Researchers from Drexel University in the US and Dalian University in China have succeeded in producing a new electrically conductive nanomaterial that is flexible enough to fold, but strong enough so that it does not break. The researchers believe that the new material could be used in diverse applications, for example in electrical energy storage, water filtration and protection from electromagnetic radiation.
![A polymer-MXene composite nanomaterial developed by researchers at Drexel University that is both strong, electrically conductive, and flexible enough to fold. [Courtesy of Drexel University]](https://www.hayadan.org.il/images/content3/2014/11/NANO_GELLER-500x416.jpg)
[Translation by Dr. Nachmani Moshe]
Researchers have succeeded in producing a new electrically conductive nanomaterial that is flexible enough to fold, but strong enough not to break. The researchers believe that the new material could be used in diverse applications, for example in electrical energy storage, water filtration and protection from electromagnetic radiation.
Researchers from Drexel University in the US and Dalian University in China have succeeded in producing a new electrically conductive nanomaterial that is flexible enough to fold, but strong enough so that it does not break. The researchers believe that the new material could be used in diverse applications, for example in electrical energy storage, water filtration and protection from electromagnetic radiation.
Finding or making a tiny material capable of being useful in storing and transmitting electric current, and one that can be shaped into multiple shapes, is a rare discovery in the field of materials science. The tensile strength (the strength of the material during stretching) and the compressive strength (the ability of the material to withstand the weight placed on it) are important characteristics for these materials since due to their very small size, these values almost completely depend on their physical properties.
"Take, for example, the electrode found in a small lithium-ion battery that powers your wristwatch; Ideally, the conductive material in this electrode should be as tiny as possible - so you won't be wearing a bulky watch and it will still be able to operate for as long as possible," said Michel Barsoum, a professor in the College of Engineering. "But what if we were interested in turning the watch band itself into a battery? So, we would still want to use a conductive material that would be tiny in size and able to store energy in it, but it would have to be flexible enough to be wrapped around your wrist. As you will see, by changing only one physical property of the material - its flexibility or tensile strength - we get a new world of possibilities." This novel and flexible material, which the group has identified as an electrically conductive polymer nanocomposite, is the latest product of ongoing research in Drexel University's Department of Materials Science and Engineering into a family of two-dimensional composites known as MXenes.
The research team carefully examined this family of materials, much like a paleontologist carefully brushing through sediment to uncover a scientific treasure that was buried in the ground. Since the invention of the layered carbide material in 2011, engineers have been looking for ways to take advantage of the chemical and physical composition of the material in order to create conductive materials with a variety of other useful properties.
One of the most successful ways they have developed to help these materials demonstrate their full range of capabilities is a process known as intercalation, during which a variety of chemical compounds are added to the mixture in a liquid state. This process allows the molecules to settle between the layers of the layered material and thus change the physical and chemical properties of the finished material. One of the most impressive properties, and the first that the researchers uncovered, is the ability of these materials to store energy.
In order to create the flexible conductive polymer, the researchers combined titanium carbide with polyvinyl alcohol (PVA) - a polymer commonly used as an adhesive in the paper industry and as an ingredient in hair gel. In addition, the researchers combined the material with other polymers, for example PDDA.
"The uniqueness of this family of materials (MXenes) stems from the fact that their surface is full of functional groups, such as a hydroxyl group, which leads to a strong chemical bond between the material particles and polymer molecules, while maintaining the electrical conductivity of the separate layers. This composition gives rise to a composite nanomaterial with a unique combination of properties," explains the lead researcher. The findings of the research were recently published in the scientific journal Proceedings of the National Academy of Sciences, and within them the researchers report that the material exhibits an increased ability to store electric charge compared to the original material and that it is 400% stronger. "We have shown that the volumetric capacity of a polymer-MXene composite nanomaterial can be much higher compared to conventional carbon-based electrodes or even compared to graphene material," notes the lead researcher. "When the MXene material is mixed with the PVA polymer containing a small amount of electrolytic salt, the polymer acts as an electrolyte, but it also improves the electrical capacity since it slightly increases the interlayer space between the MXene particles, which allows more ions to penetrate deep into the electrode; In addition, these ions also remain trapped near the MXene particles with the help of the polymer. With the help of these conductive electrodes and in light of the fact that no liquid electrolyte is used at all, we will eventually be able to avoid metallic current collectors altogether and develop lighter-weight and smaller super-collectors."
The experiments also showed that the composition has hydrophilic properties, which means that it could be used in water treatment systems, for example, as a membrane for water purification and desalination, since the material remains stable in an aqueous environment without being destroyed or decomposed. In addition, since the material is extremely flexible, it can be rolled into a tube or cylinder shape, when early experiments showed that this shape even increases its mechanical strength. The researchers' next step will be to examine how varying compositions of the material MXene with the various polymers will affect the properties of the resulting material.
