Superhydrophobic Window Cleaning

The difference between superhydrophobic and hydrophobic is like night and day.  The Water Fed Pole experts among us look down on hydrophobic surfaces with much disdain.  And for good reason. As much as they try, these surfaces still cling to water leaving millions of very fine water drops. Which can leave deposits if the rinse water does not have an ultra low TDS, or is contaminated by something else.  Because of this they are more in favor of hydrophylic glass which is water loving.  This causes water to come together in large sheets and run off the glass slowly taking all of these little drops with it. But even this surface is not truly hydrophylic. In reality it is a blend of both hydrophylic and hydrophobic.  You see the water loving/hating properties of all glass surfaces is measured by the contact angle or the CA.  Getting that right for a water fed pole is a bit tricky.  Not that it can't be done.  Using the right chemistry and technique it should be quite possible.  But consider the advantages of a truly "super" hydrophobic surface.  I want to draw attention to this technology because recently there has been more progress in building this animal.

A man called Chunlei Guo professor of optics at the University of Rochester has developed a superhydrophobic surface on metals using a fempto-second laser.  Such a device it is claimed is capable of creating the heat power equal to the wattage of the entire North American power grid.  Using this type of laser Chunlei Guo has been able to create a unique pattern of micro and nanoscopic structures on metal that are intrinsically part of the metal surface.  This process is quite different from those in use today that rely on chemistry.  This is rather physical optics.  The superhydrophobic effects of a laser etched metal surface are much more enhanced then those of a chemically treated metal surface.  This type of surface is also not subject to "wearing off" since it truly is a part of the metal  In fact it IS that metal.  It is a reshaping of that metal surface.  So it is far less likely to degrade over time.

Since the contact angle (CA) of this type of surface is at least 150 degrees, if you were to use a water fed pole to clean it you would not have to be concerned about leaving little drops of water behind.  First there shouldn't be much dirt on it to begin with because superhydrophobic surfaces are considered self cleaning.  If you were to clean with a WFP it would not take very long.  It should happen at lightning speed.

Implementing this technology on metals is quite acceptable. But using it on glass is not.  At least not at this time from what I have read.  The problem lies in the need to create a double pattern on the glass surface.  The first pattern laid down is microscopic.  The second is nanoscopic.  This unique double pattern is what produces the superhydrophobic effect.  In fact, the pattern is critically necessary to create a superhydrophobic surface with a contact angle in excess of 150 degrees. HOWEVER.   It also interferes with incident light.  That is any visible light striking the surface is scattered in such a way as to produce a kind of haze, or translucence.  No one wants their windows to be translucent unless they ordered them that way! They want them to be transparent.  Or as we put it, crystal clear. 

I don't doubt that someday soon someone will develop a superhydrophobic surface with a contact angle (CA) of 150 degrees for transparent window glass.  But it will have to be transparent, and relative inexpensive.  I haven't mentioned many of the benefits of such a surface.  But there are many. Especially for window glass.  To make my point all I have to do is reference a project going on right now in Israel.  Where a million square feet of glass are being treated with a product called Enduroshield.  This is a chemical hydrophobic coating. The suggested application cost is around three bux per square foot.  The cost to the contractor is about fifty cents per square foot.  Even if those figures are somewhat inaccurate, I think you would still agree that the end cost to the owner will still be quite high.  That cost must match the level of perceived value. So what do you think?  Is there a market for superhydrophobic window glass?

Written by Henry Grover Jr.
henrygroverjr@gmail.com

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