Nanowire Clothing Offers Warmth, Could Aid In Climate Change Fight

It’s going to be another chilly week for many of us in the northern latitudes. Too bad this metallic-nanowire-embedded cloth isn’t in our gloves and caps yet.

Stanford University scientists developed a process to coat textile fibers with the nanowires, which together form a conductive network throughout the cloth. They say their flexible material, which is composed of silver nanowires and carbon nanotubes, is knit together so closely that the space left between individual strands is shorter than the wavelength of infrared radiation. That means a wearer’s body heat can’t easily pass through the material and gets reflected back to provide warmth.

The empty spaces between nanowires are controlled through the production process to remain between 200 and 300 nanometers. Heat generated by the human body is shed in the form of infrared radiation at a considerably longer wavelength of 9 micrometers. This means that the textile appears like a solid barrier to the radiation. Yet 200 nm holes are big enough to allow water molecules to pass through unobstructed, keeping the fabric breathable and dry.

Besides a major bump in passive insulation, the nanowire coating also provides a network for active heating. Since the material is conductive, it begins warming up when an electricity source is attached. Their research showed that applying less than 1 volt to the cloth caused it to heat to just above body temperature in a few minutes.

“The metallic nanowires form a conductive network that not only is highly thermal insulating because it reflects human body infrared radiation but also allows Joule heating to complement the passive insulation,” the team write in a paper published recently in the journal ACS Nano Letters. “The breathability and durability of the original cloth is not sacrificed because of the nanowires’ porous structure.”

Their invention may one day prove useful for more than those looking to take a hike outdoors in the dead of winter. In fact, the researchers say their work was motivated by the desire to decrease the massive amount of energy that is dumped into homes and offices every winter to heat building occupants.

Almost half of the world’s energy consumption goes to indoor heating. When that energy is generated from fossil fuels, keeping warm becomes a contributor to climate change. They say they developed the material as part of a growing body of research looking to move the onus of heating building occupants from the structure to the individual. Collectively, the devices that enable this paradigm shift are called personal thermal management.

“Metallic nanowire cloth has great potential to reduce the energy used on indoor heating because of its personal thermal management capabilities while retaining the wearability and breathability of normal cloth,” they write.

The idea isn’t cloistered in a few labs around the world. Huge energy savings that can be realized from engineered clothes, advanced efficient body and space warmers and others have gotten some big players involved. The U.S. energy department’s advanced research agency is backing work in it to reduce building energy consumption.

And researchers from major universities as well as companies like Gentherm and Nike are developing ideas for the components needed. A Princeton team is working on fabric-embedded batteries to power thermal management systems while a UCLA group is developing a wearable sensor that monitors thermal comfort. Another, from the University of Maryland, is looking into textile fibers that change phase to suppress cooling. The U.S. Army, meanwhile, is developing insulation that adapts to different temperatures for use in sleeping bags, blankets and clothing. Their approach uses three polymers as batting that gets thicker when temperature decreases.

More than 12 quadrillion BTUs of energy are poured into homes and commercial structures every year for space heating and cooling in the U.S., a number that comprises 12 percent of all domestic energy consumption. Combine new wearable thermal management systems with better insulation, smart windows, and an innovative concept to use smart heaters in buildings for directional thermal management and some serious energy savings could be realized.

“This nanowire cloth can efficiently warm human bodies and save hundreds of watts per person as compared to traditional indoor heaters,” the creators of the nanowire-embedded textile conclude.

Top Image: Side-by-side comparison of thermal images of a human hand with a normal glove and with a silver nanowire (AgNW) glove, proving the scalability and effectiveness of the dip-coated AgNW cloth. Image courtesy Cui et al./ACS Nano Letters.