01 · Maximum bubble pressure
Accessing adsorption at the shortest interfacial ages
Maximum bubble pressure tensiometry is one of the most widely used approaches for dynamic surface tension at short surface ages.
Gas is driven through a submerged capillary and a bubble grows at the capillary tip.
The pressure rises as the bubble curvature changes, reaches a characteristic maximum and then falls as the bubble continues to grow and detaches.
At the appropriate geometric condition, the capillary pressure contribution to the pressure maximum is related to surface tension.
02 · Pressure signal
The measured pressure contains more than capillary pressure
The measured pressure signal contains more than the desired capillary pressure.
Hydrostatic pressure due to immersion depth, hydrodynamic pressure losses associated with gas and liquid motion, and pneumatic effects of the measuring system can contribute.
Accurate dynamic tensiometry therefore requires a pressure balance and correction strategy rather than direct conversion of a raw pressure maximum into γ.
03 · Pressure balance
Conceptual pressure balance
Pressure balance — conceptual form
The precise correction terms depend on instrument geometry, capillary radius, flow conditions and analysis protocol.
04 · Interfacial age
Surface lifetime is not identical to bubble time
A key methodological distinction is the separation of the bubble period into deadtime and surface lifetime.
The bubble time may include intervals that do not correspond to the age of the interface at the pressure maximum used to determine γ.
Treating the complete cycle time as “surface age” can therefore distort a dynamic surface-tension curve, especially at the shortest times.
Rigorous instruments and protocols explicitly define the relevant lifetime.
05 · Comparison
Consistent interface histories are required
This distinction becomes particularly important when comparing data from different bubble-pressure devices.
Two instruments can report measurements at nominally similar bubble frequencies while creating different actual interface histories because of differences in capillary geometry, pneumatic volume or bubble growth profile.
Cross-instrument agreement requires consistent definitions and appropriate corrections.
06 · Experimental interpretation
Why equilibrium extrapolation is hazardous
Because bubble-pressure measurements are optimized for short times, it can be tempting to extrapolate γ(t) toward infinite surface age to estimate equilibrium tension.
Such extrapolation is model dependent and can be inaccurate when the measured time domain does not contain the slow relaxation processes that dominate the approach to equilibrium.
A long-time equilibrium method is preferable when the equilibrium value itself is the principal quantity of interest.
08 · References
Scientific literature
- 1.T. Young, An Essay on the Cohesion of Fluids, Philosophical Transactions of the Royal Society of London 95 (1805) 65–87.
- 2.P. S. Laplace, Traité de Mécanique Céleste, Supplement to Book X, Paris, 1805.
- 3.A. I. Rusanov and V. A. Prokhorov, Interfacial Tensiometry, Studies in Interface Science, Vol. 3, Elsevier, Amsterdam, 1996.
- 4.D. Möbius and R. Miller (Eds.), Drops and Bubbles in Interfacial Research, Studies in Interface Science, Vol. 6, Elsevier, Amsterdam, 1998.
- 5.V. B. Fainerman and R. Miller, Maximum bubble pressure tensiometry: theory, analysis of experimental constraints and applications, in: Bubble and Drop Interfaces, 2011, pp. 75–118.
- 6.J. Meissner, J. Krägel, C. Frese, S. Rupert, V. B. Fainerman, A. V. Makievski and R. Miller, Comparative studies of dynamic surface pressure using different maximum bubble pressure tensiometers, SÖFW-Journal 130 (2004) 41–46.