Auto Wash Paint Using Ultra-Hydrophobic Principle.

                                   Robust self-cleaning surfaces are on their way to your home. How will you feel when your car gets cleaned itself? Or clothing that were stained badly would regain back? Great… Is that you are waiting for…? Then say thanks to researchers from UCL, Imperial College London and Dalian University of Technology (China), who have developed a new paint that can be applied to clothes, paper, glass and steel to make resilient surfaces that can self-clean even after being scratched or scuffed. According to the study the paint, made from coated titanium dioxide nanoparticles, is extremely repellent to water but, unlike other waterproof coatings, continues to work even when damaged or exposed to oil. Because it is so hard-wearing, it could be used for a wide range of applications, from clothing to cars.

Being waterproof it allows materials to self-clean as water forms marble-shaped droplets that roll over the surface, acting like miniature vacuum cleaners picking up dirt, viruses and bacteria along the way. For this to happen, we have to create rough and waxy surfaces by designing our own paint and combining it with different adhesives to help the surfaces withstand damage. This study shows how the new paint made from coated titanium dioxide nanoparticles can give a wide-range of materials self-cleaning properties, even during and after immersion in oil and following damage to the surface. According to the study, this paint is suitable for applications such as car bodies, where frequent scratching can occur, though it could also be used to create art using the water droplets’ patterns, or for easy-clean surfaces in hospitals.

We can use different coating methods to create the water repellent surfaces, depending on the material. I.e. depending on the surface on which it is applied, the coating can be sprayed, dipped, or painted onto a surface. An artist’s spray-gun was used to coat glass and steel, dip-coating for cotton wool and a syringe to apply the paint onto paper. All the materials became waterproof and self-cleaning as water droplets of different sizes were seen bouncing instead of wetting the surface, removing the dirt applied by the researchers. This was maintained after damage was inflicted on the surfaces.

Their experiments showing the behaviour of the treated surfaces against controls can be seen this video demonstration. Examples contain videos of treated cotton-wool being dipped into blue coloured water and emerging pristine white with no trace of contamination, and treated paper remaining dry and clean after being exposed to dirt and water.

This is an ultra-hydrophobic (water-repelling) paint which is an ethanolic suspension of perfluorosilane-coated titanium dioxide nanoparticles, that can be applied to a variety of surfaces, and that stays on once applied. Once the coating is applied to a surface, the ethanol must evaporate for 180 seconds before it is ready for use. The active ingredient, coated titanium dioxide nanoparticles, in the paint cause liquid to bead up and roll off the paint, instead of clinging to it. As those droplets roll across the painted surface, they suck up any dirt, viruses, bacteria or other non-liquid contaminants that are in their path.

Lotus leaf microscopic image

Scientists have come up with a self-cleaning paint-like coating taking inspiration from the nature; yes a large-leaved lotus plant. By chemically copying the lotus' micro-rough, waxy surface, they have produced this 'superhydrophobic' treatment. The extremely water-repellent coating means water droplets stay spherical and roll around picking up, and removing, dirt and dust. And because they have used two different-sized nano-molecules to create the rough texture, they have found that oil contamination does not spoil the self-cleaning properties. This could make it an ideal surface treatment for bearings and gears, which need to be kept clean, but also, need to be lubricated with oil.

Durability which has been a limiting factor in many previously-developed self-cleaning paints has been accomplished, since the paint remained adhered to the various surfaces and retained its hydrophobic qualities, even after being exposed to conditions designed to simulate real-world wear and tear which includes being scuffed with sandpaper or scratched with a knife.  It also kept working after exposure to oil, something that can't be said for all of the previous attempts.

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