A presentation for the Sigma Xi virtual competition

1. The Optimization of Transparency
and Durability and the Effects of
Rigorous and Consistent Use on
Superhydrophobic Surfaces

2. Simone Griffith1 and Ekaterina Khlystova1
1North Carolina School of Science and Mathematics

3. Goals
• Make durable, transparent self-cleaning
glass
• Use Octadecyltrichlorosilane (OTS) to make more
hydrophobic glass than Methyltrichlorosilane (MTS)
• Use multiple layers of alkyltrichlorosilane to
improve durability of hydrophobic glass
• Use sodium hydroxide as a catalyst to make more
transparent glass than hydrochloric acid
• Use 0.05mL of catalyst to make more transparent
glass than 0.1mL of catalyst

4. Introduction
• Millions of dollars and hours of labor are spent every year on
window cleaning around the world.
• Hydrophobic glass is self-cleaning as the water forms droplets
and rolls easily off the surface, carrying any particles with it.
• Self-Assembled Monolayers (SAMs), specifically the
alkyltrichlorosilane group which can bond to glass, form a
nonpolar layer, and make glass hydrophobic.
• Longer silane chains, such as those of OTS, yield more
hydrophobic glass, whereas short chains, such as those of
MTS yield less hydrophobic surfaces. In our project, we seek
to optimize the hydrophobicity, transparency, and durability of
silane-coated glass in order to make widespread distribution of
self-cleaning glass a tangible reality.
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5. Abstract
Hydrophobic glass is self-cleaning, meaning a spray with water can easily wash away foreign
particles. However, self-cleaning glass is not yet in widespread commercial use. This project focuses
on improving the durability and transparency of self-cleaning glass to facilitate future use in public.
Basic recipes for the hydrophobic self-assembled monolayers (SAM) methyltrichlorosilane (MTS) and
octadecyltrichlorosilane (OTS) were applied onto glass slides with one or two layers, and with varying
amounts of either hydrochloric acid or sodium hydroxide, which act as catalysts. Each glass slide was
analyzed for transparency using FT-IR spectroscopy. Hydrophobicity was measured by finding the
contact angle of a small drop of water on the slides in a homemade goniometer. Durability was tested
by measuring hydrophobicity after placing the slides in water and into a shaker for a total of 44 hours.
We found that glass slides with two layers of SAM were initially slightly less hydrophobic than their
single layer counterparts. Overall, hydrophobicity appeared to decrease with use; however, a second
layer of SAM helped prevent deterioration during the first 24 hours with slides catalyzed with NaOH,
and we found that OTS SAMs retained their hydrophobicity longer than MTS SAMs. Finally, we
observed that SAMs made with NaOH had the highest contact angle to absorbance ratio. The amount
of catalyst, however, had insignificant effects on the slide. Our work addressed key issues present in
the use of silane-coated glass and provides a foundation for hydrophobic glass to be commercially
available for everyday use.

6. Figure 1: Sonicator
Figure 2: Solutions
Figure 3: Goniometer
Figure 4: FTIR
Figure 5: Shaker
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7. Methods
Goniometer
• We made a goniometer from a cardboard box and other supplies
Cleaning
• Sonicate in water and ethanol; dry in oven
Recipes
• Prepare each of the SAM recipes containing MTS, OTS, and different amounts of
NaOH and HCl
Application
•Place 2 glass slides in each vial; cool in refrigerator; rinse slides with
toluene, ethanol, a 1:1 mixture of ethanol and water, and water; place 2
layers slides back in refrigerator
Contact
Angles
• Photograph water on glass slides in the goniometer; determine hydrophobicity
using ImageJ software
Transparency
• Place slides in a FT-IR Spectrophotometer to measure absorbance at a certain
wavelength
Durability
• Lay slides in containers with water in a shaker for 24 hours; take contact angle
pictures; repeat after 20 hours

8. Results
Graph 1 compares the
average contact angle of
OTS slides treated identically
after 0 hours, 24 hours, and
44 hours of shaking to those
with an additional layer. It
reveals that, when made with
NaOH, adding an additional
layer generally helps the
slides retain hydrophobicity
after use.
Graph 2 compares the
average contact angle of
slides with different MTS
recipes and layers after
0 hours, 24 hours, and
44 hours of shaking.
Slides made with NaOH
retained hydrophobicity
better after 24 hours.
MTS 0.05mL HCl 1
Layer is an outlier in the
data. Reproducing these
tests in the future will
indicate whether this
data point is reliable.
Graph 3 indicates the optimal
ratios of hydrophobicity to FT-IR
absorbance; the trends indicate
that overall NaOH is the better
catalyst to use. Additionally,
slides coated with OTS tend to
maximize the ratio, with no
particular trend indicating the
optimal number of layers or
amount of catalyst. The contact
angle of the MTS 0.05mL HCl 1
Layer slide was unexpectedly
high and further study is
necessary to determine why this
outlier occurred and whether it
will occur again in duplicate tests.

9. 0
20
40
60
80
100
120
140
160
Control OTS 0.05mL
HCl 1 Layer
OTS 0.05mL
HCl 2 Layer
OTS 0.05mL
NaOH 1
Layer
OTS 0.05mL
NaOH 2
Layer
OTS 0.1mL
HCl 1 Layer
OTS 0.1mL
HCl 2 Layer
OTS 0.1mL
NaOH 1
Layer
OTS 0.1mL
NaOH 2
Layer
ContactAngle(°)
OTS Treatment
Graph 1: Hydrophobicity in OTS Treated Slides
0 Hours
24 Hours
44 Hours

10. 0
20
40
60
80
100
120
140
Control MTS 0.05mL
HCl 1 Layer
MTS 0.05mL
HCl 2 Layer
MTS 0.05mL
NaOH 1
Layer
MTS 0.05mL
NaOH 2
Layer
MTS 0.1mL
HCl 1 Layer
MTS 0.1mL
HCl 2 Layer
MTS 0.1mL
NaOH 1
Layer
MTS 0.1mL
NaOH 2
Layer
ContactAngle(°)
MTS Treatment
Graph 2: Hydrophobicity in MTS Treated Slides
0 Hours
24 Hours
44 Hours

11. 0
10
20
30
40
50
60
70
80
90
Control MTS,
0.1mL
NaOH,
1 Layer
MTS,
0.05mL
HCl, 2
Layer
MTS,
0.1mL
HCl, 2
Layer
OTS,
0.05mL
HCl, 1
Layer
MTS,
0.05mL
NaOH,
1 Layer
OTS,
0.1mL
HCl, 1
Layer
OTS,
0.05mL
HCl, 2
Layer
MTS,
0.1mL
HCl, 1
Layer
MTS,
0.05mL
NaOH,
2 Layer
OTS,
0.05mL
NaOH,
2 Layer
OTS,
0.1mL
NaOH,
2 Layer
OTS,
0.05mL
NaOH,
1 Layer
MTS,
0.1 mL
NaOH,
2 Layer
OTS,
0.1mL
NaOH,
1 Layer
MTS,
0.05mL
HCl, 1
Layer
RatioofContactAngletoIRAbsorbancy(º)
Type of Treatment
Graph 3: Hydrophobicity and Transparency

12. Discussion
• OTS-coated slides had higher contact angles than the MTS-coated slides
immediately after application. OTS slides also retained more hydrophobicity
after 24 hours and after 44 hours than their MTS counterparts.
• Although an additional layer of silane initially seems to decrease the
hydrophobicity of the glass slide, it appears to be more durable and retain
hydrophobicity more than the single-layer slides after 24 hours in the shaker for
only slides made with NaOH. This trend is not present after 44 hours in the
shaker.
• The contact angle to absorbance ratio was highest when OTS and NaOH were
used, indicating these substances improve transparency and hydrophobicity.
• There were some inconsistencies and outliers in the data we collected.
Duplication of the tests performed will help determine if this data is reliable and
why the outliers occurred.

13. Conclusion
• Our questions for this project were: will a second layer of SAM withstain heavy
use better than a single layer on glass? Will the amount and type of catalyst
improve transparency? We found that:
o Slides made with OTS were more hydrophobic than those made with MTS,
which supported findings from readings.
o A second layer of alkyltrichlorosilane initially decreases the hydrophobicity of
glass slides.
o In the silanes catalyzed with NaOH, the second layer of silane increases
glass hydrophobicity after 24 hours of shaking, before rapidly decreasing in
hydrophobicity after 44 hours.
o Slides made with NaOH catalyst generally had a higher ratio of contact angle
to absorbance. These slides were the most hydrophobic and the clearest.
o The amount of catalyst used was inconsequential.

14. Future Work
The following questions have yet to be answered and will be addressed in our future work in this
subject area:
• If our tests are duplicated, will the outliers still exist in the data?
• Why does adding a second coat initially decrease the contact angle but exhibit a trend of greater
contact angles after testing for NaOH slides?
• How can the mechanism behind additional layers of alkyltrichlorosilanes be analyzed further
using scanning electron microscopy (SEM)?
• Is it possible to make one layer of alkyltrichlorosilane as durable as multiple layers?
• What other methods of testing could model everday use, and how would these methods affect
hydrophobicity?
• Is NaOH the best catalyst available for low absorbance and high hydrophobicity and why was it
better than HCl?
• Is there a more effective and less labor-intensive alternative to coating glass with
alkyltrichlorosilanes?
• How can we reduce error and inconsistencies?

15. Acknowledgements
Dr. Myra Halpin, North Carolina School of Science and Mathematics
• Preparation of Transparent Superhydrophobic Glass Slides: Demonstration of Surface
Chemistry Characteristics, Jessica X. H. Wong and Hua-Zhong Yu, Journal of Chemical
Education 2013 90 (9), 1203-1206
• Contact Angle Measurements Using a Simplified Experimental Setup. Guillaume Lamour,
Ahmed Hamraoui, Andrii Buvailo, Yangjun Xing, Sean Keuleyan, Vivek Prakash, Ali Eftekhari-
Bafrooei, and Eric Borguet: Journal of Chemical Education 2010 87 (12), 1403-1407
• Performance and durability of octadecyltrichlorosilane coated borosilicate glass, Kirkpatrick, R.,
and C. L. Muhlstein, Journal of Non-Crystalline Solids, 2007, v. 353, p. 2624-2637.
References