Contact angle, θ (theta), is
a quantitative measure of wetting of a solid by a liquid
. The contact angle is geometrically defined as the angle formed by a liquid at the three-phase boundary where a liquid, gas, and solid intersect.
Why do we care about contact angle?
Determining the contact angle will
allow you to know the quality of a material surface prior to an adhesion process
such as coating, sealing, soldering, adhesive bonding, printing or painting.
Why do we measure contact angle?
The contact angle is important wherever
the intensity of the phase contact between liquid and solid substances
needs to be checked or assessed: coating, painting, cleaning, printing, hydrophobic or hydrophilic coating, bonding, dispersing etc.
What is the purpose of this test Why are contact angles measured between liquid drops and solid biomaterial surfaces?
Contact angle measurements are
used to determine the ability of a solid substrate to repel a liquid
. In the simplest case, the hydrophobicity (water-repellent property) of the substrate is tested by setting a drop of water on the substrate surface.
What are the applications of angle of contact?
Contact angle measurement (Figure 1) is a well-known technique in many fields such as
contamina- tion control, adhesion, surface treatments, and polymer film modification
. The measurement of contact angles yields data which reflect the thermodynamics of a liquid/ solid interaction.
What is a good contact angle?
Contact angle is a measure of wettability
Water contact angle will immediately give an indication of the wettability of the solid. If the measured contact angle is above
90 degrees
, the solid is said to have poor wetting and is termed hydrophobic. If the contact angle is below 90 degrees, a term hydrophilic is used.
Why is the contact angle of water Zero?
The angle of contact does not depend on the manner of contact. When a liquid has concave meniscus, the angle of contact is acute. When it has a convex meniscus, the angle of contact is obtuse. For
pure water and perfectly clean glass
, the angle of contact is 0°.
How do I find my contact angle?
The sessile drop method
is by far the most commonly used method to measure contact angle. It involves a syringe pump to produce the droplet of liquid (usually water), and a camera to observe the droplet on a substrate.
How do you find contact angle?
Locate the point at which the droplet outline intersects the solid surface.
The angle between the droplet outline and the solid surface
is the contact angle.
How do you measure hysteresis contact angle?
Contact angle hysteresis by needle method
As
the contact line between the substrate and the drop is increasing
, the advancing contact angle is measured. When the liquid is sucked slowly off the substrate and the contact line is withdrawing, the receding contact angle is measured.
How do you reduce contact angle?
If a sufficiently small volume of liquid is added to a drop, the contact line will still be pinned, and the contact angle will increase. Similarly,
if a small amount of liquid is removed from a drop
, the contact angle will decrease.
What does a high contact angle mean?
A high contact angle (pictured right) indicates that
the surface has low wetting
– that is, the liquid droplet will not spread very much onto the surface. A low contact angle (left, below) indicates that the surface is high wetting, meaning that the water droplet spreads out more on the surface.
What is the relation between contact angle and wettability?
On a homogeneous solid surface, angle θ is independent of the volume of the liquid drop. Obviously, since the tendency for the liquid to spread increases as θ decreases, the contact angle is a useful
inverse measure of spreadability or wettability
.
What is the value of angle of contact for pure water?
Because normal water or tap water has some impurities in it, it forms an acute angle of contact with the glass. But in case of pure water and clean glass, the angle of contact will be
[{0^ circ }]
since it is pure and does not have any type of impurities (like salt) dissolved in it.
When can we have angle of contact 90?
When the angle of contact is between the
solid and liquid
is ${90^0}$, cohesive force is equal to adhesive force because they will be in equilibrium state and we will get the flat meniscus in this case. Hence, option (C) is correct.
How does surface tension affect contact angle?
The effect of surface tension on capillary pressure is more complicated: on one hand, the capillary pressure is directly
proportional
to the surface tension. On the other hand, high surface tension liquids typically also have higher contact angles, which lower the capillary pressure.
