It is known that the surface/interfacial tension tension can be measured by pendant drop method and the following equation: IFT=deltaro*g*de^2/H. 1/H is function of ds/de (1/H=f(ds/de)). I used this function for 1/H and it is okay for gas/liquid systems. When I used this this function for liquid-liquid mixtures, such as water-hexane (T=298.15 K and P=1 bar), it does not answer. Is 1/H different for liquid-liquid mixtures?
Dear Mr Khosharay,
I've read in a paper that if the density difference between the two phases studied was less than 0.01 g/cm3, the pendant drop method can't be used to measure the interfacial tension.
If you would like to send you this reference paper.
Yours sincerely,
Fahimeh
@ Fahimeh Kashani
Yes, you are right, but the difference of densities is about 346 kg/m^3. I think my problem is shape factor.
A relationship between S and H as well as references to its sources are tabulated in Adamson's book on Physical Chemistry of Surfaces. Are you certain that your experimental system falls in the bounds of the assumptions behind the relationship for S and H? For example, is your tip too wide or too narrow? Finally, when you say "... it does not answer", what specifically do you mean?
@ Jeffrey J Weimer:
Dear Professor
I mean that my measured value of IFT is 36 mN/m for water-hexane, while according to the references, it is about 50 mN/m.
The values 50 and 36 are the same order of magnitude. Have you done a statistical test of significance for differences between your value and the reference value? Certainly, measurements of 50 ± 5 and 36 ± 5 done on an infinite population statistics basis are possibly different within one standard deviation (67% confidence). They are however probably not different within two standard deviations and certainly not different within three.
Otherwise, is your experimental system EXACTLY the same as that used in the reference? What about the purity of the liquids? What about the temperature control?
@ Jeffrey J Weimer
Yes, it is exactly the same. I am sure about the purity of liquids.
My concerns remain. What does your statistical significance test show about the confidence in the difference between your measurement and the reference measurement? How was the surface tension of the other value measured? When you change to the water/hexane system, does the ratio of de/ds relative to the needle diameter violate the requirements to use the approximation of a correlation between S and H?
@ Jeffrey J Weimer
When I measure surface tension (a drop of liquid in air) with this glass needle (OD=1/16 inch=1.587 mm), the values have good agreement with the literature (see attachment=5.pdf, My article about my apparatus). I have tested it with water and alcohols. I used the correlation in m2.pdf for relation between S and H (see attachments) But when I use this for water-haxane (drop of hexane in water), the value of measurement is so different from the literature. I used the correlation in m2.pdf for relation between S and H (see attachments). I do not why this problem exist.
Article Experimental and modeling study of the surface tension and i...
Your analysis in your paper is thorough. What is the experimental restriction behind the correlation you used? Have you violated the experimental restriction in some way only with hexane+water? What does your analysis show when you did a statistical comparison of difference between your value and the reference? Do you have more than one reference for the hexane+water system and how do they compare?
Perhaps you have measured a more accurate value for hexane+water. You must confirm for yourself whether this is true. Investigate every possible mistake that you could have made from experiment to data analysis.
Keep us updated on your progress.
@ Jeffrey J Weimer
Thanks a lot. I search for one reference. This was used for liquid-liquid systems:
[1] Niederhauser, D.O. and Bartell, F.E. A. (1947). Corrected Table for Calculation of Boundary Tensions by Pendant Drop Method, Research on Occurrence and Recovery of Petroleum, A Contribution from API Research Project, 27,114-146.
But I do not find it. How can I find this reference?
I recommend the book by Adamson on Physical Chemistry of Surfaces for a wealth of references.
Article The Measurement of Surface Tension by the Pendant Drop Technique
http://rspa.royalsocietypublishing.org/content/346/1646/349.short
Article The Determination of Interfacial Tension by Video Image Proc...
Article Interfacial tension of immiscible polymer blends: Temperatur...
Article Determination of Surface Tension and Contact Angle from the ...
ps ... Your images are so sharp that you could do better by the computational profile analysis rather than continuing to use the ds/de estimation. I believe the image analysis method is referenced in more recent literature, and someone may have developed software for it (for example in ImageJ).
I recommend the article published in the Journal of Petroleum Science and Engineering (JPSE) for measuring the H parameter based on various S (S = ds/de) values. Please read Table 3 in the article.
"Developing a novel procedure in utilizing pendant drop method for determination of ultra-low interfacial tension and surface tension in near-miscibility conditions"
Article Developing a novel procedure in utilizing pendant drop metho...
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Thermodynamics