Nano-processed silk leaves you feeling cool

Remember that bit in Back to the Future when Marty McFly gets soaked, but his self-drying jacket kicks in and saves the day? Well we’re not quite there yet, but scientists have now successfully used nanotechnology to produce a form of silk that gives you, in their words, wearable air-conditioning! Exposed to direct sunlight, it actually keeps your body cooler than the surroundings by using nanoparticles glued onto the strands of the silk to bat away ultraviolet rays that would normally heat up the material and the wearer. By radiating your - and the shirt’s - heat off into space, it cleverly means you’re cooler than the surrounding air and not just because you look good! Stanford University’s Shanhui Fan told Iacopo Russo how it works...

Shanhui - Well, we have demonstrated is that nano-processed silk when placed under direct sunlight by itself can reach a temperature that is 3.5 degrees Celsius below ambient and therefore a person wearing such a nano-processed silk in an outdoor setting is essentially wearing his own air conditioning.

Iacopo - So how did you treat the silk?

Shanhui- Native silk absorbs ultraviolet light absorption of ultraviolet light gives rise to heating of the textile. We introduced aluminium oxide nanoparticles into the silk. A nanoparticle just looks like a little ball, except they are very, very small. The nanoparticle that we put in is designed so that it reflects strongly the ultraviolet light.

Iacopo - How did the nanoparticle stick to the silk?

Shanhui - We put a chemical bonding agent to ensure that the particle connected to the protein in the silk in a strong way.

Iacopo - So they're not just going to be washed away after a cycle in the washing machine?

Shanhui - In fact, we did many cycles in the washing machine and then confirmed that the particles are still there after many washing cycles.

Iacopo - Okay. That's good. So now we've got our engineered silk. How did you measure its cooling properties?

Shanhui - We do two measurements. In the first measurement we simply take a silk, put it under the sun and measure its temperature. In that case we see a temperature that's about 3.5 degrees Celsius below the ambient air temperature. The next thing that we did, which is to try to simulate the silk when a person is wearing it, is that we place this on top of a artificial skin with a heat source to simulate the thermal property of the human body, and put it outside under the sun. And what we see is that the nano-processed silk has a temperature that's about 8 degrees. Celsius below that of the native silk.

Iacopo - Right. Just to clarify, if you put a piece of silk or cotton out in the sun, it will usually be hotter than the air around it, right?

Shanhui - Yes. And in our nano-processed silk its temperature after is colder than the environment.

Iacopo - Amazing. And are there no other wearable materials that can currently do that?

Shanhui - No. So this really is quite an unusual textile that we have created.

Iacopo - Could this process be scaled to make T-shirts?

Shanhui - I believe so. In fact, we have a picture of a shirt made out of the silk. You certainly can make that kind of scale.

Iacopo - I guess this means if I wear this T-shirt next summer, I won't have to use the air conditioning as much. So I will save energy essentially.

Shanhui - That's right. But also in an outdoor situation, where air conditioning may not be readily available, you will actually feel cooler.