# Relationship between contact angle and wettability To calculate real surface free energies of the solid the actual contact angles should be used. The relationship between roughness and wettability was defined . The relationship between Contact Angle and Surface Tension finally explained. Shows how Wettability is connected to these phenomenon. The contact angle (wetting angle) is a measure of the wettability of a solid by a there is a relationship between the contact angle θ, the surface tension of the.

Angles measured in such a way are often quite close to advancing contact angles.

### Contact angle - Wikipedia

Equilibrium contact angles can be obtained through the application of well defined vibrations. This complexity is further amplified when one attempts to incline the surface. Experimental apparatus to measure pendant drop contact angles on inclined substrates has been developed recently. An automated system allows for tilting the substrate and analysing the images for the calculation of advancing and receding contact angles.

The dynamic sessile drop method[ edit ] Main article: Sessile drop technique The dynamic sessile drop is similar to the static sessile drop but requires the drop to be modified. A common type of dynamic sessile drop study determines the largest contact angle possible without increasing its solid—liquid interfacial area by adding volume dynamically.

Contact Angle and Wetting Properties

This maximum angle is the advancing angle. Volume is removed to produce the smallest possible angle, the receding angle. The difference between the advancing and receding angle is the contact angle hysteresis. A method for calculating average advancing and receding contact angles on solids of uniform geometry.

Both sides of the solid must have the same properties.

## Contact angle

The wetting tendency is larger, the smaller the contact angle or the surface tension is. Introduction The contact angle is an angle that a liquid creates with a solid surface or capillary walls of a porous material when both materials come in contact together. This angle is determined by both properties of the solid and the liquid and the interaction and repulsion forces between liquid and solid and by the three phase interface properties gas, liquid and solid. The balance between the cohesive forces of similar molecules such as between the liquid molecules i. The traditional definition of a contact angle is the angle a liquid creates with the solid or liquid when it is deposited on it. A less traditional definition is the angle a liquid creates with the sides of a capillary when it rises in it to create a meniscus.

• Contact Angles

Hydrophobic surface left and hydrophilic surface right. Figures used with permission from Wikipedia The smaller the contact angle - cohesive forces are weaker then adhesive forces and molecules of the liquid tend to interact more with solid molecules then liquid molecules.

The larger the contact angle - cohesive forces are stronger then adhesive forces and the molecules of the liquid tend to interact more with each other then with the solid molecules. Thermodynamics Thomas Young 13 June — 10 May proposed treating the contact angle of a liquid with a surface as the mechanical equilibrium of a drop resting on a plane solid surface under the restrains of three surface tensions: Another approach avoids specifying the field of intermolecular forces between solid and liquid and instead offers a thermodynamic solution.

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The same effect is what causes porous materials to soak up liquids. Capillary forces pull a wetting liquid has a low contact angle with the surface, it wets the surface.

Assuming that there are no other factors involved e. This phenomenon can be described with the Young-Laplace equation and the Laplace pressure inside a capillary. Illustration of capillary rise and contact angle in a capillery. Measuring methods Many measuring methods have been described in the literature but only a few of them have been found to be widely applicable. The Sessile Drop Method The most frequently used is the goniometer-telescope measurement of sessile-drop contact angles.