Architectural Record BE - Building Enclosure

Smart Glass Solutions for Interior Commercial Structures

Innovative switchable glass products using polymer dispersed liquid crystal (PDLC) technology provide privacy on demand and other benefits for a range of applications
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Sponsored by Polytronix, Inc.
By Robyn M. Feller
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How PDLC Technology Works

We’re all familiar with liquid crystal display (LCD) applications that we see in our daily lives—they’re everywhere, from our flat-panel television screens, personal computers, and smart phones to digital watches, clocks, and calculators. How many of us, though, stop to consider how this technology works? It’s really quite simple. The liquid crystals are arranged in a matrix array (millions for LCDs), and when electricity is applied, the light is manipulated differently, allowing light to pass through individual elements. This action forms the figures, numbers, and other images we see displayed. PDLC takes it a step further, whereby liquid crystals aren’t arranged in matrix arrays but rather in domains where the microscopic liquid crystal droplets can react synchronously with other droplets to an applied electric field.

Photos showing the glass with power on and off, and diagrams showing how it works.

Images courtesy of Polytronix, Inc.

With PDLC products, when the power is turned on, the liquid crystals align and the window is clear. When the power is turned off, the liquid crystals return to their normal scattering positions and the glass becomes a translucent white pane, providing total privacy. Pictured here is the technology at work in a hospital setting.

With PDLC products, when the power is turned on, the liquid crystals align and the window is clear. The power draw is very low—just 0.5 watts/square foot. When the power is turned off, the liquid crystals return to their normal scattering positions and the glass becomes a translucent white pane. Generally speaking, in its opaque state, more than 96 percent of the parallel light is blocked. This results in a high level of privacy, although half of the total light transmits through the glazing. When switched to a clear state, you can see through the material like you would with a traditional piece of glass, with approximately 75 percent total light transmission.

PDLC glazing is a sandwich of conventional glass laminated to liquid crystal technology. A typical interior glazing unit is made of a sheet of 5- or 6-millimeter annealed glass on each side, with the liquid crystal switchable privacy film packaged in between. The film package consists of two layers of transparent conductive films enclosing PDLC material. The film includes electrical wiring that connects to a transformer, which supplies power for the pane’s operation.

PDLC is a medium whose light-scattering power is adjustable through applying an electric field. In their natural (uncharged) state, the PDLC droplets randomly align. The ordinary refractive index of these liquid crystals does not match that of the polymer so the incident light is scattered white translucent. When an electric field is applied across the material, the PDLC droplets reorient and incident light can pass through, resulting in the transparent state.

According to Sang Lam, senior business development manager for Polytronix, Inc., “PDLC technology looks like glass, but it’s actually film based. In fact, making the switchable film is a different field in and of itself. The film construction consists of two pieces of film with a proprietary liquid crystal mix that gets sandwiched in. The manufacturer will put electrodes on, allowing the film to be turned on and off. The film is what essentially creates the ‘magic’ for PDLC.” Lam adds that the glass construction is a separate piece of the puzzle. You take that switchable film and sandwich it between two pieces of glass using an adhesive (interlayer), such as polyvinyl butyral (PVB), thereby protecting the film within the glass.

Diagram showing PDLC film construction and glass construction.

Image courtesy of Polytronix, Inc.

PDLC film construction



Diagram showing PDLC film construction and glass construction.

Image courtesy of Polytronix, Inc.

PDLC glass construction


Types of PDLC Switchable Products

There are two distinct smart glass products that utilize PDLC technology. Usage of each would depend upon the specific needs of a project. Generally speaking, for quick retrofits with low or moderate costs, self-adhesive films would be the right option. Alternatively, for new builds and renovations meant to last, the laminated PDLC glass would likely be the better choice. Here we will take a quick look at these two product types: laminated switchable PDLC glass and self-adhesive switchable PDLC film.

Laminated Switchable PDLC Glass

There are three different types of glass that can be used in laminated switchable PDLC glass:

  • Annealed (weakest)
  • Chemically strengthened (about two times stronger)
  • Tempered glass (about four times stronger)

All three will exude a greenish tint due to the iron content in the glass. Annealed and tempered glass can be made with a low-iron content, which would give those types a whiter appearance.

Self-Adhesive Switchable PDLC Film

With self-adhesive switchable PDLC film, the adhesive layer is applied directly onto the window, just like a window tint. The self-adhesive film utilizes a dry, or a nonaqueous, application. That is, no water or other aqueous solutions are needed to apply the film to an existing glass panel. Care should be exercised to properly insulate the wiring so as to avoid electrical shock.

 

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