It’s the dead of January, and your living room is so cold that the chill seeps into your bones, and you can barely feel your fingertips. You might crank up the thermostat. But soon you could be cozying up in a self-heating sweater.
Engineers at Stanford University have figured out how to coat clothing in a meshwork of silver nanowire so that it not only insulates better than regular clothes but also generates its own heat. And cheap versions could hit store racks in three years, predicts Yi Cui, an associate professor of materials science and engineering at Stanford who led the project, described in Nano Letters last November.
Cui and his colleagues came up with the idea for the fabric when considering that nearly half of the world’s energy consumption goes toward heating buildings — which contributes to up to a third of global greenhouse gas emissions. To reduce energy waste and keep heat indoors, most engineers have tried to boost the insulating properties of building materials. But the Stanford team turned its focus to keeping people warm. Regular clothing can do this by trapping heat, but it allows much of that heat to dissipate back into the surrounding air.
Since silver can conduct electricity, a mini battery could deliver a small voltage to heat up the nanowires for extra warmth.
Why not use metal? The surface would reflect heat radiating from the body back onto the skin. But metal is hard, and people want clothing “to be soft and still breathe,” Cui says. The solution: soft, ultrathin nanowire. Cui decided on silver — cheaper than gold but more stable than copper, which forms a green crust when exposed to air. And since silver can conduct electricity, a mini battery could deliver a low-voltage current to heat up the material for extra warmth. To coat the fabric, Cui’s group immersed it in a solution that left behind a thin nanowire layer when dried, producing a fabric that still lets sweat escape and nanowires that don’t flake off in the wash.
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SOURCE: Ozy, Melissa Pandika