Which is the best way to decrease the surface tension? Surfactant or boiling?
Is contact angle same in same surface tension of soap water and boiling water solutions?
0 mN/m, at the critical point.
"Best" is a relative concept.
Contact angle reacts differently to surfactant and temperature - even if water|air tension is the same, the contact angles will be, most probably, different (Young equation involves also the surface tensions of the solid surfaces - you need to account for the respective surface entropies and the affinities of the surfactant for water|solid and solid|air when TPC angle is considered).
Thank you Mr. Radomir I Slavchov for your answer. Cricitical temperature of water is 374°C. I need to get the least possibility in liquid state. We can reduce the surface tension by heat treatment or by surfactant. Does contact angle same in same surface tension of soap water and boiling water solutions on a similar solid substrate?
Dear Dr. Sukamanchi,
At boiling temperature, pure water is with surface tension of about 60 mN/m. With a suitable non-ionic surfactant you can decrease it to about 30 mN/m at room temperature. I guess then that surfactant is the better choice.
And once again - no, if you have the same decrease of the surface tension of water caused by heat or surfactant, the contact angle with any solid will be most probably different in the two cases, considering Young equation.
Boiling does not reduce surface tansion of water drastically, as boiling at 100 C is far away from the critical point, were surface tension is zero. Surfactants are capable to reduce surface tension drastically. Foam bubbles separating from bulk water is the shining example. Surfactants not only reduce surface tention, but induce disjoinng pressure between the surfaces, keeping either foam or a colloidal sytem stable. The mechanism is described in the paper attached.
Typical surfactants with hydrocarbon chain as a tail reduce surface tension of water to 26-28 mN/m. Some fluorinated surfactants can reduce it to about 18 mN/m, as far as I remember.
Surfactant is a bad choice because it hinders the evaporation. See Lehmann: Study of Surface Tension, Natural Evaporation, and
Subcooled Boiling Evaporation of Aqueous Surfactant Solutions, 2016
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