Featured paper: Conductive cotton thread for sewing wearable electronics.

SEM image of a conductive thread.
SEM image of a conductive thread.

The “old-fashioned” sewing thread universally used, for example, to sew buttons, has recently been transformed by a Brazilian scientific team into an electrically conductive and multifunctional material. In fact, the various uses of this new sewing thread go far beyond sewing. It works very well as a mini electric heater, as a component of supercapacitors (devices that store and release energy, similar to batteries) and as a bactericidal agent. In addition, the thread is flexible and comfortable to the touch, and retains its electronic properties even after being washed, twisted, curled or folded repeatedly.

With these characteristics, this fiber can play an important role in wearable electronics – the set of electronic devices designed to be worn on the human body, incorporated into clothing or accessories.

“As the thread is a basic element for the design of textiles, we imagine that any wearable product can make use of this technology”, says Helinando Pequeno de Oliveira, a professor at the Brazilian Federal University of the Vale de São Francisco (Univasf) and leader of the scientific team that developed the conductive and bactericidal thread. Together with three other authors, all linked to Univasf, Oliveira authors an article reporting this work, which was recently published in the journal ACS Applied Materials and Interfaces.

The conductive  and bactericidal fiber of Oliveira and his collaborators is made of a composite material: cotton thread of 0.5 mm diameter, coated with carbon nanotubes and polypyrrole. The resulting material presents, in addition to high electrical conductivity, good electrochemical activity – necessary characteristic for it to be used in supercapacitors.

To make the conductive  fiber, the Univasf team developed a very simple process, formed by two main stages. In the first step, pieces of cotton thread are submerged in a paint of carbon nanotubes, previously modified in order to increase their interaction with the cotton. As a result, the thread is coated by a continuous network of interconnected nanotubes.

The second step is intended to coat the fibers with a second material: polypyrrole. To do this, a solution is initially formed by pyrrole and the solvent hexane, in which the fibers coated with nanotubes are submerged. Thereafter, another solution is poured over this preparation. The second solution consists of water and some compounds, which will be incorporated in very small amounts into the chemical composition of the polypyrrole in a process called “doping” of the material. At the interface between both solutions, which do not mix, the small pyrrole molecules are bound together, resulting in the formation of polypyrrole macromolecules that are deposited on the surface of the fibers. This process, in which a polymer forms at the interface between two solutions, is called “interfacial polymerization”. “Given the good polypyrrole doping level (optimized for this synthesis) and its strong interaction with the functionalized nanotubes, the resulting fibers display excellent electrical properties,” says Professor Oliveira.

The scientific team also produced some variants of this sewing conductive  thread. For example, a fiber without carbon nanotubes and another fiber whose polypyrrole coating was produced by means of non-interfacial polymerization. However, the lines with carbon nanotubes and interfacial polymerization showed the best electrical and electrochemical performance.

Heaters and supercapacitors made of cotton fibers

First and second generation supercapacitor prototypes based on conductive sewing lines.
First and second generation supercapacitor prototypes based on conductive sewing lines.

“The high electrical conductivity (together with the good porosity of the material) made of the material a great prototype for application in electrodes of supercapacitors”, says Oliveira. “These properties also made it possible to use it as an electric heater with very low operating voltages (of the order of a few volts). In addition to these applications, the antibacterial potential of the matrix”, he adds.

In addition to testing the performance of the conductive and bactericidal fiber in isolation in the laboratory, Oliveira and his collaborators developed a proof of concept. “We used a needle to sew the thread in a glove”, says the professor. With this we could monitor the temperature that the hand, wearing this glove, would reach when we connected the device to a power supply,” he explains.

The heating system tested on the glove can be adapted to a variety of contexts, such as an ambulatory version of thermotherapy (therapeutic heating of body regions, which is often used in physiotherapy sessions)with the added advantage of antibacterial action. This property is particularly interesting in materials that are used in contact with the skin, since, in this way, they avoid diseases and odors. In the case of polypyrrole, the action occurs when the material electrostatically attracts the bacteria and promotes the breakdown of its cell wall, inhibiting its proliferation.

Local heating (in degrees centigrade) provided by the conductive thread sewn to the index finger of the glove, after applying an electric voltage of 12 V.
Local heating (in degrees centigrade) provided by the conductive thread sewn to the index finger of the glove, after applying an electric voltage of 12 V.

A possible wearable product based on the conductive sewing thread is a thermal jacket.It could be powered by a solar cell incorporated into the jacket, or by means of triboelectric devices, which would reap the energy generated by the user’s movement of the jacket.The resulting energy would be stored in a supercapacitor made with the conductive fiber. Tailored to the jacket, the supercapacitor would provide electricity to the heater when needed.
Another example is the energy storage t-shirt, in which Professor Oliveira’s group is currently working to generate a marketable product. We are currently optimizing the production of supercapacitors in pieces of cotton and lycra fabrics as a way to connect them directly to portable power generators, thus enabling the development of energy storage t-shirts,” says Oliveira.

Science and technology developed in the backlands

The work reported in the ACS Appl. Mater. Interfaces and their developments were fully carried out at the Materials Science Research Institute of Univasf, on the campus of the municipality of Juazeiro, located in the north of the state of Bahia. Univasf, which has six campuses located in the interior of the states of Bahia, Pernambuco and Piauí, was created in 2002 and inaugurated in 2004. In the same year, Oliveira became a professor at the institution.

The development of the conductive cotton lines was born from a thread of research on electronics and flexible devices, created in 2016. In 2017, the idea became the theme of the master’s work of Ravi Moreno Araujo Pinheiro Lima, guided by Professor Helinando Oliveira, within the Postgraduate Program in Materials Science at Univasf – Juazeiro, created in 2007. Post-doc José Jarib Alcaraz Espinoza, who was optimizing syntheses of conductive polymers for supercapacitors, adapted a methodology to interfacial polymerization in cotton. With this, the researchers realized that the conductor lines worked as good supercapacitor electrodes, and fabricated these devices. At the same time, with the collaboration of Fernando da Silva Junior, a doctoral student of the institutional postgraduate program Northeast Network of Biotechnology, the team tested the action of the material against the bacterium Staphylococcus aureus, responsible for a series of infections of varying degrees of severity not human.

“These results reflect Brazil’s investment in the internalization of its network of federal teaching and research institutions. With this, the migration of the sertanejo towards the great capitals in the search for knowledge has been reduced. Now there is also more science being produced in the northeastern backlands”, says Professor Oliveira. “However, recent cuts in S & T have launched a huge cloud of uncertainty about the future of science in the country (and in particular about these young institutions). The Brazilian government does not have the right to throw so many dreams in the trash. Science needs to overcome this crisis,” completes the researcher.

Photo of the research group led by Professor Oliveira at the Institute for Research in Materials Science. To the right, in blue, the authors of the article.
Photo of the research group led by Professor Oliveira at the Institute for Research in Materials Science. To the right, in blue, the authors of the article.

[Paper: Multifunctional Wearable Electronic Textiles Using Cotton Fibers with Polypyrrole and Carbon Nanotubes. Ravi M. A. P. Lima, Jose Jarib Alcaraz-Espinoza , Fernando A. G. da Silva, Jr., and Helinando P. de Oliveira. ACS Appl. Mater. Interfaces, 2018, 10 (16), pp 13783–13795. DOI: 10.1021/acsami.8b04695]

Featured paper: Advanced material for ultra-capacity supercapacitors.

[Paper: One-step electrodeposited 3D-ternary composite of zirconia nanoparticles, rGO and polypyrrole with enhanced supercapacitor performance. Alves, Ana Paula P.; Koizumi, Ryota; Samanta, Atanu; Machado, Leonardo D.; Singh, Abhisek K.; Galvao, Douglas S.; Silva, Glaura G.; Tiwary, Chandra S.; Ajayan, Pulickel M. NANO ENERGY, volume 31, January 2017, 225–232. DOI: 10.1016/j.nanoen.2016.11.018.]

Advanced material for ultra-capacity supercapacitors.

Supercapacitors are electrical storage devices with a particular feature of releasing large amounts of energy in a short time interval. They are already used, for example, in electric or hybrid vehicles, camera flashes and elevators, but they can still be improved – largely with the contribution of Materials Science and Technology – for current and potential applications. Putting it simply, a supercapacitor consists of two electrodes, positive and negative, separated by a substance containing positive and negative ions (the electrolyte).

An article recently published in the scientific journal Nano Energy (Impact Factor 11,553) reports on a contribution from an international and interdisciplinary scientific team to develop materials that improve the performance of supercapacitors. Using a simple and easily scalable process, the team of researchers from Brazil, the United States and India produced electrodes made of a composite material composed of polypyrrole (PPi), reduced graphene oxide (rGO) and zirconium oxide (ZrO2) nanoparticles. By combining the three materials, the scientists were able to generate a large surface area and high porosity electrode – basic characteristics to promote the interaction of the electrolyte ions with the surface of the electrodes and therefore enhance the performance of the supercapacitor.

“Our unique contribution was the synthesis, in a single and simple stage of electrodeposition, of a hybrid containing graphene, zirconium oxide and polypyrrole, and the experimental demonstration of considerable gains in electrochemical properties, parallel to the theoretical modeling in order to understand the role of the components of the material”, states Glaura Goulart Silva, professor in the Department of Chemistry at the Federal University of Minas Gerais (UFMG) and a corresponding author of the paper.

In addition to preparing samples of the ternary (i.e., composed of three elements) composite PPi/rGO/ZrO2, using the same method for comparison purposes, the team prepared samples of the PPi/rGO binary composite, and pure polypyrrole samples. The three materials were analyzed using XPS (spectroscopy of X-ray excited photoelectrons), SEM (Scanning Electron Microscopy), Raman spectroscopy and transmission electron microscopy to determine their composition, structure and morphology.

As seen in the SEM images of the figure below, the scientists noted that the addition of graphene oxide and zirconia nanoparticles significantly changed the morphology of the material. While the pure polypyrrole had formed a cracked, wire-like film, the graphene composite had a granular morphology, with no cracks, and the zirconium oxide material had a leaf-like appearance.

At the end of the experimental stage of the study, the scientists performed a series of tests to measure the performance of the three materials as supercapacitors. The results showed that the capacity to store electrical charges (capacitance) had increased up to 100% in the ternary composite with respect to the polypyrrole. Moreover, instead of decreasing this performance due to the use of the electrode, it increased by 5% after 1,000 recharges in the binary and ternary composites.

This was the first paper that presented the introduction of zirconium oxide nanoparticles in polypyrrole and graphene electrodes for supercapacitors. Therefore, the team performed computational modeling to analyze the role of zirconium oxide in the performance of the composite. The simulations confirmed the beneficial effects of the nanoparticles on the stability of the material, directly related to extending the life of the electrodes.

Illustrative diagram of charge storage and interaction of ions near the surface of pure polypyrrole electrodes (PPi), reduced graphene oxide (PPi/rGO) and polypyrrole PPi/rGO/ZrO2 (above), based on the morphology associated with the SEM images of the surface of the electrodes with the respective materials under carbon fiber substrate (below). Image by Ana Paula Pereira Alves for her PhD thesis.
Above, illustrative diagram of charge storage and interaction of ions near the surface of pure PPi electrodes, PPi/rGO electrodes, and PPi/rGO/ZrO2 electrodes, based on the morphology associated with the SEM images of the surface of the electrodes with the respective materials under carbon fiber substrate (below). Image by Ana Paula Pereira Alves for her PhD thesis.

“There is great potential in the application of these new composites in supercapacitors due to the need to increase the energy density provided by the device, in parallel with its miniaturization,”declares Professor Goulart Silva. “The alternative developed in the work in question allows better performance in terms of cycling stability with gains in the safety of the supercapacitor. The use of supercapacitors and batteries in electric and hybrid cars is one of the technological fronts where these materials can be applied,” she adds.

From the reader's left: Professor Glaura Goulart Silva (UFMG), Professor Pulickel Ajayan (Rice University) and Ana Paula Pereira Alves, a recently graduated doctor from UFMG.
From the reader’s left: Professor Glaura Goulart Silva (UFMG), Professor Pulickel Ajayan (Rice University) and Ana Paula Pereira Alves, a recently graduated doctor from UFMG.

The work is part of the doctorate in Chemistry of Ana Paula Pereira Alves, conducted with the guidance of Professor Goulart Silva and defended in February of this year at UFMG with a thesis about synthesis and characterization of advanced materials for supercapacitors. During her doctoral work at the University of Minas Gerais, Pereira Alves carried out intensive training in synthesis techniques and physical-chemical analysis of conjugated polymers and graphene and in the characterization of supercapacitors. In 2015, she went to the United States for a one-year “sandwich” internship, with the support of the National Council for Scientific and Technological Development (CNPq), in the Department of Materials Science and Nanoengineering at Rice University, in the research group of Professor Pulickel Ajayan (researcher with h=139 index according to Google Scholar), who has collaborated with Professor Goulart Silva’s group since 2010. “Professor Ajayan has systematically proposed radical innovations in synthesis and design of batteries and supercapacitors, with significant international impact in the area,” she adds.

The experimental work reported in the paper was carried out at Rice University, with the presence of all authors, including those from Brazil and India, and also Professor Goulart Silva, who was there in February 2016, with the support of Minas Gerais Research Foundation (Fapemig). “The highly interdisciplinary environment of the Department of Materials Science and NanoEngineering at Rice made possible for the engineers, physicists, and chemists to come together to work on a current major problem.”, says Goulart Silva.

The computational modeling was carried out by Brazilian researchers from the State University of Campinas (Unicamp) and the Federal University of Rio Grande do Norte (UFRN) –among them Professor Douglas Galvão (Unicamp), who has maintained a scientific collaboration with Professor Ajayan since before the beginning of this research.

“I consider this work to be an excellent example of success, where the competence of the Brazilian groups joined that of a highly productive and impactful group in the international scenario and complement each other,” declares Goulart Silva. “The stability and increase of investments in research and development in Brazil are essential for endeavors as this to be widespread. Research is an investment that needs to be done over the long term, without setbacks, to enable a high rate of return in terms of materials, technologies and highly qualified people. Ana Paula Alves is now a young doctor in search of the opportunity to put together her research group and hence train new students and hence contribute to face the challenges of our country,” reaffirms Goulart Silva.