Do you buy expensive moisturisers in a bid to combat the ravages of age, or does catching a mid-afternoon whiff of your pits have you reaching for the roll-on?
We smear various lotions and potions on our skin every day and, while we might take note of their active ingredients, we may not consider how they’re delivered.
Those ingredients are often expensive but in order to work, they need to remain suspended, separate to the lotion, until they come in contact with skin. How is this achieved?
Liquid marbles
Liquid marbles are one type of delivery vehicle for expensive ingredients in, for example, moisturisers and deodorants.
A drop of liquid is covered by a shell of “hydrophobic”, or water-repellant, powder.
The shell protects the liquid from the outside world, so you can transport the liquid by rolling the drop along surfaces.
Liquid marbles were discovered by two French scientists, Pascale Aussillous and David Quéré in 2001.
They observed that if hydrophobic lycopodium powder spores are poured onto the surface of water, an object inserted into the water will come out covered with powder, but perfectly dry.
From this, Aussillous and Quéré realised that a powder-coated drop of water no longer sticks to surfaces. Instead it rolls and bounces.
A major problem for developing liquid marble products has been the limited number of powders hydrophobic enough to coat drops of common liquids.
This changed when the Australian scientist Karen Hapgood started to use liquid marbles to make capsules from powdered drugs. She found less hydrophobic powders, of drugs such as salicylic acid (which is also used in acne treatment), could at least partially coat drops of water.
Recently my colleague Rossen Sedev at the Ian Wark Research Institute and I showed how the particle wettability (the extent to which a liquid wets the particles) determines what happens when a liquid drop is mixed with powder. This will help people designing liquid marbles choose the best combination of powder and liquid.
Dry skin? Try dry water
Although liquid marbles were discovered in 2001, inventors already knew that large volumes of water could be mixed with some powders to produce a fluffy, apparently dry powder, called “dry water”.
The first dry water patent was filed in 1968 by Evonik Degussa GmbH, a German chemical manufacturer, who then invented a new cream by mixing dry water with small amounts of oil.
Rubbing the cream into skin releases the water and leaves the finished makeup to be spread evenly in a matte finish.
It’s almost oil-free and is found in cosmetics used by people with sensitive skins who avoid oily, emulsion-based foundations.
But practical applications for liquid marbles and dry water aren’t limited to the cosmetic industry.
New applications
Liquid marbles are being developed by scientists excited by their potential to act as sensors.
The Israeli scientist Edward Bormashenko showed liquid marbles could be used to detect water pollution by solvents or petroleum.
A drop of water coated in fluoropolymer particles will float on a pool of water until the pollutant penetrates into the powder and breaks the shell apart.
The powder coating is also permeable to gas. Wei Shen filled powder shells with indicator solutions and showed that the liquid marbles can detect ammonia and hydrochloric acid gas.
You can coat liquids such as molten metals with a protective powder shell, and store dangerous chemicals and increase the rate of chemical reactions using dry water.
So next time you smooth your pricey moisturiser onto those fine lines and wrinkles, spare a thought for the ingredients released from their powdery prisons to work their magic on your skin.