Even though clothing is a fundamental human need, it doesn’t seem to be advancing as rapidly as many others. That said, scientists have now created a printable textile that can cool, detect movement, and generate electricity without external systems or multiple layers.
Researchers in the Grainger College of Engineering at the University of Illinois have created a zirconium oxide (ZrO₂) nanocomposite textile material that combines passive cooling and biomechanical energy harvesting.
The material uses radiative cooling to reflect 96% of incoming solar radiation, keeping the wearer cool outdoors, plus it can also radiate away the wearer’s thermal energy. Furthermore, the material senses motion by detecting the triboelectricity generated as the wearer moves against the textile. This extremely small amount of electricity can serve as a signal for integrated technologies. It can also serve to power small wearables, according to the researchers.
University of Illinois, Urbana-Champaign
We spend nearly 100% of our lives in clothes. It follows that they should do more than shield us from the elements. It’s this line of thought that has led scientists to invent clothes with health monitoring, climate adaptation, interactive control, and self-healing among other features. The problem is that most of these functions require active, complex systems and, in many cases, multiple assembled layers with different functions.
The University of Illinois researchers’ solution bypasses these requirements by combining multiple functionalities into a single 3D-printed textile. At its heart is a zirconium oxide (ZrO₂) nanocomposite. Zirconia happens to have two properties the researchers can exploit at once. Optically, its high refractive index makes it very good at scattering sunlight. Electrically, its dielectric properties help it accumulate triboelectric charge when it makes and breaks contact with another material.
Therefore, the researchers developed a material useful for both radiative cooling and motion-powered electricity generation. What’s more, the material is printable via direct ink writing, an extrusion-based form of additive manufacturing
Unlike regular fabric that absorbs a significant amount of the sun’s heat and transfers it to the wearer’s body, the new textile reflects 96% of the sun’s incoming radiation. In addition, the material has 97% mid-infrared emissivity, making it very effective at radiating its wearer’s body heat away as infrared radiation. Under outdoor sunlight, the researchers measured the textile at around 3-6 °C below ambient air temperature. For context, humans can detect 1 °C (1.8 °F) differences in air temperature under normal conditions.
University of Illinois, Urbana-Champaign
The other potential functions of the material lie in its ability to generate electricity.
You know that little static shock you can get after rubbing your feet across a carpet? That is real electricity. The same thing happens with the new textile, as the wearer moves and their skin brushes against it. The repeated mechanical motion generates a detectable electronic pulse. The paper, published in the journal Advanced Science, reports a peak power density of about 47 mW/m² and stable electrical output over more than 30,000 operating cycles.
While this amount of electricity is not remotely enough to charge your phone, it’s useful for many other applications, including sensing. Connected to the right sensor, that small electrical signal can indicate when the wearer is moving. The signal level can also indicate how much movement is taking place. The fabric can also connect to a control system, where the signal acts as a trigger.
The researchers demonstrated this functionality by combining the fabric with an underlying conductive textile layer to create an adaptive thermal management system. When the wearer was stationary, the passive radiative cooling kept things cool. Conversely, when they moved, the triboelectricity generated a signal that activated the underlying conductive layer to start heating.
Important clarification: the ZrO₂ material did not generate the heat itself, but simply provided the signal that activated the underlying layer. The conductive layer came with its own electronics, including heating elements, a DC power supply, a solid-state relay, and an Arduino microprocessor.
It does seem somewhat counterintuitive that heating is triggered when the wearer is in motion, a state that itself generates body heat. However, the researchers designed this setup as an intentional experiment. The triboelectricity generated can be applied to various other systems. For example, the textile sewn into nightwear can activate alarms when it detects a predetermined amount of motion.
