What Is PDLC Smart Glass?

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 engineered into end-products such as smart windows, smart glass displays and smart consumer electronics, giving privacy, security and energy efficiency.

What is a Liquid Crystal?

A liquid crystal is a hybrid between (i) a liquid which flows like a fluid and (ii) a crystal which is normally found as a solid, exhibiting short- or long-range symmetry.

Why does PDLC require a polymer?

The polymer allows the liquid crystals to be embedded into a film, which can then be sandwiched between panels of glass or plastic. The polymer has constant optical properties which do not vary across it’s structure, and hence is considered ‘isotropic’.

In contrast, the liquid crystal itself is ‘anisotropic’, since it’s 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 PDLCs is a result of its ability to change it’s transparency (technically called the ‘transmittance’) when an electrical stimulus is applied to it. This is normally by way of an alternating voltage, which exerts an alternating electric field across the PDLC material.

Nevertheless, the PDLC is only as smart as the control system which stimulates the change, which can be driven by a push button switch, a light sensor, or a 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 an electrical signal 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.

Where can we find PDLC smart glass?

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

PDLC smart glass is composed of :-

  • Outermost panels of normal float glass (or sometimes acrylic) sandwiched around:
  • Inner panels of optically clear PET plastic (polyethylene terephthalate), sandwiched around:
  • ITO (Indium Tin Oxide) which is a transparent conductor, sandwiched around:
  • a PDLC core comprised of liquid crystal droplets, suspended in a polymer.

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 more like a capacitor, where the applied signal alternates between positive and negative voltages at the plates of the capacitor, causing an alternating electric field throughout the PDLC dielectric, which 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?

  • 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)
  • Reduction of the carbon footprint of the building thanks to the solar control, which reduces HVAC needs, both in summer and in winter
  • 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 (i.e. hospitals and clinics, since the PDLC smart glass can replace unhygienic curtains and blinds which often carry microbes and germs, and this also improves air quality)
  • 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

Are the only states of PDLC just ON and OFF?

No, the transmittance (level of transparency) of the PDLC can be varied from 0% in the OFF state up to any value you want until you reach the maximum transmittance (normally 70% or 80%). This is done by simply altering the voltage from 0 Vac up to 100 Vac, which is typically the maximum recommended voltage. This can be done electrically with a variable isolating transformer, or electronically with a switched-mode smart glass dimmer.

References

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

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