Hydrophilic vs. hydrophobic. The meaning of contact angle
Hydrophilicity, comes from the Greek ύδωρ, (water) and φιλία (friendship). It refers to a physical property of a material that can transiently bond with water (H2O) through hydrogen bonding.
A hydrophilic material is a friend of water. Friends like to come closer, so a water droplet would spread on a hydrophilic surface. Furthermore water can enter the pores of a hydrophilic material and totally wet it. Most natural materials are hydrophilic.
The evaluation of hydrophilicity is made through water contact angle measurements. A water droplet would occupy as long surface of the hydrophilic material as possible. So the water contact angle will be significantly low.
Hydrophobicity comes also from the Greek ύδωρ, (water) and φόβος (fear). It refers to the physical property of a material (known as a hydrophobic) that repels a mass of water.
Water would be afraid of a hydrophobic material. So a water droplet would try not to touch large area of the surface and the shape of the droplet would be spherical. Hydrophobic natural materials are waxes, oils and fats.
The evaluation of hydrophobicity is made through water contact angle measurements. A water droplet would be spherical so the water contact angle will be significantly high.
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4 comments
Your site has good and revelant information on hydrophobic surfaces. Have been in this field since the middle 80’s with ENVICOAT.
J. Trato
Thank you, Mr. Trato!
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I am working on chemical synthesis of ZnO nanomaterials. I have studied contact angle for my samples(as-deposited and annealed). The surface morphology istudy shows flakelike morphology with no any morphological changes after annealing. The contact angle decreses due to annealing probably due to increase roughness in the sample.
The contact angle decrases for increasing the surface roughness..It is in accordance with wenzals law..But for practical evidence we measure roughness on surace profiler which gives roughness in Angston unit and theorotical we use quantity “r” as roughness factor in the equation ..
The question is what is the relationship between the roughness and the roughness factor…
Plz do reply
yours sincerely
Dear friend,
thank you for your question. Unfortunately there is no way to connect the roughness r
of Wenzel’s equation with the roughness (ra or r rms) estimated rom a tip profilometer.
You must use an optical profilometer or even better an AFM to measure the roughness
on the surface of ZnO nanomaterials.
The above instruments have the appropriate software and estimate the ratio of the rough surface to the smooth surface which is the roughness r of the Wenzel’s equation.
Best regards,
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