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May 2008
 
Sixth International Symposium on Contact Angle, Wettability and Adhesion
In March we announced that we are again sponsoring the Symposium on Contact Angle, Wettability and Adhesion. This event is organized by our colleagues Dr. Kash Mittal and Dr. Robert H. Lacombe of MST Conferences (www.mstconf.com) and will be held at the University of Maine, July 14-16, 2008. If you are a surface scientist or researcher interested in better understanding the importance of contact angle, wettability and adhesion of liquids on surfaces, or if you are interested in learning more about the latest developments in the field of contact angle and wettability, this symposium is an invaluable resource.

In conjunction with this upcoming symposium the folks at MST Conferences have published their own newsletter, Material Science and Technology Newsletter, Volume 5, No. 1, Winter Spring 2008. We have agreed to help distribute a copy of it for them but it's too large to send as a file attachment to this message. Therefore, we point you to the following link where you can read, print, and download the newsletter:

http://www.ramehart.com/pdf/cas_2008.pdf

We think you will find this publication to be of particular interest since we contributed the material for five of the seven articles. At the end of the document you will find registration and lodging information. Good luck and we look forward to seeing you in Maine.
 
Superhydrophobicity and Superhydrophilicity
Last month's edition of this newsletter presented a detailed look at superhydrophobicity including what is referred to as the Lotus Effect. This article generated a number of questions from our readers and customers relative to the capacity of our instruments to measure the contact angles in the extremes. As a result we were prompted to develop two videos (shown below but also on our website at http://www.ramehart.com/goniometers/diadv.htm)

The first video, shown above, illustrates how we measure superhydrophobic contact angles - in this case with DROPimage Advanced. We have successfully measured superhydrophobic surfaces which have contact angles in excess of 170°. Typically any contact angle over 150° is considered superhydrophobic. A hydrophobic condition exists when water prefers not to wet and the resulting contact angle is high. Hydrophobic molecules are often non-polar and thus prefer other neutral molecules. Many (but not all) hydrophobic surfaces are also lipophilic (attracted to oils). The silicones are a notable exception. So the answer is, yes, any current-generation ramé-hart goniometer can measure superhydrophobic contact angles.

The converse of superhydrophobicity is superhydrophilicity. In an absolute sense, when complete wetting occurs, the contact angle is 0° or very close to it. In these cases, it's not possible to quantify the degree of wetting or measure a non-existent contact angle. So, when we speak of measuring the degree of superhydrophilicity, we would be more correct to simply refer to very low contact angles. We would consider any contact angle under 10° to be very low and as illustrated in the video above, these types of conditions can also be measured using any ramé-hart contact angle goniometer.

One of the most exciting developments in the arena of extremely high and low contact angles is an effect called photocatalysis. Recent research1 shows how glass coated with titanium oxide becomes superhydrophilic after being exposed to light. By controlling the light waves it's possible to create both hydrophobic and hydrophilic conditions on the same surface. There are myriad commercial applications for this phenomenon: side-view mirrors on vehicles and commercial windows can be made to be more self-cleaning.

On a side note, there are no fewer than nine papers on superhydrophobic behavior that will be presented at the above-referenced Contact Angle Symposium. See the Preliminary Program on their website for more details.

1 Japan Nanonet Bulletin, 44th Issue, May 12, 2005.
 

Regards,

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