This document summarizes research into creating a hydrophobic organosilica coating on steel and aluminum surfaces. The coating is created using a sol-gel method. Testing found that the coating increased the water contact angle as the surface roughness increased, with a maximum contact angle of 108 degrees. Characterization of the coating found the particles were between 0.4-0.8 micrometers. In conclusion, a hydrophobic silica coating was successfully created that increases water contact angle with rougher surfaces.

1. Hydrophobic Organosilica Coating on Steel and Aluminum
Manufacturing and Materials Engineering
MAHMOOD M.H, P.h.D. Candidate

2. When water drops on a plant, such as leaf of lotus flower, the
water drops can easily roll off over the leaves surface. This is
usually referred to the Lotus effect [1]. This effect is related to
hydrophobicity phenomenon. This natural super hydrophobicity
has recently received much attention and has attract scientist to
imitate this surfaces property. The high surface tension on the
surface of the lotus leaves causes the water that drop onto the
surface of the leaves have a spherical shape and easily removed by
rolling over the surface and drops.
Introduction

3. Lotus Leaf Superhydrophobicity
Close-up of a lotus leaf with water droplets
Electron microscope photograph of
the surface of a lotus flower leaf

4. Hydrophobicity comes from the Greek word Hydro (water)
and Phobicity (fear), it refers to the physical property of a
material that reject a mass of water on its surface.
Some of the common natural Hydrophobic materials are waxes,
oil and fats.
WHAT IS HYDROPHOBICITY ?

5. Hydrophilicity, also comes from the Greek word Hydro (water)
and Philicity (friendship) it refers to a physical property of a
material that can make bond with water’s hydrogen bonding.
Furthermore it allows the liquid to enter the pores of a material and
totally wet it.
Almost all natural materials are hydrophilic in nature.
WHAT IS HYDROPHILICITY ?

7. Young's equation is used to describe the interactions between the
surface forces and measure surface energy.
www.ramehart.com/contactangle.htm

8. Super hydrophilic
Normal hydrophilic
Normal hydrophobic
Super hydrophobic

9. To fabricate material that has the super hydrophobic
character, must have the appropriate surface morphology
that sufficiently rough. This is to allow the formation of
the trapped air pocket underneath the water droplets.
ROUGHNESS AND HYDROPHOBICITY

10. Hydrophobic Coating Applications

11. EXPERIMENTAL WORK
The super hydrophobic organo silica has been coated on steel and
aluminum surface using sol-gel method, then the coating was characterized
based on the silica content on the coating. The results show that the highest
contact angle achieved is 108 degree. The coated organosilica was
characterized by using Field Emission Scanning Electron Microscope
(FESEM). The size of particle and surface topography was measured using
Scanning Electron Microscope (SEM). Contact angle is determine by using
Image-J software with drop analysis plugin by analyzing the photography
taken parallel to the water droplet resting on the substrate surface. Surface
roughness was measured by using Mitutoyo surface test SJ-400 machine.

12. Structure and size of resulted Organosilica coating Figure 2, have
average particles size between 0.4 and 0.8 micrometer.
RESULTS AND DISCUSSION
Figure 2: Organosilica coated sample

13. Figure 3: Water contact angle as a function of surface roughness
Water contact angle of hydrophobic organosilica coating as a function of
surface roughness is shown in figure 3, for both steel and aluminum
substrates
It is clearly seen that water contact angle increases with surface roughness of
coating.

14. • Hydrophobic silica had been successfully fabricated
using sol-gel method.
• The highest water contact angle has been achieved
by this type of coating is 108 degree
• Water contact angle is found to be affected by
surface roughness
CONCLUTIONS

15. REFERENCES
[1] Xiu Y., Hess D.W., and Wong C.P (2007) “A Novel Method to Prepare
Superhydrophobic, Self-Cleaning and Transparent Coatings for Biomedical
Applications”, 1218-1223
[2] Bhushan, B., and Jung, Y. C., (2011). Natural and biomimetic artificial
surfaces for super hydro-phobicity, self-cleaning, low adhesion, and drag
reduction.Progress in Materials Science, 56(1), 1-108.
[3] Jisr R.M., Ramile H.H., and Schlenoff J.B, (2005) “Hydrophobic and
ultrahydrophobic multilayer thin films from perfluorinated polyelectrolytes”,
Angewandte Chemie, International Edition: 782-785
[4] Ma M.L., Hill R.M , Lowery J.L, Fridrikh S.V and Rutledge G.C, (2005)
“Electrospun poly(styrene-block-dimethylsiloxane) block copolymer fibers
exhibiting superhydrophobicity”, Langmuir, 5549-5554
[5] Zhu L.B, Xiu Y.H., Xu J.W., Tamarisa P.A., Hess D.W. and Wong C.P,
(2005) “Superhydrophobicity on two-tier rough surfaces fabricated by controlled
growth of aligned carbon nanotube arrays coated with fluorocarbon”, Langmuir:
11208-11212.

16. Thank you