Advanced Manufacturing

Smart Materials:

Windshields Modulate Light, With Liquid

When it comes to smart materials, Keith Goossen at the University of Delaware has a newer, cheaper idea for eco-friendly windows and windshields: Liquid. Goossen’s glass contains fluid-activated panels that change from transparent to opaque states – an achievement that he hopes will provide a more affordable, commercial appeal to consumers. The 3D-printed smart materials switch from transparent to reflective a thousand times without degrading.

The glass, which may someday support new kinds of windows or windshields, has an unconventional design.

“To modulate light, something has to move, whether it is an electron cloud in a crystal, or a shutter,” Goossen told Tech Briefs in a Q&A.” I wondered if moving a fluid could be effective,”

What the Smart Materials Look Like

Smart materials are not a new concept, but consumers are not necessarily ready to pay thousands of dollars for a switchable window. With his team’s simple design, however, Goossen believes costs will go down and spur adoption of the technology.

The prototype glass is mainly two plastic sheets separated by a thin cavity. The plastic contains tiny, retroreflective, cube-shape structures, bouncing light back to its source like a bicycle reflector.

The plastic panel is reflective when dry. Once the chamber is then filled with a fluid called methyl salicylate — an inexpensive wintergreen extract with similar optical properties to the retroreflective plastic — the facet reflectivity disappears, the light passes through, and the panel becomes transparent.

Goossen shared his latest smart material prototype in March 2018 at the SPIE Smart Materials and Nondestructive Evaluation for Energy Systems IV  conference in Denver.

Some of the prototype designs are retro-reflective in the reflective state, meaning that a ray of light upon the panel will be reflected exactly back towards its source. 

“Our smart glass has higher reflectivity in the reflective state, and greater transparency in the transparent state, than other smart-glass technologies,” Goossen said in the Tech Briefs interview.

Since the presentation, Goossen and his team at the University of Delaware have manufactured 3D-printed 8 x 10-inch prototypes. Larger ones are in store.

“We already know what material system and fluid we will use, and it should actually have better optical performance than our 3D printer prototypes.”

Questions in the Tech Briefs Q&A article include:

What are the advantages of this kind of smart glass?

“While current switchable transparency glasses, such as electrochromic glasses, cost thousands of dollars per square meter, we are targeting hundreds of dollars per square meter.”

What inspired you to do this work?

“My career has been mostly in optics, particularly a field of optics known as optical modulators…” 

What kinds of technology work needs to be done for the system to be commercialized?

For our smart glass to be commercialized, particular issues of our optofluidic system need to be acceptable for the application”

What needs to happen for “smart glass” to catch on with consumers?

“Consumers are simply unwilling to pay thousands of dollars for a switchable window.”

Read the Tech Briefs Q&A