Bubble pressure tensiometer

The sensoric principle of the dynamic bubble-pressure tensiometer is based on the differential Laplace pressure between two capillaries from which a controlled gas flow is released. At the lower end of a capillary which points into the liquid, a gas bubble is formed which increases its radius with increasing gas pressure (see... 

Recently, a very practical bubble pressure tensiometer was developed using elegant pressure transducer mechanics which only needs one capillary made from a high-tech polymer [51, 52]. The tensiometer is able to measure at different immersion depths but needs calibration in order to make the resulting data comparable to surface tension values from other sources. It was shown in a series of measure-... 

The LAUDA measuring instruments program covers systems for measuring the surface and inteifacial tension of liquids. Available devices include ring plate tensiometers (automated and nonautornated), drop volume tensiometers, bubble pressure tensiometers, and film balances. 

Dynamic surface tensions have also been measured by the bubble pressure tensiometer MPT2 and the drop volume tensiometer TVT1, both manufactured... 

Fig, 4.12. Schematic design of the maximum bubble pressure tensiometer MPT2 from LAUDA... 

Alternatively, interfacial tension can also be measured continuously with area changes, with an expanding or contracting pendant-drop instrument adapted to oscillatory measurements as described by Bhardwaj and Hartland (74). Dilational data are obtained without introducing shear as the interfaee is expanded and contracted. This is also often achieved with an expanding drop volume or bubble-pressure tensiometer (65). Nikolov et al. (170) have recently developed this technique and an instrument to study oiLwater systems. 

The design of a bubble pressure tensiometer changes from instrument to instrument, according to the specific measurement procedures. As an example, Fig. 14 illustrates the schematic diagram of the tensiometer BPA (SINTERFACE) equipped with a gas flow oscillation analyser to measure the bubble surface lifetime. 

Figure 14. Schematic diagram of maximum bubble pressure tensiometer using a gas flow oscillation analyser (BPA, SINTERFACE Technologies).

Fig. 9 Dynamic surface tension of mixtures between a highly surface-active model suspension and solutions (1 g/L) of modified natural polymers at the same mixing ratio (volume suspension volume polymer) of 10 1 dynamic surface tension, was measured by bubble pressure tensiometer (t = 60 s)...

Figure 12.1. Schematic of a maximum bubble pressure tensiometer (MPT2, LAUDA, Germany)...

The ring method enables the static surface tension of the dispersion to be determined. When polymer dispersions are applied on large-scale coating machines, it is also important how fast the surface tension of a freshly generated surface is able to decrease. A device which permits this dynamic surface tension to be measured is the maximum bubble pressure tensiometer [5]. In this method, gas bubbles are blown... 

Viscosity and density of the component phases can be measured with confidence by conventional methods, as can the interfacial tension between a pure liquid and a gas. The interfacial tension of a system involving a solution or micellar dispersion becomes less satisfactory, because the interfacial free energy depends on the concentration of solute at the interface. Dynamic methods and even some of the so-called static methods involve the creation of new surfaces. Since the establishment of equilibrium between this surface and the solute in the body of the solution requires a finite amount of time, the value measured will be in error if the measurement is made more rapidly than the solute can diffuse to the fresh surface. Eckenfelder and Barnhart (Am. Inst. Chem. Engrs., 42d national meeting, Repr. 30, Atlanta, 1960) found that measurements of the surface tension of sodium lauryl sulfate solutions by maximum bubble pressure were higher than those by DuNuoy tensiometer by 40 to 90 percent, the larger factor corresponding to a concentration of about 100 ppm, and the smaller to a concentration of 2500 ppm of sulfate. 

Methods. All experiments were performed at 25°C. Critical micelle concentrations were determined using the maximum bubble pressure method on a SensaDyne 6000 surface tensiometer. Dry nitrogen was used as the gas source for the process and was bubbled through the solution at a rate of 1 bubble/sec. Cmc s measured using the Wilhemy plate method were in agreement with those obtained from the bubble tensiometer however, the bubble pressure method was used since it is less susceptible to error due to impurities and the nitrogen environment makes pH control easier. 

Figure 3 contains dynamic data for ff-LG received by three methods the maximum bubble pressure method in the time range 0.001 s to 100 s, the drop volume method for times in the range 5 s to 500 s, and the profile analysis tensiometer PAT l in the time range from 10 s up to several hours. 

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... 

The graphs shown in Fig. 4.35 are the dynamic surface tensions of three mixtures of CioDMPO and CmDMPO measured with the maximum bubble pressure method MPT2 (O) and ring tensiometer TE2 (O). Although there is a general theoretical model to describe the adsorption kinetics of a surfactant mixture, model calculations are not trivial and a suitable software does not exists. 

Wasan and his research group focused on the field of interfacial rheology during the past three decades [15]. They developed novel instruments, such as oscillatory deep-channel interfacial viscometer [20,21,28] and biconical bob oscillatory interfacial rheometer [29] for interfacial shear measurement and the maximum bubble-pressure method [15,29,30] and the controlled drop tensiometer [1,31] for interfacial dilatational measurement, to resolve complex interfacial flow behavior in dynamic stress conditions [1,15,27,32-35]. Their research has clearly demonstrated the importance of interfacial rheology in the coalescence process of emulsions and foams. In connection with the maximum bubble-pressure method, it has been used in the BLM system to access the properties of lipid bilayers formed from a variety of surfactants [17,28,36]. 

The graph in Fig. 41 shows the dynamic surface tensions of a mixtured solution of CioDMPO and C14DMPO measured with the maximum bubble pressure method BPAl (O) and profile analysis tensiometer PATl ( ). The theoretical curves shown were calculated due to the adsorption kinetics model for surfactant mixtures discussed above (Miller et al. 2003). 

Most of the instruments allow only the measurement of surface and interfacial tensions, without a sufficient control of the drop/bubble size. Advanced models provide very accurate controlling procedures. The instrument described here in detail represents the state of the art of drop and bubble shape tensiometers. The possibility to study bubbles in addition to drops opens a number of features not available by other instruments less loss of molecules caused by adsorption from extremely diluted solutions (small reservoir in the small single drop), long time experiments with very small amounts of a sample, easy application of a pressure sensor for additional measurement of the capillary pressure inside the bubble. Moreover, high quality sinusoidal relaxation studies can be performed by inserting a piezo system which can be driven such that very smooth changes of the bubble surface area are obtained. 

A technique has been developed (1,2,4) for the continuous measurement of emulsion surface tension with an instrument similar to the bubble densitometer. A schematic of the bubble surface tensiometer is shown in Figure 4. The construction of the bubble cell is similar to that for the bubble densitometer, except in this case the two orifices are mounted at equal depths and have different radii. Differential back pressure between the two orifices is measured and filtered as before. In this case, due to the fact that the two orifices are at the same depth, the liquid head terms in the pressure signals from the two orifices cancel when the pressures are differenced by the transducer, leaving a signal which after filtering, is proportional to the orifice radii and to the surface tension of the test fluid. Since the orifice radii are constant, their effect is absorbed into a calibration constant, and the instrument provides a voltage signal proportional to the surface tension of the test fluid. 

The dynamic surface activity of the commercial rhamnolipid mixture JBR425 fi om Jeneil was determined as a function of concentration and time with the maximum bubble pressure method using an online bubble tensiometer (Sita T60). Figure 11.14 highlights the good surfactancy properties of rhamnolipids, with low minimum surface tension and moderate dynamics, meaning a relatively fast decrease of surface tension at new surfaces and low bubble lifetimes. 

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