Bubble pressure tensiometry

About 150 years ago Simon [174] proposed the maximum bubble pressure method for measurements of surface tensions of liquids. Due to technical problems, this method was believed to be unreliable. During the last 20 years, however, more than 200 publications have been published on theoretical and experimental aspects of the bubble pressure tensiometry making this method to the most frequently used one for the very short adsorptions times from few milliseconds to some seconds. One of the advantages of this technique is the small amount of liquid required for the surface tension measurements, which is particularly important in studies of biological liquids [175]. 

Since precise electrical pressure transducers are available, the progress in designing commercial instruments is tremendous. Instruments from several producers are available now. In a recent book the principles of the bubble pressure tensiometry and the theoretical backgrund have been summarised by Fainerman and Miller [176], As an example, the tensiometer MPT2 from Lauda is shown schematically in Fig. 4.12. This device has some... 

Typically, narrow capillaries are used in the bubble pressure tensiometry (reap <0.01 cm), so that no correction with respect to the sphericity of the bubble is needed and the equation for the calculation of surface tension reads... 

This paragraph summarised the state of the art of the bubble pressure tensiometry and presents experimental results showing the capacity of this technique for a deeper understanding of adsorption kinetic mechanisms. The subsequent paragraph describes the drop and bubble shape methodology and demonstrates the complementarity of the two experimental techniques. 

Limitations on neutron beam time mean that only selected surfactants can be investigated by OFC-NR. However, parametric and molecular structure studies have been possible with the laboratory-based method maximum bubble pressure tensiometry (MBP). This method has been shown to be reliable for C > 1 mM.2 Details of the data analysis methods and limitations of this approach have been covered in the literature. Briefly, the monomer diffusion coefficient below the cmc, D, can be measured independently by pulsed-field gradient spin-echo NMR measurements. Next, y(t) is determined by MBP and converted to F(0 with the aid of an equilibrium equation of state determined from a combination of equilibrium surface tensiometry and neutron reflection. The values of r(f) are then fitted to a diffusion-controlled adsorption model with an effective diffusion coefficient which is sensitive to the dominant adsorption mechanism 1 for... 

Fainerman VB, Miller R. (2004) Maximum bubble pressure tensiometry — an analysis of experimental constraints. Adv Colloid Interface Sci 108-109 287-301. 

Kjellin, U.R.M., Reimer, J., Hansson, P. An investigation of dynamic surface tension, critical micelle concentration, and aggregation number of three nonionic surfactants using NMR, time-resolved fluorescence qnenching, and maximum bubble pressure tensiometry. J. Colloid Interface Sci. 2003, 262, 506-515. 

The two methods maximum bubble pressure and profile analysis tensiometry complement each other experimentally and cover a total time range of nine orders of magnitude from about lO" seconds up to 10 seconds (many hours). The example given in Fig. 33 shows the dynamic surface tension of two Triton X-100 solutions measured with the instruments BPA and PAT (SINTERFACE Technologies) over the time interval of 7 orders of magnitude. As one can see, the experiments cover the beginning of the adsorption process and the establishment of the equilibrium state. 

FIGURE 19.1 Dynamic surface-tension data for n-alkyldimethylphosphine oxides, as measured by maximum bubble-pressure technique (O), drop-volume tensiometry ( ), and de Nolly ring tensiometry (A), and model fit ignoring reorientation (dotted line) and incorporating reorientation (solid line). (From Fainerman, V. B., et al. 2000. Adv. Colloid Interface Sci. 86 (1-2) 83-101. With permission.)... 

All drop and bubble methods are based on the Laplace equation of capillarity. In order to study dynamic aspects of adsorption, the growing drop or bubble and the expanded drop methods are suitable (3). In Figure 12.13, the schematic of a static or growing drop instrument is shown. In applications of capillary pressure tensiometry, an equation which is equivalent... 

There are a variety of simple and inexpensive techniques for measuring contact angles, most of which are described in detail in various texts and publications and will be mentioned only briefly here. The most common direct methods (Fig. 17.4) include the sessile drop (a), the captive bubble (b), the sessile bubble (c), and the tilting plate (d). Indirect methods include tensiometry and geometric analysis of the shape of a meniscus. For solids for which the above methods are not applicable, such as powders and porous materials, methods based on capillary pressures, sedimentation rates, wetting times, imbibition rates, and other properties, have been developed. 

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