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Bio mimicry of cactus separates oil from water



August 8, 2013
Opuntia microdasys Photo Peter coxhead

Opuntia microdasys Photo Peter coxhead

Scientists can now separate oil from water by mimicking the conical shape of cactus spines.

Opuntia microdasys Photo Stan Shebs

Opuntia microdasys Photo Stan Shebs

Chinese researchers observed that cactus spines on Opuntia microdasys, or bunny-ear cactus, were able to harvest water from the air. As small water droplets coalesce on each spine’s surface, its conical shape combined with surface tension pushes the water droplets to the base of the spine.

Although oil and water don’t mix, processes such as homogenisation suspend such small oil or fat droplets through water that they are then impossible to extract. By mimicking nature’s methods, it’s now possible to mechanically separate even the tiniest suspended oil droplets from water.

Very small half-millimetre copper spines arranged in a hexagonal pattern can attract the oil, encourage micron-sized drops to coalesce and then pull the oil droplets to the bottom of each cone. The cone’s shape causes a pressure difference in the tip of each droplet compared to the bottom, which pulls the liquid down along the conical spine. The method worked successfully with wide variety of oils including petrol and vegetable oil.

The research has been published in the journal Nature Communications. Future work will focus on removing suspended oil droplets from air when it is aerosolised in compressed air, which will improve air filters.

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