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

86

88

90

92

94

96

98

100

0 100 200 300 400 500 600 700 800 900

% W

eig

ht lo

ss

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

Co

nta

ct a

ng

le

(Deg

ree)

Weight fraction of 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

Co

nta

ct a

ng

le (

Deg

ree)

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)