Adding water to solids can actually make them stronger, providing engineers with exciting new material composites

Some findings are just counterintuitive. I mean, you'd think that adding water to materials would always make them softer, right ? Well according to Yale researchers, that's not necessarily the case. The team found that you could improve the strength of a composite by 30 percent by embedding droplets of water into its structure.

Scientists can make composite materials stronger by up to 30 percent by embedding water. Image credits: The Speaker.

Adding pockets of water to solids can actually make them stronger, offering new perspective in engineering, especially in plastic engineering (the technique doesn't work with metals, ceramics or other structural materials). Engineers will also be able to add other properties (such as electromagnetism) to materials by embedding droplets of liquid. By understanding the interaction between water and other materials, researchers can also develop other, more advanced materials in the future.

“This is a great example of how different types of physics emerge at different scales,” Dr. Eric Dufresne, associate professor of mechanical engineering and materials science at Yale and principle investigator of the study, told The Speaker. “Shrinking the scale of an object can really change how it behaves.”

Usually, embedding liquids (especially water) into the structure of another material makes the entire structure weaker, not stronger. However, as this research showed, surface tension could sometimes turn things around. Surface tension is the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.a contractive tendency of the surface of a liquid that allows it to resist an external force.

“Surface tension is a force that tries to reduce the surface area of a material,” Dufresne said. “It is familiar in fluids–it’s the force that pulls water into a sponge, makes wet hair clump together and lets insects walk on water. Solids have surface tension too, but usually the ‘elastic force’ of the solid is so strong that surface tension doesn’t have much of an effect. The ‘elastic force’ of a solid is what makes a solid spring back to its original shape after you stop pushing on it."

Duresfne called this technology “a new knob to turn” for engineers, who can now have more control over the properties they choose to include in their materials - these properties can be mechanical, electrical and even optical.

“As the solid gets stiffer, the liquid droplets need to be smaller in order to have this stiffening or cloaking effect. By embedding the solid with droplets of different materials, one can give it new electrical, optical or mechanical properties. On the simple scale, they could lower the cost be replacing expensive polymers with simple liquids. More excitingly, embedded droplets could provide an electromagnetic handle to actuate structures.”

Journal Reference: Robert W. Style, Rostislav Boltyanskiy, Benjamin Allen, Katharine E. Jensen, Henry P. Foote, John S. Wettlaufer, and Eric R. Dufresne. Stiffening solids with liquid inclusions.