Hydrophobic and hydrophilic are words used to describe the interface between a surface to a liquid, specifically how likely a liquid is to spread (wet out) or bead up.
Hydrophilic Surface
A hydrophilic surface is considered “wettable”. This means the surface is inviting to liquids and they will spread out easily. The more easily they wet out, the more hydrophilic a surface is.
Application Options: Food wrap, medical packaging, lenses, automotive displays, mirrors, solar panels.
These are all examples of materials that one may consider “Anti-Fog” applications. To create an antifog, you often need a special coating. To adjust the hydrophobicity of the substrate/film. This coating allows the condensation to spread thin and evenly across the surface. The coating has an absorbent quality, which temporarily holds the moisture. This results in the ability for light to pass through without scattering, resulting in an “anti-fog appearance”.
Hydrophobic Surface
A hydrophobic surface not inviting to liquids, as described in the word “phobic”, liquids do not want to spread across the surface and will bead up away from the surface to have less contact.
Application Options: Touchscreens, outdoor labels, flexible electronics.
These non-polar items are often listed as “waterproof” or “water-resistant”, and they have a coating that is typically silicone or wax based. These coatings naturally repel the water, creating a greater contact angle, and create a barrier between the substrate and the liquid.
Water Contact Angle
How hydrophilic or hydrophobic surfaces can be measured is by the water contact angle of a droplet of liquid using a goniometer. The water contact angle quantifies the wettability of the surface by measuring the angle of the liquid droplet to the surface that the droplet sits on. The greater the contact angle, the more hydrophobic the surface. The lower the contact angle, the more hydrophilic.
Example results for a Hydrophilic surface:
• Complete wetting: 0° contact angle.
• Good wetting: 45° contact angle.
• Bad Wetting: 95° contact angle
Conclusion
Tekra offers a wide variety of films with varying levels of hydrophilic and hydrophobic properties, depending on your application. We are able to perform water contact angle testing upon request, and we offer R&D services and custom coating if you have specific values you need met for your market.
Contact your Tekra representative today to find out more about our current line up and our full research and development capabilities! 800-448-3572.
