South Korean researchers created material that can turn from transparent to opaque within a milisecond

Transparent window shutters act as LCD screens to transform view

A technology developed by South Korean researchers would allow those living in uninspiring neighbourhoods to change the view from their windows with the flip of a switch.

The transparent light shutters created by the team from South Korea's Pusan National University rely on liquid crystal technology that can be turned from opaque to transparent within a millisecond. While the transparent state functions as a regular window, when opaque the surface can serve as an LCD screen on which images could be projected to improve the appeal of a room.

While the idea is not entirely new, the South Korean team believes their solution tackles some of the major problems faced by earlier concepts.

Experiments with light-emitting diodes as well as liquid crystals that can be turned from a transparent to opaque state by scattering or absorbing light haven’t led to practical solutions.

"The transparent part is continuously open to the background," explained Tae-Hoon Yoon, the group's primary investigator. "As a result, they exhibit poor visibility."

The South Korean team therefore decided to use scattering and absorption simultaneously. To do this, Yoon's group created polymer-networked liquid crystals cells doped with dichroic dyes.

In their design, the polymer network structure scatters incoming light, which is then absorbed by the dichroic dyes. The light shutters use a parallel pattern of electrodes located above and below the vertically aligned liquid crystals.

When an electric field is applied through the electrodes, the axes of the dye molecules are aligned with that of incoming light, allowing them to absorb and scatter it. This effectively negates the light coming at the screen from its backside, rendering the display opaque and the screen's images fully visible.

"The incident light is absorbed, but we can still see through the background with reduced light intensity," Yoon said.

In its resting state, this setup lets the light pass through, so power need only be applied for the transformation from a transparent window to an opaque monitor. As the display's on-off switch is an electric field, it provides a response time of less than one millisecond - far faster than that of contemporary light shutters, which rely on the slow relaxation of liquid crystals to act as their off switch.

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