Hydrophobic Lenses on Sunglasses

Hydrophobic lenses are one of the most important elements to surf sunglasses.  You do not have to be a Greek major to understand what hydrophobic means.  Hydro = water.  Phobic = fear of.  Hydrophobic lenses are “scared of water” or more appropriately, repel water.

 

The Limits of Hydrophobic Lenses

Hydrophobic lenses are not perfect.  They do not completely clear of water every time you dunk you sunglasses, but they do much better than ordinary lenses.  The hydrophobic coating is the last layer to go onto the lens – if any film (like the oil from your hands) gets on the lenses, the hydrophobic coating become ineffective.  It is important to clean the lenses well before heading into the sea and to not touch the lenses with your fingers when you are surfing.  It is advisable to carry a microfiber cleaning cloth in your board shorts so you can clean the lenses while surfing.

 

 

How do Hydrophobic Coatings Work?

A water molecule is polar and tends to be attracted by other polar molecules, notabley other water molecules.  This phenomenon creates surface tension – instead of covering a surface evenly, limited quantities of water tend to form individual drops.

 

Hydrophobic molecules are neutral and non-polar; they are happy all by themselves, they don't attract anything.  Water is more attracted to itself than to a hydrophobic surface so an individual water drop on a hydrophobic surface will “cling to itself”.  This creates a high contact angle (see image).  Because of this the contact area of the drop on the surface is minimized, limiting surface friction.  Since hydrophobic surfaces do not form bonds with water and they limit friction they send water off the lens better than normal materials.  Perfect for surf sunglasses lenses!

 

Other Benefits of Hydrophobic Lenses

Hydrophobic surfaces are also anti-static.  Dust and other dirtying particles are not attracted to them and sometimes if they do happen to collide they just fall right off.  When they do get dusty and dirty they clean easier than lenses that do not have hydrophobic coatings.