Tint Glass with Dyed Liquid Crystals

Tint Glass – In a Nutshell

Liquid crystals sit somewhere between solids and liquids, being able to flow as a fluid, but also exhibiting some crystal-like properties.

When we apply a voltage, they change their orientation to align with the electric field, which results in them either scattering light (milky white appearance) or transmitting light (appearing transparent).

This article focuses on liquid crystals which incorporate dichroic (i.e. dual-color) dyes, where an applied voltage rotates not only the liquid crystals (the ‘hosts’), but also rotates the dyes (considered ‘guests’ in the host material).

Hence, we call this type of tinted smart glass ‘Guest-Host Liquid Crystal’ (GHLC) glass, or more commonly ‘Dyed Liquid Crystal’ (DLC) glass.

Rotating Dyes to Tint Glass

When the dyes rotate such that their long axis is perpendicular to the electric field component of the incoming light waves, they transmit the light unimpeded, and the glass appears transparent.

When the dyes are oriented parallel to the electric field component of light, they absorb it and thus appear dark to the user. The tint glass now appears opaque.

Applications of Dyed Liquid Crystal (DLC) tint glass include:

• Smart windows for buildings and vehicles
• Display devices, such as mobile phones, laptops, etc
• Optical storage media
• Thin-film polarisers
• Electrically-switched laser protection devices, and
• Spectroscopy of biological systems.

Previously, we have shown the details of how liquid crystals work, so you may be wondering:-

Why Another Tint Glass Variant?

Well, it turns out that Dyed Liquid Crystals have some distinct advantages:-

• They not only scatter light (giving privacy), they also block it, which can reduce the amount of light and heat coming into offices and residences.
• They do not require polarisers, which reduces the cost.
• The lack of polarisers also means lower-power operation than other liquid crystal based glass.
• The switching time of DLC glass is typically below 1 second, and the haze observed is around 3-4%.

Importantly, dyed liquid crystal-based tint glass can be manufactured on plastic film. This allows for roll-to-roll (R2R) manufacturing, which offers economies of scale and ultimately lower costs.

It’s not all good news though. 

Tint glass needs power to maintain its transparency, in contrast to electrochromic or electrophoretic glass, which only require power to change tint.

How Does DLC Tint Glass Work?

When we dissolve a dye into a liquid crystal, the dye aligns itself with the long axis of the liquid crystals. In fact, it intersperses itself with the liquid crystals.

When we apply a voltage, the liquid crystals form electrical dipoles, with one end positively charged and the other negative.

The liquid crystals then act under the electric field and rotate to align with it. 

This causes the dyes (dissolved within) to also rotate with them, which alters their coloration to the viewer.

Dichroic Dyes for Tint Glass

By now, it is apparent that dichroic dyes are the ‘secret sauce’ of this particular smart glass configuration.

A dichroic dye produces different colors, depending on the direction of viewing. 

Examples of dichroism (or pleochroism when multiple colors are observed), can be found in gemstones such as andalusite, emerald, and tanzanite. The term ‘pleochroic’ comes from pléōn meaning ‘more’ and khrôma meaning ‘color’.

If an electric field rotates a liquid crystal ‘host’ and its dichroic dye ‘guest’, this results in different colorations, with one normally being transparent, and the other dark.

The ratio of one to the other is called the ‘dichroic ratio’.

Examples of dichroic dyes include:-

• Anthraquinone 
• Azomethines
• Indigoid
• Thioindigoid
• Merocyanine
• Azulenes
• Perylenes, and
• Tetrazines

Tinted DLC Smart Film Samples

If you are looking for samples of Dyed Liquid Crystal film, look no further than our Samples Shop, where you can see the optical and electrical specifications, and order a sample.

You can see images of the DLC sample below:-

Below are the optical and electrical characteristics of the Dyed Liquid Crystal (self-adhesive) film:-

Outlook for Tint Glass

While there are many smart glass technologies that tint on-demand, this article presents a technology which matches our criteria:-

• Availability: this technology is available to buy right now, in contrast with other smart glass technologies which are still in the R&D stage.
• Cost: DLC smart film and smart glass are more cost-effective than some alternatives, such as some brands of electrochromic glass and especially compared to SPD smart glass.
• Performance: the visible light transmittance (VLT) and haze of DLC smart glass are amenable to building facades and transportation.

The smart glass sector is evolving rapidly though, so follow us on our Linkedin Public Group to see new technologies and exciting advances in this area.