Researchers at MIT’s Media Lab and Harvard University have discovered that mixing solids and liquids enhances the optical properties of both materials. They found that changing the temperature of a solid-liquid mixture dramatically alters the way that light is diffused. The researchers also built a computer model that can be used to design custom liquid-solid mixtures for specific purposes. Potential applications for the researchers’ new approach include: calibrating imaging systems, creating materials for holographic video screens, or creating tunable optical devices for imaging, sensing, and photography.
It’s hard to find a solid and liquid that have exactly the same refractive index at room temperature. But if the speed at which the refractive index changes for solid and liquid is different — which is the case for most solids and liquids — then at a certain temperature they will exactly match, to the last digit. That’s why you see this giant jump in transparency.
The particular fluid and glass that were used in the prototype were chosen because they have very similar refractive indices, meaning light is scattered through them at similar speeds. The researchers discovered that changing the mixture’s temperature altered the refractive indices. A temperature change of ten degrees increases the diffusivity of their device tenfold, and a change of 42 degrees changed it a thousandfold. The study is described in a paper that published in the journal ACS Photonics.