Course: CH506M Laboratory Report Guidelines (July-Dec 2024)
Laboratory Manual
Course: Analytical techniques
Equipment: Optical tensiometer
Group No.:
Name Roll No. Contribution in Experiment Report (%)
Shiam Babu R CE24D502 25
Aryan Raj CH24M101 25
Arka Sanyal CH24D507 25
Shubham Tyagi CH24M104 25
1. Objective:
• To Determine the Contact Angle (CA) and Surface tension/Interfacial tension (ST/IT) using
Optical tensiometer
2. Theory:
The contact angle (CA) represents the angle formed between the meeting point of a liquid and a solid
surface. To be more precise, it defines the angle between the tangent of the liquid-vapor interface and the
tangent of the solid-liquid interface where they intersect. This angle is a measure of how well a liquid wets
a solid surface, as described by the young’s equation. The concept involves establishing a thermodynamic
equilibrium among three phases: the liquid phase (L), the solid phase (S), and the gas or vapor phase (G).
If we denote the interfacial energy between the solid and vapor as, the interfacial energy between the solid
and liquid as, and the interfacial energy between the liquid and vapor (also known as surface tension) as,
then the equilibrium contact angle can be determined through the Young equation using these parameters.
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Course: CH506M Laboratory Report Guidelines (July-Dec 2024)
Adhesive interactions between a liquid and a solid surface led to the expansion of a liquid droplet across
the substrate. Meanwhile, cohesive forces within the liquid compel the droplet to gather into a spherical
shape, avoiding contact with the surface. The depicted angle in the illustration, known as the contact angle
(θ), denotes the point where the liquid-vapor interface intersects with the solid-liquid interface. Adhesive
and cohesive forces establish this angle's value, striking a balance between them. When the inclination of
a droplet to spread over a flat, solid surface intensifies, the contact angle diminishes. Consequently, the
contact angle inversely reflects the degree of wettability. An angle measuring less than 90° (referred to as
a low contact angle) generally signifies a strong propensity for surface wetting, causing the fluid to cover
a substantial portion of the surface. Conversely, angles exceeding 90° (designated as a high contact angle)
commonly indicate an aversion to surface wetting, prompting the fluid to minimize contact and assume a
compact, spherical form.
Contact Angle Degree of Solid-Liquid Liquid-Liquid
(CA) Wetting
θ=0 Perfect wetting Strong Weak
0 < θ < 90° High wettability Strong Strong
Weak Weak
90° ≤ θ < 180° Low wettability Weak Strong
θ = 180° Non-wetting Weak Strong
Pendant drop shape analysis
Surface tension measurements can be done with optical tensiometer by so-called. pendant drop shape
analysis (or reversed pendant drop). The shape of the drop of liquid hanging on the needle is determined
from the balance of forces which include the surface tension of that liquid. The surface tension can be
related to the drop shape by the equation.
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Course: CH506M Laboratory Report Guidelines (July-Dec 2024)
𝛾 = Δ𝜌𝑔𝑅2/𝛽
where γ is surface tension, Δρ is density difference between fluids, g is gravitational constant, R is radius
of drop curvature at apex, and β is a shape factor. β, the shape factor, can be defined through the Young-
Laplace equation expressed as 3D first order equations as shown in the figure below.
3. Experimental Set-Up
1) Stage level adjustment 2) Stage height adjustment 3) Stage height lock 4) Stage linear adjustment 5)
Stage rail lock 6) Stage lateral adjustment 7) Syringe lateral adjustment 8) Liquid dispenser holder 9)
Syringe height adjustment 10) Manual dispenser adjustment 11) Syringe clamp 12) LED light source 13)
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Course: CH506M Laboratory Report Guidelines (July-Dec 2024)
Sample stage with sample attachment clips 14) Camera lens focus adjustment 15) Camera lens zoom
adjustment 16) Level adjustment feet 17) Camera tilt indicator 18) Camera tilt adjustment 19) Power
button and status indicator light.
5. Experimental Procedure
➢ Place a clean calibration ball and its magnetic holder on the sample stage underneath the dispenser.
Lift or lower the sample stage to bring the ball into the image on-screen. Lift the dispenser away
from the image. Adjust the zoom from the lens zoom adjustment. A recommended default zoom
setting is such that the calibration ball fills most of the image.
➢ Press “Calibration invalid” and accept the calibration ball diameter (standard 4 mm) to complete
the calibration. After the calibration is done, do not change the zoom or focus from the focus ring
otherwise the calibration must be redone.
a) Instructions for water contact angle (WCA) measurements
Sessile drop WCA experiments
✓ For sessile drop experiments it is recommended to adjust the camera angle to -2 degrees.
✓ When a manual syringe is used, clean the syringe, fill it with the studied liquid and attach the
syringe to the syringe clamp.
✓ If an automatic single liquid dispenser is used, the tubing’s need to be filled. This can be done using
the device control buttons or by manually pushing liquid through the tubings and the needle. Click
dispense to push liquid from the tubing. The dispensing should be performed until there are no air
bubbles left in the tubing.
✓ When a disposable pipette dispenser is used, the OneAttension software will automatically
recognize the dispenser. Please select which tip size is used from the recipe. (Note! The Automatic
single liquid dispenser should not be connected at the same time). Fill the dispenser using the
device control buttons.
b) Instructions for Surface tension and interfacial tension (ST/IT) experimental procedure
✓ For pendant drop experiments it is recommended to adjust the camera angle to 0 degrees.
✓ Clean the syringe, place the liquid into it and attach it to the syringe clamp. With a standard surface
tension measurement, lower the sample stage so that it is out of the way.
✓ With a standard interfacial tension measurement place the less dense liquid in the syringe, the
denser liquid in a cuvette and the cuvette on the sample stage.
✓ Change the syringe needle to a hook needle and attach the filled syringe to the syringe clamp.
✓ From the Start tab choose the Pendant drop experiment.
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6. Observations and Calculations
Input Data for Heavy Phase - Water:
• Total Surface Tension (γtot): 72.800 mN/m
• Dispersive Component (γd): 21.800 mN/m
• Polar Component (γ+ and γ-): 25.500 mN/m each
• Density (ρ): 0.9982 g/cm³
• Viscosity (η): 1.006 mPa.s
• Temperature: 20.000 °C
• Molecular Weight: 18.015 g/mol
Input Data for Light Phase - Air:
• Density (ρ): 0.0012 g/cm³
• Temperature: 20.000 °C
• Molecular Weight: 0.029 g/mol
7. Results and Discussion
✓ Obtained results for sessile drop analysis over steel plate: Contact Angle - 71.921°
• The contact angle of 71.921° obtained from the sessile drop analysis indicates moderate wettability of
water on the steel plate. This value suggests that water spreads reasonably well on the steel surface but
does not completely wet it. The contact angle is influenced by the surface roughness and chemical
composition of the steel plate, which can affect the adhesive forces between the water and the steel
surface. Understanding the wettability of water on steel surfaces is crucial for applications such as
corrosion prevention, coating adhesion, and lubrication. For instance, in corrosion prevention, a lower
contact angle would indicate better wetting and potentially more effective protective coatings. In
coating processes, the contact angle can influence the uniformity and adhesion of the coating material.
Additionally, in lubrication, the contact angle can affect the distribution and effectiveness of lubricants
on metal surfaces.
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Course: CH506M Laboratory Report Guidelines (July-Dec 2024)
Figure 1: Water drop over the steel plate
✓ Obtained results for pendant drop shape analysis: Surface Tension (γ) - 72.181 mN/m
• The surface tension of water measured by the pendant drop method is 72.181 mN/m, which is close to
the known value of 72.800 mN/m for water at 20°C. This slight difference can be attributed to
experimental conditions and measurement precision. Surface tension is a critical parameter in various
applications, including coating processes, inkjet printing, and the formation of emulsions and foams.
Accurate surface tension measurements are essential for designing processes that involve liquid
interfaces, such as in the development of detergents, surfactants, and emulsifiers. For example, in inkjet
printing, the surface tension of the ink affects droplet formation and deposition on the substrate,
influencing print quality. In the formation of emulsions and foams, surface tension plays a key role in
stabilizing the dispersed phases, which is important in food processing, pharmaceuticals, and
cosmetics.
Figure 2: Pendant drop of water
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Course: CH506M Laboratory Report Guidelines (July-Dec 2024)
• The close agreement between the measured surface tension and the known value validates the accuracy
of the experimental setup and procedure. The data obtained from both sessile drop and pendant drop
analyses are consistent with the expected behavior of water at 20°C, demonstrating the reliability of
the optical tensiometer. This consistency is important for ensuring that the instrument can be used
confidently in various research and industrial applications. The findings have practical implications
for various industrial applications where the interaction between water and steel surfaces is critical.
The consistency of the results with known values also highlights the precision and accuracy of the
experimental methods used.
8. Conclusion
This experiment successfully demonstrated the application of an optical tensiometer for measuring the
contact angle and surface tension of water, providing insight into water’s interaction with steel surfaces.
The observed contact angle of 71.921° indicates moderate wettability, useful for applications like coating
and corrosion control in steel-related industries. Additionally, the surface tension value of 72.181 mN/m,
closely matching the known standard, confirms the reliability and accuracy of the optical tensiometer in
measuring liquid interface properties. Overall, this experiment underscores the importance of precise
wettability and surface tension measurements in optimizing various industrial applications, affirming the
potential of optical tensiometry in enhancing surface treatment and fluid interaction studies.
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