uniformities in local conductivity. The THz measurements are quantitatively consistent with four-point probe measurements of the same areas.

Assessment of the Influence of Fabric Structure on Their Electro-Conductive Properties

Electro-conductive fabrics are key materials for designing and developing wearable smart textiles. The properties of textile materials depend on the production method, the technique which leads to high conductivity, and the structure. The aim of the research work was to determine the factors affecting the electrical conductivity of woven fabrics and elucidate the mechanism of electric current conduction through this complex, aperiodic textile material. The chemical composition of the material surface was identified using scanning electron microscopy energy dispersion X-ray spectroscopy. The van der Pauw method was employed for multidirectional resistance measurements. The coefficient was determined for the assessment of the electrical anisotropy of woven fabrics. X-ray micro-computed tomography was used for 3D woven structure geometry analysis. The anisotropy coefficient enabled the classification of electro-conductive fabrics in terms of isotropic or anisotropic materials. It was found that the increase in weft density results in an increase in sample anisotropy. The rise in thread width can lead to smaller electrical in-plane anisotropy. The threads are unevenly distributed in woven fabric, and their widths are not constant, which is reflected in the anisotropy coefficient values depending on the electrode arrangement. The smaller the fabric area covered by four electrodes, the fewer factors leading to structure aperiodicity.

Aluminum-Doped Zinc Oxide Improved by Silver Nanowires for Flexible, Semitransparent and Conductive Electrodes on Textile with High Temperature Stability

In order to facilitate the design freedom for the implementation of textile-integrated electronics, we seek flexible transparent conductive electrodes (TCEs) that can withstand not only the mechanical stresses encountered during use but also the thermal stresses of post-treatment. The transparent conductive oxides (TCO) typically used for this purpose are rigid in comparison to the fibers or textiles they are intended to coat. In this paper, a TCO, specifically aluminum-doped zinc oxide (Al:ZnO), is combined with an underlying layer of silver nanowires (Ag-NW). This combination brings together the advantages of a closed, conductive Al:ZnO layer and a flexible Ag-NW layer, forming a TCE. The result is a transparency of 20-25% (within the 400-800 nm range) and a sheet resistance of 10 Ω/sq that remains almost unchanged, even after post-treatment at 180 °C.

Electronic textiles: New age of wearable technology for healthcare and fitness solutions

Sedentary lifestyles and evolving work environments have created challenges for global health and cause huge burdens on healthcare and fitness systems. Physical immobility and functional losses due to aging are two main reasons for noncommunicable disease mortality. Smart electronic textiles (e-textiles) have attracted considerable attention because of their potential uses in health monitoring, rehabilitation, and training assessment applications. Interactive textiles integrated with electronic devices and algorithms can be used to gather, process, and digitize data on human body motion in real time for purposes such as electrotherapy, improving blood circulation, and promoting wound healing. This review summarizes research advances on e-textiles designed for wearable healthcare and fitness systems. The significance of e-textiles, key applications, and future demand expectations are addressed in this review. Various health conditions and fitness problems and possible solutions involving the use of multifunctional interactive garments are discussed. A brief discussion of essential materials and basic procedures used to fabricate wearable e-textiles are included. Finally, the current challenges, possible solutions, opportunities, and future perspectives in the area of smart textiles are discussed.

Toward Sustainable Wearable Electronic Textiles

Smart wearable electronic textiles (e-textiles) that can detect and differentiate multiple stimuli, while also collecting and storing the diverse array of data signals using highly innovative, multifunctional, and intelligent garments, are of great value for personalized healthcare applications. However, material performance and sustainability, complicated and difficult e-textile fabrication methods, and their limited end-of-life processability are major challenges to wide adoption of e-textiles. In this review, we explore the potential for sustainable materials, manufacturing techniques, and their end-of-the-life processes for developing eco-friendly e-textiles. In addition, we survey the current state-of-the-art for sustainable fibers and electronic materials (i.e., conductors, semiconductors, and dielectrics) to serve as different components in wearable e-textiles and then provide an overview of environmentally friendly digital manufacturing techniques for such textiles which involve less or no water utilization, combined with a reduction in both material waste and energy consumption. Furthermore, standardized parameters for evaluating the sustainability of e-textiles are established, such as life cycle analysis, biodegradability, and recyclability. Finally, we discuss the current development trends, as well as the future research directions for wearable e-textiles which include an integrated product design approach based on the use of eco-friendly materials, the development of sustainable manufacturing processes, and an effective end-of-the-life strategy to manufacture next generation smart and sustainable wearable e-textiles that can be either recycled to value-added products or decomposed in the landfill without any negative environmental impacts.

A Review of Electro Conductive Textiles Utilizing the Dip-Coating Technique: Their Functionality, Durability and Sustainability

The presented review summarizes recent studies in the field of electro conductive textiles as an essential part of lightweight and flexible textile-based electronics (so called e-textiles), with the main focus on a relatively simple and low-cost dip-coating technique that can easily be integrated into an existing textile finishing plant. Herein, numerous electro conductive compounds are discussed, including intrinsically conductive polymers, carbon-based materials, metal, and metal-based nanomaterials, as well as their combinations, with their advantages and drawbacks in contributing to the sectors of healthcare, military, security, fitness, entertainment, environmental, and fashion, for applications such as energy harvesting, energy storage, real-time health and human motion monitoring, personal thermal management, Electromagnetic Interference (EMI) shielding, wireless communication, light emitting, tracking, etc. The greatest challenge is related to the wash and wear durability of the conductive compounds and their unreduced performance during the textiles' lifetimes, which includes the action of water, high temperature, detergents, mechanical forces, repeated bending, rubbing, sweat, etc. Besides electrical conductivity, the applied compounds also influence the physical-mechanical, optical, morphological, and comfort properties of textiles, depending on the type and concentration of the compound, the number of applied layers, the process parameters, as well as additional protective coatings. Finally, the sustainability and end-of-life of e-textiles are critically discussed in terms of the circular economy and eco-design, since these aspects are mainly neglected, although e-textile' waste could become a huge problem in the future when their mass production starts.

Toward autonomous wearable triboelectric systems integrated on textiles

One of the major requirements of smart textiles is to achieve the integration of an energy source for powering embedded electronic systems. In this context, textile triboelectric nanogenerators (T-TENGs) are particularly well suited to imperceptibly play this role in the core of textiles, making them highly appealing for the development of future autonomous systems. This article reviews the wide range of topics related to T-TENGs technology starting from triboelectric generation (textile device and behavior modeling) up to the complete integration of power transfer (rectifier) circuits on textiles. The modeling part deals with the current mathematical models of the triboelectric charge transfer in order to highlight efficient power transfer circuits. Then the materials and architectures used to fabricate different types of T-TENGs are described. Finally, the methods and technologies to seamlessly integrate the power transfer circuit into textiles are discussed: from realizing electrically conductive tracks through to integrating electronic component on textiles.

Electronic Features of Cotton Fabric e-Textiles Prepared with Aqueous Carbon Nanofiber Inks

Cotton woven fabrics functionalized with aqueous inks made with carbon nanofibers (CNFs) and anionic surfactant are prepared via dip-coating followed by heat treatment, and their electronic properties are discussed. The e-textiles prepared with the inks made with the highest amount of CNFs (6.4 mg mL^–1) show electrical conductivities (σ) of ∼35 S m^–1 and a negative Seebeck (S) of −6 μV K^–1 at 30 °C, which means that their majority carriers are electrons. The σ(T) of the e-textiles from 30 to 100 °C shows a negative temperature effect, interpreted as a thermally activated hopping mechanism across a random network of potential wells by means of the 3D variable range hopping (VRH) model. Likewise, their S(T) from 30 to 100 °C shows a negative temperature effect, conveniently depicted by the same model proposed for describing the negative Seebeck of doped multiwall carbon nanotube mats. From this model, it is deduced that the cause of the negative Seebeck in the e-textiles may arise from the contribution of the impurities found in the as-received CNFs, which cause sharply varying and localized states at approximately 0.085 eV above their Fermi energy level (E_F). Moreover, the possibility of a slight n-doping from the cellulose fibers of the fabrics and the residuals of the anionic surfactant onto the most external CNF graphitic shells present in the e-textiles is also discussed with the help of the σ(T) and S(T) analysis.

Selective Electroless Copper Plating of Ink-Jet Printed Textiles Using a Copper-Silver Nanoparticle Catalyst

The electroless copper plating of textiles, which have been previously printed with a catalyst, is a promising method to selectively metallise them to produce high-reliability e-textiles, sensors and wearable electronics with wide-ranging applications in high-value sectors such as healthcare, sport, and the military. In this study, polyester textiles were ink-jet printed using differing numbers of printing cycles and printing directions with a functionalised copper–silver nanoparticle catalyst, followed by electroless copper plating. The catalyst was characterised using Transmission Electron Microscopy (TEM) and Ultraviolet/Visible (UV/Vis) spectroscopy. The electroless copper coatings were characterised by copper mass gain, visual appearance and electrical resistance in addition to their morphology and the plating coverage of the fibres using Scanning Electron Microscopy (SEM). Stiffness, laundering durability and colour fastness of the textiles were also analysed using a stiffness tester and Launder Ometer, respectively. The results indicated that in order to provide a metallised pattern with the desired conductivity, stiffness and laundering durability for e-textiles, the printing design, printing direction and the number of printing cycles of the catalyst should be carefully optimised considering the textile’s structure. Achieving a highly conductive complete copper coating, together with an almost identical and sufficiently low stiffness on both sides of the textile can be considered as useful indicators to judge the suitability of the process.

Fabrication of functional polyester fibers by sputter deposition with stainless steel

The effects of sputtering technological parameters (sputtering power, pressure, and time) on properties of stainless steel (SS)-sputtered polyester (PET) fiber were investigated. The variations in properties such as surface morphology, tensile strength, abrasion resistance, and electromagnetic shielding effectiveness of the prepared PET fiber sputtered under various parameters were discussed. The results indicated that the uniformity and denseness of the sputtered SS film were positively dependent upon the predetermined sputtering variables. The properties such as the breaking strength and abrasion resistance of SS-sputtered PET were remarkably enhanced as compared to the pristine one. It was found that the disorientation of macromolecules in fiber was mainly responsible for the deteriorated strength following wet and/or dry heating. In addition, a woven fabric composed of SS-sputtered fiber exhibited electromagnetic shielding capability. This research indicates that the metal deposition onto textile surfaces using magnetron sputtering is a straightforward approach for potential use in multifunctional materials.

Digitally-embroidered liquid metal electronic textiles for wearable wireless systems

Electronic textiles capable of sensing, powering, and communication can be used to non-intrusively monitor human health during daily life. However, achieving these functionalities with clothing is challenging because of limitations in the electronic performance, flexibility and robustness of the underlying materials, which must endure repeated mechanical, thermal and chemical stresses during daily use. Here, we demonstrate electronic textile systems with functionalities in near-field powering and communication created by digital embroidery of liquid metal fibers. Owing to the unique electrical and mechanical properties of the liquid metal fibers, these electronic textiles can conform to body surfaces and establish robust wireless connectivity with nearby wearable or implantable devices, even during strenuous exercise. By transferring optimized electromagnetic patterns onto clothing in this way, we demonstrate a washable electronic shirt that can be wirelessly powered by a smartphone and continuously monitor axillary temperature without interfering with daily activities.

Polymer-Based Electrophoretic Deposition of Nonwovens for Medical Applications: The Effect of Carrier Structure, Solution, and Process Parameters

Hyaluronate and alginate are non-toxic and biocompatible polymers, which can be used for surface modification and functionalization of many kinds of materials. Electrophoretic deposition (EPD) has several advantages, including its versatility, simplicity, and ability to coat substrates with complex shapes, and is used for the creation of antimicrobial or hydrophobic coatings on metallic biomaterials, among other applications. However, its utilization for applying biopolymer layers on textiles is very limited due to the more complex structure and spatial characteristics of fibrous materials. The aim of this research was to analyze the effects of selected EPD process parameters and the structural characteristics of fibrous carriers on the kinetics of the process and the microscopic characteristics of the deposited layers. The influence of solution characteristics, process parameters, and carrier structures obtained using two different techniques (melt blown and spun-bonded) were analyzed. The morphology and structure of the created deposits were analyzed using scanning electron microscopy and computed tomography, and molecular structure analysis was performed with Fourier Transform Infrared spectroscopy. The surface mass and thickness of fibrous poly (lactic acid)-based carriers were analyzed in accordance with the respective standards. This study serves as a basis for discussion and further development of this method with regard to fibrous materials for medical applications.