'Slipperiness' of coatings

[Falstaff]

Hello,

We are looking for a test of actual 'slipperiness', rather than just contact angle. We are producing superhydrophobic AR coatings, but realise that the contact angle is only related to 'slipperiness' for a particular top-coat material. the contact angle is useful to us for establishing monitoring of our processes, but 'slipperiness' is, we think, more fundamental to making the coatings superior to normal hydrophobic coatings.

Consequently, we wondered if anyone has any information on how to measure this attribute directly. We have heard of an inclined plane method, and also that there is an 'ease of cleaning' test devised by Colts.

Many thanks, if you are able to help.

Best Regards,

Falstaff.

[rbaker]

Here is what you are looking for.

ASTM D1894 - Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting

[Chris Ryser]

The surface of a unprotected AR coating looks like the Rocky Mountains under a microscope, where this irregular surface reflects the light. Seen under the microscope, the valleys would collect dirt and facial grease that was hard to remove.

We worked at it and came up with a solution that actually worked. By filling these valleys with a transparent media that would still reflect the light as wanted; we created a way that would block the dirt from penetrating into those areas.


Over the years, all these coatings that came on the market from different suppliers that were claiming a better contact angle than the next one, being more slippery than the next one, all forgot the original duty of such coatings, to prevent dirt and grease from reaching the bottom of the valley.

So the contact angle, and being more or less slippery, is a big put on and has nothing to do with original idea of locking out the hard to remove dirt or grease, as explained above.

We chose to use a material that had already been proven in the medical surgery field and that could be converted for the use on AR coatings where it works well, and can be seen at:

http://www.eng.buffalo.edu/Courses/ce435/Polysiloxanes/