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|ASTM D 7334|
Recently ASTM International released a new
standard for characterizing surface wettability: "Practice for Surface
Wettability of Coatings, Substrates and Pigments by Advancing Contact
Angle Measurement."1 The primary motive for this new standard
has been to develop a highly quantifiable method for predicting
adhesion, printability and paintability. Surfaces that produce contact
angles lower than 45° are said to have good wetting while even more
hydrophilic surfaces with contact angles in the 10° to 20° range are
said to have excellent wetting. As contact angle decreases, wetting
increases and so too does adhesion and the likelihood that coatings will
stick to the surface and look good over time.
Water is used to measure the advancing (or maximum) contact angle (as opposed to the static or receding contact angle). In addition to characterizing the surface properties, contact angle can also be used to detect cleanliness and determine the efficacy of processes such as rinsing, etching, and solvent wiping (for example, on plastics).
Coatings can suffer from myriad defects - pinholing, skinning, cratering, and crawling to name a few.1 Contact angle is used to predict the success of applying a particular coating to a treated or untreated surface. Moreover, the relative success of the various surface treatments can also be predicted by understanding how the treatments affect wettability.
This is the first standard published by ASTM that uses contact angle to address coatings and will be of interest to anyone involved in the manufacture of paint or its application. Interestingly, the standard "is intended to supplement the manufacturer's instructions for the device being used to make the measurements, but is not intended to replace them."2
|Switchable Wetting Properties|
In an effort to control wetting,
researchers in Sweden have developed a novel approach that reverses the
contact angle and spreading of a water droplet by electrochemically
reducing or oxidizing a polymer surface.1 These same
researchers are applying this method to induce wettability in order to
control the flow of water on a polyaniline surface.2 This
technique can aid researchers involved in micro- and nano-fluidics - a
somewhat new discipline focused on precisely controlling the movement of
fluids on a surface at the microscopic and nanoscopic levels. A
commercial example of nanofluidics can be found in an inkjet printhead.
By altering the electrochemical state of a polymer, these Swedish researchers claim to have invented a reversible wettability switch which can toggle between lyophobic and lyophilic molecules to switch wetting properties of a surface.3
The ability to control wetting plays a key roll in the development of such diverse and emerging technologies as fuel cells and biotechnical devices. Since nanofluidics is so new, expect to see in the future many new applications that operate by controlling wetting properties.
We're pleased to announce
that with the recent release of Microsoft Windows 7, we have upgraded
all (3) editions of our DROPimage software to run on Windows 7. In our
bench tests the new version of Windows is more stable and faster than
both Vista and XP. Additionally, there are a number of new features in
Windows 7 that make it compelling. The Snipping Tool, for example, makes
it super easy to capture a picture from your screen to save, email, or
print out. This little tool will be a great benefit to our customers who
like to send us pictures of their contact angle and surface tension
measurements for comment and evaluation. Then there's Windows 7's Pin, Jump Lists, Snap, Peek, and Shake.
Sounds like a new dance. Beginning in 2010 all new ramé-hart systems
will ship with Windows 7.
|Call for Papers|
On behalf of our friends at
MST Conferences, we'd like announce a call for papers for the upcoming
Seventh International Symposium on Contact Angle, Wettability, and
Adhesion which will be held in Danbury, CT, June 23-25, 2010. If you or
a colleague are interested in presenting a paper, please email a
200-word abstract to Dr. Lacombe at
email@example.com by December 15th. For more details, go to:
http://tinyurl.com/yecf55e If you are planning on attending, then we
look forward to seeing you there. ramé-hart instrument co. has been a
symposium sponsor for many years.
On behalf of everyone at ramé-hart instrument co., we'd like to wish everyone a Happy Holiday and a Prosperous New Year. Thank you to all of our customers for helping to make 2009 a good year for us despite the many economic challenges that are shared by all.