What Is PDLC Smart Glass?

What is a Liquid Crystal?

A ‘liquid crystal’ is a material with properties midway between a liquid and a solid. It contains rod-shaped structures which reorient themselves when we apply an electric field, either scattering or transmitting light.

Liquid crystals were first discovered in 1888 by Friedrich Reinitzer (1857-1927), an Austrian botanist, who was studying cholesterol in plants. If you want to know more, check out our article at this link.

Why disperse liquid crystals in a polymer?

The polymer enables the liquid crystals to cure into a film; then, manufacturers sandwich this film between panels of glass or plastic.

The polymer has constant optical properties which do not vary across its structure, and hence is considered ‘isotropic’.

In contrast, the liquid crystal itself is ‘anisotropic’, since its optical characteristics are not constant across its structure.

Is PDLC Glass ‘smart’?

The smartness of PDLC comes from its ability to scatter light, or to transmit light, depending on the electrical voltage applied to it.

This voltage is normally an alternating voltage (typically 36-110 Vac), which exerts an alternating electric field across the PDLC material.

We should remember that PDLC film or glass is only as smart as the ‘control system’ which drives it. This can be a simple push button switch, a light sensor, or a building automation system.

How does PDLC smart glass work?

Initially, the randomly oriented liquid crystals scatter light when no voltage is present; however, applying a voltage forces them to align, which allows light to pass through.

Does PDLC smart glass become ‘opaque’?

The correct term is translucent, since light still gets through, but is scattered in many directions. The glass would be ‘opaque’ only if the light was blocked or absorbed.

There are however some PDLC products which mix dyes into the liquid crystals, thus giving a (permanent) dark colour, and this can result in some of the light being blocked, giving an ‘opaque’ result.

Where can we find PDLC smart glass?

PDLC smart glass can be found in commercial and residential smart windows, consumer electronics and display cases for retail and museums, as well as in healthcare, hospitality and transportation.

Liquid crystals can also be found in high-resolution displays for near-eye wearables and as medical & industrial thermometers.

Why does PDLC glass scatter light?

The liquid crystals change their refractive index in relation to the isotropically transparent polymer in which they are immersed, thereby creating multiple step boundaries throughout the material.

It is this change in refractive index at each boundary which causes light to change course. Since the PDLC material contains millions of liquid crystals, each with a boundary facing a slightly different way, the light is scattered in many directions. 

The net effect is to ‘hide’ whatever is behind the PDLC smart glass.

What is the structure of PDLC glass?

(Images courtesy of Smartglass International)

PDLC smart glass is composed of :-

• a PDLC core layer, typically 1.5mm thick, comprised of liquid crystal droplets suspended in a polymer film,
• layers of ITO (Indium Tin Oxide), a transparent conductor,
• optically clear PET plastic (polyethylene terephthalate),
• outermost panels of float glass, which can be low-iron or tempered (or alternatively acrylic).

Does PDLC smart glass conduct electricity?

No, the internal PDLC layer is plastic and does not conduct electricity, since it is electrically insulative.

Rather, it behaves as the internal dielectric layer of a capacitor, where the applied AC signal on the plates of ‘the capacitor’ causes an alternating electric field throughout the PDLC film.

This is what aligns the liquid crystals with the frequency of the signal (normally 50 Hz or 60 Hz).

How much light does PDLC glass transmit?

When not connected to a voltage, typically the transmittance can be as low as 2% if the material contains dyes, or up to 65% when the PDLC is not dyed.

When connected to a voltage, the transmittance can reach 70%-80%, but this value varies from manufacturer to manufacturer.

Are liquid crystals only available as artificial materials?

Not at all; natural occurrences of liquid crystals include proteins, soaps, detergents, and even some types of clay.

What are the major reasons for using PDLC smart glass?

• Reduction of the building-wide carbon footprint thanks to dynamic solar control. This reduces the demands on climate control systems all year round, thus contributing to the goals of the European Climate Law
• Enhanced security (since the glass is shatter-proof thanks to the internal plastic lamination)
• Privacy (thanks to the scattering of light, essentially hiding whatever is behind the smart glass), which obviates the need for motorised blinds, shutters and curtain systems
• Glare reduction (again thanks to the scattering effect)
• Reduced colour fading of interior furnishings and artworks, thanks to the rejection of UV
• Creative marketing, since when the PDLC smart glass is off, the scattering effect creates a screen upon which you can project images.

Which sectors are using PDLC glass?

• Transportation
• Architectural (residential and commercial)
• Interior design
• Retail advertising
• Healthcare (since PDLC smart glass can replace unhygienic curtains and blinds which often carry germs)
• Banking, thanks to the privacy afforded to ATMs and as internal partitions
• Hospitality, especially bathrooms, since more natural light can penetrate interior spaces which sometimes lack windows to the outside world.

Can the PDLC glass be dimmed?

Yes, the glass can be dimmed by varying the applied voltage from 0% in the OFF state up to the maximum transmittance (typically 70% or 80%).

This is achieved by altering the voltage with a variable isolating transformer, or electronically with a switched-mode smart glass dimmer.

Where can I buy samples of PDLC smart film or glass?

You can buy cost-effective samples right here on Smartglass World, on our Samples page. Here are examples of PDLC smart film and PDLC smart glass available from our stock, ready to ship worldwide:

Where can I find companies to install PDLC smartglass in my home?

You can check out our Search page, where you can specify the type of technology, the role of the company (e.g. manufacturer, distributor, or installer) as well as the types of smartglass products you are looking for (e.g. smartglass windows, walls, skylights, etc).

You can also specify product characteristics, such as minimum visible light transmittance (VLT), desired operating voltage, or maximum power dissipation:

The results are produced after hitting the ‘Show Results’ button:-

References

1. Hans Kelker, “History of Liquid Crystals,” Mol. Cryst. Liq. Cryst. 21,1-48(1973).
2. “Polymer-dispersed liquid crystal technology, Industrial evolution and current market situation.” H. Hakemi.
3. “Gauzy Ltd. a new industrial development approach in PDLC technology”, H. Hakemi.
4. “Applications of high-resolution solid-state NMR spectroscopy to polymers”, Jack L. Koenig, in Spectroscopy of Polymers (Second Edition), 1999.
5. Polymer Dispersed Liquid Crystals, materiability.com