Waterproof Clothes

Another technology barrier falls by the wayside as textile and materials science researchers perfect an ultra-hydrophobic spray. No more getting your clothes wet in a downpour.

From the Guardian:

I hate being rained on. I especially hate it when it’s cold. You’d have thought that with all our 21st-century Google-Glass exploring-Mars engineering marvellousness, we would have made more progress on the problem of rain. But no. The umbrella is a few thousand years old and is nowhere near an optimal solution, especially in blustery windy weather. Wet-weather clothing works if you wear it, but most people don’t because it looks so awful.

From a materials-science perspective, the best solution for the British weather would be an invisible waterproof coating that you can spray on the clothes you actually do want to wear. Excitingly such materials have now been invented; they borrow tricks from nature, and they may yet get us singing in the rain.

Traditional waterproofing involves materials that are hydrophobic – in other words molecules that repel water. Waxes and other oily materials fall into this category because of the way they share their electrons at an atomic scale. Water molecules are polar, which means they have plus and minus charged ends. Waxes and oils prefer their electrons more equally distributed and so find it hard to conform to the polarity of water, and in the stand-off they repel each other. Hence oil and water don’t mix. This hydrophobic behaviour is bad for vinaigrettes but good for waterproofing.

Nature uses this trick too but is much better at it. Go into a garden during a rain shower and have a look at how many leaves repel water so effectively that water droplets sit like jewels glistening on their surface. Lotus leaves have long been known to have this superhydrophobic property, but no one knew why until electron microscopes revealed something very odd about the surface of the lotus leaf. There is a waxy material there, yes, but it is arranged on the surface in the form of billions of tiny microscopic bumps. When a drop of water sits on a hydrophobic surface it tries to minimise its area of contact, because it wants to minimise its interaction with the non-polar waxy material.

The bumps on the lotus leaf drastically increase this area of waxiness, forcing the droplet to sit up precariously on the tips of the bumps. In this, the Cassie-Baxter state, the droplet becomes very mobile and quickly slides off the leaf. So by manipulating just the bumpiness of its surface, lotus leaves are far better at repelling water.

The mobility of the droplets has another effect. By zooming around the surface of the leaf rather than sticking, the droplets of water collect small particles of dust, hoovering them up. This cleaning mechanism of these superhydrophobic surfaces is called the lotus effect.

Superhydrophobic surfaces have been synthesised and studied in labs for decades, but it is only recently that commercial versions have been produced. Now there are quite a few coming on to the market (eg neverwet.com), and they are impressive – when water is poured on to these surfaces it behaves like mercury and bounces off.

The trick, as with the lotus leaf, is to create a microscale patterned non-polar surface. The fact that these sophisticated surfaces can be sprayed out of a can is a triumph of nanotechnology. As with the lotus leaf these coatings not only keep things dry, they also keep them clean, since a lot of what constitutes dirt arrives on your clothes as splashes of liquid that subsequently dry leaving a residue. If the droplets of bolognese sauce, curry or mud don’t stick but bounce off, then they won’t leave a stain.

There are many other applications for these coatings, such as reducing the window cleaning bills on skyscrapers; keeping paint clean on cars; making sofas immune to red wine; and in its key role as waterproofer extraordinaire, keeping your mobile phone safe when it is dropped down the loo.

Read the entire article here.