February 2012

In the past few years more and more people are using their fingers to interact with devices. Tablets, GPS's, smartphones, and HMI's (Human Machine Interface, such as automotive touchscreen displays) are getting smarter and doing more and requiring more input. Keyboards and pointing devices on mobile products are problematic due to space limitations. Voice recognition is still not very good and requires a lot of processing power. And so more and more the input device for today's generation of mobile devices is the touchscreen.

The downside to touching touchscreens is the buildup of finger oils which make it hard to see the screen underneath and can attract abrasive particles which further damage the screen. To overcome this problem, device designers are developing oleophobic coatings and materials which repel fingerprints and smudges while still allowing the screen to be clearly seen.

Just as "hydrophobic" means fear of water, "oleophobic" means fear of oil. An oleophobic surface resists oils and exhibits low wetting properties with oils (and usually water too). Since oils have a lower surface tension than water, they have a higher propensity to wet even on surfaces that are hydrophobic such as PTFE. In short, making a surface oleophobic is often more a challenge than making a surface hydrophobic.

While an oleophobic surface may not be completely fingerprint proof, any oils left on the surface will bead up with a high contact angle and can be easily wiped off.

Most of today's oleophobic coatings are applied using a vacuum and vapor thin film deposition processes. In one common method, an electron beam vaporizes dielectric material within a vacuum chamber. The layer of vaporized material is vacuum sealed to the glass or polycarbonate substrates forming microscopic peaks and valleys as shown above. Next an oleophobic layer is deposited and vaporized. The evaporative oleophobic material creates a permanent chemical bond with the first layer of dielectric material filling into the valleys. Once these two layers are applied to the substrate, no future reapplication is necessary.

One of the problems with current generation oleophobic thin film coatings is their durability. Apple iPhone users complain on forums of ghost like circles in areas where the coating has worn off. Repetitive use such as gaming seems to accelerate the problem.

An alternate solution is the use of an oleophobic screen protection film such as 3M's Vikuita product. The advantage is that it can easily be replaced and it may enhance the display – making it brighter, whiter, with better color and easier to see in a variety of conditions. The downside is that the user has to purchase and install multiple screen films over the course of a product's life – which is an expense and an inconvenience.

Researchers and material scientists are working on new and innovative ways to make touchscreens more oleophobic and durable while maintaining high optical quality. Many of these innovators are turning to ramé-hart instrument co. Our most simple Model 190 is capable of measuring the contact angle of any liquid on any surface. More advanced requirements, such as the capacity to measure advancing and receding contact angles, perform dynamic or time-dependant studies, and measure surface energy and surface tension, call for a more advanced instrument such as our Automated Model 290 or 590 Goniometer / Tensiometer. If you are developing or testing oleophobic coatings or materials and need a way to characterize the modified surfaces, don't hesitate to contact us to see how we can help you.

Since the ball is 4mm in diameter, the distance measured in both directions should be very close to 4mm as shown above. Note that this check can be done with both DROPimage Standard and Advanced.

Regards,

Carl Clegg
Director of Sales
Phone 973-448-0305
www.ramehart.com
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