PDLC smart film installation, UK, 2013. Credits: Intelligent Glass, MATT Architecture and Will Pryce Photography.
PDLC stands for ‘Polymer-Dispersed Liquid Crystals’ which can be applied as a self-adhesive plastic film onto existing glass, or engineered into glass end-products such as smart (switchable) windows, smart displays and consumer electronics, giving privacy, security and energy efficiency.
What is a Liquid Crystal?
A ‘liquid crystal’ is a thermodynamically stable ‘mesophase’ of matter which resides in between the solid phase and the liquid phase.
Liquid crystals were first discovered in 1888 by Friedrich Reinitzer (1857-1927), an Austrian botanist, who was studying cholesterol in plants. He observed that the material known as cholesteryl benzoate had two melting points, with the first resulting in an initial ‘cloudy liquid state’ and the second giving a ‘clear state’. The cloudy liquid state is what we now refer to as a liquid crystal.
Whereas solids are highly ordered, and liquids (and gases) have no such internal order, molecules of a liquid crystal lie somewhere in between. Liquid crystals contain rod or disc-shaped structures (called ‘mesogens’) which point along a common axis, called a ‘director’. They are easily polarisable (typically with an electric field).
If you want to know more about liquid crystals, check out our article at this link.
Why are liquid crystals sometimes dispersed in a polymer?
The polymer allows the liquid crystals to be mixed and cured into a film structure, which can then be sandwiched 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, but rather can vary under application of an electric field.
Why is PDLC considered to be ‘smart’?
The smartness of PDLC comes from its ability to refract light randomly (i.e. to scatter light), or to transmit light, depending on the electrical voltage applied to it. This 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 digital building automation system.
How does PDLC smart glass work?
With no applied voltage, the liquid crystals are randomly oriented and scatter the light which enters. When a voltage is applied, the liquid crystals orient themselves parallel to each other, allowing light through.
Does PDLC smart glass become ‘opaque’?
No, the correct term is translucent, since light still gets through, albeit 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 colouration, and this can result in some of the light being blocked, giving an ‘opaque’ result.
What are the applications for 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. See below for more examples.
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 PDLC.
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, sandwiched within:
- layers of ITO (Indium Tin Oxide), a transparent conductor, sandwiched within:
- Inner panels of optically clear PET plastic (polyethylene terephthalate), sandwiched within:
- outermost panels of float glass, which can be low-iron and 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%. When connected to a voltage, it can be up to 80%, but this maximum value varies from manufacturer to manufacturer.
Are PDLCs only available as artificial materials?
Not at all; common examples of 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, which 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)
- 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 lacking windows to the outside world.
What form factors are PDLC glass available in?
- Switchable Toughened Glass
- Switchable Laminated Glass
- Switchable Double-Glazing
- Switchable Window Film
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
- Hans Kelker, “History of Liquid Crystals,” Mol. Cryst. Liq. Cryst. 21,1-48(1973).
- “Polymer-dispersed liquid crystal technology, Industrial evolution and current market situation.” H. Hakemi.
- “Gauzy Ltd. a new industrial development approach in PDLC technology”, H. Hakemi.
- “Applications of high-resolution solid-state NMR spectroscopy to polymers”, Jack L. Koenig, in Spectroscopy of Polymers (Second Edition), 1999.
- Polymer Dispersed Liquid Crystals, materiability.com
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