Microscopic water droplets can sometimes turn into bleach after a hitting a surface. Now, researchers are starting to better understand this strange phenomenon. A series of experiments suggest that it may be down to having the right conditions for water molecules to receive an electron from the surface. The phenomenon may also be linked to why some viruses survive less well in humid conditions.
Three years ago, at Stanford University in California and his colleagues the phenomenon when they sprayed small drops of water in the presence of hydrogen peroxide 鈥� the main ingredient in bleach. Since then, they have investigated whether a similar phenomenon may occur as water droplets .
However, other researchers the effect. Some have suggested the natural presence of ozone in the lab could be .
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To investigate what is going on, Zare and his team devised an experiment where they could better control the interaction between the water droplets and the surface. First, they mixed water with a dye that glows in the presence of hydrogen peroxide. The mixture didn鈥檛 glow when left in a storage container.
The researchers then injected the mixture into microscopically narrow channels made of the glass-like material silica. The channels maximised the contact between the water and the surface, giving more opportunity for hydrogen peroxide to form.
The liquid glowed as it passed through the channels. The team鈥檚 measurements suggest hydrogen peroxide formed at a concentration of 0.0019 grams per litre when passing through the silica channels, about 2000 times less than the concentration of salt in oceans. The researchers saw similar effects with nine other materials.
Zare and the team hypothesised that electrons from the channels were moving into water and causing the water molecules, which are made of two hydrogen atoms and one oxygen atom, to reconfigure into hydrogen peroxide molecules, which have an additional oxygen.
They tested the idea in multiple ways, such as by treating the silica surface with a chemical that removed any molecules that could give up electrons. Less hydrogen peroxide formed than before, which provided evidence in favour of their idea.
at the University of Colorado Boulder says that the new experiment is a step towards understanding the phenomenon. There are probably more factors that determine whether hydrogen peroxide forms when water droplets hit a surface, but pinpointing a mechanism for how this happens is one piece of the puzzle, she says.
Because hydrogen peroxide can be used as a disinfectant, Zare says that it could partly explain why some viruses don鈥檛 survive as well during the summer when the air is more humid. Tiny water droplets in the air could collide with floating specks of dirt to generate the effect, he says.
However, the idea needs further testing, says at Virginia Tech. The link between humidity and the survival of viruses outside of the body is currently a mystery, she says.
PNAS
