-----Original Message-----
From: Jones Beene
Dinner guest will call it "dynamite." If anything changes, I will post
directly to you to avoid taking up bandwidth on what could be little
more than a cooking lesson ...
<><><><><>
No, please, let's keep it on the list. Bloody list hasn't seen any
experimentation in ages.
Patent US6743467 sez:
"BACKGROUND ART
Hydrophobic coatings are water-proof coatings which have immediate uses
in reducing icing and fouling of other surface. Such coatings can also
render protected surfaces resistant to attachment by water soluble
electrolytes such as acids and alkalies, and by microorganisms.
In the past, surfaces have been protected against encrustation,
corrosion, icing and fouling by means of coatings containing polymer
films, hydrophobic solid fillers and hydrophobic liquids. One
disadvantage of the use of such coatings is that they do not achieve
multi-purpose protection since they are not generally versatile enough
to protect against damage from a variety of causes.
It is well understood that the wettability of various materials is
dependent on both the physical and chemical heterogeneity of the
material. The notion of using the contact angle .theta. made by a
droplet of liquid on a surface of a solid substrate as a quantitative
measure of the wetting ability of the particular solid has also long
been well understood. If the liquid spreads completely across the
surface and forms a film, the contact angle .theta. is 0.degree.. If
there is any degree of beading of the liquid on the surface of the
substrate, the surface is considered to be non-wetting. For water, the
substrate surface is usually considered to be hydrophobic if the
contact angle is greater than 90.degree..
Examples of materials on which liquid droplets have high contact angles
include water on paraffin, in which there is a contact angle of about
107.degree.. Many applications require a hydrophobic coating with a
high contact angle of at least 150.degree., and preferably at least
165.degree..
A "gel" is a substance that contains a continuous solid skeleton
enclosing a continuous liquid phase. The liquid prevents the solid from
collapsing, and the solid prevents the liquid from escaping. The solid
skeleton can be formed by linking colloidal particles together.
The present inventors have now developed methods for producing
materials which, when coated on a surface, render that surface
hydrophobic. "
What is meant by 'contact angle'? Is this the slope of the water bead
at the surface of the hydrophobic material?
(Note: these inventors are Aussies. One is named Jones.)
Terry
