My understanding is that as the surface energy increases -- that is, the attractive forces between the liquid and the surface become stronger -- the contact angle increases. If the surface energy decreases -- the liquid has less attractive forces with the surface -- then the contact angle will decrease. Surface tension in the liquid, stemming from the intermolecular forces between individual liquid molecules pulls the drop into a sphere. Doing this reduces the overall surface area of the liquid, and thus the amount of interaction between the liquid and the surface. And, this squeezes the contact angle down. Forming interactions with the surface means fewer interactions with other like-molecules, so this will only be favorable if the interaction strength and/or number formed with the surface is stronger than the intermolecular interactions of the liquid.

Mason Lee

Under isobaric-isothermal conditions, your surface energy is more accurately called the Gibbs surface energy. It is equal to the specific surface energy (surface tension) X surface area. Therefore, it is better to talk about the effect of interfacial surface tension on the surface Gibbs energy. Choose your examples, look at interfacial tension and draw conclusions.

Hydrophilic surface - a surface that is well wetted by water, contact angle 90.

The degree of wetting is characterized by the dimensionless value of the cosine of the contact angle.

Data Yu.A.Mirgorod, R.V. Grebennikova. Glossary on Colloid Chemistry.

How surface energy affects the contact angle with ANY solvents?

The solvent contains polar molecules. The solid can be a metal or an oxide. In reality, with rare exceptions, its surface is covered by a dielectric film. When a polar molecule adsorbs, it induces an image charge which modifies the internal energy of the last layers and induces changes in order. The result is a normal field and a field parallel to the surface, which spreads the dipoles over the surface. This pattern is verified by slow electron spectrometry and surface potential measurements. On the surface of an atomically pure metal, adsorption occurs on defects, particularly dislocations. The effect is to attenuate the oscillations of conduction electrons, i.e. to localize them around image charges. If the density of adsorption sites is sufficient, a maximum coverage is reached, beyond which physical adsorption becomes unstable and is transformed into chemical adsorption. The dielectric function, which describes the interaction of electromagnetic waves with matter, and the equation of state, which describes the evolution of internal energy, justify this presentation of the effects of surface energy on the contact angle. The technique used to measure charge properties makes it possible to measure the parameters of the equation of state.

Regards

How surface energy affects the contact angle with ANY solvents?

The solvent contains polar molecules. The solid can be a metal or an oxide. In reality, with rare exceptions, its surface is covered by a dielectric film. When a polar molecule adsorbs, it induces an image charge which modifies the internal energy of the last layers and induces changes in order. The result is a normal field (zerozeta) and a field parallel to the surface, which spreads the dipoles over the surface. This pattern is verified by slow electron spectrometry and surface potential measurements. On the surface of an atomically pure metal, adsorption occurs on defects, particularly dislocations. The effect is to attenuate the oscillations of conduction electrons, i.e. to localize them around image charges. If the density of adsorption sites is sufficient, a maximum overlap is reached, beyond which physical adsorption becomes unstable and is transformed into chemical adsorption. The dielectric function, which describes the interaction of electromagnetic waves with matter, and the equation of state, which describes the evolution of internal energy, justify this presentation of the effects of surface energy on the contact angle. The technique used to measure charge properties makes it possible to measure the parameters of the equation of state.

Regards

Claude Le Gressus

Thanks for your answer in detail.

I have some questions want to consult you,

As a hydrophobic substance, it's bonds on the surface are not electron-polarizable, they cannot form hydrogen bonds. As a result, water exhibits repulsion towards hydrophobic substances, allowing water molecules to form hydrogen bonds with each other. So water becomes a ball on the surface.

But now is the opposite situation, not electron-polarizable solvent on the electron-polarizable solid surface, will the solvent form bonds with itself and becomes a ball as well?

Thank you very much!

Best regards

In a hydrophobic substance, the majority of defects are holes and the surface potential is positive. Conversely, the potential of a hydrophilic material is negative, and its defects are predominantly electron traps. All properties - toughness, coefficient of friction, breakdown, breakdown field.... - vary with surface potential. They are minimal if the surface is neutral and increase with potential until the internal energy of the surface layers reaches the maximum value at which it transforms. This is confirmed by numerous experimental results. Viscosity at the interface between liquid and solid also depends on the surface energy of the solid. It determines the spreading speed of the liquid. The ratio between surface energy and viscosity has the dimension of a velocity. We can therefore consider that a drop will spread if the surface is not neutral, and that a spread drop will reform into a sphere if, for whatever reason, the surface energy is reduced.

This can be achieved, for example, by applying a potential to the sample, or by switching from physical adsorption to chemical adsorption.

Have a nice week