Mechanical Engineering Experiment: Contact Angle Measurement Report

This report delves into the theory and practical aspects of contact angle measurement using the imaging method, a crucial technique for understanding surface wettability. It begins with an introduction to contact angle, its definition, and its significance in characterizing the interaction between solids and liquids, including the use of Young's equation. The report then discusses various factors influencing contact angle, such as temperature, pressure, salinity, impurities, and surface roughness, explaining their effects on liquid wettability. It highlights how increasing pressure and temperature can affect the contact angle and wettability, while also examining the impact of salinity and impurities on surface tension and adhesion forces. The report also examines the relationship between surface roughness and wettability, including the phenomena of advancing and receding contact angles. Finally, it concludes by summarizing the unique characteristics of solids, liquids, and gases under various conditions, and their impact on the equilibrium contact angle. The report references several sources to support its findings.

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Instructor
Mechanical Engineering
16 May 2019
Contact Angle Measurement Using Imaging Method
Theory
Qualitatively, a contact angle is the perceptible portrayal of microscopic phenomena such as
pressure, temperature, salinity, impurity, surface roughness interfacial tension etc. Contact angle
is the interior angle framed by the substrate being utilized and the digression to the drop interface
at the obvious crossing point of all three interfaces. This crossing point is known as the contact
line. Young's equation is used to define the contact angle. The contact point may likewise be
straightforwardly estimated to compute the proportion of interfacial surface pressures if the
interfacial surface strains are obscure (Al-Bazzaz, Waleed, Salah, & Mohammed, 2018).
Discussion
Contact angle is dependent on surface wettability of surfaces by liquids, gases and hence is
affected by a variety of factors hence the outcomes in the experiment. The relationships of these
factors and the contact angle is as discussed as follows;
i. Temperature and pressure
When the pressure is increased, the contact angles tend to become smaller. As the contact angle
reduces due to increasing pressure, the system changes from weak oil wet to intermediate
wettability. From the results obtained in the tables 2 and 3, it can be seen that the contact angle
increases from 47.08 (table 2) to 90.1 degrees (table 3). This is an indication that the system
achieves more surface wettability at higher temperatures. Similarly, it can be noted that the
contact angle reduces when temperatures rises due to increased surface wettability at higher
temperatures (Mohammadi, Finlay, & Roa, 2019).
ii. Salinity
Salinity alters surface wetting properties of liquids hence affects the contact angle. High salinity
increases surface wetting of water and reduces gas absolute permeability. Salinity affects the
thickness of liquid drop(s) by reversing the muscovite/water interfacial charge. Therefore,
salinity affects liquid wettability such that; reduction in divalent ion content while keeping the

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ion strength constant leads to improved wettability hence decreases the contact angle
(Mohammadi, Finlay, & Roa, 2019).
iii. Impurities
Impurities increases surface tension of liquids by modifying the molecular bonding
characteristics. Adhesion forces increases as a result limiting the wetting properties of the liquid.
With poor surface wettability of the liquid, the contact angle is increased. Addition of impurities
reduces surface wettability hence improved contact angles (Mohammadi, Finlay, & Roa, 2019).
iv. surface roughness interfacial tension
Surface roughness improves surface wettability as a result of the chemistry of the surface. For
instance, hydrophobic surfaces become more hydrophobic when surface roughness is enhanced.
This marks a manifestation of interfacial tensions when both surfaces interact at the point of
contact between liquid and the system. Effects of contact angle hysteresis manifest on rough
surfaces as well (Jordin, 2017).
v. receding and advancing of contact angle
Advancing contact angle is a measure of liquid-solid cohesion. The stronger the liquid-solid
cohesion, the less the surface wettability hence enhanced contact angle. Receding contact angle
measures liquid-solid adhesion. When the liquid-solid adhesion is stronger, more wettability
manifest hence reduced contact angle (Dalton, et al., 2017).
Conclusion
Solids, liquids, and gases possess unique characteristics at unique temperature and pressure
conditions or surface conditions hence each achieves a unique equilibrium contact angle. Factors
such as impurities, temperature, pressure, surface tension, salinity, surface roughness etc.
impacts liquids wettability on surfaces. Consequently, effects on surface wettability hence
produces unique determinations of contact angle based on the existing factors or surface
characteristics.

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References
Al-Bazzaz, Waleed, Salah, and Mohammed, 2018. Investigation Wettability
Contact Angle Measurement in Kuwaiti Heavy Oil Reservoir and Modeling
Using 2D Imaging Technologies [online]. OnePetro. Available from:
https://www.onepetro.org/conference-paper/SPE-193706-MS [Accessed 16
May 2019].
Dalton, E., L., Crandall, M., D., Goodman, L, A., and King, S.J., 2017.
Evaluation of Methods to Measure Contact Angles of Supercritical CO2 and
Brine in Sandstone Cores Using Micro-CT Imaging [online]. Evaluation of
Methods to Measure Contact Angles of Supercritical CO2 and Brine in
Sandstone Cores Using Micro-CT Imaging (Conference) | OSTI.GOV. Available
from: https://www.osti.gov/biblio/1510815-evaluation-methods-measure-
contact-angles-supercritical-co2-brine-sandstone-cores-using-micro-ct-
imaging [Accessed 16 May 2019].
Jordin, M., 2017. [online]. contact angle measurement method of drop shape
analysis instrument_USA KINO Industry Co., Ltd. Available from:
http://www.surface-tension.org/news/54.html [Accessed 16 May 2019].
Mohammadi, Finlay, and Roa, 2019. Determination of contact angle of
microspheres by microscopy methods [online]. Proceedings International
Conference on MEMS, NANO and Smart Systems. Available from:

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https://www.academia.edu/15512893/Determination_of_contact_angle_of_mi
crospheres_by_microscopy_methods [Accessed 16 May 2019].