1) Diatomaceous earth was treated with different length alkyltrimethoxy silanes (n = 0, 2, 7, 11, 15, 17) to modify the surface properties. 2) Thermogravimetric analysis and contact angle measurements showed surfaces became superhydrophobic for chain lengths n ≥ 12 and hydrophobic for n < 12. 3) Contact angles over 150° were achieved when coatings contained 50% or more modified diatomaceous earth.

1. Materials : diatomaceous earth (untreated), alkyltrimethoxy silane, p-toluenesulfonic acid,
amine, hexamethylene diisocynate, tetrahyrofuran, and toluenewere used as received.
1. Thermogravimetric analysis (TGA) of different chain length alky silane on DE
M.A. Helanka Perera and Frank D. Blum
Department of Chemistry, Oklahoma State University, Stillwater, OK 74078
 Polyurethane film with untreated DE, on its own, was not
hydrophobic. It had contact angle of 81o. Polyurethane coating
itself has 72o.
 CH3(CH2)n-Si(OCH3)3 treated DE surfaces become,
superhydrophobic n ≥ 12, hydrophobic n < 12
Observations:
Acknowledgements
Observations:
Introduction
FIGURE 1. The TGA curves of DE treated with different chain length
alkyltrimethoxy silanes.
FIGURE 2. The contact angles of polyurethane coatings as
different chain length alkyltrimethoxy silane on DE.
 Contact angles larger than 150° can be obtained when 50%
or more modified DE is used in the coatings
Experimental
Results
Conclusions
The lotus effect has inspired many studies on formation of superhydrophobic surfaces that have
a static water contact angle larger than 150oC and a roll-off angle of less than 10oC.
Superhydrophobic materials are generally water repellent, a feature that is strongly influenced
by both composition and geometric structure (or surface roughness).1 A variety of methods and
materials have been used to generate superhydrophobic surfaces such as polymers, carbon based
materials and silica.1-3
Diatoms are unicellular algae inhabiting fresh and saltwater. A diatomaceous earth (DE) skeleton
is made of 80-90% 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.4
Due to these micro- and nano-structures DE can be used in formation of superhydrophobic
coatings. Due to higher amount of silica DE itself is a hydrophilic material adding different
chain length n-alkyltrimethoxy silane onto DE able to explain the development of
hydrophobicity on DE as chain length.
Effect of alkyl chain length on the surface properties of
silane-treated diatomaceous earth coatings
References
c. Contact angle with different weigh percentages of silanted DE
FIGURE 3. The contact angles of polyurethane coatings as a
function of the amount of the 3.6% C18-TMS.
2. Contact angle measurements
Observations:
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. Differential scanning calorimetry (DSC)
DE + Toluene
Alkyltrimethoxy silane
CH3(CH2)n-Si(OCH3)3
n = 0, 2, 7, 11, 15, and 17
p – toluenesulfonic acid
50 oC, 2hr
Modified DE
Thermogravimetric analysis
(TGA)
Differential scanning
calorimetry (DSC)
Contact angle analysis
Characterization
85
90
95
100
0 500
%weight
Temperature (oC)
0.26
0.28
0.3
-40 60
Heatflowrate
(W/g)
Temperature (oC)
0.25
0.27
0.29
0.31
0.33
-40 -20 0 20 40 60 80
Heatflowrate(W/g)
Temperature (oC)
C18-TMS
C16-TMS
C12-TMS
C8-TMS
C3-TMS
FIGURE 4. The DSC curves of DE treated with different chain
length alkyltrimethoxy silanes.
a. Contact angle : Effect of carbon chain length
b. Contact angle with different amount of surface treatment on DE
0
20
40
60
80
100
120
140
160
180
0 1 2 3 4
Contactangle(Degrees)
% of grafted silane on DE
C16-TMS
C18-TMS
 CH3(CH2)n-Si(OCH3)3 treated surfaces become, superhydrophobic n ≥ 12,
hydrophobic n < 12,
Contact angles can be as high as 150° when DE with more than 2 % coupling agent is
used.
Contact angles larger than 150° can be obtained when 50% or more modified DE is used
in the coat.
A simple and inexpensive process has been developed to produces hydrophobic polymeric
coatings with treated DE.
(1) Shanmugharaj, A. M.; Yoon, J. H.; Yang, W. J.; Ryu, S. H. Journal of Colloid and Interface
Science 2013, 401, 148.
(2) García, N.; Benito, E.; Guzmán, J.; Tiemblo, P. Journal of the American Chemical Society
2007, 129, 5052.
(3) Grundke, K.; Zschoche, S.; Pöschel, K.; Gietzelt, T.; Michel, S.; Friedel, P.; Jehnichen, D.;
Neumann, A. W. Macromolecules 2001, 34, 6768.
(4) Tu, K. L.; Sharon, V. R.; Fung, M. A. Journal of Cutaneous Pathology 2011, 38, 762.
(5) Sohn, E.-H.; Ahn, J.; Kim, B. G.; Lee, J.-C. Langmuir 2010, 27, 1811.
Figure 3. The contact angle of polyurethane coatings as weight
fraction of C16-TMS and C18-TMS on DE (50% modified DE on
the surface).
Superhydrophobic
Hydrophobic
Superhydrophobic
Hydrophobic
Hydrophobic
Superhydrophobic
 Melting temperature increase as length of alkyl chain length increase from 12 to 18.
This due to the increasing of van der Waal interaction between the longer alkyl chain
lengths.5