Young equation and contact angle

[@pesselatchicomo9088]

Amazing and enjoyable.❤

[@IndiraYessenaliyeva]

Genius explanation, thank u 🙏

[@abbaszeinijahromi]

Excellent video series

[@JohnSmith-xx9th]

I like the Wilhelmy Plate Method - with the advancing and receding contact angles.

[@azemisamsuri6198]

Very good lecture

[@baghalimathapa1302]

Thank you for fantastic delivery on the methamatical derivations. Is it possible to do a video on the theory of dropshape analysis for measuring surface tenstion? Especially the mathematical part.

[@BoffyBlunt]

Many thanks for your kind words. I will consider this request when I record new videos later this year.

[@baghalimathapa1302]

@@BoffyBlunt That will be highly appreciated. Thank you.

[@RohitSingh-ku9nf]

Prof. Martin, Greetings of the day. Thankyou for the great explanation, however I am unable to imagine that can such a situation arise where both phase 1 & phase 2 has equal tension w.r.to solid I.e., theta = 90.

[@BoffyBlunt]

This can happen when neither phase has a preference for the solid surface.

[@athxyzgod]

why isn't R=r as it is a sphere ?

[@BoffyBlunt]

This is correct for a zero contact angle. Yes, the meniscus is part of a sphere, but unless we are completely wetting, the radius of curvature is larger than the inscribed radius of the capillary tube.

[@СергейКалинин-г5ш]

Hello, Prof.Martin! I'm impressed by your lectures, but you explain "interfacial tension" matter a bit incorrectly. The key is in intermolecular interaction. The molecules at the interface are pulled into volume so the average distances between molecules at the interface become large than inside the volume. Due to this increase of distance you have additional increase in potential energy for the molecules at the interface. Moreover the increase in distance is the tension! That is why the matter is called surface tension. So energy per unit area, sigma, is the PROPERTY of the fluid at certain temperature. Surface energy Wsurf=sigma*Area. Moreover, once you explain Young's equation you don't use the equilibrium of border line which surrounds the water droplet, i.e. molecules of the interface of each phase pull the border line due to tension and that is why the balance equation is introduced in such simple form. In other words, tension force, F, is proportional to the length of border line, i.e. F=sigma*length. If you consider a small segment of border line then F=sigma*dL. There is no sense to introduce "broken bonds" or similar physics because these are secondary matters. Having say that I'm really expressed by subsequent course where you 've introduced the percolation matter, snap off and trapping. Your triangle example is very helpful in understanding of layering or swelling of layers while imbibition. Sorry for my runglish, i.e. Russian English!

[@BoffyBlunt]

Thank you for your comment. You are indeed correct in your physical interpretation as to why the interface between two fluids can be considered literally as a tension. Thank you for adding this explanation in the comments. In my video I kept the idea simple as a change in energy following the approach written by a Nobel Prize winner in Physics: 10. Capillary and Wetting Phenomena: Drops, Bubbles, Pearls, Waves, P-G de Gennes, F. Brochard-Wyart and D. Quéré, Springer (2002).

[@СергейКалинин-г5ш]

@@BoffyBlunt Thank you, prof.Martin! You actually motivate me to look for the answer. I'm 44 years old, but it sometimes difficult to realise that you missed something in the school and you need to prepare for the lectures for your colleagues. Books on the subject in oil and gas industry are very poor in terms of physics explanation. Wikipedia also gives final result for Young equation without fundamentals in terms of Newton's law, simple sketch with arrows etc. I found thorough explanation in the lectures of school teacher Pavel Victor from Odessa city. He is really genius in explaining the matter with various examples and simple experiments. kzbin.info/aero/PL1Us50cZo25mikFg7yYkpmpNK7tGcub35&si=8Ya9_1Wds98tp1zo