Examples of Surface Characterization and Modification Experiences

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Surface Characterization
Jacob Feste
November 20th
, 2014

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Abstract
The objective of the experiment was to determine the surface properties, specifically
the surface energies and tensions of various materials. The materials tested in this experiment
include a glass slide, parafilm, red silicone, polystyrene, and aluminum. In order to determine
the surface energies of these materials, each of the materials were subjected to droplets of
water and ethanol. The contact angle of these droplets were measured by both a contact angle
meter and Tantec’s half angle method. The contact angles measured then give a direct
correlation to the surface energies of these materials. The results displayed that red silicone
had the largest mean contact angle and polystyrene had the smallest with water, with red
silicone, parafilmand aluminum all over 90 degrees. All of the contact angles with ethanol were
small (less than 45 degrees), with red silicone at the largest and glass slide with the smallest.
These results conclude that red silicone has the lowest surface energy and critical surface
tension with parafilm and aluminum low as well and polystyrene had the highest of these
properties with glass slide high as well. They also conclude that ethanol has a much lower
surface tension than water.
Introduction
Surface properties are very important properties to consider in biomedical applications.
The specific surface properties measured in the experiment include surface energy and
indirectly, surface tension. The surface energy of a surface formed between two different
compounds correlates to the altercations of intermolecular bonds when the surface is formed.
It also correlates to the degree of the forces of cohesion, the intermolecular attraction between
similar molecules, and adhesion, the intermolecular attraction between dissimilar molecules,
between the two compounds. The surface energy of a material is important for factors such as
the degree of wetting, or spreading of a liquid over a surface. The lower the surface energy
between the material and liquid, the more adhesion the dissimilar molecules have with each
other and consequently the more the liquid is able to spread out over the surface, or the more
wetting will occur. Wetting is an important aspect of surface interactions and is directly related
to surface tension and the interfacial free energy of the surface. It can be generalized that
wetting occurs when the surface tension of the liquid is lower than the critical surface tension
of the surface it is in contact with. In terms of the interfacial free energy of the surface; the

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higher the interfacial free energy of the surface the more wetting, or spreading, of the liquid
will occur, and vice versa. Different biomedical applications may call for different desirable
surface energies and degrees of wetting between the surface of the material being used and
the liquid it will be in contact with in the body, for instance, blood. In order to determine the
surface energy of a created surface between a material and a liquid, measurement of the
contact angle of the applied liquid provides one of the simplest and reliable methods of
determining this. The contact angle is the angle at which the edge of the liquid makes with the
surface it is applied to. The contact angle is a function of the surface free energies of the liquid
and the solid. Young’s equation gives the following relationship.
Eq. (1): Γsv = Γsl + Γlvcos(Θ).
Where Γsv is the solid surface free energy, Γsl is the solid/liquid interfacial free energy, Γlv is the
liquid surface free energy and Θ is the contact angle of the liquid droplet with the surface. The
contact angle can be measured quite simply by methods such as Tantec’s half angle method or
by contact angle meter, which makes it a very simple and efficient tool for understanding the
surface energy between a liquid and a solid. In correlation to the wetting of the liquid, complete
wetting occurs when the contact angle is zero and therefore also has a very high interfacial
surface energy with the surface tension of the liquid much lower than the critical surface
tension of the surface. With this experiment using water as its primary liquid for testing, this
tends to occur with strongly hydrophilic solids. In general, if the solid is less hydrophilic it will
exhibit lesser degrees of these properties given and the liquid will form a bead as it is not
completely wetted. This property is exhibited when the contact angle is between zero and
ninety degrees. A contact angle greater than ninety degrees suggests a hydrophobic solid and
almost no wetting. As suggested, the surface properties of different materials vary immensely
based on their chemical make-up and properties. Metals generally have a high surface energy
and high critical surface tension likely due to their high energy of the metallic bonds. Polymers,
on the other hand, are much more varied in these properties and may have either high or low
surface energies and are directly determined by their chemical make-up and structure.
Polymers that exhibit hydrophilic characteristics with frequent high-energy bonds such as
covalent bonds can be suggested to have a high surface energy, and vice versa. Composites will
generally have a very high surface energy as the polarity of the cation-anion bonding greatly
increases hydrophilicity and the ionic bonding between these molecules contains very high
energy.
In this experiment, our goal was to determine the surface properties of various
materials including glass slide, parafilm, red silicone, polystyrene, and aluminum. In order to
determine these properties each of these materials were tested by using both water and
ethanol as the liquid and measuring the contact angle formed. In order to measure the contact
angles formed, both a contact angle meter and Tantec’s half angle method were used. While
the contact angle meter simply uses specified machine to make this measurement, Tantec’s
half angle method is a little more complex in nature. Tantec’s half angle measurement proves

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to be efficient as it eliminates error from the small, random tangent line of the droplet
measured. For instance, a droplet may have a very brief, steep slope on its base but rounds off
in a way at which this steep slope isn’t a completely accurate measurement of the true contact
angle but is comparatively close and hard to measure accurately. The contact angle meter
measures this angle. Tantec’s half angle method is a way of verifying the accuracy of this
implication. Tantec’s equation is given as:
Eq. (2): Θ = 2* arc tan (H/R)
Where Θ is the solved, not measured, contact angle. H is the height of the droplet and R is the
radius of the droplet’s base. Both of these methods are performed in order to give accurate
representation of each contact angle. By finding the contact angle of these surfaces, we are
able to accurately give estimations of their surface energies. The surface energies of the
measured materials may be hypothesized by their chemical properties and structure. The glass
slide in this experiment can be suggested to have a high surface energy and therefore a small
contact angle. This is due to glass’s identity as a composite. Glass generally has the formula
SiO2, but most glass and most likely the one tested in this experiment are generally have
sodium carbonate added to increase toughness [1]. The bonding between the anionic oxygen
and cationic sodium create a polar, hydrophilic environment and the energy of these bonds are
very high. Parafilm is composed of a mixture of paraffin wax and polyolefins [2]. Paraffin wax
has a composition anywhere from C20H42 to C40H82 [3], while polyolefins consist of
hydrocarbons with double bonded carbons [4]. This composition suggests hydrophobicity. The
double bonded carbons are decently high in energy but are few in number compared to the
amount of single bonded hydrocarbons. Parafilm can conclude to have a relatively low surface
energy. Red silicone has a structure similar to glass but without the cationic sodium, and
therefore is a polymer. It consists of alternating silicon and oxygen atoms [5], which are not
very polar bonds and not too high in energy as the carbon bonds seen in some of the other
tested polymers. It can infer to have a very low surface energy. Polystyrene is made up of
hydrocarbon chains with phenyl rings branching off [6]. While the hydrocarbon chains may
provide little to surface energy, the phenyl rings each contain three double bonds, and are
found at every other carbon in the hydrocarbon chain. With the decently high energy of these
double bonds in combination with the very high concentration of these bounds, polystyrene
can be suggested to have a very high surface energy. The final material, aluminum, is a post
transition metal. Metals such as aluminum generally have a very high critical surface tension
and a high surface energy. However, metals are also very smooth and hard and resist adhesion
to other molecules such as water. Therefore aluminum will likely have low surface energy in
this experiment due to this sense of hydrophobicity. In terms of the liquids tested, both water
and ethanol are used. Water is commonly seen in the body, and the suggestions listed regard to
their surface energies with water due to polarity or hydrophilicity reasons. Ethanol is much
different than water in that it is much more polar due to its hydroxyl group. Therefor it may be
hypothesized that the surface energies will be much greater in ethanol than in water, indicated
by small contact angles. In regards to the experiment performed, a null hypothesis that each of

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these surfaces will give the same contact angle for both liquids, and therefore have the same
surface energy, is suitable. However a true hypothesis based on the information presented may
be made if this null hypothesis is rejected. If each of these materials are subjected to water
droplets, then the hydrophilic surfaces with the high bond energies, glass slide and polystyrene,
will exhibit small contact angles between zero and ninety degrees and therefore have the
highest surface energies. The hydrophobic materials, red silicone, parafilm, and aluminum, will
show large contact angles greater than ninety degrees in water. It can also be hypothesized that
if these materials are subjected to both water and ethanol droplets, then the materials will
have a much higher surface energy and much smaller contact angle with ethanol than with
water due to polarity.
Procedures
Equipment/Supplies and Materials Used
I. Contact Angle Meter
II. Sample Surfaces
a. Glass Slide
b. Parafilm
c. Red Silicone
d. Polystyrene
e. Aluminum
III. Water
IV. Ethanol
V. Syringe
The procedure of this experiment was done to measure and record the contact angle of
ethanol and water on the surface listed above. A syringe was first used to drop five droplets of
water in a line on the surface of the glass slide. This procedure was done two times for water
and twice for ethanol. Each droplet contained 15 microliters of water/ethanol. Using the
laboratory materials and the contact angle meter, the left most point of the water/ethanol
droplet was aligned with y axis, and the bottom surface of the droplet was aligned with the x
axis. The contact angle meter was then also used to measure the height, diameter, contact
angle and tantec’s half angle for each water droplet. The contact angle meter was also used to
measure the radius, contact angle, and tantec’s half angle of each droplet of ethanol. This

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procedure was repeated for each material surface type. Ten measurements were recorded in
total for each ethanol and water droplet on each surface type. All observations and data
obtained was subsequently recorded.
Results
I. Water:
Table 1: GlassSlide CalculationsforHeight,Diameter,ContactAngleMeasurements,and Percent
Error Calculations for each Water Droplet along with mean and standard deviation measurents
Glass Slide
Droplet Height
(mm)
Diameter
(mm)
Contact Angle Meter
(degrees)
Tantec's 1/2
Angle (degrees)
Percent
Error
1 10 36 55 58.11 5.35%
2 10 36 55 58.11 5.35%
3 10 30 60 67.38 10.95%
4 10 38 58 55.52 4.47%
5 10 34 50 60.93 17.94%
6 10 34 65 60.93 6.68%
7 12 24 78 90.00 13.33%
8 10 30 70 67.38 3.89%
9 10 30 60 67.38 10.95%
10 8 30 53 56.14 5.60%
Height(mm) Diameter(mm)
Contact Angle Meter
(degrees)
Mean 10 32.2 60.4
Standard Deviation 0.94280904 4.157990968 8.500980336
Table 2: Parafilm Calculations for Height, Diameter, Contact Angle Measurements, and Percent
Parafilm
Droplet Height
(mm)
Diameter
(mm)
Contact Angle Meter
(degrees)
Tantec's 1/2 Angle
(degrees)
Percent
Error
1 14 24 99 98.80 0.21%
2 14 24 100 98.80 1.22%
3 16 22 97 110.98 12.60%
4 16 24 100 106.26 5.89%
5 14 22 100 103.69 3.55%
6 14 22 95 103.69 8.38%
7 16 20 100 115.99 13.79%
8 12 24 100 90.00 11.11%

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9 14 24 100 98.80 1.22%
10 14 24 98 98.80 0.81%
Contact Angle Meter
(degrees)
Mean 14.4 23 98.9
Standard
Deviation 1.26491106 1.414213562 1.728840331
Table 3: Red Silicone Calculations for Height, Diameter, Contact Angle Measurements, and
Percent Error Calculations for each Water Droplet along with mean and standard deviation
measurents
Red Silicone
Droplet Height
(mm)
Diameter
(mm) Contact Angle Meter Tantec's 1/2 Angle
Percent
Error
1 22 30 110 111.43 1.28%
2 22 30 110 111.43 1.28%
3 22 30 110 111.43 1.28%
4 22 30 115 111.43 3.21%
5 20 30 110 106.26 3.52%
6 22 30 110 111.43 1.28%
7 22 32 110 107.95 1.90%
8 22 30 110 111.43 1.28%
9 22 30 115 111.43 3.21%
10 22 32 110 107.95 1.90%
Contact Angle Meter
(degrees)
Mean 21.8 30.4 111
Standard
Deviation 0.63245553 0.843274043 2.108185107
Table 4: PolystyreneCalculationsforHeight,Diameter,ContactAngleMeasurements,and Percent
Polystyrene
Droplet Height
(mm)
Diameter
(mm)
Contact Angle Meter
(degrees)
Tantec's 1/2 Angle
(degrees)
Percent
Error
1 10 22 60 84.55 29.03%
2 10 30 55 67.38 18.37%

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3 8 30 50 56.14 10.94%
4 10 28 50 71.08 29.65%
5 10 30 40 67.38 40.64%
6 8 28 45 59.49 24.36%
7 6 30 45 43.60 3.20%
8 8 30 48 56.14 14.51%
9 8 16 62 90.00 31.11%
10 8 16 62 90.00 31.11%
Contact Angle Meter
(degrees)
Mean 8.6 26 51.7
Standard
Deviation 1.34989712 5.81186526 7.73232752
Table 5: AluminumCalculationsforHeight,Diameter,ContactAngleMeasurements,and Percent
Aluminum
Droplet Height
(mm)
Diameter
(mm)
Contact Angle Meter
(degrees)
Tantec's 1/2 Angle
(degrees)
Percent
Error
1 14 24 99 98.80 0.21%
2 14 24 100 98.80 1.22%
3 16 22 98 110.98 11.70%
4 16 24 100 106.26 5.89%
5 14 22 100 103.69 3.55%
6 14 22 95 103.69 8.38%
7 16 20 100 115.99 13.79%
8 12 24 100 90.00 11.11%
9 14 24 100 98.80 1.22%
10 14 24 100 98.80 1.22%
Contact Angle Meter
(degrees)
Mean 14.4 23 99.2
Standard
Deviation 1.26491106 1.414213562 1.619327707
II. Ethanol:

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Table 6: Glass Slide Calculations for Height, Radius, Contact Angle Measurements, and Percent
Error Calculationsforeach EthanolDropletalong with mean and standard deviation measurents
Glass Slide
Droplet
Height(mm) Radius (mm)
Contact Angle Meter
(degrees)
Tantec's 1/2 Angle
(degrees) PercentError
1 2 7.7 21 29.12 27.89%
2 2 8 25 28.07 10.94%
3 2 8 25 28.07 10.94%
4 2 18 25 12.68 97.15%
5 4 10 30 43.60 31.20%
6 4 14 30 31.89 5.93%
7 4 14 30 31.89 5.93%
8 4 14 30 31.89 5.93%
9 4 14 30 31.89 5.93%
10 4 14 30 31.89 5.93%
Contact Angle Meter
(degrees)
Mean 3.2 12.17 27.6
Standard Deviation 1.03279556 3.499222136 3.306559138
Table 7: ParafilmCalculationsforHeight,Radius,ContactAngleMeasurements,and PercentError
Calculations for each Ethanol Droplet along with mean and standard deviation measurents
Parafilm
Droplet
Contact Angle Meter
(degrees)
Tantec's 1/2 Angle
1 4 14 30 31.89 5.93%
2 6 14 40 46.40 13.79%
3 6 14 40 46.40 13.79%
4 6 14 41 46.40 11.63%
5 6 14 40 46.40 13.79%
6 6 14 40 46.40 13.79%
7 6 14 40 46.40 13.79%
8 6 14 40 46.40 13.79%
9 6 14 40 46.40 13.79%
10 6 14 40 46.40 13.79%
Contact Angle Meter
(degrees)

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Mean 5.8 14 39.1
Standard
Deviation 0.63245553 0 3.212821536
Table 8: Red Silicone Calculations for Height, Radius, Contact Angle Measurements, and Percent
Red Silicone
Droplet
Contact Angle Meter
(degrees)
Tantec's 1/2 Angle
1 6 14 41 46.40 11.63%
2 6 14 43 46.40 7.32%
3 6 14 42 46.40 9.48%
4 5 14 41 39.31 4.31%
5 5 14 40 39.31 1.76%
6 6 14 42 46.40 9.48%
7 4 14 40 31.89 25.43%
8 6 14 40 46.40 13.79%
9 6 14 41 46.40 11.63%
10 5 14 41 39.31 4.31%
Contact Angle Meter
(degrees)
Mean 5.5 14 41.1
Standard
Deviation 0.70710678 0 0.994428926
Table 9: Polystyrene Calculations for Height, Radius, Contact Angle Measurements, and Percent
Polystyrene
Droplet
Contact Angle Meter
(degrees)
Tantec's 1/2 Angle
1 4 14 37 31.89 16.02%
2 4 14 39 31.89 22.29%
3 4 14 39 31.89 22.29%
4 4 15 39 29.86 30.60%
5 4 14 38 31.89 19.16%
6 4 14 38 31.89 19.16%
7 4 14 38 31.89 19.16%
8 4 14 38 31.89 19.16%

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9 5 14 38 39.31 3.33%
10 4 14 37 31.89 16.02%
Contact Angle Meter
(degrees)
Mean 4.1 14.1 38.1
Standard
Deviation 0.316227766 0.316227766 0.737864787
Table 10: Aluminum Calculations for Height, Radius, Contact Angle Measurements, and Percent
Aluminum
Droplet
Height(mm)
Radius
(mm)
Contact Angle Meter
(degrees)
Tantec's 1/2 Angle
1 5 14 40 39.31 1.76%
2 5 14 38 39.31 3.33%
3 5 16 30 34.71 13.56%
4 5 14 38 39.31 3.33%
5 5 14 38 39.31 3.33%
6 5 14 38 39.31 3.33%
7 5 14 38 39.31 3.33%
8 5 14 38 39.31 3.33%
9 6 14 40 46.40 13.79%
10 6 14 40 46.40 13.79%
Contact Angle Meter
(degrees)
Mean 5.2 14.2 37.8
Standard
Deviation 0.42163702 0.632455532 2.898275349
Table 11: T-test results of Water/Ethanol Contact Angles on different material surfaces.
Comparison p-values Degreesof Freedom Significance T-critical
watervs. ethanolon polystyrene 0.000169981 18 95% 1.734
wateron glassvs.aluminum 4.40203E-08 18 95% 1.734
water on red silicone vs.
polystyrene
1.37602E-10 18 95% 1.734
watervs. ethanolon parafilm 1.60002E-17 18 95% 1.734

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Discussion
The results of this experiment accurately reinforce the implications made about the
various material’s surface energies and the differences between the water and ethanol. With
water, polystyrene had the lowest mean contact angle at 51.7 degrees with the lowest mean
height of the water droplet at 8.6mm indicating the most wetting. Glass slide also had a low
mean contact angle at 60.4 degrees with a low mean height at 10 mm. Red silicone had the
highest mean contact angle at 111 degrees and the highest mean droplet height at 21.8mm.
Parafilm and aluminum also had high mean contact angles greater than 90 degrees, with
parafilm at 98.9 degrees and aluminum at 99.2 degrees. These results indicate that polystyrene
had the highest surface energy and most wetting occur, with glass slide having a high surface
energy and wetting as well. With their mean angles under 90 degrees, it can also be implied
that these materials are somewhat hydrophilic as well. The results also indicate that red
silicone had the lowest surface energy with water, and that little wetting occurred. Parafilm and
aluminum also had low surface energies with water and experienced little wetting. With red
silicone, parafilm, and aluminums mean contact angles greater than 90 degrees, it can also be
suggested that these materials are hydrophobic and therefore experience little adhesion with
water. The tests performed with the ethanol droplets gave much different results. Glass slide
had the lowest mean contact angle at 27.6 degrees with a mean droplet height of 3.2mm, while
red silicone had the highest mean contact angle at 41.1 degrees with a droplet height of
5.5mm. Parafilm, polystyrene, and aluminum had mean contact angles of 39.1, 38.1, and 37.8,
respectively. The main conclusion these results support is that ethanol was much different than
water in that all of the materials had relatively high surface energies indicated by their low
contact angles (all less than 45 degrees) and therefore experienced much more wetting. These
results can be primarily explained by the much higher degree of polarity in ethanol than water.
This therefor indicates that ethanol has a much lower surface tension than water; a low enough
surface tension to cause a high degree of wetting in all of the surfaces while water’s surface
tension was low enough to only cause a decent degree of wetting in the glass slide and
polystyrene. Multiple t-tests were performed to determine whether or not different variables
impacted the contact angle of different surfaces, as illustrated in table 11. The null hypothesis
being tested for each of these tests was that the factors had no impact on the contact angle
and therefore the contact angles should be the same with the different variables. The first t-
test tested whether or not the different liquids, water and ethanol, had an impact on the
contact angle formed with polystyrene. The p values indicate that they do indeed have an
impact as illustrated by the data. The next t-test tested whether or not the contact angle with
water on the glass slide vs water on aluminum was the same. The p values also indicate that

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they were much different. The third t-test tested water on red silicone vs water on polystyrene.
Once again, the p values suggest a large difference. Finally, a t-test was performed to determine
if water vs ethanol had an effect on the contact angle formed on parafilm. The p values suggest
a big difference as well. All of the t-tests performed rejected the null hypothesis. That is,
whether the liquid is water or ethanol has an impact on the contact angle, and the same liquid
applied to two different surfaces will give different contact angles. The main implication these
tests conclude is that no two liquids or solid surfaces will give the same contact angle and
therefore the contact angle is impacted by the liquid composition and the solid composition.
This is supported by the data given for each material subjected to the different liquids.
The variations between the contact angles are a direct result of the composition of both
the liquid and the surface. Factors such as the hydrophilicity of the solid, the energy of the
bonds in the solid, and the surface tension of the liquid in respect to the lower critical surface
tension of the solid have a big impact on the contact angle and surface energy. Polystyrene and
the glass slide’s contact angles were likely small and indicating a high surface energy with water
due to their hydrophilicity and bond energies as expected. They also had high enough lower
critical surface tensions to allow water to spread. Parafilm, red silicone, and aluminum has large
contact angles greater than 90 degrees suggesting low surface energy likely due to their
hydrophobic nature and smaller lower critical surface tensions in which the water’s surface
tension was not low enough to cause much wetting. The chemical make-up of these materials
as previously examined suggest this hydrophobic nature and therefore these results were
expected. On the other hand, all of the surfaces showed small contact angles less than 45
degrees and therefore high surface energies with ethanol. This is likely due to ethanol being
much more polar than water while having a low enough surface tension to surpass all of the
materials lower critical surface tensions. This allowed more wetting to occur and is indicated by
the small droplet heights found in each of the tests. The strikingly similar small contact angle
values were likely due to the ethanol being able to spread a similar amount for each material
due to its low surface tension and the high polarity of ethanol allows it to disrupt the bonds of
each surface as well, hydrophobic or not. This suggests that the properties of ethanol seemingly
overwhelmed the properties of the surfaces to the extent at which the contact angles were
almost entirely a factor of the ethanol and not the surface, as indicated by the similar values. As
previously identified by Eq. (1) (Young’s equation), the contact angle is a function of the surface
energies of the system. The greater the contact angle, the less the surface energy of the solid.
This is due to the liquid being able to spread more on higher energy surfaces as the higher
energy surfaces have a higher lower critical surface tension for which the liquid to be lower
than which allows the spreading. This is illustrated by our results as the surfaces with the
chemical make-up indicating high surface energies gave small contact angles while those
indicating low surface energies gave high angles. In generally, the more polar or hydrophilic a
surface is the higher its surface energy. This is due to the molecules being more susceptible to
rearrangement than non-polar molecules as polar bonds are easier to break when their polar
counterparts are present from another surface. In addition, the energy between the bonds is

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also an important factor as the energy of a bond that is disrupted is released upon disruption,
which applies to the surface energy. Therefore, a material that exhibits a large degree of
hydrophilicity in order to allow bond rearrangement, in addition to these bonds being of high
energy, would expect to have a high surface energy. On the other hand, a completely non-
polar, hydrophobic in which bond rearrangement is nearly impossible in addition to very low
bond energies would expect to have a low surface energy. These properties also correlate to
surface tension as the hydrophilic, high energy material would have a much higher lower critical
surface tension for the liquid to be lower than and spread than would the hydrophobic, low
energy material. The critical surface tension of glass is 73 dynes/cm[7], parafilm is 23 dynes/cm
[8], red silicone is 24 dynes/cm [9], polystyrene is 64 dynes/cm [10], and aluminum is 500
dynes/cm [11]. The critical surface tension indicates how likely a liquid will spread on a surface,
with the highest spreading the most. These known values correlate pretty accurately to the
measured contact angles, and glass and polystyrene have high critical surface tension values
with low measured contact angles and red silicone and parafilm have low values with high
contact angle measurements. Aluminum, on the other hand, follows a different pattern with an
incredibly high critical surface tension but with a large contact angle over 90 degrees. While the
critical surface tension may be high for aluminum suggesting a small contact angle, this large
angle and low surface energy may be a result of the its inherent hydrophobicity. Aluminum is
indeed a metal and therefore may be too smooth and hard to allow adhesion. I would use
Polystyrene as a cell culture surface because it has the lowest contact angle with water and
therefore the highest free surface energy. It also has an intermediate critical surface tension
and is not too smooth or hard like aluminum. This is important as polystyrene’s high surface
energy allows the cells to spread or wet very efficiently in order to grow and proliferate. Water
and ethanol had a large difference in contact angle measurements in which ethanol gave similar
and much lower angles. This was previously discussed and likely due to ethanol’s higher polarity
and lower surface tension than water. Ethanol’s low surface tension was seemingly low enough
for each of the materials critical surface tensions unlike water in which it was allowed more
wetting. It also was polar enough to move bonds around in which water couldn’t. Limitations on
sessile drop contact angle measurements primarily lie on the principle of its local-only
application and its requirement of a liquid to solid interface. It is also limited on the fact that it
requires a flat solid surface. An application may call for different geometrical shapes of which
this method would only test the flat surface properties of a material. There may be variations in
properties between a curved surface of a material and a flat one. There are various ways of
characterizing free surface energy. One of these methods is the Fowkes method. The Fowkes
method is an efficient, accurate way to measure the surface energy of a nonpolar solid [12]. It
uses the equation Γs= Γs
d=0.25 Γl(1+cos Θ)2 and it’s advantage lies in the fact that it
simplifies the free surface energy measurements for non-polar solids while being highly
accurate in doing so [12]. Another method is the Owens-Wendt method [12]. This method uses
the simplicity and accuracy of the Fowkes equation but its advantage allows its application to
polar solids as well by using two measuring liquids and a few more substitution equations [12].
Thirdly, the Van Oss-Chaudhury-Good method builds on the Fowkes equation even more than

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the Owens-Wendt method by using three measuring liquids with three more substitution
equations to solve the system [12]. It is more difficult to perform than the Owens-Wendt
method but its advantage lies in its seemingly perfect accuracy due to its complexity and may
also be used for polar solids and polymers [12]. There are also a variety of methods performed
to manipulate surface energies. One method reverses the surface tension by applying an
electric potential through embedded electrodes [13]. Another method uses laminar flows or UV
light to generate irreversible surface tension gradients [13]. A final method applies a very small
positive charge, less than 1 volt, causing an electrochemical reaction and creating an oxide layer
on a metal which lowers its surface tension [14].
Conclusion
The goal of this experiment was to identify the relative surface energies of a glass slide,
parafilm, red silicone, polystyrene, and aluminum. In order to achieve this, droplets of both
water and ethanol were separately induced on each material and the contact angle of these
droplets measured using a meter and Tantec’s half angle method for accuracy. Water and
ethanol were used in order to determine how the composition of the liquid droplet used effects
the surface energy of the system. By measuring the contact angle we are able to obtain a
relative surface energy of the surface due to the contact angle being a function of surface
energy. It was hypothesized that the glass slide and polystyrene would have the smallest
contact angle and therefore the highest surface energy with water. This was due to the
chemical composition of the two: the glass being a polar, hydrophilic composite material with
high bond energies due to the cation-anion bonds and the polystyrene being hydrophilic with a
large multitude of high energy double bonds. Parafilm, red silicone, and aluminum were all
foreshadowed to have large contact angles greater than 90 degrees due to their hydrophobic
natures of their chemical composition. It was also hypothesized that ethanol droplets would
produce much smaller contact angles and therefore much higher surface energies for each of
the materials than water. This was implied due to the higher polarity of ethanol from its
hydroxyl group and its lower surface tension than water. All of the objectives were met in this
experiment and all of the hypothesized outcomes were proven to be true from the data. To first
provide that the contact angle is indeed effected by both the solid surface composition and the
composition of the liquid droplet, multiple t-tests were performed with different variables
involving the solid and liquid composition as illustrated in table 11. These t-tests all rejected the
null hypothesis and prove that both the solid and liquid composition have an impact. The data
also supports the implications made on how the composition impacts the contact angle as
illustrated by tables 1-10 above. When subjected to the water droplets, polystyrene had the
lowest mean contact angle at 51.7 degrees with the glass slide low as well at 60.4 degrees. Both
of these also showed a good degree of wetting proved by their low mean droplet heights. These

16 | P a g e
properties support that polystyrene and the glass slide had the highest surface energy with
water. On the other hand, red silicone had the largest mean contact angle at 111 degrees with
parafilm and aluminum large as well at 98.9 degrees and 99.2 degrees, respectively. These
materials also had relatively large droplet heights as well and therefore primarily beaded. These
angles over 90 degrees support their hydrophobic compositions. In terms of the liquid
composition, our data also supports the hypothesis that ethanol will exhibit smaller contact
angles and give higher surface energies than water due to its chemical composition. The mean
contact angles were low for each material, all lower than 45 degrees and following a similar
order of size to that of the water droplets but much more similar in value. It can therefore be
concluded that the surface energy of a surface is directly impacted by both the liquid being
administered and the solid surface. More specifically, the more polar and the lower the surface
tension of the liquid the smaller the contact angle and the higher the surface energy as a liquid
is able to enable bonds to rearrange much more efficiently with a higher polarity and lower
surface tension. In addition, materials with hydrophilic or polar compositions, containing bonds
with high energy, and having a larger lower critical surface tension will give smaller contact
angles and therefore have higher surface energies and vice versa. While the experiment
seemed to be performed pretty accurately, there is always the possibility of error. The main
possibility for error would likely lie in the focusing of the machine. The glass slide and
polystyrene tests weren’t as focused as the other three tests for water which could give
inaccurate measurements. Human error was also a strong possibility because the counting of
very small boxes at a large extent could easily be miscounted and skew the data slightly.
However, the use of ten droplets for each material helped eliminate much of this possibility for
error. This experiment would need a large amount of error to give inaccurate conclusions of
which was most likely not the case and therefore the conclusions in this experiment likely
provide to be accurate implications. Understanding the surface properties of a material is very
important for biomedical applications and the increasing discovery of these properties may lead
to endless applications.
References
[1] "Is Glass a Polymer?" Is Glass a Polymer? N.p., n.d. Web. 03 Dec. 2014.
[2] "Parafilm® Barrier Films - Comparison of Properties." Parafilm M® Laboratory Barrier Film. N.p., n.d. Web. 03
Dec. 2014.
[3] "Paraffin." Princeton University. N.p., n.d. Web. 03 Dec. 2014.
[4] The Editors of Encyclopædia Britannica."Polyolefin (chemical Compound)."Encyclopedia Britannica Online.
Encyclopedia Britannica,n.d.Web. 03 Dec. 2014.

17 | P a g e
[5] The Editors of Encyclopædia Britannica."Silicone(chemical Compound)."Encyclopedia Britannica Online.
[6] The Editors of Encyclopædia Britannica."Polystyrene(chemical Compound)." Encyclopedia Britannica Online.
[7] "The Critical SurfaceTension of Glass." - The Journal of Physical Chemistry (ACS Publications). N.p., n.d. Web. 03
Dec. 2014.
[8] Verlag, Vincentz. "Dynamics of SurfactantEnhanced Spreading." European Coatings Journal (1998): n.
pag. European-coatings.com. Web. 03 Dec. 2014.
[9] Andriot, M. "Silicones in Industrial Applications."N.p., n.d. Web.
[10] Nueman, Micheal R. An Introduction to Biomaterials. 2nd ed. N.p.: n.p., n.d. Print.
[11] "Composite Material." Uotechnology. N.p., n.d. Web.
[12] Żenkiewicz, M. "Methods for the Calculation of SurfaceFree Energy of Solids." AMME. N.p., n.d. Web.
[13] Desai,Tejal,Sangeeta Bhatia,and Mauro Ferrari. BioMEMS and Biomedical Nanotechnology Volume III
Therapeutic Micro/Nanotechnology. Boston (MA): Springer, 2007.Print.
[14] "Researchers Control Surface Tension to ManipulateLiquid Metals." NC State News Researchers Control
Surface Tension to Manipulate Liquid Metals Comments. N.p., n.d. Web. 03 Dec. 2014.

18 | P a g e
Surface Wetting Modifications via Small-Scale Topography and
Nanomaterial Applications
Jacob Feste
University of Arkansas, Biomedical Engineering, jtfeste@email.uark.edu

19 | P a g e
Abstract
The goal of this experiment is to determine how changes in surface topography and
surface chemistry influence the wettability and SFE of a surface. Glass, Teflon, and aluminum
were subjected to contact angle measurements using primarily-polar water and primarily-
dispersive DIM. The glass samples included bare glass, sandblasted glass, and sandblasted glass
treated with FAS-17. The aluminum samples included sandblasted aluminum and sandblasted
aluminum treated with FAS-17. The Teflon samples included bare Teflon and sanded Teflon.
The glass samples increased in wettability and SFE upon sandblasting while decreasing
significantly and becoming hydrophobic upon sandblasting and FAS-17 treatment. The
sandblasted aluminum samples resulted in significantly increased wettability and SFE upon FAS-
17 treatment. The Teflon samples, on the other hand, decreased in wettability and SFE upon
sanding.
Nomenclature
𝜃, 𝜃𝛾= Measured contact angle (degrees)
𝜃∗
= True contact angle (degrees)
𝛾𝑠𝑙 = Solid-liquid interfacial energy/surface tension (mN/m)
𝛾𝑙𝑣 = Liquid-vapor interfacial energy/surface tension (mN/m)
𝛾𝑠𝑣 = Solid-vapor interfacial energy/surface tension or SFE (mN/m)
𝛾𝑠𝑣
𝑑
= Dispersive component of 𝛾𝑠𝑣 (mN/m)
𝛾𝑙𝑣
𝑑
= Dispersive component of 𝛾𝑙𝑣 (mN/m)
𝛾𝑠𝑣
𝑝
= Polar component of 𝛾𝑠𝑣 (mN/m)
𝛾𝑙𝑣
𝑝
= Polar component of 𝛾𝑙𝑣 (mN/m)
𝑟= Surface roughness parameter (unitless)
𝑓= Areal surface fraction (unitless)
Introduction
The objective of this experiment is to perform a variety of surface modifications on
various materials and observe their surface wettability in order to determine how the
modifications impact their surface characteristics. Surface wettability is observed when a liquid
substance is applied to a solid surface. When a drop of liquid is applied to a solid surface, the
liquid will arrange itself in a specific geometry that minimizes the total energy of the solid-liquid

20 | P a g e
interaction [2]. The energy of the solid-liquid system is dependent on factors such as
attractive/repulsive intermolecular interactions, electrostatic contributions, and polar
contributions [1]. Therefore, surface wettability is primarily influenced by the chemical
composition of the liquid and the surface, of which these factors reside. While these factors are
too small to be observed, the resulting geometry gives implications about the influence that
these factors have on the total energy of the solid-liquid-vapor interaction. The geometry of a
liquid applied to a surface may be analyzed to characterize surface wettability by measuring the
contact angle between the two phases. The contact angle is given as 𝜃𝛾 in the following figure:
Figure (1): Contact angle and surface tension relationships for a solid-liquid system [3].
By measuring the contact angle, other parameters such as surface tension may be determined.
Surface tension may be described as the amount of work needed to increase the surface area of
the interface, and is dependent on the sum of the cohesive forces [4]. According to figure (1),
surface tension arises between the solid and liquid (𝛾𝑠𝑙 ), liquid and vapor (𝛾𝑙𝑣 ), and solid and
vapor (𝛾𝑠𝑣 ). The contact angle measurement and surface tension values are related for a variety
of physical properties. For instance, the “force” balance at the solid-liquid-vapor interface in the
x-direction is given by:
Equation (1): 𝛾𝑠𝑣 = 𝛾𝑠𝑙 +𝛾𝑙𝑣 cos⁡𝜃𝛾
Furthermore, the contact angle may be described in terms of the interfacial surface tensions via
the Young equation [6]:
Equation (2): 𝑐𝑜𝑠𝜃𝛾 =
𝛾 𝑠𝑣 −𝛾 𝑠𝑙
𝛾𝑙𝑣
These relationships may be used to calculate the surface tensions and free energies involved in
the system, and therefore the influences of the cohesiveforces. However, the relationships given
by equation (1) and equation (2) involve many surface tension variables, of which are usually
unknown. These equations also assume a perfectly smooth and symmetrical solid surface while
not accounting for the inherent roughness involved in every surface [5]. The surface free energy
(SFE), or the surface tension between the solid and vapor interaction (𝛾𝑠𝑣 ), thermodynamically

21 | P a g e
represents the wetting behavior of the system and is defined as the reversible work required to
create a new unit of surface area. The Young equation requires a known solid-liquid interfacial
energy (𝛾𝑠𝑙) in order to calculate an estimated SFE, of which fails to consider other important
interactions. Interactions such as dispersive, polar, ionic, hydrogenic, and other interactions may
be accounted for by considering 𝛾𝑠𝑙 as a function of the other two interfacial energies
(𝛾𝑠𝑣 ⁡and⁡𝛾𝑙𝑣 ) [5]. Owens and Wendt accounted for both dispersive and polar interactions to
generate the following relationship:
Equation (3): 𝛾𝑠𝑙 = 𝛾𝑠𝑣 + 𝛾𝑙𝑣 − 2(√ 𝛾𝑠𝑣
𝑑 ∗ 𝛾𝑙𝑣
𝑑
+ √𝛾𝑠𝑣
𝑝
∗ 𝛾𝑙𝑣
𝑝
)
By applying this relationship to the Young equation, the contact angle relationship is given as:
Equation (4): (1 + cos𝜃𝛾)𝛾𝑙𝑣 = 2(√ 𝛾𝑠𝑣
𝑑 ∗ 𝛾𝑙𝑣
𝑑
+ √𝛾𝑠𝑣
𝑝
∗ 𝛾𝑙𝑣
𝑝
)
Finally, the SFE of a solid may be calculated by measuring the contact angles of two different
liquids and applying them to equation (4). A primarily-dispersive liquid and a primarily-polar
liquid are desired for simpler calculations [5]. In addition, the contact angleitselfmay be analyzed
in order to give general assumptions about the surface. By applying water to a solid surface, the
resulting contact angle may be measured in order to estimate the hydrophilicity/hydrophobicity
and polarity of the solid material. Hydrophilic materials are polar, “water-loving” materials that
only require a smallamount of energy to form new surfaces with water. Thesematerials willhave
a high SFE with water. Hydrophobic materials are nonpolar and act to avoid water, requiring a
large amount of energy to form new surfaces [7]. Therefore, a contact angle between 10o and
90o indicates a polar, hydrophilic material with significantdegree of interfacial surfaceformation,
with an angle less than 10o considered superhydrophilic. On the other hand, a contact angle
between 90o and 150o indicates a nonpolar, hydrophobic material with little surface formation,
with an angle greater than 150o considered superhydrophobic [5].
The previous equations relate the contact angles of solid-liquid-vapor interactions to the
surface tensions of the systemfor a perfectly smooth and solid surface. These equations may be
utilized in order to determine estimated values such as SFE. Such values may be considered only
as estimates as the equations only account for interfacial interactions, however fail to account
for the inherent roughness involved in every surface. Surface roughness has an impact on the
wettability of all surfaces and may be modified in order to produce a surfacewith desired surface
characteristics. There are currently two models that may be used to account for surface
roughness, the Wenzel model and the Cassie-Baxter model [8]. The Wenzel model accounts for
the complete wetting of roughened surface and is given as:
Equation (5): 𝑐𝑜𝑠𝜃∗
= 𝑟𝑐𝑜𝑠𝜃
with the surface roughness parameter, 𝑟, being greater than one for a roughened surface and
increasing with roughness. The surface roughness parameter is given as the ratio of roughened

22 | P a g e
surface area to the projected surface area. The true contact angle, 𝜃∗
, is then given by relating
this parameter to the contact angle of a perfectly smooth surface composed of the same
material, or 𝜃 [5]. This model ultimately accounts for surface roughness via an increase in surface
area, represented by the surface roughness parameter. The Cassie-Baxter model, however,
accounts for surface roughness in a different fashion. Instead of considering the gaps that result
from roughness as increased surface area, this model considers the gaps as thermodynamically
stable air-filled valleys. The Cassie-Baxter model considers the surface as a composite material
composed of the surface material and the air-filled valleys, with the impact of roughness
accounted for by the ratio of wetting surface area to the total surface area [5]. The Cassie-Baxter
relationship is given as:
Equation (6): ⁡𝑐𝑜𝑠𝜃∗
= 𝑓𝑐𝑜𝑠( 𝜃 + 1) − 1
where 𝑓 is the arealsurface fraction described as the ratio of wetting surfacearea to total surface
area and is less than or equal to one for all surfaces [5]. The relationships given by these models
highlight the significant impact that surface roughness has on wettability. According to these
models, by modifying the surface roughness of a material it is possible to modify its surface
wettability. Surface wettability may be modified by changes in either surface topography or
surface chemistry. Surface topography may be modified by removing material from the surface
(top-down) or adding material to the surface (bottom-up) [5]. Surface chemistry modification is
similar to the bottom-up modification method, however surface chemistry modification involves
material addition by the attachment of molecules through covalent bonds. Surfaces may be
chemically modified at specific sites and with molecules of desired chemical properties in order
to produce a surface with desired surface characteristics. This modification, referred to as
chemical functionalization, can be a difficult and complex procedure to perform due to its high
specificity and sensitivity. Self-assembling structures allow for easier surface chemistry
modifications due to their ability to self-organize. Thin films called self-assembled monolayer
films (SAMs) are formed by dispersing the chemically active material in a solvent and applying it
to the substrate (surface) in the liquid phase. The SAM molecules will then self-organize over
time due to chemisorption and van der Waals forces [9]. This process results in a thin film
covalently bound to the surface with binding dependent on the chemical composition of the film
and the applied surface. This experiment will perform top-down surface topography
modifications via sandblasting and surface chemistry modifications via SAM application in order
to determine the influence that these modifications have on surface wettability. The
simultaneous effects that both of these modifications have on surface wettability will also be
determined by applying nanoparticle films to sandblasted materials. Finally, the impact that
surface roughness has on wettability at the micro/nanoscale will be further explored by sanding
amaterial and observing changes in wettability. The contact angles for eachtrial will be measured
using two different liquids in order to calculate SFE.
Materials

23 | P a g e
Substrate materials:
 Glass slides (bare and sandblasted)
 Teflon sheets (bare only)
 Aluminum alloy plate (bare and sandblasted)
Surface modification materials:
 SNOWTEX ST-PS-M colloidal SiO2 nanoparticles (20%-by-weight solution)
 FAS-17 and denatured ethanol
 220 grit sandpaper
Liquids for contact angle and surface energy measurements:
 Deionized water
 Diiodomethane (DIM)
Materials for sample preparation:
 Acetone
 Isopropyl alcohol
 Deionized water
 Several 50 mL and 800-1000 mL beakers
Equipment:
 Sonicator
 Scale (with .1 g resolution)
 Hotplate (with magnetic stirrer)
 Timer
 Tweezers and diamond scribers
 CA goniometer with camera
 Optical microscope
Samples Tested (one of each):
 Bare aluminum
 Bare glass
 Bare Teflon
 Sandblasted aluminum
 Sandblasted glass
 Sanded Teflon
 SiO2 nanoparticles on sandblasted aluminum
 FAS-treated sandblasted glass

24 | P a g e
Procedures
SiO2 Nanoparticle Deposition on Sandblasted Al:
1. Dilute 25g of SNOWTEX with 25g of deionized water in a 50 mL beaker to produce
a 10%-by-weight SiO2 nanoparticle solution.
2. Stir for 20 minutes with a magnetic stirrer.
3. Carefully dip a sandblasted aluminum sample into the nanoparticle solution for
several seconds using tweezers to deposit a nanoparticle film on the sample
surface.
4. After dipping, place the sample on a 300oC hot plate for several seconds to
evaporate any moisture in the nanoparticle films.
FAS-17 Treatment of Sandblasted Glass:
1. In a 50 mL beaker, add 0.3 g of FAS-17 and 14.3g of denatured ethanol to make a
solution of FAS-17 and denatured ethanol for a solution with 1.6 mmol of FAS-17
per mole of solution.
2. Submerge the sandblasted glass sample in the FAS-17 solution for 10 minutes to
deposit an FAS-17 film on the sample surface.
3. Afterward, place on a 130°C hotplate for 10 minutes to evaporate any remaining
solvent.
Teflon Roughening:
1. Use 220 grit sandpaper to roughen a 1”x1” area of Teflon sheet.
2. Rub in random directions for 20 sec.
3. Use a diamond scribe to mark the back side of these samples.
Water Contact Angle Measurements:
1. Contact angle measurements should be performed on all samples using deionized
water as the probe liquid.
2. Using the goniometer, drop a ~1 µL deionized water droplet onto the sample
surface.
3. Take 3 measurements at different locations on each sample for averaging
purposes.
4. Repeat each step using ~2 µL diiodomethane (DIM) droplets for all samples except
the SiO2 nanoparticles on sandblasted aluminum.
Note: Gloves should be worn at all times when handling samples, and take special
care to not touch or otherwise damage the sample surfaces.

25 | P a g e
Note: The Teflon samples are fairly malleable; if a sample will not sit flatly on the
goniometer stage, it can usually be flattened by clamping one end of the sample
with tweezers and “torqueing” the free end until the sample is flat.
Cleaning Procedure for Teflon:
1. Sonicate for 5 mins in isopropyl alcohol.
2. Rinse with deionized water and dry with nitrogen.
Cleaning Procedure for the Remaining Samples:
1. Sonicate for 20 mins in acetone
2. Sonicate for 10 mins isopropyl alcohol 3.
3. Rinse with deionized water and dry with nitrogen
Results
Figure (2): Average water contact angle measurements for each sample including standard
deviations.

26 | P a g e
Figure (3): Average DIM contact angle measurements for each sample including standard
deviations.
Figure (4): Average water and DIM contact angle measurements for each sample for comparison.

27 | P a g e
Figure (5): Surface free energy (SFE) calculations for each sample.
Figure (6): Microscope images from left to right: glass (10x), sandblasted glass (10x), FAS-17
treated sandblasted glass (10x).
Figure (7): Microscope images from left to right: sandblasted aluminum (10x), FAS-17 treated
sandblasted aluminum (10x), FAS-17 treated sandblasted aluminum (50x).

28 | P a g e
Figure (8): Microscope images (10x) of bare Teflon (left) and sanded Teflon (right).
Discussion
The results of this experiment successfully illustrate how the chemistry and roughness
of a surface impact a surface’s wettability and surface free energy. According to figure (2), the
hydrophilic materials include bare glass with an average contact angle of 53.4o, sandblasted
glass with an average contact angle of 16.4o, sandblasted aluminum with an average contact
angle of 77.1o, and FAS-17 treated sandblasted aluminum with an average contact angle of
11.9o. The hydrophobic materials include FAS-17 treated sandblasted glass with an average
contact angle of 127.2o, bare Teflon with an average contact angle of 107.6o, and sanded Teflon
with an average contact angle of 137.5o. The hydrophilic materials are considered polar
materials due to their high wettability with primarily-polar water molecules while the
hydrophobic materials are considered nonpolar materials. The primarily-dispersive, nonpolar
DIM droplets were also applied to each surface with the resulting contact angles measured in
order to calculate the SFE for each surface. The application of DIM accounted for the dispersive
interactions (𝛾𝑙𝑣
𝑑
= 50.8
𝑚𝑁
𝑚
, 𝛾𝑙𝑣
𝑝
= 0
𝑚𝑁
𝑚
) as opposed to the polar interactions accounted for by
water application (𝛾𝑙𝑣
𝑑
= 21.8
𝑚𝑁
𝑚
, 𝛾𝑙𝑣
𝑝
= 51
𝑚𝑁
𝑚
). Together, the contact angle measurements for
the different liquids allow the presence and magnitude of each interaction and on each of the
surfaces to be estimated. The average contact angle measurements using DIM droplets are
given by figure (3) with the average contact angle measurements for both water and DIM
droplets given by figure (4). All but the two most hydrophilic materials, sandblasted glass and
FAS-17 treated sandblasted aluminum, gave a decrease in contact angle measurements when
DIM was applied as opposed to water. An average decrease was expected due to a smaller
liquid-vapor surface tension for DIM (𝛾𝑙𝑣 = 50.8
𝑚𝑁
𝑚
) compared to water (𝛾𝑙𝑣 = 72.8
𝑚𝑁
𝑚
).
Compared to the contact angle measurements with water, the DIM measurements for bare
glass decreased only slightly from 53.4o to 49.9o. The liquid-vapor dispersive forces of DIM are
slightly more than twice that of water and similar in value to the liquid-vapor polar forces

29 | P a g e
present in water, while DIM contains no liquid-vapor polar forces. Therefore, the polar
interactions decrease by almost twice the amount of which the dispersive interactions increase
from water to DIM application. With similar contact angles for both liquids, bare glass likely
experiences almost twice the amount of dispersive interactions than it does polar interactions,
while containing a significant degree of both. This assumption may be further supported by the
sandblasted glass results. The sandblasted glass was more hydrophilic than bare glass and gave
a significant contact angle increase from water to DIM application of 16.4o to 39.2o. The
significant increase in polar interactions, indicated by the smaller contact angles measured for
water, are likely due to the roughened surface having a larger amount of surface area exposed.
With a larger surface area, polar interactions at the surface increase as more surface is available
for these interactions. The dispersive interactions increased only slightly upon the sandblasting
of glass, suggesting that the polar interactions for this surface increase by a larger magnitude
than the dispersive interactions as roughness increases. When the sandblasted glass was
treated with FAS-17, the resulting surface became hydrophobic with large contact angles of
127.2o for water and 105.7o for DIM. While the Wenzel model likely describes the contact angle
changes due to roughness for the other two glass samples, the Cassie-Baxter model likely
explains the large contact angles resulting in treatment. The application of the FAS-17 film likely
results in thermodynamically stable air-filled valleys that significantly increase the contact
angles measured. These valleys are likely formed due to the sandblasted glass material being
polar enough to form covalent bonds with the FAS-17 film upon immediate contact and at the
tip of the ridges. This results in a thin layer of filmlying directly above the surface of the treated
material, of which shields a large degree of the polar and dispersive forces involved in the
material. The surfaces of the different glass samples are given by figure (6). The smooth nature
of the bare glass supports a strong presence of dispersive forces while the roughness seen in
the sandblasted glass supports an increased surface area of which polar forces may interact.
The sandblasted aluminum samples resulted in a different pattern upon treatment. The
sandblasted aluminum sample resulted in slightly hydrophilic contact angles of 77.1o for water
and 46.9o for DIM. The dispersive interactions for this material are likely similar to its polar
interactions as the contact angles decrease from water to DIM is similar to the relative decrease
in the total liquid-vapor interaction from water to DIM. The sandblasted aluminum treated with
FAS-17 resulted in highly hydrophilic contact angles of 11.9o for water and 25.1o for DIM. The
strong polar forces outweigh the dispersive forces upon treatment as the contact angle
decreases and polarity increases significantly upon treatment. The initial polar forces before
treatment were not strong enough to allow covalent bonding of the filmat the surface unlike
the sandblasted and treated glass sample. Instead, the film molecules likely bind at random
sites within the sandblasted ridges to increase overall roughness and therefore give a decrease
in contact angles, suggested by the images in figure (7). Both of the aluminum samples,
therefore, likely follow the Wenzel model. The Teflon samples resulted in hydrophobic contact
angles of 107.6o for bare Teflon with water and 137.5o for sanded Teflon with water. The DIM
contact angle measurements were much less with a contact angle of 70.1o for bare Teflon and
89.3o for sanded Teflon. These results indicate small polar and dispersive interactions for these

30 | P a g e
sample. The increase in contact angles upon sanding may be explained by the Cassie-Baxter
model. By sanding the Teflon, small ridges are formed of which are small enough to form air-
filled valleys between them, decreasing surface roughness and resulting in larger contact
angles. The very small sizes of the ridges are further supported by the images in figure (8).
Finally, the SFE measurements for each sample are given by figure (5). These values generally
represent the strength of the interactions involved in each sample as previously discussed,
increasing with decreasing contact angles. Sandblasted aluminum treated with FAS-17 had the
smallest contact angles and the largest SFE of 77.97808 mN/m while sandblasted glass treated
with FAS-17 had the largest contact angles with the smallest SFE of 6.856499 mN/m. In
conclusion, surface wettability may be largely altered via modification. By increasing surface
roughness, the surface wettability may follow the pattern of the Wenzel model and increase, or
roughness may result in air-tight valleys and follow the pattern of the Cassie-Baxter model with
a decrease in wettability. Similarly, SAM treatment may significantly increase or decrease
wettability based on its binding formations.
References
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Publishing, 2005.
[2] S. Hartland, Surface and Interfacial Tension: Measurement, Theory, and Applications, (2004).
[3] Lotfi, M., M. Naceur, and M. Nejib. Cell Adhesion to Biomaterials: Concept of
Biocompatibility. N.p.: INTECH Open Access, 2013.
[4] Agrawal, Abhinandan. "Definition of Surface Tension." Definition of Surface Tension. MIT,
n.d. Web. 30 Nov. 2015.
[5] Zou, Min. "Surface Wetting Modifications Through Small-Scale Topography and
Nanomaterials." NUE Lab Module. University of Arkansas, n.d. Web. 30 Nov. 2015.
[6] C.M. Mate, Tribology on the Small Scale, 1st ed., Oxford University Press, 2008.
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Examples of Surface Characterization and Modification Experiences

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