Talk:Contact angle

Young–Laplace equation for a three-dimensional drop
I suggest to removed the part starting with "The Young–Laplace equation for a three-dimensional drop is highly non-linear.". The reasons: 1. It lacks explanation of the symbols of the equations, making it meaningless. 2. It is in the wrong section (it is in thermo). 3. It is a detail that does not need to be in the article, and for sure not so high up.

Verbatim text
Text in the measurement techniques section is copied verbatim without citation from the reference at the end of the page pointing to kruss.info. This is in bad form and should be rectified.

Edit Picture Needed
In the last diagram of the page, a mysterious tensoin arrow is labeled as "SG", I believe this is supposed to be SV. Someone fix it!

Wouldn't it also be nice if the tension arrows were scaled according to the Young Equation?

It would be good to show an example on this page of both a -phobic and -philic contact angle.204.227.241.18 22:14, 15 August 2007 (UTC)

Any idea how the drop size effect contact angle?

150 degrees?
How can you have a contact angle greater than 90? Does anyone have a picture of this?--UltraHighVacuum 20:56, 12 December 2006 (UTC)
 * This is answered in the text 'typical contact angles', with pictures if you follow links. —The preceding unsigned comment was added by Berland (talk • contribs) 09:27, 17 January 2007 (UTC).

further information: actually, the contact angle can be more than 90 degrees. If the liquid's cohesive forces dominate over the adhesive forces between the liquid-surface interface, then the liquid will, rather than 'wet' the surface, become a 'ball'. Due to this, the contact angle, defined as the tangent to the contact surface, will exceed 90 degrees.

Table of angles
It sounds like materials have a characteristic contact angle with water, eg gold 77° copper 85° silicon 32°. Is there a place we can get all this data for many substances so that we can have a table of angles? Graeme Bartlett (talk) 23:16, 23 January 2012 (UTC)

Should vibration methods be mentioned to complement the Tadmor equation approach
The discussion below is about the possibility of adding a description of another technique to evaluate the equilibrium contact angle, namely vibration technique. The problem, as it appears from the rather long discussion below, is that there is no agreement as to which vibration method is correct (vibration amplitude, frequency, direction etc. were not yet agreed upon in the literature so which one should be used in the wiki file?). While the Tadmor equation is currently the more frequently used one in the literature, vibration techniques appeared historically at an earlier stage, which can add another dimension to their description.


 * Can anyone add a description of vibration experiments to obtain the equilibrium contact angle? I think it can be a good addition to the Tadmor equation which is currently the only way — Preceding unsigned 06:40, 12 September 2012 (UTC)

The Tadmor equation is currently the only equation that both derives the equilibrium contact angle analytically, and does it as a function of measurable parameters (the Young equation for example, uses the solid-vapor and solid-liquid surface tensions which are not measurable). Being the only one, it is not receiving undue weight (WP:UNDUE, though if other equations can provide a thermodynamic relation of the Young contact angle as a function of measurable parameters, they should be presented as well. There are 3 complementary equations in the article -- the Young and Young-Dupré equations can only be used properly in combination with the Tadmor equation, as appears in recent textbooks and over 60 recent papers. Please make sure this equation remains in this article. A description of vibration experiments can be added, but I am not sure if there is an agreement in the literature about this method.

Reply: please do not erase my comments from the Talk page. The equilibrium contact angle was derived by Young in 1805, and can also be measured by means of vibration (though there is no agreement on the exact vibration method). The Tadmor paper has been cited about 60 times (not quite the same as saying that the equation has appeared in 60 papers) and I don't think that elevates it to the level of importance requiring inclusion in this short article without mentioning any of the vibration techniques. Roccas1 (talk) 14:41, 11 August 2012 (UTC)


 * In fact the Tadmor equation appears or used in more that 60 papers (not just cited) including papers by Israelachvili (see: LANGMUIR Volume: 28   Issue: 41   Pages: 14609-14617). It was cited even more times, which is remarkable in view of the short time period since it was introduced. Anyway, see reply below.  —

Reply: Sure, just go ahead and add a description of vibration techniques, I am willing to go over it and if needed refine it. Note though that the equilibrium contact angle is not a measurable parameter - you will always get a contact angle hysteresis and the value of the equilibrium contact angle will be somewhere between the advancing and receding contact angles. Its location within this spectrum can only be found out from the Tadmor equation. There is a paper (I think it is by dela Volpe but not sure, I wonder if you can find it, because I must have misplaced it somehow) that describes how one can vibrate a surface and reach an equilibrium contact angle. I love this paper and I think it should be addressed as well here. The readers of this wiki article are not aware of the subtlety between the "as placed" contact angle and the Young contact angle, and adding the explanation of the surface vibration technique can add merit to the article. While I believe that the equilibrium reached with the vibration technique is the Young contact angle, I never saw a thermodynamic proof for it. On the other hand there is such a proof with the Tadmor equation. The reason I believe that the vibration technique does provide the Young equilibrium is that I checked once, and it resulted in values which were very close to the values obtained with the Tadmor equation. Anyway, thank you for discussing this with me, let's try to resolve this issue.

Reply: Surfaces have been created with no measurable hysteresis (e.g. by Zisman). The use of vibration to reach Young's angle has been described in several papers (Andrieu et al., Decker & Garoff, della Volpe et al. as you say, and others). It can be understood in terms of overcoming energy barriers which is a concept that goes back to Shuttleworth & Bailey and through a line of prominent papers since then such as Bikerman, Good, Johnson & Dettre, Neumann & Good, etc. I would consider this to be the widely accepted way of thinking about hysteresis, which should appear in this article. Roccas1 (talk) 17:03, 19 August 2012 (UTC)

Reply: The Decker & Garoff paper is another one of my favorites, I think that adding a description of it or another vibration method/s can add merit to this wiki article. Regarding wide acceptability by the community, if I consider the citation index, I see that per year the Tadmor equation is more widely cited than, for example, the Decker & Garoff paper. The Della Volpe paper has an even lower citation index, and the Andrieu paper I couldn’t even find (I will be happy if you provide a reference). Moreover, a large fraction of the papers citing the Tadmor equation actually use the equation to calculate equilibrium values. I counted at least 10 papers only in the past year that used the Tadmor equation (not just cited it), and I couldn’t find any such papers for, say, the Decker & Garoff method. I searched quite a bit, and though I didn’t check all of them, the citing papers, if at all deal with vibrations, seem to have different vibration directions (vertical, horizontal, but not at a slope), frequencies, amplitudes, and drop size – all these will result in different apparent equilibrium angles, and yet I found no paper that is cited by others for its exact vibration method resulting in an apparent lack of agreement on a specific vibration methodology.

So, while the Tadmor equation is by far more "widely accepted" than any vibration method as a way for determining the Young equilibrium contact angle, I see no problem in describing vibration methods in this article as well. What do you think?

By the way, Zisman could not have gotten zero hysteresis as this would result in no pinning and hence sliding of the drop from that location. — Preceding unsigned

Physics
Advantages and disadvantages 157.47.24.232 (talk) 15:48, 24 February 2024 (UTC)