Dear fellow researchers,
for my research I measured the dynamic surface tension of gelatine solutions (0.1, 1, and 2 %) with a bubble pressure tensiometer BP100 (Krüss).
The measurements for 1 and 2 % indicate that the dynamic surface tension increases from a value of around 65 mN/m to nearly 70 mN/m and afterwards it decreases again to around 60 mN/m.
Did anyone observe that behaviour for gelatine or another protein before?
What might be the reason for that?
Best regards,
Pascal
Hi Pascal,
You say the dynamic surface tension has a trend, with measuring time or with the dynamics used for the measurement? It is common for polymers at very high dynamics to show a lower value than at medium dynamics. In fact what you see is that at very high dynamics (fast formation of bubbles) shear is induced which prevents individual chains to interlock. Now, if you lower dynamics the resulting shear is lower and polymers may interact, this causes a higher viscosity which in turn is erroneously reported as a higher surface tension. If you lower the dynamics even further (very slow bubble formation) you see that the time is sufficient to allow gelatine to reach the bubble surface and lower the surface tension. Given the fact that the solution viscosity is still higher, the observed value at low dynamics may be too high in this case.
I've seen trends like this before mostly with interacting polymers in solution. What I recommend is to verify the surface tension with a static method like Wilhelmy-plate. You will see that you find a lower value.
Kind regards, Leo
These are some very interesting explanations. Thank you.
Just to get this straight: do you mean that at low surface ages the formation of bubbles is fast which in consequence causes a high dynamic and therefore no possible entanglement?
And with high surface ages the formation of bubbles is slow resulting in low dynamics and possibly ?
Best regards,
Pascal
Dear Pascal,
I have to agree with Dr. Vleugels, it is possibly better to use surface tension measurements using a Wilhelmy plate first.
As you know you are, with gelatin, dealing with a protein that can aggregate/crosslink. Its behaviour is pretty complex (and varies a lot between individual batches). Very much depends on how you treat the sample (is it in urea and then diluted, is it heated to let say 100 oC first in order to get monomers, what is the dependence on temperature anyway (in other words does your results differ when you perform them at let say 10, 20, 30 en 50 oC?) etc. etc.).
Best thing to do is characterise these things first in a static method. Perhaps it is a good idea to perform your measurements also with a more ‘simple’ surfactant (a small peptide with well-known properties, a detergent or lipid?) in order to get your technique into firm grip?
Anyway welcome into the world of science, nothing is easy right? Wish you good luck.
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