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​Utilization of Graphene on Wearable Technologies.

Graphene is one of the most used and known products to be launched in the industry as they are a huge part of almost all the industries and are benefitting them thoroughly. However, in recent times wearable technologies have proclaimed the usage of graphene in them is exceeding all the ways of success that come through it.

Wearable technologies are an integral part of today’s world and are being used at such a large scale. So to enhance the quality of production of wearable technologies, the utilization of graphene in their production has massively increased.

Ever since this has happened, wearable technologies have become famous and their uses have increased too. This is a fact fully one of the best uses of graphene and is paving way for the future success of graphene in the said field. However, graphene combined with other products makes wearable technologies one of the best products.

Introduction

In 2004, Graphene was isolated for the first time, becoming a new material. Graphite’s single layer makes up the graphene and that single layer is utilized in pencil lead. Graphite fragments were repeatedly separated by Geim and Novoselov with sticky tape for isolating the graphene for the first time until one-atom-thick flakes were made by them.

Remarkable structure

The structure of graphene is unique and remarkable, however, its discovery is simple. A 2-dimensional crystalline structure is possessed by graphene; the flat layer of atoms is made up of carbon’s hexagonal rings, giving it a structure like a ‘honeycomb’. 0.33 nanometres is the approximate thickness of the layer itself. It was a belief of many people that the existence of 2-dimensional molecules is not possible because of thermal instability, but graphene changed this belief.

Unique characteristics

Graphene has remarkable characteristics due to its structure. According to experiments, now graphene is the most robust material that we know, which makes graphene almost 200 times stronger as compared to steel because of graphene’s lack of defects and strong electrostatic forces. Due to its hexagonal, flat structure which provides the electrons with a little resistance against the movement, graphene is a remarkable conductor of electricity and heat. The weight of graphene is 0.77 milligrams per square meter only and it is a very strong, and lightweight material.

Graphene is extremely flexible. According to research, graphene can’t break even when it is stretched up to 25% of its original length. All of these characteristics of graphene are excellent on their own. Although, when all of them are combined in one material, it makes graphene an excellent material with excellent applications in industries of different types.

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Properties of graphene

Mechanical properties

Graphene’s inherent strength is another excellent characteristic of graphene. In comparison with A36 structural steel’s 400,000,000 and Aramid’s (Kevlar) 375,700,000 Pascals, the ultimate tensile strength of graphene is 130,000,000,000 Pascals (or 130 gigapascals). Thus, graphene is the strongest material that’s ever been discovered due to the strength of graphene’s 0.142 Nm-long carbon bonds.

Graphene is extremely strong but the interesting point is that its weight is 0.77 milligrams per square meter despite its strength which makes it an extremely light material. A 1 square meter of paper is almost 100 times heavier as compared to graphene. Graphene’s single sheet (which has a thickness relative to a single atom) weighs less than 1 gram and is sufficient in size for covering a complete field of football.

Electronic properties

Graphene has many beneficial characteristics. One of them is its zero-overlap semimetal (with both electrons and holes as charge carriers) with extremely high electrical conductivity. A total of 6 electrons are contained by the carbon atoms; 2 electrons in the outer shell and 2 of them in the inner shell. In an individual carbon atom, all of the 4 outer shell electrons are available for chemical bonding, however, in graphene, each of the carbon atoms is connected to the other 3 carbon atoms on the 1-dimensional plane, leaving 1 electron free and available for electronic conduction in the 3rd dimension.

The location of these highly mobile electrons is below and above the graphene sheet and they are known as pi (π) electrons. The overlapping of these pi orbitals takes place and carbon to carbon bonds in graphene are enhanced. Graphene’s electronic characteristics are fundamentally dictated by these pi orbitals’ anti-bonding and bonding (the conduction and valance bands).

Optical properties

Another interesting and rare characteristic of graphene is its capability of absorbing a rather large 2.3% white light, particularly considering that its thickness is of one atom only which is because of its already mentioned electronic characteristics; the electrons functioning like massless charge carriers with extremely high mobility. It was proved some years ago that the Fine Structure Constant determines the amount of white light that is absorbed, instead of being dictated by material specifics. Adding graphene’s another layer increases the white light’s amount that is absorbed by almost the same value i.e. 2.3%. Over the visible frequency range, the opacity of graphene is πα ≈ 2.3% which equates to a universal dynamic conductivity value of G=e2/4ℏ (±2-3%).

What is the current usage of Graphene?

The properties of graphene open a lot of doors for graphene so graphene can be utilized in numerous applications. It has been 15 years since its isolation and many of the products of graphene have come to the market since and every year, the expansion of graphene into new sectors continues.

Equipment

Graphene’s first appearance was in one of the markets in applications with low entry barriers, like sports equipment. Graphene is incorporated into a new tennis racket line’s frame due to its flexibility and strength by the multimillion-dollar company Head within this industry, graphene was incorporated into their honey sticks by Grays, graphene-improved bicycle tires are launched by Vittoria and Goodyear, and an extremely lightweight bicycle frame infused with graphene was previously showcased by standard graphene in Korea.

Thermal regulation

Graphene’s other early adopter was sports clothing because of graphene’s durability and thermal regulation in textiles, with Deewear initially resulting in the way along with Directa Plus. A sportswear brand, known as Inov-8, worked with the National Graphene Institute that is based in Manchester, UK, for releasing the first graphene-enhanced running show of the company in 2018, expanding into full range eventually. According to Inov-8, graphene-enhanced rubber is 50% more elastic and 50% stronger as compared to the elasticity and strength of regular rubber.

Graphene-based separation membranes

It has been long since the emergence of the idea of using graphene sheets containing nanopores as the saturation membranes from the theoretical simulation studies. Functionalized nanopores in the graphene monolayers were designed by Kral et al. Molecular dynamics simulations showed that they provide a highly selective passage of the hydrated ions. Only those ions can pass through these ultrasmall pores of ∼5 Å diameter that are partly stripped of their hydration spells. For instance, the passage of K+, Na+, and Li+ cations with 9:14:33 ratio by a fluorine-nitrogen-terminated pore, however, it also blocks the anion’s passage.

The passage of Br-,Cl-, F- anions with 0:17:33 ratios is allowed by the hydrogen-terminated pore however it also blocks the cation’s passage. In energy storage, molecular separation, and desalination systems, these nanopores can have potential applications.

Stretchable and Flexible micro batteries

Due to the massive uprise of low power devices and wearable technologies needing onboard energy, there should be a rapid emergence of stretchable and flexible micro batteries on the world market. The applicability field is very large without any doubt as the main impacted sectors will include sports, wellness, smart cards, medical and healthcare (medical diagnostic devices, medical sensors, and skin patches), electronic textile, soft and printed electronics, Internet-of-things (IoT), etc. Although, under mechanical and chemical strains, most of the micropower sources go through the electrical contact’s loss subsequently and the production of multiple fractures.

Overcoming technological issues

We need the conception of particular micro batteries that show high electrochemical performance with enhanced mechanical characteristics for overcoming these technological issues.Currently, the ideal choice of power sources for wearable electronics are the stretchable and flexible lithium-ion batteries (LIBs) because of high rate capability, long cycle life, and high power and energy densities, but there have been investigations on the other systems including aluminum-air batteries, silver-zinc batteries, and sodium-ion batteries too.

Literature review

Various approaches have been proposed in the literature to develop soft micro-batteries by utilizing various configurations like helically and wavy coiled spring structures, porous/sponge configuration, bridge-island battery design, origami, and kirigami. Textiles have been used for fabricating and designing electrochemical energy storage devices like LIBs and supercapacitors (SCs) because of their high surface area, lightweight, and high mechanical flexibility. Although, under stretched and bent conditions, challenges like surface’s lower covering by the low stability, multidirectional stretchability, and active material, still designs micro batteries with promising mechanical and electrochemical characteristics.

Nanostructured Electrodes for High Performance flexible and rigid micro batteries

All-solid state micro batteries currently have their volume’s major part occupied by the inactive materials like packaging, current collectors, and substrates, etc. 3D geometries at the sub-micrometer scale is envisioned as a better contact between the electrolyte and electrodes and it can be established for increasing their electrochemical performance. For small footprint areas, high power capability and energy density are indeed shown by the 3-dimensional microstructured batteries. 3-dimensional electrodes can be designed by proposing various approaches.

Nano-architecture materials

Nano-architecture materials like self-supported titania nanotubes were grown by Ti’s simple anodization and they can be further exploited for the fabrication of micro-batteries with advanced electrochemical characteristics. The all-solid-state LIB based on self-supported TiO2 as an anode, LNMO as a cathode, and a polymer electrolyte that is made up of polyethylene oxide carrying LiTFSI, was reported first by Plylahan et al. Different strategies were used by

Flexible and biocompatible high-performance solid-state micro-battery for  implantable orthodontic system | npj Flexible Electronicsthe same group for drastically improving this kind of battery’s performance.

Self-supported LTO-CNTs were explained by Liu et al. on a SS foil that is capable of functioning as an anode material for the flexible Li-ion micro battery. A template of ZnO hexagonal nanorod arrays was used first for growing TiO2 nanotubes on the SS foil substrate. Then, after post-annealing and chemical lithiation processes, the LTO nanotube arrays were attained.

Composites

LTO−CNTs composites were attained by glucose’s carbonization, adsorbed on the LTO nanotube’s surface. Good specific capacity is showed by the self-supported LTO-CNTs arrays at extremely fast rates because of the short Li+ diffusion path, good structural stability, and high surface area. A flexible separator was used in an organic liquid electrolyte to separate an LCO layer and LTO-CNTs arrays for obtaining a full lithium-ion micro battery. Under bent and flat states, a light-emitting diode (LED) can be powered by the micro battery according to the sources.

Additional works

There were reports of additional works based on arrays of 3-dimensional microstructured electrodes for the flexible Li-ion micro-batteries. A Lithium-ion micro battery was demonstrated by Pikul et al. in another work. The presence of a sacrificial porous scaffold micro battery is involved in this process and it serves as a template for NiSn and LiMnO’ssequential electrodeposition. The utilization of carbon-microelectromechanical systems (C-MEMS) is another promising method for the fabrication of 3-D micro-batteries.

Photolithography and Pyrolysis techniques

Pyrolysis techniques and photolithography were utilized for getting the carbon rods to function as both the anode and the current collector. Then, there was electrochemical polymerization of the PPYDBS films on one set of carbon arrays. Carbon rods were used as an anode to assemble the 3D micro battery, those rods were covered with a liquid electrolyte and an electrodeposited PPYDBS film as a cathode.

Graphene and Wearable Technology

According to researches, RFID tags for patients can be created by using graphene. Vitals like heart rate and body temperature can be monitored by the wearable, integrated with other 2D materials. They can help in the transmission of data to the station of the nurse wirelessly. Healthcare would be streamlined by simplifying the process for gathering the data of the patient. It is the most conductive, strongest, and thinnest material in the world. Integration of it into wearables will usher in a new era of devices. The potential of being mass-produced is possessed by graphene ink, and according to research, graphene ink can adhere to various materials – skin and clothing.

Electronic textiles

A new age of wearable technology is promised by electronic textiles that power, sense, or communicate other devices. However, current e-textiles make recycling or disposal tough as it heavily depends on metals like copper, silver, and gold. An effective metal-free alternative can be formed by using nanomaterials like carbon in graphene’s form.

Wearable electronics

Even while being repeatedly flexed, bent, stretched, and washed during usage, wearable electronics should continue working. Chemical vapor deposition (CVD) was used by researchers for the growth of multilayered graphene and transferred it onto a cellulose-based textile in order to create such kind of wearable electronic and devices from graphene. Graphene’s thin layers can be turned into antennas by using a coplanar waveguide (CPW) design approach, which can also be utilized in wearable communication systems for talking to various devices somewhere else on the external systems or the body.

Planar graphene antennas

Layer misalignment is avoided when planar graphene antennas are created with CPW, and it is easy integrating them with fabrics and textiles and is compatible with new production methods like lamination and other add-on textile methods. Chemical doping or external field is used to tune the device itself from the microwave to the terahertz range. According to the researchers, 6GHz of operational bandwidth is showed by the test devices, and that operational bandwidth is approximately double the value that has been reported previously for the graphene devices. As compared to screen-printed conductive textiles, better surface coverage is offered by the CVD-grown graphene sheets.

Prototype devices

Even on repeated blending, the prototype devices faced a slight change only in performance. The prototype devices were put through washability tests too. According to Ozden-Yenigun, the scale of multi-layer graphene synthesis is the major limitation left now.

Current Wearables Use Rigid Sensors That Limit Effectiveness

In recent years, the fame of wearable technology has significantly increased. There are predictions that by 2022, the United States market will value at $51.6 billion which shows a rapid growth at 15.51% CAGR from 2016 to 2022. The device monitors the vitals of the wearers as they are utilized for benefitting the health of the wearers. The device aids them in improving and tracking their fitness levels, and it also stops them from getting common health problems like stress-related complications, heart failure, hypertension, and more. Rigid sensors and electronics construct the current wearables and they have a soft outer shell. Current wearables are prevented by rigid sensors and electronics from being as accurate and efficient as they can be as there is no optimum contact of the sensors with the skin.

Overcoming the drawback

The Spanish team tries to overcome the drawback, they developed a sensor that is transparent and flexible and allows the collection of vitals’ most accurate and specific measurements. Spanish Team developed a system for achieving this by using ambient light. A sensor is made of graphene that is innovative and can detect that light, and it is covered with the semiconducting nanoparticle’s layer for measuring these vital signs.

Importance of graphene

Right now, the focus of the developers of the next generation of wearable devices is on finding out how 2-dimensional materials can be utilized for augmenting the designs of the technologies that are being used currently. There are various characteristics of the 2-dimensional materials that appeal to the improved wearables development, like stability, biocompatibility, mechanical flexibility, optic transparency, and electrical conductivity to the biological electrolytes. Graphene is an example of a 2-dimensional material and it is being successfully utilized for making tattoo-like devices that are capable of measuring numerous vitals with impressive accuracy.

A graphene-based supercapacitor that's also…. a t-shirt? – pv magazine  International

The Development of an Improved Device

Journal Science Advances recently published a study that outlined how the researchers made a revolutionary transparent and flexible wearable device that can deliver accurate and continuous measurements of vital signs like blood pulse oxygenation, heart rate, respiration rate, and exposure to ultraviolet radiation. The device’s benefits are that its read-out is formed on a connected device, and the device can function without any battery when charged without a wire through a phone.

Bracelet

The bracelet is made for adapting to the surface of the skin and allowing optimized contact for continuous measurements. A light sensor is incorporated in it which is flexible too and can utilize light information for determining the changes in the blood vessels’ volume because of the cardiac cycle and then it calculates the vitals by using this information. Moreover, a graphene health patch is developed by the researchers and that patch can adhere to the cellphone’s screen for giving real-time measurements from a finger’s touch.

Unique feature

The design’s most rare characteristic is that this design utilizes ambient light for the collection of measurements, and for enabling a device that promotes health marker’s continuous monitoring while consuming little energy. There was a construction of a flexible UV patch prototype by utilizing this core technology. This prototype also functions without a battery and is capable of collecting reliable, and continuous data which is then utilized for alerting the wearers of the danger of over-exposure.

Implications for the Healthcare’s Future

What the Barcelona team achieved will have an excellent and huge effect on the wearable technology’s landscape. There have been successful demonstrations of the graphene-quantum-dots usage in completely flexible wearable devices, and they have now the opportunity for the development of commercially ready wearable devices based on this technology that may allow establishing enhanced health-monitoring wearables.

Conclusion

Wearable technologies are highly beneficial for the industries that are taking a role in them but also for their consumers. Graphene is the very product that is contributing to the advancements of all types as its properties and characteristics are excellent in their nature which is extremely beneficial for the enhanced productivity of wearable technologies. Quality production of wearable technologies is important and plays an integral role in building up the industries.

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