Anti-Fogging Glass

Car windows, eyeglasses, camera lenses, even our bathroom mirrors are all victims of the frustrating effects of fogging. Fogging can pose hazard when it inflicts automobile windscreens; glass fogs up when warm, moist air comes into contact with it and cools to form thousands of tiny water droplets on the glass. The droplets scatter light, reducing the visibility through the glass.

Existing Technology

Fog is caused when steam condenses on a cool surface and then forms minuscule water droplets due to the water's surface tension. Water molecules are more attracted to each other than to air molecules and form a spherical shape to maximise contact between water molecules, which leaves as few as possible exposed to the air.

But water is also attracted to glass, and if this attraction is enhanced, it can overcome the surface tension. Previous anti-fog coatings have capitalised on this using titanium dioxide surfaces which increase the attraction between the water and glass. This overcomes surface tension so the water spreads out in sheets.

However, these coatings first need to be charged by UV light which means they do not work for long in the dark. And they tend to stop working altogether after three months.

Latest Anti-Fogging Glass

Super-hydrophillic

Super-hydrophillic - water loving - coating is composed of nano-particles made of silica, the same material that glass is made from, to create a coating with a rough surface, although it looks smooth to the naked eye. Polymer chains are used to assemble these very tiny particles of Glass onto a surface. A polymer chain is a long chain-like molecule with positive charge and the glass particles with negative charge are taken. So positive to negative attractive force can be used to build these layers up onto the surface. The net result is we create a very porous coating, that is, a coating that has lots of holes in it.

The silica particles form layers of tiny pores, each a thousand times smaller than the width of a human hair. The pores attract the tiny droplets of water that make up the foggy surface. Stacked ten to twenty layers thick, with air pockets in between, these pores create what's called a "wicking" effect, which forms the water droplets into a uniform sheet. When a droplet is dropped on that surface, the water is drawn into these pores instantaneously and wicked away into a uniform sheet. The result is no water droplets on the surface that can scatter light and a nice transparent lens in this case.

This cheaply produced technology added benefit of increasing the clarity of unfogged glass. It reduces the glare and allows more than 99 percent of light to pass through the glass, compared to untreated glass that scatters between four and eight percent of light. Because of the thin film coating that is filled with holes, it means that the coating also acts as an anti-reflection coating. That is, it will allow more light to pass through.

The super-hydrophilic materials with self-cleaning action are currently in use for side view mirrors of vehicles and exterior materials of buildings.

Super-hydrophobic

Super-hydrophobic - water-fearing – coating is made by adding a second, ultra-thin layer of water-repelling molecules. Then the large surface area created by the roughness of the surface has the opposite effect. It increases the repulsion between the water and glass, causing the water to form droplets.

These could be used to form self-cleaning surfaces, where water that lands on the surface is snapped up into droplets that grow larger and larger until they finally roll away, taking the dirt with them. This is the method a lotus leaf naturally uses to clean itself.

Application

• Windshields and windows

• Solar panels

• Lenses for cameras, endoscopes, laparoscopes, and other optical devices

• Eyewear – goggles and glasses

• Dental mirrors

Advantages

• Stable over time

• Inexpensive

• Does not require UV-light activation

• Excellent optical properties (high transmittance; low reflectance and refractive index)

Acid-Etched Glass

Acid etching is a process that uses a strong acid to cut into another substance. It is used for both industrial and artistic purposes. For example, etching can be used to prepare flooring like cement for painting or refinishing, while artists use it to create detailed pictures on metal or glass.

Acid-etched glass has a distinctive, uniformly smooth and satin-like appearance. Acid-etched glass admits light while providing softening and vision control.

Origin of Acid-etched glass

During the middle ages, acid glass-etching was somehow clouded with controversy since its acid medium, hydrofluoric acid, caused too much of a health risk to the artisans. In fact the acid was so potent that users were found to have been poisoned even by its mere fumes. Accidents most often happened where a skin contact with the acid dissolved into the tissues, which later resulted in mutilation or loss of the artisan’s fingers. As a result, acid etched glass craftsmanship lacked refinement and thus lost its luster as an art collection.

Now, there are etching tools such as swivel knives, pick knives, adhesive masks aside from the squeegee which makes it possible for an ordinary person to work on acid glass-etching.

Acid-Etching Glass production

Acid etched glass is produced by acid etching one side of float glass. Etched glass is created by cutting a design stencil that is made of an abrasive resistant material, such as vinyl or rubber. The resulting stencil is called a resist. The resist is then secured onto the glass to be etched. A blaster gun, powered by an air compressor, is used to bombard the glass with the abrasive. Every part of the glass that is not covered by the resist will take the frosted effect while the parts protected by the resist will remain clear, thus producing a piece of etched glass.

Etching glass - Hydrofluoric acid

Glass is etched by hydrofluoric acid, or by hydrofluoric acid gas. The gaseous acid has the property of producing a surface which resembles ground glass in its appearance; the liquid acid produces clear etching. Etching glass, therefore, consists of 2 distinct branches. First, the production of a dull image on a clear surface (when the gas is used) and second, the production of a clear image on a surface previously ground or dulled by means of the liquid acid.

The glass plate to be etched is cleaned and gently warmed until hot enough to melt wax. The surface is then covered with an equable layer of white wax, by rubbing the wax over it. When cold, the design is cut out of the wax with a graver. A shallow leaden trough, about the size of the plate (but a trifle smaller) is obtained, into which is placed a small quantity of finely - powdered fluorspar. This must be weighed and then gently sifted over the bottom of the trough. To every 2 parts by weight of fluorspar add 3 of good oil of vitriol. Stir quickly with a wooden stick, and place on the hob or other warm place. Vapour will soon rise.

Now the trough is removed and covered over with the waxed and graved plate, wax side downwards. In a very short time, the acid will have etched the bare portions of the glass. When sufficiently etched, remove the wax by melting. To prepare the liquid acid for clear etching, place 2 parts fluorspar and 3 of sulphuric acid in a leaden retort, the tube of which must dip into a leaden bottle half - filled with water.

Apply heat to the retort as long as the water will absorb the fames generated. If a ground glass be prepared with wax, as above, and a ledge of wax or putty be made round it, on pouring the liquid acid on the plate, clear lines on the dull ground will result; or a "flashed" colored glass may, by the same means, a colorless picture on a colored ground can be done. The sheets of clear glass may themselves be dulled by exposing them, without previously waxing, to the fumes of the acid gas.

Applications

Acid etched glass is perfect for both interior and exterior applications. Architecture and construction, like in houses, restaurants, hotels, commercial buildings, etc. They are found in many residential applications such as home decoration like furniture components. Some of the suggested applications are:

• Interior partitions
• Railings
• Shelves
• Shower and bath enclosures
• Doors and windows
• Glass walls
• Kitchens
• Interior and exterior doors