One means water fearing (hydrophobic).
The other means water loving (hydrophilic).
Yet both share one common function: they can be used as a protective coating on your glass.
Nevertheless, hydrophobic and hydrophilic coatings are in fact different. From their properties to their functions, both protective coatings have a different way of working.
Difference #1: Water’s reaction when touching the coated surface
When water comes into contact with a glass surface that has been treated with a hydrophobic coating, the chemical makeup behind the coating will cause the water to immediately bead up.
Hence the name hydrophobic “water-fearing” coating. It pushes the water away.
Think of it like a nonstick pan. The food and oils move across the surface of the pan very smoothly and can be wiped off with “one fell swoop”.
Conversely, when water comes into contact with a glass surface that has been treated with a hydrophilic coating, the chemical makeup behind the coating water will cause the water to smooth out and spread itself across the glass surface. Hence the name hydrophilic “water-loving” coating.
In this example, think of the water as hugging the glass surface. It pulls the water closer.
The graphic below will help give you an idea of what happens when water touches the surface of each coating.
Difference #2: How they keep surfaces clean
A three-step process, that starts with the sun.
Step 1: After a hydrophilic coating has been applied to the surface of glass, the coating will need around 5-7 days of exposure to daylight before fully activating.
Step 2: Once activated, the coating (from the UV light) will decompose any organic materials on the glass, reducing the adherence to the glass.
Step 3: Finally, the rain (assuming it rains on the coated glass) will wash away the dirt by spreading out (its “hugging” component) on the glass, forming a “sheet”. It is here where the dirt particles on the surface are picked up by the water and washed off the glass.
However, the question of what happens to the water left on the surface, remains an obstacle for hydrophilic coatings.
Where does it go? If it just stays there, will the excess water on the glass create hard water stains? Or is it indeed, “self-cleaning” glass?
The slicker the better.The goal behind any hydrophobic coating is to make it impossible or, as impossible as possible, for hard water to cling to the surface of the glass.
This performance is measured through higher contact angles and sliding angles.
So, once any water comes into contact with the glass surface, it is immediately repelled from the surface and rolls right off.
This will reduce the amount of water and minerals that can stick to the glass causing hard water stains, as well as making it easier to clean the surface when minerals and contaminants are left behind.
A much simpler cleaning process overall and one that does not rely on any environmental factors around it to do the cleaning for it.
Difference #3: Where they can be applied
1) Good for exterior glass on buildings and homes
Because of its conditional abilities to clean dirt and dust off of glass, hydrophilic coatings are best used for outdoor glass applications such as windows on exterior buildings and homes. Especially in hard to reach places.
However, weather also plays a crucial role for hydrophilic coatings as you’ll need living conditions where the sun and rain both come out to play.
If one of those weather conditions is missing from the equation, for example at night, the hydrophilic coating cannot work.
Finally, as they are meant to clean dirt off glass, hydrophilic coatings are not effective on indoor glass such as, shower doors and/or glass railings – whose biggest culprits are hard water stains and smudging, respectively.
1) Good for shower doors, glass railings, exterior glass on windows and commercial buildings
By protecting against hard water stains (through a slicker glass surface) hydrophobic coatings are ideal for glass shower doors and other silica based surfaces in your home.
However, similar to hydrophilic coatings, one can argue that hydrophobic coatings are also great for outdoor applications on commercial or residential buildings – especially if you are in a place where it rains quite often. This is because of the hard water stains that are left on glass when water is left on the surface. As it is, a hydrophobic coating will cause the water to repel off the surface and slide right off.
And in areas where there is a lack of rain (or no rain at all), a hydrophobic coating can still protect against dust, debris, leaching and the like; whereas hydrophilic coatings cannot operate without some sort of rain or water hitting the surface.
For a more in-depth analysis of hydrophilic and hydrophobic coatings be sure to see our infographic explaining the pros and cons of each of them, which will help provide valuable insight into both types of coatings.