Nano/micro roughness causes an increase or decrease in the the contact angle depending on the nature of solid substrates. Trapped air causes an increase in the contact angle for hydrophobic surfaces. What is the role of trapped air for hydrophilic surfaces?
roughness increases the surface area , hydrophobic surface trapped the air , and increase in roughness leads to higher hydrophobicity but hydrophil surface with large surface are or higher roughness leads to increase polar interaction with water droplet and decrease water contact angle
Hi Sukamanchi,
As you know that air consists of oxygen and nitrogen in major amount compared to the others. Atomic oxygen have high capability of bonding with water molecules forming hydrogen bonding. as well as with something else that have similar properties to water. In summary, the role of air trapped for hydrophilic surface is conducted by oxygen atoms that have ability to bind water molecules or other molecules with similar properties with water.
Dear all,
the increase in roughness leads to an increase of both specific surface area and surface irregularities. Both parameters enhance the an extra interactions with the other phase. Regards
roughness increases the surface area , hydrophobic surface trapped the air , and increase in roughness leads to higher hydrophobicity but hydrophil surface with large surface are or higher roughness leads to increase polar interaction with water droplet and decrease water contact angle
Thank you for all your answers. The trapped air between the rough projects can help to suspend the liquid drop from hydrophobic surface but in hydrophilic surfaces, how the trapped air can be replaced by liquid drop? On a hot cooking pan water drop can roll-off easily even the pan is hydrophilic in nature. Actually, the hot air between the pan and water helps to roll-off easily.
Liquid can never wet a really hot surface, because it is partially vaporized on the surface and form a film of vapor to prevent the liquid from wetting the surface so it has to roll off. It's not air that got trapped but vapor constantly forming underneath the liquid drop. You may know that liquid nitrogen won't burn your skin, because skin is just too hot for it. That's totally extreme condition which we usually don't consider when talking about wettabilities.
On hydrophobic and hydrophilic I think you can try papers of Prof. Lei Jiang. They've been working on this topic for years and you can easily find many reviews on it. I believe it will answer your questions perfectly.
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