Glass that changes to opaque

Written by charong chow
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Glass that changes to opaque
Chromogenic materials in "smart glass" modify their light transmission properties with an electrical current. (Andrew Bret Wallis/Brand X Pictures/Getty Images)

Smart glass technology refers to a type of transparent glass that becomes opaque with a flip of a switch. Chromogenic materials in the glass modify their light transmission properties with an electrical current. In 1704, the first electrochromic materials, which change colours with an electrical charge, were found, but they were not commercially applied till the 1930s. It was in the early 1970s that smart glass technology took off, with numerous companies patenting glass with the ability to change opacity in used in architecture, automotive mirrors, museum exhibitions and more.

Liquid-Crystal Glass

In an instant, liquid-crystal glass changes from milky white to hazy clear. Two clear or tinted sheets of laminated glass, with two plastic interlayers, sandwich a liquid crystal film. The normal or off state is opaque, and when electric current is applied, it turns clear, with no in-between state. Needing constant electrical current to stay transparent, there is not much energy saving in this glass. It was designed for bank screens, display cases and other commercial interior applications.

Suspended Particle Device Smart Window

Suspended-particle-device (SPD) smart windows utilise conductive film with suspended, light absorbing, microscopic particles between two panes of glass. The glass is dark when there is no electrical charge, but when it is charged, the particles change the glass to clear, with a great control over the transparency. However, it needs constant electricity to remain transparent.

Electrochromic Glass

Electrochromic glass has a microscopically-thin coating of an electrochromic section sandwiched between layers of glass, which changes from clear to dark with the application of electricity. However, it can respond slowly, with an "iris effect," where opacity change starts from the outer portions of the glass and works its way toward the middle.

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