# Talk:Spinning drop method

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The spinning drop method has seen some attempts to widen the range of applications. Princen Zia and Mason showed in their article

Measurement of Interfacial Tension from the Shape of a Rotating Drop journal of colloid and interface science 23 p.99-107

that the shape of a spinning drop can be expressed in terms of elliptic integrals. The time the article was published (1967) solving this set of implicit equation to determine the interfacial tension was not possible because of the lack of sufficiently powerful computers.

In 2002 a German company developed a software that did fit the drop profile extracted by image processing to the theoretical shape by using non linear optimization algorithms. —Preceding unsigned comment added by Jensolerieger (talkcontribs) 09:31, 19 October 2010 (UTC)

## Vonnegut's equation derivation

The derivation of Vonnegut's equation in the article is not correct (c.f. Vonnegut's original paper). I plan to post a correct derivation shortly--just giving notice.Drock221989 (talk) 04:20, 2 May 2013 (UTC)

The problems with the original derivation were (a) a math error in the second total energy equation (R^2 instead of R^4 in the first term, which coincidentally made the derivative of that erroneous total energy equation work out to Vonnegut's equation) and (b) failing to account for the fact that, for this droplet, L is a function of R, and thus cannot be treated as a constant when one takes the derivative of E with respect to R. Instead, one must substitute in L=V/piR^2 (as V is a constant and thus independent of R) and then take the derivative of the total energy equation. V=piLR^2 can then be substituted back into this derivative and the resulting equation solved for sigma. Drock221989 (talk) 05:36, 2 May 2013 (UTC)

## Comment on comparison with other methods

We did state that the Vonnegut restriction does not longer hold .. cause the mathematical exact solution is known .. right? Lemma: The possible precision of a spinning drop experiment is limited by

a, the precision of scaling b, the precision of rotation speed c, the precision of shape parameter alpha (as in common papers) d, the precision of the density difference

and thus as accurate as any physical measurement is. Says: no limits in interfacial tension as long as the width to height ratio is not too close to 1. The same goes for similar methods like pendent / sessile drop too.

Note:Comments by 84.130.130.241 (talk), moved from article on 09:28, 20 April 2017 (UTC)

Tomásdearg92 (talk) 09:28, 20 April 2017 (UTC)