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August 2012 |
| The Amazing Properties of Graphene |
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Andre Geim and Konstantin Novoselov of the
University of Manchester were awarded the 2010 Nobel Prize in Physics
"for groundbreaking experiments regarding the two dimensional material
graphene"1. As it turns out, Graphene, the world's thinnest
material at only a single atom thick, has some amazing properties.
For example, researchers at Rensselaer Polytechnic Institute and Rice
University2 discovered that samples of gold, copper, and
silicon coated with a single layer of graphene exhibited no change in
contact angle. According to Dr. Koratkar at Rensselaer, "The single
layer of graphene was so thin that it did not significantly disrupt the
non-bonding van der Waals forces that control the interaction of water
with the solid surface. It’s an exciting discovery, and is another
example of the unique and extraordinary characteristics of graphene."3 Graphene is made of carbon atoms arranged in a chicken-wire fence pattern. The material has superior mechanical properties: it's strong, flexible, does not crack or break apart easily, and can coat many types of surfaces. Graphene is also impermeable; water cannot pass through it. Exactly for this reason researchers were surprised that while a water drop cannot pass through the film, it is still so thin that the drop can sense the presence of the underlying material and wet according to that material. “We found that van der Waals forces are not disrupted by graphene. This effect is an artifact of the extreme thinness of graphene—which is only about 0.3 nanometers thick,” Koratkar said. “Nothing can rival the thinness of graphene. Because of this, graphene is the ideal material for wetting angle transparency.”3 As additional layers of graphene are added to the surfaces, the transparent wetting behavior gradually diminishes. By the time six layers of graphene are added to a surface, the van der Waals forces see primarily the carbon coating and not the underlying surface. There are many potential applications for a thin nanomaterial that creates an impermeable film while not affecting the wetting properties of the underlying material. Take copper tubing in a humidifier application, for example. A layer of graphene on a copper tube could prevent oxidation while not affecting the wetting properties of the underlying copper. Dr. Koratkar and other researchers at Rensselaer have also discovered methods for using modified graphene sheets to dramatically alter the wetting properties of a surface.4 For example, surfaces coated with graphene sheets which are sonicated in water become superhydrophilic. Conversely, surfaces coated with sheets which are treated in acetone take on superhydrophobic behavior. By precisely controlling the amount of water and acetone used to treat the graphene, researchers can customize the wetting properties of a surface over a wide spectrum of contact angles. By controlling the number of graphene layers placed on a surface, material scientists can control the transparency effect of graphene. And by modifying the graphene layers using sonication with controlled levels of water and solvent, they can precisely control the wetting properties of many surfaces. Expect graphene to take on an increasingly important role in material design and development and open up new windows in controlled wetting behavior. 1 "The Nobel Prize in Physics 2010". Nobelprize.org. 30 Jul 2012 http://www.nobelprize.org/nobel_prizes/physics/laureates/2010/index.html 2 DOI:10.1038/nmat3228 3 http://news.rpi.edu/update.do?artcenterkey=2978 4
DOI: 10.1002/adma.200903696 |
| Dispensing Needles and Tips |
|
All ramé-hart goniometers and tensiometers
use one of two methods for dispensing. The default method which is
included with every instrument is a microsyringe assembly with stainless
steel dispensing needle. Our standard needle size for water is 22 gauge.
However, we carry every size from 8 to 33 gauge. As the gauge number
increases, the diameter decreases. As a rule, you should use a lower
gauge (i.e., larger diameter) needle as viscosity of your liquid
increases. If you are trying to form pendant drops and the drop is
riding up the side of the needle, you can use a higher gauge (i.e.,
smaller diameter) needle to overcome this condition. We also carry solid
PTFE needles (14 to 22 gauge) which inhibit wetting due to the
hydrophobic property of PTFE. We carry inverted needles in sizes from 10
to 28 gauge which are useful for captive bubble, inverted pendant drops
in liquid/liquid studies, and inverted sessile drops using the
Environmental Fixture or Environmental Chamber and Cover with Stage. We
also carry disposable tips in sizes from 14 to 27 gauge.
The other method for dispensing is using our software-controlled Automated Dispensing System which is designed to work with disposable tips. We offer 30µL and larger 250µL tips which are made of polypropylene. We also include with new Automated Dispensing Systems, and offer separately for users of legacy dispensers, a needle adapter which permits the dispenser to work with any standard needle. Additionally, we offer custom-made needles per our customer's specifications including coaxial and triaxial needles. For a chart of all of our standard needles including sizes and dimensions, please consult this needle chart. All standard needles and tips can be ordered online at www.ramehartstore.com.
If you are looking for needles for a
particular dispensing application or need a custom-made needle, please
contact
us for more information and a quotation. |
|
Carl Clegg |
