I am trying to measure the maximum bubble pressure required to detach an air bubble from a needle which is submerged in a bath of surfactant solution in order to measure the dynamic surface tension.
I currently have a syringe driver (as part of a contact angle goniometer system from Kruss) but all the force/pressure sensors I have found so far are too bulky to fit into the system.
Any suggestions of any small sensor I would be able to attach to the system, or any other (simple) way of measuring the pressure required to detect a submerged air bubble from a syringe needle, would be greatly appreciated.
Dear Christopher,
you have a difficult task... The main problem is that the pressure to detach the air bubble is very small and the process of detachment of the bubble occurs quick and somewhat unpredictable... As you do not mentioned about the precision and accuracy you need to achieve in such measurements, I can propose the following procedure:
1) Take a plastic syringe with needle and remove their piston (syringe 1)
2) In the place of their piston you should adapt some tube connected to a flexible hose (prefer a small diameter hose). The other end of this hose you should connect to a graduated U shaped glass tube containing water, alchool or another liquid with well known density in order to obtain a U-type manometer (see the link http://www.engineeringtoolbox.com/u-tube-manometer-d_611.html).
3) Now, take another syringe with needle and piston (syringe 2) and carefully introduce their needle in the body of the "syringe 1" perforanting it. You can use the syringe driver to actuate the piston of this "syringe 2" if you want, but I suggest you to try this with your hand firstly...
4) Then, put the needle of the "syringe 1" into your surfactant solution in order to perform the experiment
5) I suggest that you use a good video camera to record all process (specially the U-type manometer which you constructed) since the bubble formation until its detachment. So, you can play the record slowly, frame to frame in order to read the manometer in the exact moment the air bubble detaches...
In the rest, I wish you patience!
Dear Christopher,
you have a difficult task... The main problem is that the pressure to detach the air bubble is very small and the process of detachment of the bubble occurs quick and somewhat unpredictable... As you do not mentioned about the precision and accuracy you need to achieve in such measurements, I can propose the following procedure:
1) Take a plastic syringe with needle and remove their piston (syringe 1)
2) In the place of their piston you should adapt some tube connected to a flexible hose (prefer a small diameter hose). The other end of this hose you should connect to a graduated U shaped glass tube containing water, alchool or another liquid with well known density in order to obtain a U-type manometer (see the link http://www.engineeringtoolbox.com/u-tube-manometer-d_611.html).
3) Now, take another syringe with needle and piston (syringe 2) and carefully introduce their needle in the body of the "syringe 1" perforanting it. You can use the syringe driver to actuate the piston of this "syringe 2" if you want, but I suggest you to try this with your hand firstly...
4) Then, put the needle of the "syringe 1" into your surfactant solution in order to perform the experiment
5) I suggest that you use a good video camera to record all process (specially the U-type manometer which you constructed) since the bubble formation until its detachment. So, you can play the record slowly, frame to frame in order to read the manometer in the exact moment the air bubble detaches...
In the rest, I wish you patience!
The technique to measure the excess pressure by Walter seems well described and looks workable. A simple calculation shows the radius of the bubble inside a liquid will grow to a value such that r^4 is proportional to surface tension divided by density. It is because whatever is pressure inside the bubble has to be reflected in increased volume of the outside surfactant liquid. And if the increased volume counter pressurizes more than the excess pressure inside this bubble, the bubble will break off. Hope I am correct.
I've built just such a system and it is not so hard. You can buy inexpensive electronic sensors to very accurately measure pressure (far more accurate than a U shaped manometer). A number of things to consider. Connect the pressure meter as close as possible to the tip of the orifice - it takes some time for the pressure wave to reach the sensor so minimising the distance is important. Rather than use a syringe needle use a fine bore glass capillary and draw it out to make the opening very small. The smaller the opening the higher the pressure you will measure and the more accurate your measurements will be. To apply the Laplace pressure to determine the surface tension you need to accurately measure the radius of the opening. An easy way to do this is to purify some ethanol and use the literature value for the surface tension to calibrate the radius. You would be best recording the volatage from the pressure sensor on a computer with a fast card to ensure you get the maximum accurately - it occurs briefly so you need rapid acquisition. It is easy to set it up to automatically measure 100's of bubbles allowing the errors to be reduced.
Other things to consider. Hydrostatic pressure will matter, you need to correct for it. If the surfactant changes the way the bubble grows as it passes through the orifice (ie the contact angle) this will influence your results - so surfactant may have and adverse effect on your results if it adsorbs to the orifice material. Finally, this is NOT a good way to measure dynamic surface tension because you need to make the bubbles grow slowly to get good measurements. If you grow them rapidly you wont accurately measure the maximum. There are much better ways to measure dynamic surface tension that involve oscillating pendant drops or studying jets.
Thank you all for your help I will get on with having a play and let you know how I get on.
Dear Vincent, I'm also interested in the electronics (electronic manometer, sensor, etc.) you have used... Can you post a link to the manufacturer web site and indicate the model of electronic manometer you used? The sensor can be used to measure the pressure of He2 or N2 gases? It works at low temperature?
Thank you for the tip!
The system I built was nearly 10 years ago, so the sensors have probably improved greatly since then. They work for all gases. There is a wide range. You need to choose the pressure range for your application. Here is one with a very low pressure range. http://australia.rs-online.com/web/p/pressure-sensors/5351224/. The same company offer a number of units for different pressure ranges. I don't know about the temperature range - this should be in the spec sheet.
Note you can break them by putting too much pressure differential across them. Depending on your application you may also want to check the response time.
Very interesting...
I will search for the commercial representant of Gems in Brazil for more informations.
Thank you very much Vincent !
I agree with Vincent's advice. I'd also advise a fast data logging system to capture the transient pressure fluctuations. Although not directly applicable, we published a paper describing an economical approach to pressure measurement and logging which you may find a useful starting point.
Greswell R., Ellis P., Cuthbert M., White R., Durand V., 2009. The design and application of an inexpensive pressure monitoring system for shallow water level measurement, tensiometry and piezometry. Journal of Hydrology 373, 416-425.
Differential Pressure transducer of MKS model 223 BD-00100AABS (range= 100 milibars) coupled with reading pannel MKS model PR-2000 will fit very well. You don't need to convert Volts in Pascal. Just connect the pressure transducer to your system and you will measure the pressure. Better variant is if you can connect it with PC and record the data directly. This is achievalbe as well. Just get in touch with MKS - it is German company. Good luck!
It sound very problematic, maybe you could try to put the whole system under high controlled pressure and observe by which pressure the buble explode or blow up.
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