The document describes a study that developed a simple and inexpensive process to produce superhydrophobic polymeric coatings using diatomaceous earth (DE) treated with fluorosilane (FS). Thermogravimetric analysis and contact angle measurements showed that coatings achieved superhydrophobicity, defined as having a water contact angle greater than 150 degrees, when the weight fraction of FS-treated DE was above 0.025. Both epoxy and polyurethane coatings containing weight fractions of FS-treated DE greater than 0.25 exhibited contact angles above 160 degrees, indicating superhydrophobicity is relatively independent of the type of polymer used. Scanning electron microscope images supported these results by showing distinct

1. Materials : diatomaceous earth (untreated), polyol, bisphenol A epoxy resin, fluoro-
silanol, amine, hexamethylene diisocynate, tetrahyrofuran, and hexane were used as
received.
1. Thermogravimetric analysis (TGA) of different weight percentages of FS
on DE
M.A. Helanka Perera, Abhijit Paul, Balika Khathiwada, and Frank D. Blum
Department of Chemistry, Oklahoma State University, Stillwater, OK 74078
 Epoxy film with untreated DE, on its own, was not superhydrophobic. It had contact
angle of 110o. Epoxy coating itself has 96o.
 When the weight fraction of FS on DE was above 0.025, the maximum
superhydrophobicity was obtained and after that the contact angles remained constant with
changing amounts of FS.
Observations:
Acknowledgements
Observations:
Introduction
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0 100 200 300 400 500 600 700 800 900
%Weightloss
Temperature oC
DE only
0.9% HFTMS
1.8% HFTMS
2.6% HFTMS
3.8% HFTMS
4.6% HFTMS
5.4% HFTMS
6.2% HFTMS
6.8% HFTMS
7.8% HFTMS
8.5% HFTMS
8.9% HFTMS
8.9% HFTMS
FIGURE 1. The TGA curves of DE treated with different amounts
of FS.
FIGURE 2. The contact angles of epoxy coatings as weight fraction of
FS on DE.
 Contact angles increased with increasing amounts of treated DE and went
above 160o with both epoxy and polyurethane coatings. The ultimate contact
angles were the same for both polyurethane and epoxy coatings.
Experimental
Results
Conclusions
Wettability is important for various kinds of solid surfaces for many applications.
Contact angles of water droplets on surfaces can estimate wettability. Surfaces with
very high water contact angles, particularly larger than 150o are usually called
superhydrophobic(SH) surfaces.1 A combination of suitable surface roughness and
low-surface-energy materials is responsible for formation of superhydrophobicity.2
Materials with –CF3 groups, for example, generally have low surface energies in
different applications.3,4
Diatoms are unicellular algae inhabiting fresh and saltwater. A diatomaceous
earth (DE) skeleton is made of silica and it has a unique morphology (pattern of
nanostructures, such as pores, ridges, areoles and others). The sizes of diatoms range
from 2 µm to several millimeters.5 Due to these micro- and nano-structures DE can
be used in formation of superhydrophobic coatings.
Fluorosilane (FS) treated DE can make an inexpensive superhydrophobic
coating with a simple coating procedure.
Superhydrophobic Polymer Surfaces with Silane-treated
Diatomaceous Earth
ReferencesSamples coated onto glass slides
Binder solution with treated DE
Epoxy
binder
Effect of FS
(0% - 8.5% FS treated DE)
DE + FS
H+ catalyst
Treated DE
Effect of DE & polymer
(3.6% FS treated DE)
Polyurethane
binder(PU)
Binder solution with treated DE
Samples coated onto glass slide
Contact angle measurements Contact angle measurements
Contact angle images of water
droplets
 A simple and inexpensive process has been developed to produce superhydrophobic
polymeric material with DE.
 Superhydrophobic properties of DE are relatively independent of type of polymeric
material that was used (epoxy and polyurethane).
 Contact angles above 160° were observed with weight fractions of silanized DE
greater than 0.25.
b. Contact angle with different weigh percentages of silanted DE
FIGURE 3. The contact angles of epoxy and polyurethane coatings as a
function of the amount of the 3.6% FS-DE.
Figure 5. SEM micrographs of coating obtained from PU and 3.6% FS-DE with variation in
the amount of treated DE D) 0% E) 10% & F) 60%.
D E F
a. Contact angles with different weight percentages of FS
2. Contact angle measurements
0
50
100
150
0 0.02 0.04 0.06 0.08
Contactangle
(Degree)
Weightfractionof FS on DE
 SEM images of PU and epoxy coatings without FS-DE, resulted films with no distinct
features.
 The dependence of the contact angles on the amount of treated DE (3.6%) is consistent
with the results from the SEMs. Similar surface structures appear in the SEMs after
about 0.20 weight fraction of DE. Below this amount, the surface has a fair amount of
the polymer on it. DE on the surface is responsible for both the low surface energy
(fluorinated coupling agent) and surface roughness necessary for the superhydrophobic
effect.
Observations:
1. Sun, T.; Feng, L.; Gao, X.; Jiang, L. Acc. Chem. Res. 2005, 38, 644-652.
2. Hazlett, R. D. J. Colloid Interface Sci. 1990, 137, 527-533.
3. Coulson, S. R.; Woodward, I.; Badyal, J. P. S.; Brewer, S. A.; Willis, C. J. Phys. Chem. B
2000, 104, 8836-8840.
4. Nishino, T.; Meguro, M.; Nakamae, K.; Matsushita, M.; Ueda, Y. Langmuir 1999, 15,
4321-4323.
5. Tsai, W.-T.; Lai, C.-W.; Hsien, K.-J. J. Colloid Interface Sci. 2006, 297, 749-754.
A B
Figure 4. SEM micrographs of coating obtained from epoxy and 3.6% FS-DE with variation
in the amount of treated DE A) 0% B) 10% & C) 60%.
B C
Epoxy
binder
0
20
40
60
80
100
120
140
160
180
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Contactangle(Degree)
Weight fraction of 3.6% FS-DE
Polyurethane coating
Epoxy coating
The authors acknowledge the financial support of the National Science Foundation (USA) under
Grant No. DMR-1005606 and the Oklahoma State University. We also thank Stewart Kennedy
(Dry Surface Coatings, Guthrie, OK) and John Simpson, ORNL for assistance with this work. We
also thank the Aldrich Chemical Company for partial travel support.
3. Scanning electron micrographs (SEM)