Solids can be harder due to the liquid

Is the liquid, of course, softer than the solid, and whether putting liquid droplets into a solid will make it softer? No, Yale University researchers have discovered that by incorporating droplets of appropriate size into solids, they can make solids harder. Their findings could pave the way for composite materials that use liquid to supplement optical or electrical functions without affecting hardness.

The secret lies in the surface tension of the liquid . If liquid droplets are introduced into the solids too large, the surface tension is inadequate to keep the droplets from retaining the state when the solid is subjected to mechanical stress. As a result, deformed water drops and solids become weaker. Conversely, if the droplet is small enough, its surface tension remains intact. This not only keeps the droplets from deforming, but also increases the hardness of the surrounding solids.

Led by materials scientist and mechanical engineering Eric Dufresne, the Yale team tested by dipping droplets of ionic liquid (a liquid salt) a few microns in diameter into a piece of silicone. When the material was stretched continuously, the researchers found that it was 30% stiffer than pure silicon.

Eric Dufresne said: "Research shows that the importance of surface tension is inversely proportional to size, so a seemingly insignificant force for large things eventually becomes a strong enough force. For very small things, this can have a dramatic effect on the whole material. "

The research has just been published in the journal Nature Physics.