Contact Angle Measurement Using Imaging Method

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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.