KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY
COLLEGE OF ENGINEERING
DEPARTMENT OF PETROLEUM ENGINEERING
EXPERIMENT: SURFACE TENSION AND INTERFACIAL TENSION
NAME: GAND OBED FIIFI FRANCIS
INDEX NUMBER: 3521718
LAB SUPERVISOR: MR. MICHAEL OBBO
GROUP NUMBER: THREE (3)
DATE: 9TH MARCH, 2021
TABLE OF CONTENT
TABLE OF CONTENT ............................................................................................................. 2
INTRODUCTION ..................................................................................................................... 4
AIM OF THE EXPIREMENT................................................................................................... 4
LITERATURE REVIEW .......................................................................................................... 4
MATERIALS AND APPARATUS ........................................................................................... 5
METHOD AND PROCEDURE ................................................................................................ 6
PRECAUTIONS ........................................................................................................................ 7
EXPERIMENTAL DATA AND OBSERVATION .................................................................. 8
OBSERVATIONS ..................................................................................................................... 8
CALCULATIONS ......................................................... Ошибка! Закладка не определена.
DISCUSSIONS ........................................................................................................................ 12
EFFECTS OF TEMPERATURE ON SURFACE TENSION ................................................. 13
CONCLUSION ........................................................................................................................ 13
REFERENCES ........................................................................................................................ 13
FIGURE 1: ATTENSION SIGMA 700/701(TENSIOMETER) ............................................... 6
FIGURE 2: A GRAPH OF THE SURFACE TENSION OF TAP WATER AT ROOM TEMP.
WITH RESPECT TO TIME ...................................................................................................... 9
FIGURE 3: A GRAPH OF THE SURFACE TENSION OF HEXANE AT ROOM TEMP. WITH
RESPECT TO TIME ............................................................................................................... 10
FIGURE 4: A GRAPH OF THE INTERFACIAL TENSION OF HEXANE AND TAP WATER
AT ROOM TEMP. WITH RESPECT TO TIME. ................................................................... 11
TABLE 1: EXPERIMENTAL DATA OF SURFACE TENSION OF TAP WATER WITH
RESPECT TO TIME ................................................................................................................. 8
TABLE 2: EXPERIMENTAL DATA OF THE SURFACE TENSION OF HEXANE WITH
RESPECT TO TIME ................................................................................................................. 9
TABLE 3: EXPERIMENTAL DATA OF THE INTERFACIAL TENSION OF HEXANE AND
WATER WITH RESPECT TO TIME ..................................................................................... 10
INTRODUCTION
AIM OF THE EXPIREMENT

To determine the surface tension of tap water.

To determine the surface tension of hexane.

To determine the interfacial tension of hexane and tap water.

To study the effects of temperature on surface tension (surface phenomenon).
LITERATURE REVIEW
The cohesive forces between liquid molecules are responsible for the phenomenon known
as surface tension (ST). The molecules at the surface do not have the similar neighboring atoms
on all sides and thus they cohere more strongly to those directly associated with them on the
surface. This forms a surface “film” which makes it more difficult to move an object through the
surface than move it when it is completely immersed. The same situation applies also at the
interface of the two liquids that do not mix together. In this case the term interfacial tension (IFT)
is used. If the surface area of the liquid is increased, more molecules are present at the surface, and
work must be done for this to occur. Therefore, the surface has excess Gibbs energy relative to the
interior of the liquid. There are several different units for surface and interfacial tension; typically,
mN/m (which is equivalent to dynes/ cm) is used.1
One of the main factors affecting surface tension of pure liquids is the temperature.
Experimentally it has been found that the surface tension decreases almost linearly with
temperature. When temperature increases, the molecular thermal activity increases causing a
decrease in cohesive interaction. This causes decrease in surface tension.2
Surface tension of pure liquids is also easily affected by certain impurities, called
surfactants. Surfactants are amphiphilic molecules that include both hydrophobic (non-polar, water
insoluble) and hydrophilic (polar, water soluble) segments. When surfactants are dissolved in
water they orientated at the surface so that hydrophilic parts are in water and hydrophobic parts
are in air. The surface tension is reduced as some of the water molecules are replaced by the
surfactant molecules and interaction forces between surfactant and water is less than between two
water molecules. The effectiveness of surfactant molecule is determined by the amount of
surfactant needed and the minimum surface tension value that can be reached. This can be studied
with critical micelle concentration (CMC) measurements as micelles are formed when the
surfactant concentration is high enough to saturate the surface.2
The measurement of the surface and interfacial tension can be done by using Sigma force
tensiometer. It is based on the force measurements of the interaction of a probe at the liquid-gas or
liquid-liquid interface. A probe is hang on the balance and brought into contact with the liquid
interface tested. The forces experienced by the balance as the probe interacts with the surface of
the liquid can be used to calculate the surface tension. The forces present in this situation depend
on the following factors; size and shape of the probe, contact angle between the probe and the
liquid and surface tension of the liquid. The size and the shape of the probe are easily controlled.
The probe is made of platinum which ensures the zero contact angle between the probe and the
liquid to be studied. Two types of probes are commonly used; the Du Noüy ring and the Wilhelmy
plate. A metal rod can also be used when the sample volume is limited.1
MATERIALS AND APPARATUS

Hexane

Tap water

Sigma Tensiometer (One Attension software)

Standard vessel

Small vessel

Du Noüy ring (probe)
FIGURE 1: ATTENSION SIGMA 700/701(TENSIOMETER)
METHOD AND PROCEDURE
For the surface tension of tap water;

The Du Noüy ring was placed on the hook in the measuring chamber.

The measurement chamber was opened; the stage was lowered and the small vessel
containing the tap water was placed on the stage after which it was raised again for the Du
Noüy ring to hang just above the surface of the tap water.

The measurement chamber was closed and the One Attension software was opened on a
computer connected to the tensiometer.

On the One Attension software, surface tension(ST)/interfacial tension(IFT) was selected,
the probe selected was with ring, the experiment name was typed, the vessel used in the
tensiometer which was the small vessel was selected and the phase was selected for the
surface tension experiment.

Finally, the program was ran to start the measurement of the surface tension of the tap
water.
For the surface tension of hexane;

The Du Noüy ring was placed on the hook in the measuring chamber.

The measurement chamber was opened; the stage was lowered and the small vessel
containing the hexane was placed on the stage after which it was raised again for the Du
Noüy ring to hang just above the surface of the hexane.

The measurement chamber was closed and the One Attension software was opened on a
computer connected to the tensiometer.

On the One Attension software, surface tension(ST)/interfacial tension(IFT) was selected,
the probe selected was with ring, the experiment name was typed, the vessel used in the
tensiometer which was the small vessel was selected and the phase was selected for the
surface tension experiment.

Finally, the program was ran to start the measurement of the surface tension of the hexane.
For the interfacial tension of water and hexane;

With the Du Noüy ring already in place in the measurement chamber, the stage was lowered
and the standard vessel containing hexane and tap water with hexane (light phase) settling
on top was placed on the stage after which the stage was raised for the Du Noüy ring to
touch the hexane-water contact of the mixture.

The measurement chamber was closed and the One Attension software was opened on a
computer connected to the tensiometer.

On the One Attension software, surface tension(ST)/interfacial tension(IT) was selected,
the probe selected was with ring, the experiment name was typed, the vessel used in the
tensiometer which was the standard vessel was selected after which the phase was selected
for the interfacial tension experiment of the hexane and tap water mixture.

Finally, the program was ran to start the measurement of the interfacial tension of the
hexane and water mixture.
PRECAUTIONS

The tensiometer was placed on a level and stable ground to avoid rupturing of the meniscus
which will lead to the restart of the measurement which will intend prolong the experiment.

The stage was lowered before placing any of the vessels on top.

The measurement chamber was closed before the One Attension program was ran.

For the measurement of the interfacial tension of the hexane and water mixture, the stage
was raised so the Du Noüy ring will touch the hexane-water contact so as to measure
interfacial tension and not surface tension of the hexane.
EXPERIMENTAL DATA AND OBSERVATION
OBSERVATIONS
When the One Attension was ran and the ring was above the surface for the surface tension
and in the hexane and water mixture, the force was zeroed. As the ring touched the surface for the
surface tension experiment, there was a slight positive force due to the adhesive force between the
ring and the surface. The ring was then pushed through the surface due to surface tension which
caused a small increment force (the same thing also happened in the case of the interfacial tension).
The ring broke the surface and there was a small positive force which was measured due to the
supporting wires of the ring. When lifted through the surface, the measured force started to
increase. The force kept increasing. The maximum force was reached. After the maximum, there
was a small decrease of the force until the ring was pushed back below the surface.3
TABLE 1: EXPERIMENTAL DATA OF SURFACE TENSION OF TAP WATER WITH
RESPECT TO TIME
No.
Time / sec
ST / (mN/m)
F/L (mN/m)
F (mN)
1
63.387
69.091
73.754
8.879
2
83.238
68.778
73.443
8.841
3
104.238
68.743
73.408
8.837
4
124.529
68.723
73.389
8.835
5
144.888
68.662
73.328
8.828
6
165.698
68.622
73.328
8.828
7
186.927
68.636
73.302
8.825
8
207.375
68.610
73.276
8.821
9
227.966
68.499
73.166
8.808
10
248.464
68.523
73.190
8.811
A Graph of surface tension of tap water at room temperature.
69,2
Surface Tension (mN/M)
69,1
69
68,9
68,8
68,7
68,6
68,5
68,4
60
80
100
120
140
160
180
200
220
240
Time (s)
FIGURE 2: A GRAPH OF THE SURFACE TENSION OF TAP WATER AT ROOM TEMP. WITH
RESPECT TO TIME
TABLE 2: EXPERIMENTAL DATA OF THE SURFACE TENSION OF HEXANE WITH
RESPECT TO TIME
No.
Time / sec
ST / (mN/m)
F/L (mN/m)
F (mN)
1
45.500
16.139
18.523
2.230
2
62.509
16.144
18.529
2.231
3
79.649
16.154
18.539
2.232
4
96.570
16.158
18.544
2.232
5
112.950
16.180
18.568
2.235
6
129.880
16.187
18.575
2.236
7
146.977
16.186
18.573
2.236
8
163.879
16.188
18.576
2.236
9
180.538
16.212
18.601
2.239
10
197.638
16.207
18.596
2.239
A Graph of surface tension of hexane at room temperature.
16,22
Surface Tension (mN/m)
16,21
16,2
16,19
16,18
16,17
16,16
16,15
16,14
16,13
40
60
80
100
120
140
160
180
200
Time (s)
FIGURE 3: A GRAPH OF THE SURFACE TENSION OF HEXANE AT ROOM TEMP.
WITH RESPECT TO TIME
TABLE 3: EXPERIMENTAL DATA OF THE INTERFACIAL TENSION OF HEXANE AND
WATER WITH RESPECT TO TIME
No.
Time / sec
ST / (mN/m)
F/L (mN/m)
F (mN)
1
71.627
32.758
34.141
4.110
2
90.946
32.235
33.639
4.050
3
111.464
31.885
33.301
4.009
4
132.187
31.661
33.086
3.983
5
152.855
31.484
32.915
3.963
6
174.144
31.355
32.791
3.948
7
195.164
31.237
32.677
3.934
8
216.553
31.156
32.600
3.925
9
237.395
31.041
32.489
3.911
10
258.694
30.983
32.433
3.904
A Graph of interfacial tension of hexane and water at room
temp.
33
32,8
Surface Tension (nM/m)
32,6
32,4
32,2
32
31,8
31,6
31,4
31,2
31
30,8
60
80
100
120
140
160
180
200
220
240
260
Time (s)
FIGURE 4: A GRAPH OF THE INTERFACIAL TENSION OF HEXANE AND WATER AT
ROOM TEMP. WITH RESPECT TO TIME.
CALCULATION
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑜𝑓 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑡𝑒𝑛𝑠𝑖𝑜𝑛/𝑖𝑛𝑡𝑒𝑟𝑓𝑎𝑐𝑖𝑎𝑙 𝑡𝑒𝑛𝑠𝑖𝑜𝑛 =
𝑠𝑢𝑚 𝑜𝑓 𝑣𝑎𝑙𝑢𝑒𝑠
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑣𝑎𝑙𝑢𝑒𝑠
For the average surface tension of tap water;
69.091 + 68.778 + 68.743 + 68.723 + 68.662 + 68.662 + 68.636 + 68.610 + 68.499 + 68.523
10
= 𝟔𝟖. 𝟔𝟗𝟑𝒎𝑵/𝒎
=
For the average surface tension of hexane;
16.139 + 16.144 + 16.154 + 16.158 + 16.180 + 16.187 + 16.186 + 16.188 + 16.212 + 16.207
10
= 𝟏𝟔. 𝟏𝟕𝟔𝒎𝑵/𝒎
=
For the average of the interfacial tension of hexane and water;
32.758 + 32.235 + 31.885 + 31.661 + 31.484 + 31.355 + 31.237 + 31.156 + 31.041 + 30.983
10
= 𝟑𝟏. 𝟓𝟖𝟎𝒎𝑵/𝒎
=
DISCUSSIONS
For the experiment of the surface tension of the tap water, it was seen that the surface
tension decreased with time and this was as a result of the decrease in the cohesive force with time
between the molecules of the tap water. Also, it can be observed that the surface tension of that of
the hexane also decreased gradually with time and as said for that of the tap water, the forces within
the molecules of the hexane decreased with time. For the experiment concerning the interfacial
tension of the hexane and tap water, the same decrement in the values of the interfacial tension
was seen and since force it directly proportional to the interfacial tension, it can be said that the
decrement was also as a result of the decrease in the force.
Now comparing the average surface tension of the tap water experiment to that of the liquid
hexane (68.693 and 16.176 respectively), it can be noted the average surface tension of the tap
water is higher than that of the hexane and this is because the affecting cohesive force and since
surface tension is proportional to the force and there is a decrease in the force there will be a
decrease in the surface tension as compared to that of tap water which has a strong cohesive force.
Hence, obtaining an average surface tension of the tap water higher than that of the hexane.
Surface tension observed between two liquids; water and hexane are known as the
interfacial tension. This is defined to the interface of two immiscible liquids. The surface tension
of water at room temperature was found to be 68.693 mN/m while that of liquid hexane; 16.176
mN/m. The interfacial tension which is “surface tension” between the two liquids was found to be
31.580 mN/m which is lower when compared to water but higher relative to liquid hexane. This
is due to the fact that the polar to non-polar attraction between the unlike molecules yields an
attractive force lower than the cohesive force in the polar liquid but higher than cohesive force in
the non-polar liquid; hexane.
EFFECTS OF TEMPERATURE ON SURFACE TENSION
One of the main factors affecting surface tension of pure liquids is the temperature.
Experimentally it has been found that the surface tension decreases almost linearly with
temperature. When temperature increases, the molecular thermal activity increases causing a
decrease in cohesive interaction. This causes decrease in surface tension.2
CONCLUSION
Both surface tension and interfacial tension depend on the force of attraction between the
molecules of the fluid(s); the stronger the force of attraction, the greater the value of either the
surface tension or the interfacial tension and vice versa. Also, temperature has an effect on surface
tension and it is inversely proportional.
REFERENCES
1. Susanna Lauren, PHD, Biolin Scientific. Surface and Interfacial Tension and their
Measurement Techniques. Attension [TN 2], page 1.
2. Susanna Lauren, PHD, Biolin Scientific. Surface and Interfacial Tension and their
Measurement Techniques. Attension [TN 1], page 3.
3. Susanna Lauren, PHD, Biolin Scientific. Surface and Interfacial Tension and their
Measurement Techniques. Attension [TN 2], page 2.
4. Gibbs. J. W. (2002) [1876-1878], “On the equilibrium of heterogeneous substances”, in
Bumstead, H. A.; Van Nameeds, R. G., The Scientific Papers of J. Willard Gibbs, 1,
Woodbridge, CT: Ox Bow Press, pp. 55-80, ISBN 091802477