Solution Deposition of Conformal Gold Coatings on Knitted Fabric for E-Textiles and Electroluminescent Clothing

The vision for wearable electronics involves creating an imperceptible boundary between humans and devices. Integrating electronic devices into clothing represents an important path to this vision; however, combining conductive materials with textiles is challenging due to the porous structure of knitted textiles. Stretchability depends on maintaining the void structure between the yarns of the fabric; filling these voids with conductive materials stiffens the textile and can lead to detrimental cracking. The authors demonstrate the solution-based metallization of a knitted textile that conformally coats individual fibers with gold, leaving the void structure intact. The resulting gold-coated textile is highly conductive, with a sheet resistance of 1.07 Wsq-1in the course direction. The resistance decreases by 80% when the fabric is stretched to 15% strain, and remains at this value to 160% strain. This outstanding combination of stretchability and conductivity is accompanied by durability to wearing, sweating, and washing. Low-cost screen printing of a wax resist is demonstrated to produce patterned gold textiles suitable for electrically connecting discrete devices in clothing. The fabrication of electroluminescent fabric by depositing layers of device materials onto the gold-coated textile is furthermore demonstrated, intimately merging device functionality with textiles for imperceptible wearable devices

Ready-to-wear strain sensing gloves for human motion sensing

Integrating soft sensors with wearable platforms is critical for sensor-based human augmentation, yet the fabrication of wearable sensors integrated into ready-to-wear platforms remains underdeveloped. Disposable gloves are an ideal substrate for wearable sensors that map hand-specific gestures. Here, we use solution-based metallization to prepare resistive sensing arrays directly on off-the-shelf nitrile butadiene rubber (NBR) gloves. The NBR glove acts as the wearable platform while its surface roughness enhances the sensitivity of the overlying sensing array. The NBR sensors have a sheet resistance of 3.1 ± 0.6 Ω/sq and a large linear working range (two linear regions ≤70%). When stretched, the rough NBR substrate facilitates microcrack formation in the overlying metal, enabling high gauge factors (62 up to 40% strain, 246 from 45 - 70% strain) that are unprecedented for metal film sensors. We apply the sensing array to dynamically monitor gestures for gesture differentiation and robotic control

Protocol for fabricating electroless nickel immersion gold strain sensors on nitrile butadiene rubber gloves for wearable electronics

This protocol describes the fabrication of patterned conductive gold films on nitrile butadiene rubber (NBR) gloves for wearable strain sensors using electroless nickel immersion gold (ENIG) plating, a solution-based metallization technique. The resulting NBR/ENIG films are strain sensitive; resistance measurements of a patterned sensing array can be used to map human hand motions. This protocol also describes challenges related to the ENIG process and troubleshooting steps to achieve conformal gold films for strain sensing over a large working range. For complete details on the use and execution of this protocol, please refer to Mechael et al. (2021)

Stretchable Ultrasheer Fabrics as Semitransparent Electrodes for Wearable Light-Emitting e-Textiles with Changeable Display Patterns

Despite the development throughout human history of a wealth of textile materials and structures, the porous structures and non-planar surfaces of textiles are often viewed as problematic for the fabrication of wearable e-textiles and smart clothing. Here, we demonstrate a new textile-centric design paradigm in which we use the textile structure as an integral part of wearable device design. We coat the open framework structure of an ultrasheer knitted textile with a conformal gold film using solution-based metallization to form gold-coated ultrasheer electrodes that are highly conductive (3.6 ± 0.9 Ω/sq) and retain conductivity to 200% strain with R/R0 \u3c 2. The ultrasheer electrodes produce wearable, highly stretchable light-emitting e-textiles that function to 200% strain. Stencil printing a wax resist provides patterned electrodes for patterned light emission; furthermore, incorporating soft-contact lamination produces light-emitting textiles that exhibit, for the first time, readily changeable patterns of illumination

Wearable E-Textiles Using a Textile-Centric Design Approach

ConspectusElectronics worn on the body have the potential to improve human health and the quality of life by monitoring vital signs and movements, displaying information, providing self-illumination for safety, and even providing new routes for personal expression through fashion. Textiles are a part of daily life in clothing, making them an ideal platform for wearable electronics. The acceptance of wearable e-textiles hinges on maintaining the properties of textiles that make them compatible with the human body. Beneficial properties such as softness, stretchability, drapability, and breathability come from the 3D fibrous structures of knitted and woven textiles. However, these structures also present considerable challenges for the fabrication of wearable e-textiles. Fabrication methods used for modern electronic devices are designed for 2D planar substrates and are mostly unsuitable for the complex 3D structures of textiles. There is thus an urgent need to develop fabrication methods specifically for e-textiles to advance wearable electronics. Solution-based fabrication methods are a promising approach to fabricating wearable e-textiles, especially considering that textiles have been successfully modified using pigmented dyes in dyebaths and printing inks for thousands of years. In this Account, we discuss our research on the solution-based electroless metallization of textiles to fabricate conductive e-textiles that are building blocks for e-textile devices. Electroless metallization solutions fully permeate textile structures to deposit metallic coatings on the surfaces of individual textile fibers, maintaining the inherent textile structures and wearability. The resulting e-textiles are highly conductive, soft, and stretchable. We furthermore discuss ways to turn the challenges related to textile structures into new opportunities by strategically using the structural features of textiles for e-textile device design. We demonstrate this textile-centric approach to designing e-textile devices using two examples. We discuss how the structure of an ultrasheer knitted textile forms a useful framework for new e-textile transparent conductive electrodes and describe the implementation of these electrodes to form highly stretchable light-emitting e-textiles. We also show how the structural features of velour fabrics form the basis for an innovative island-bridge strain-engineering structure that enables the integration of brittle electroactive materials and protects them from strain-induced damage, leading to the fabrication of stretchable textile-based lithium-ion battery electrodes. With the vast variety of textile structures available, we highlight the opportunities associated with this textile-centric design approach to advance textile-based wearable electronics. Such advances depend on a deep understanding of the relationship between the textile structure and the device requirements, which may potentially lead to the development of new textile structures customized to support specific devices. We conclude with a discussion of the challenges that remain for the future of e-textiles, including durability, sustainability, and the development of performance standards

Stretchable metal films

The current growth of the wearable electronics market has inspired the development of soft and stretchable interfacing between electronics and the human body. Stretchable conductors are critical to the evolution of stretchable and wearable electronics. In this topical review, we discuss notable contributions to the field of stretchable metal films. Although the high conductivity of metals is an asset in electronic devices, their mechanical properties are not readily compatible with stretchable devices. We discuss the two main approaches to preserve conductivity during strain: conversion of stretching to bending strain and using topography to control cracking. These approaches lead to two contrasting electrical responses to mechanical deformation, and we discuss the application of these responses in devices as interconnects and sensors

Velour Fabric as an Island-Bridge Architectural Design for Stretchable Textile-Based Lithium-ion Battery Electrodes

The advancement of wearable electronics depends on the seamless integration of lightweight and stretchable energy storage devices with textiles. Integrating brittle energy storage materials with soft and stretchable textiles, however, presents a challenging mechanical mismatch. It is critical to protect brittle energy storage materials from strain-induced damage and at the same time preserve the softness and stretchability of the functionalized e-textile. Here, we demonstrate the strategic use of a warp-knitted velour fabric in an island-bridge architectural strain-engineering design to prepare stretchable textile-based lithium-ion battery (LIB) electrodes. The velour fabric consists of a warp-knitted framework and a cut pile. We integrate the LIB electrode into this fabric by solution-based metallization to create the warp-knitted framework current collector bridges followed by selective deposition of the brittle electroactive material CuS on the cut pile islands . As the textile electrode is stretched, the warp-knitted framework current collector elongates, while the electroactive cut pile fibers simply ride along at their anchor points on the framework, protecting the brittle CuS coating from strain and subsequent damage. The textile-based stretchable LIB electrode exhibited excellent electrical and electrochemical performance with a current collector sheet resistance of 0.85 ± 0.06 ω/sq and a specific capacity of 400 mAh/g at 0.5 C for 300 charging-discharging cycles as well as outstanding rate capability. The electrical performance and charge-discharge cycling stability of the electrode persisted even after 1000 repetitive stretching-releasing cycles, demonstrating the protective functionality of the textile-based island-bridge architectural strain-engineering design

Ready-to-wear strain sensing gloves for human motion sensing

Summary: Integrating soft sensors with wearable platforms is critical for sensor-based human augmentation, yet the fabrication of wearable sensors integrated into ready-to-wear platforms remains underdeveloped. Disposable gloves are an ideal substrate for wearable sensors that map hand-specific gestures. Here, we use solution-based metallization to prepare resistive sensing arrays directly on off-the-shelf nitrile butadiene rubber (NBR) gloves. The NBR glove acts as the wearable platform while its surface roughness enhances the sensitivity of the overlying sensing array. The NBR sensors have a sheet resistance of 3.1 ± 0.6 Ω/sq and a large linear working range (two linear regions ≤70%). When stretched, the rough NBR substrate facilitates microcrack formation in the overlying metal, enabling high gauge factors (62 up to 40% strain, 246 from 45 - 70% strain) that are unprecedented for metal film sensors. We apply the sensing array to dynamically monitor gestures for gesture differentiation and robotic control

Heterogeneous Surface Orientation of Solution-Deposited Gold Films Enables Retention of Conductivity with High Strain - A New Strategy for Stretchable Electronics

Stretchable electronic devices rely on stretchable conductors to form device interconnects and electrodes that maintain electrical performance during deformation. Although the high conductivity of metals makes them desirable materials for these applications, the lack of intrinsic stretchability of metals is a fundamental problem in stretchable electronics. Research efforts to impart stretchability to metal films on elastomers have involved configuring the films into wavy features that unbend with strain or using high surface roughness to engineer how cracks form in metal films under strain. However, the topographies used in these approaches cause problems with integrating these metal films as electrodes in thin-film devices. This paper presents a new, simple, and low-cost strategy for the fabrication of stretchable gold films with planar topography that remain highly conductive to 95% elongation. Using solution-based electroless plating to deposit gold films on the elastomer poly(dimethylsiloxane) results in a heterogeneous crystalline surface texture with misoriented grains that are strong barriers to dislocation movement. Under strain, the misoriented grains cause the formation of a unique nanoscale cracking pattern that is remarkably effective at preserving conductivity. We demonstrate that this performance, coupled with the planar topography of these gold films, makes them suitable as electrodes in intrinsically stretchable light-emitting devices

From Chlorinated Solvents to Branched Polyethylene: Solvent-Induced Phase Separation for the Greener Processing of Semiconducting Polymers

Despite having favorable optoelectronic and thermomechanical properties, the wide application of semiconducting polymers still suffers from limitations, particularly with regards to their processing in solution which necessitates toxic chlorinated solvents due to their intrinsic low solubility in common organic solvents. This work presents a novel greener approach to the fabrication of organic electronics without the use of toxic chlorinated solvents. Low-molecular-weight non-toxic branched polyethylene (BPE) is used as a solvent to process diketopyrrolopyrrole-based semiconducting polymers, then the solvent-induced phase separation (SIPS) technique is adopted to produce films of semiconducting polymers from solution for the fabrication of organic field-effect transistors (OFETs). The films of semiconducting polymers prepared from BPE using SIPS show a more porous granular morphology with preferential edge-on crystalline orientation compared to the semiconducting polymer film processed from chloroform. OFETs based on the semiconducting films processed from BPE show similar device characteristics to those prepared from chloroform without thermal annealing, confirming the efficiency and suitability of BPE to replace traditional chlorinated solvents for green organic electronics. This new greener processing approach for semiconducting polymers is potentially compatible with different printing techniques and is particularly promising for the preparation of porous semiconducting layers and the fabrication of OFET-based electronics