Self cleaning glass; a myth or a reality

Isn't it a dream come true, glass that cleans itself? No more dust, grime, calcium deposits and dirt to ruin the views?

One of the most tedious tasks in life is maintenance and cleaning. Just the words "self cleaning" will sell almost anything. There is no need to get into asking if this is a required trait or not. I think its quite obvious that most consumers will pay a bit more, within reason, for "self cleaning" glass.

What is self cleaning glass, and are there several types?

Well I would divide this area into two categories

1) Glass coated or applied with hydrophilic layer that uses photocatalytic decomposition
2) Glass coated or applied with a hydrophobic coating. Also known as the "lotus effect"

Now before you fall asleep from the words I will explain in simplicity what these terms actually mean and do and try to point out the important pluses and minuses of each type. Lets start with the two major differences; hydrophilic and hydrophobic.

Hydrophilic simply means that the glass will attract the water and make it spread out like a thin film. Hydrophobic means the glass will repel water and any water that comes in contact with the glass will tend to have a minimum amount of contact with the glass and will create spherical droplets on the surface. Start with the first type; this is glass that is based on having a film of titanium dioxide coating. The glass works in two stages. The "photocatalytic" (simply meaning the accelerated process of using the ultraviolet light to break down the organic dirt on the glass) and makes the glass hydrophilic, During the following "hydrophilic" stage rain washes away the dirt, leaving almost no streaks, because hydrophilic glass spreads the water evenly over its surface. Pluses: Under the right conditions, meaning frequent sun and rain, or if hosed down regularly will reduce the cleaning cycle required of glass. The coating is stable and has a long life span.
Minuses: Titanium dioxide-based glass cannot decompose inorganic dirt, thick non-transparent deposits, such as paint or silicone, waterstop fingerprints, or dust produced during construction. This glass also negatively reacts with silicone and will require specialist glazing. If damaged will require replacement of the glass as no onsite application is possible.
The second type of self cleaning glass is glass applied with a hydrophobic coating also known as having the "lotus effect" which refers to the very high water repellency exhibited by the leaves of the lotus flower. Dirt particles are picked up by water droplets due to a complex micro- and nanoscopic architecture of the surface which enables minimization of adhesion. This form of glass works in a similar way to "Teflon" on a frying pan. It produces a non stick surface and water will run off of this surface quickly and not streak. Glass despite looking like a smooth surface has on a microscopic scale, peaks and valleys which on untreated glass attract and deposit dirt and grime. The coating or applications of this type are silica based and create a nano scale film that covers these valleys or troths. Pluses: Works on organic and inorganic dirt alike. These type of coatings are scratch resistant and will reduces the need for use of chemicals in any cleaning required as dirt will easily wash off. This type of glass coating protects the glass from graffiti and paint. This type of coating can be reapplied on site if required. Minuses: This application, depending on the exact product, has a life span of 5 to 10 years in external conditions.
Cost wise the hydrophobic coatings and applications are usually about half the cost of the hydrophilic type glasses.
We would like to believe that there is a glass that cleans itself but it seems again that, like life, there usually is a compromise and "self cleaning" should actually be renamed into "lower maintenance" to limit customers surprise when they wake up to dirt on their glass that should have cleaned itself.

In summing up we can say that to date there still is no ideal self cleaning glass or a glass that requires zero cleaning but there certainly are some great advantages to the use of these two types of glass products which will both greatly reduce the cleaning chore and cycle.