It’s a puddle you can poke. A new material that appears to be an ordinary liquid, but can be shaped, moulded and sliced like Play-Doh or plasticine, could be used to make novel lenses or mini-containers for chemical reactions.
The material, developed by Xiaoguang Li of Tongji University in Shanghai, China, and his colleagues, relies on an extension of a technique for stabilising droplets as liquid marbles. These are water droplets coated in a hydrophobicpowder, which holds the liquid in place.
Surface tension makes the marbles spherical, and they are basically opaque because of the powder coating. Li wanted to remove both these restrictions to create a transparent liquid object that can take any shape.
To do so, the team dried a silica-based gel on glass slides, creating layers of 20-nanometre silica particles. Putting water droplets on top coated them in just a single layer of silica. “The particles on the droplet surface basically form a monolayer. Therefore the droplet is as transparent as a pure liquid,” says Li.
What’s more, once applied the particles bunch and jam together, holding the droplets in place. When the team manipulated the droplets with hydrophobic tools, they found they could form them into any shape they liked, so decided to call the new material “liquid plasticine”.
The droplets are convex so could potentially act as a liquid magnifying lens, says Li. In a variety of experiments, using coloured water to distinguish the droplets, the team were able to stick droplets together, slice them like a gooey solid, and spell out the word “water” (see video, below).
The team also put chemicals within the droplets and found that their diffusion was slower than expected. This meant the ensuing reactions were slower, making the droplets good as miniature test tubes.
“Their high transparency facilitates observation of the biochemistry process, which is a significant challenge for liquid marbles,” says Li. He believes that the droplets could have other effects on chemistry that are waiting to be discovered.
Journal reference: Soft Matter, DOI: 10.1039/C5SM02765A