Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Mixing solids and liquids enhances optical properties of both

10.06.2016

New approach can dramatically change the extent to which optical devices scatter light

By immersing glass particles in a fluid, researchers at MIT's Media Lab and Harvard University are exploring a new mechanism for modifying an optical device's diffusivity, or the extent to which it scatters light.


A mild temperature change radically alters the degree to which a solid-fluid mixture bends light.

Courtesy of the researchers

In its current form, the new diffuser could be used to calibrate a wide range of imaging systems, but the researchers believe that their mechanism could ultimately lead to holographic video screens or to tunable optical devices with applications in imaging, sensing, and photography.

In experiments, the solid-liquid mixture demonstrated much more dramatic changes in diffusivity than existing theory would have predicted, so the researchers also developed a new computer model to describe it. That model could help them devise more complex applications for the basic technology.

The researchers describe their new work in the latest issue of the American Chemical Society's ACS Photonics journal.

The fluid and the glass in the prototype were chosen because they have very similar refractive indices, meaning light travels through them at similar speeds. When light moves from a material with a high refractive index to one with a lower refractive index, it changes direction; this is the phenomenon behind the familiar illusion of a straw's appearing to bend when it's inserted into a glass of water.

The researchers' prototype exploits the fact that changes in temperature alter materials' refractive indices.

"It's hard to find a solid and liquid that have exactly the same refractive index at room temperature," says Barmak Heshmat, a postdoc in the Media Lab's Camera Culture group and corresponding author on the paper. "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."

Heshmat is joined on the paper by Ramesh Raskar, the NEC Career Development Associate Professor of Media Arts and Sciences and head of the Camera Culture group, and Benedikt Groever, a graduate student in engineering and applied science at Harvard.

Study in contrast

In their experiments, the researchers found that a temperature change of 10 degrees would increase the diffusivity of their device tenfold, and a change of 42 degrees changed it a thousandfold.

Heshmat believes that a temperature-modulated version of his team's filter could be used to calibrate sensors used in the study of material flows, the study of cells, and medical imaging.

For instance, medical-imaging systems are typically calibrated using devices called "tissue phantoms," which duplicate the optical properties of different types of biological tissues. Tissue phantoms can be expensive, and many of them may be required to calibrate a single imaging device. Heshmat believes that a low-cost version of his team's filter could mimic a wide range of tissues.

But the fundamental principle illustrated by the researchers' prototype could have broader ramifications. The effect of heat on the refractive index of either the solid or the fluid, taken in isolation, is very subtle. But when the two are mixed together, the effect on diffusivity is dramatic.

The same would be true, Heshmat argues, of other types experimental materials whose refractive indices change in response to either light or an electric field. And optical or electrical activation would broaden the range of applications for tunable optical devices.

"If you have photorefractive changes in a solid material in a solid phase, the amount of change you can get between the solid and itself is very small," he explains. "You need a very strong field to see that change in your refractive index. But if you have two types of media, the refractive index of the solid is going to change much faster compared to the liquid. So you get this deep contrast that can help a lot."

Application

In holographic displays, cells filled with a mixture of electrically responsive solid materials and a fluid could change their diffusivity when charged by an electrode, in much the way that cells filled with ionized gas change their color in plasma TVs. Adjacent cells could thus steer light in slightly different directions, mimicking the reflection of light off of a contoured surface and producing the illusion of three-dimensionality.

Liquid-solid mixtures could also be used to produce tunable diffraction gratings, which are used in some sensing applications to filter out light or other electromagnetic radiation of particular frequencies, or in tunable light diffusers of the sort photographers use to make the strongly directional light of a flash feel more like ambient light.

The computer model that the researchers describe in their paper predicts the diffusivity of a liquid-solid mixture on the basis of the physical characteristics of the solid particles -- how jagged or spiky they are -- and on their concentration in the liquid. That model, Heshmat says, could be used to develop solid particles tailored to specific applications.

###

Additional background

ARCHIVE: Imaging with an "optical brush"

ARCHIVE: Glasses-free 3-D projector

ARCHIVE: Cheap, color, holographic video

ARCHIVE: Glasses-free 3-D TV looks nearer

Abby Abazorius | EurekAlert!

More articles from Materials Sciences:

nachricht Epoxy compound gets a graphene bump
14.11.2018 | Rice University

nachricht Automated adhesive film placement and stringer integration for aircraft manufacture
15.11.2018 | Fraunhofer IFAM

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

Purdue cancer identity technology makes it easier to find a tumor's 'address'

16.11.2018 | Health and Medicine

Good preparation is half the digestion

16.11.2018 | Life Sciences

Microscope measures muscle weakness

16.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>