Smart glass or switchable glass , also called smart windows or switchable windows in its application to windows or skylights, refers to electrically switchable glass or glazing which changes light transmission properties when voltage is applied.
Certain types of smart glass can allow users to control the amount of light and heat passing through: with the press of a button, it changes from transparent to translucent, partially blocking light while maintaining a clear view of what lies behind the window. Another type of smart glass can provide privacy at the turn of a switch.
Smart glass technologies include electrochromic devices, suspended particle devices, Micro-Blinds and liquid crystal devices.
The use of smart glass can save costs for heating, air-conditioning and lighting and avoid the cost of installing and maintaining motorized light screens or blinds or curtains. When opaque, liquid crystal or electrochromic smart glass blocks most UV, thereby reducing fabric fading; for SPD-type smart glass, this is achieved when used in conjunction with low-e low emissivity coatings.
Critical aspects of smart glass include installation costs, the use of electricity, durability, as well as functional features such as the speed of control, possibilities for dimming, and the degree of transparency of the glass.
Electrically switchable smart glass
Electrochromic devices
Main article: electrochromismElectrochromic devices change light transmission properties in response to voltage and thus allow to control the amount of light and heat passing through. In electrochromic windows, the electrochromic material changes its opacity: it changes between a colored, translucent state (usually blue) and a transparent state. A burst of electricity is required for changing its opacity, but once the change has been effectuated, no electricity is needed for maintaining the particular shade which has been reached. Darkening occurs from the edges, moving inward, and is a slow process, ranging from many seconds to several minutes depending on window size. Electrochromic glass provides visibility even in the darkened state and thus preserves visible contact with the outside environment. It has been used in small-scale applications such as rearview mirrors. Electrochromic technology also finds use in indoor applications, for example, for protection of objects under the glass of museum display cases and picture frame glass from the damaging effects of the UV and visible wavelengths of artificial light.
Recent advances in electrochromic materials pertaining to transition-metal hydride electrochromics have led to the development of reflective hydrides, which become reflective rather than absorbing, and thus switch states between transparent and mirror-like.
Recent advancements in modified porous nano-crystalline films have enabled the creation of electrochromic display. The single substrate display structure consists of several stacked porous layers printed on top of each other on a substrate modified with a transparent conductor (such as ITO or PEDOT:PSS). Each printed layer has a specific set of functions. A working electrode consists of a positive porous semiconductor (say Titanium Dioxide, TiO2) with adsorbed chromogens (different chromogens for different colors). These chromogens change color by reduction or oxidation. A passivator is used as the negative of the image to improve electrical performance. The insulator layer serves the purpose of increasing the contrast ratio and separating the working electrode electrically from the counter electrode. The counter electrode provides a high capacitance to counterbalances the charge inserted/extracted on the SEG electrode (and maintain overall device charge neutrality). Carbon is an example of charge reservoir film. A conducting carbon layer is typically used as the conductive back contact for the counter electrode. In the last printing step, the porous monolith structure is overprinted with a liquid or polymer-gel electrolyte, dried, and then may be incorporated into various encapsulation or enclosures, depending on the application requirements. Displays are very thin, typically 30 micrometer, or about 1/3 of a human hair. The device can be switched on by applying a electrical potential to the transparent conducting substrate relative to the conductive carbon layer. This causes a reduction of viologen molecules (coloration) to occur inside the working electrode. By reversing the applied potential or providing a discharge path, the device bleaches. A unique feature of the electrochromic monolith is the relatively low voltage (around 1 Volt) needed to color or bleach the viologens. This can be explained by the small over- potentials needed to drive the electrochemical reduction of the surface adsorbed viologens/chromogens.
Suspended particle devices
In suspended particle devices (SPDs), a thin film laminate of rod-like particles suspended in a fluid is placed between two glass or plastic layers, or attached to one layer. When no voltage is applied, the suspended particles are arranged in random orientations and tend to absorb light, so that the glass panel looks dark (or opaque), blue or, in more recent developments, grey or black colour. When voltage is applied, the suspended particles align and let light pass. SPDs can be dimmed, and allow instant control of the amount of light and heat passing through. A small but constant electrical current is required for keeping the SPD smart window in its transparent stage.
Polymer dispersed liquid crystal devices
In polymer dispersed liquid crystal devices (PDLCs), liquid crystals are dissolved or dispersed into a liquid polymer followed by solidification or curing of the polymer. During the change of the polymer from a liquid to solid, the liquid crystals become incompatible with the solid polymer and form droplets throughout the solid polymer. The curing conditions affect the size of the droplets that in turn affect the final operating properties of the "smart window". Typically, the liquid mix of polymer and liquid crystals is placed between two layers of glass or plastic that include a thin layer of a transparent, conductive material followed by curing of the polymer, thereby forming the basic sandwich structure of the smart window. This structure is in effect a capacitor.
Electrodes from a power supply are attached to the transparent electrodes. With no applied voltage, the liquid crystals are randomly arranged in the droplets, resulting in scattering of light as it passes through the smart window assembly. This results in the translucent, "milky white" appearance. When a voltage is applied to the electrodes, the electric field formed between the two transparent electrodes on the glass causes the liquid crystals to align, allowing light to pass through the droplets with very little scattering and resulting in a transparent state. The degree of transparency can be controlled by the applied voltage. This is possible because at lower voltages, only a few of the liquid crystals align completely in the electric field, so only a small portion of the light passes through while most of the light is scattered. As the voltage is increased, fewer liquid crystals remain out of alignment, resulting in less light being scattered. It is also possible to control the amount of light and heat passing through, as discovered by Al Coat Ltd. and SmartGlass International, when tints and special inner layers are used. It is also possible to create fire-rated and anti X-Ray versions for use in special applications. In addition, Al Coat has demonstrated that patterns can be formed in the transparent electrodes or in the polymer, enabling fabrication of display devices and decorative windows. Most of the devices offered today operate in on or off states only, even though the technology to provide for variable levels of transparency is easily applied. This technology has been used in interior and exterior settings for privacy control (for example conference rooms, intensive-care areas, bathroom/shower doors) and as a temporary projection screen. It has been marketed under the name of "Polyvision privacy glass". New generation nano-technology switchable films with improved transparency are offered by Polytronix, Inc. and Scienstry, with working voltages lowered to the 12 to 48 VAC range; the lower driving voltage could extend life expectancy to some extent.
Micro-Blinds
Micro-blinds control the amount of light passing through in response to applied voltage. The micro-blinds are composed of rolled thin metal blinds on glass. They are very small so practically invisible to the eye. The metal layer is deposited by magnetron sputtering and patterned by laser or lithography process. The glass substrate includes a thin layer of a transparent conductive oxide (TCO) layer. A thin insulator is deposited between the rolled metal layer and the TCO layer for electrical disconnection. With no applied voltage, the micro-blinds are rolled and let light pass through. When there is a potential difference between the rolled metal layer and the transparent conductive layer, the electric field formed between the two electrodes causes the rolled micro-blinds to stretch out and thus block light. The micro-blinds have several advantages including switching speed (milliseconds), UV durability, customized appearance and transmission. The micro-blinds are under development at the National Research Council (Canada). One of the novelties is their simple and cost-efficient fabrication scheme.
Related areas of te
Liquid Crystal Vision || Print Collateral
... Window ... © 2001 Liquid Crystal Vision, all rights reserved
Liquid Crystals
Liquid crystals are organic materials which exhibit certain ... able to produce optical shutters, privacy windows and the digital lenses used in the first commercial liquid crystal ...
DoITPoMS TLP - Liquid Crystals - Defects
in separate window... video alone. The concept of disclinations in liquid crystals is analogous to that of a dislocation in solid materials. The TLP Introduction to Dislocations ...
PDLC FILM / PDLC GLASS - Polymer Dispersed Liquid Crystal Film/Glass ...
Polymer Dispersed Liquid Crystal Film (PDLC) / Glass / Window (liquid crystal glass, smart glass, magic glass, intelligent glass,
DoITPoMS TLP - Liquid Crystals - Observing phase transitions
in separate window... video alone. The elongated liquid crystal molecules tend to orientate along the scratches – this is why we now see uniform extinctions rather than various ...
Molecular Expressions: Liquid Crystal Wallpaper for Windows
Download our customized Molecular Expressions liquid crystal wallpaper for Windows 3.1, 95, 98, and NT.
Greenhouse experiment to use liquid crystal windows | Business ...
Greenhouse experiment to use liquid crystal windows By Randy Roguski January 08, 2008, 10:41PM. GREEN INC. A monthly look at companies embracing sustainability
Amazon.com: "liquid crystal window": Key Phrase page
Key Phrase page for liquid crystal window: Books containing the phrase liquid crystal window
PDLC Switchable Windows
Polymer dispersed liquid crystals were invented at Kent State University in 1983. A major application of these materials is in switchable windows.
Liquid Crystal Gallery | Home
Liquid Crystal Gallery presents a series of compelling cinematic programs with original music ... Windows Media Player • RealMedia Japanese Gardens Windows Media Player • RealMedia