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: Nanosheets and nanoparticles interconnected for wearable electronics.


[Paper: Self-Assembled and One-Step Synthesis of Interconnected 3D Network of Fe3O4/Reduced Graphene Oxide Nanosheets Hybrid for High-Performance Supercapacitor Electrode. Rajesh Kumar, Rajesh K. Singh, Alfredo R. Vaz, Raluca Savu, Stanislav A Moshkalev. ACS APPLIED MATERIALS & INTERFACES. 2017, 9, 8880 – 8890. DOI: 10.1021/acsami.6b14704].

Nanosheets and nanoparticles interconnected for wearable electronics

A team of researchers from the State University of Campinas (Unicamp), in Brazil, and a researcher from the Central University of Himachal Pradesh (CUHP), in India, have developed a flexible and tiny high-performance supercapacitor with a hybrid material made of graphene oxide (GO) nanosheets and iron oxide (Fe3O4) nanoparticles. The work was recently reported in the journal Applied Materials & Interfaces (impact factor 7.145), of the American Chemical Society.

“The main contribution of this work is for the new and really promising research area of flexible electronics”, says PhD Rajesh Kumar, researcher at Unicamp’s Center for Semiconductor Components (CSC) and corresponding author of the article. “Since capacitors are among the main components of electronic devices, these performant and flexible graphene oxide-based microsupercapacitors can be used in the near future as components in wearable and flexible electronic devices (mobile phones, smart watches, health monitoring devices, energy storage devices etc.)”, adds the Indian born researcher.

The genesis of the study goes back to 2015, when Rajesh Kumar, who had been working with graphene microsupercapacitors in other countries, applied for a postdoctoral fellowship to work in the group of Professor Stanislav Moshkalev, director of CSC at Unicamp. “I saw a great opportunity in this group, as their main research line is nanofabrication and nanoelectronics based on nanostructured carbon,” reports Kumar. The Indian PhD obtained a grant from CNPq, the Brazilian federal research agency, as a visiting specialist, to carry out a project in CSC – Unicamp. Initially, he made fine sheets of graphene oxide called “buckypapers”. Then, working in interaction with a group of five other people of CSC – Unicamp, he searched for new strategies to improve the properties of the material.

The CSC- Unicamp team thus faced the challenge of making a hybrid material of graphene and iron oxide with controlled structure using a simple process, and it was successful in do so by simply exposing graphite oxide and ferric chloride (FeCl3) to microwave radiation.

SEM image of the 3D hybrid material Fe3O4/rGO (left), and a representative scheme of the material´s morphology (right).
SEM image of the 3D hybrid material Fe3O4/rGO (left), and a representative scheme of the material´s morphology (right).

The obtained material presented an interesting morphology: a three-dimensional network in which interconnected graphene nanosheets form “tunnels” that harbor crystalline and multifaceted iron oxide nanoparticles of 50 – 200 nm, strongly attached to the nanosheets, as shown in the figure beside.

The morphology, structure, composition, thermal stability and other properties were analyzed using several techniques available at CSC – Unicamp and at the Indian university.

Subsequently, at Unicamp, the team tested the efficiency of the material to act as electricity storage. The tests proved the high performance of the material as a supercapacitor electrode, and the scientific team concluded that this efficiency was favored by the special morphology of the 3D hybrid material. Particularly, by the faceted nanoparticles strongly attached to the nanosheets, the separation among the nanosheets, the “tunnels” that shelter individual nanoparticles avoiding agglomerations, and the large surface area of the network of nanosheets.

“These microsupercapacitors can and for sure will, in the near future, replace the traditional capacitors in electronic devices,” says Kumar. According to the researcher, their main advantages are high performance, mechanical strength, reduced size and, most important, flexibility – an essential property for wearable electronics.

In addition, the method developed by the Unicamp and CUHP team can become a good alternative to fabricate other hybrid materials based on carbon and metal oxides.

The work was carried out with financial support from CNPq and FAPESP (the São Paulo State research foundation).

Pictures of the authors of the paper. From the readers´ left, Rajesh Kumar (Unicamp), Rajesh Kumar Singh (CUHP), Alfredo Vaz (Unicamp), Raluca Savu (Unicamp), and Stanislav Moshkalev (Unicamp).
Pictures of the authors of the paper. From the readers´ left, Rajesh Kumar (Unicamp), Rajesh Kumar Singh (CUHP), Alfredo Vaz (Unicamp), Raluca Savu (Unicamp), and Stanislav Moshkalev (Unicamp).