Maximum bubble methods

The maximum bubble pressure method is good to a few tenths percent accuracy, does not depend on contact angle (except insofar as to whether the inner or outer radius of the tube is to be used), and requires only an approximate knowledge of the density of the liquid (if twin tubes are used), and the measurements can be made rapidly. The method is also amenable to remote operation and can be used to measure surface tensions of not easily accessible liquids such as molten metals [29]. 

Correction Factors for the Maximum Bubble Pressure Method (Minimum Values of Xjr for Values of r/a from 0 to 1.50)... 

A number of experimental studies have supplied numerical values for these, using either the classical maximum bubble pressure method, in which tire maximum pressure requhed to form a bubble which just detaches from a cylinder of radius r, immersed in tire liquid to a depth jc, is given by... 

Immediately after the running test, any compressor intended for toxic, hazardous, flammable, or hydrogen-rich service should be gas tested with an inert gas to the maximum seal design pressure. The test is held at least 30 minutes and the casing and its joints checked for leaks, using a soap bubble method or other suitable means for leak detection. When no leaks are detected, the compressor will be considered acceptable. 

Hsu and Berger [43] used the maximum bubble pressure method (MBP) to study the dynamic surface tension and surface dilational viscosity of various surfactants including AOS and have correlated their findings to time-related applications such as penetration and wetting. A recent discussion of the MBP method is given by Henderson et al. [44 and references cited therein]. 

Surface tension of the nonpolarized ITIES was investigated by using the drop-weight [2,3,29], maximum bubble pressure [30] and pendant drop [4] methods. The latter method... 

There are numerous other methods for measuring surface tension that we do not discuss here. These include (a) the measurement of the maximum pressure beyond which an inert gas bubble formed at the tip of a capillary immersed in a liquid breaks away from the tip (the so-called maximum bubble-pressure method) (b) the so-called drop-weight method, in which drops of a liquid (in a gas or in another liquid) formed at the tip of a capillary are collected and weighed and (c) the ring method, in which the force required to detach a ring or a loop of wire is measured. In all these cases, the measured quantities can be related to the surface tension of the liquid through simple equations. The basic concepts involved in these methods do not differ significantly from what we cover in this chapter. The experimental details may be obtained from Adamson (1990). 

Several other methods for determining 7 —notably, the maximum bubble pressure, the drop weight, and the DuNouy ring methods (see Section 6.2) —all involve measurements on surfaces with axial symmetry. Although the Bashforth-Adams tables are pertinent to all of these, the data are generally tabulated in more practical forms that deemphasize the surface profile. 

Figure D3.5.6 Adsorption kinetics of a small molecule surfactant. Surface tension of polyoxyethylene (10) lauryl ether (Brij) at the air-water interface decreases as time of adsorption increases. Brij concentration is 0.1 g/liter, as measured by the drop volume technique and the maximum bubble pressure method (UNITD3.6).

Bendure, R.L. 1971. Dynamic surface tension determination with maximum bubble pressure method. J. Colloid Interface Sci. 37 228-238. 

An almost overwhelmingly large number of different techniques for measuring dynamic and static interfacial tension at liquid interfaces is available. Since many of the commercially available instruments are fairly expensive to purchase (see Internet Resources), the appropriate selection of a suitable technique for the desired application is essential. Dukhin et al. (1995) provides a comprehensive overview of currently available measurement methods (also see Table D3.6.1). An important aspect to consider is the time range over which the adsorption kinetics of surface-active substances can be measured (Fig. D3.6.5). For applications in which small surfactant molecules are primarily used, the maximum bubble pressure (MBP) method is ideally suited, since it is the only... 

In the Maximum-bubble-pressure method the surface tension is determined from the value of the pressure which is necessary to push a bubble out of a capillary against the Laplace pressure. Therefore a capillary tube, with inner radius rc, is immersed into the liquid (Fig. 2.9). A gas is pressed through the tube, so that a bubble is formed at its end. If the pressure in the bubble increases, the bubble is pushed out of the capillary more and more. In that way, the curvature of the gas-liquid interface increases according to the Young-Laplace equation. The maximum pressure is reached when the bubble forms a half-sphere with a radius r/s V(j. This maximum pressure is related to the surface tension by 7 = rcAP/2. If the volume of the bubble is further increased, the radius of the bubble would also have to become larger. A larger radius corresponds to a smaller pressure. The bubble would thus become unstable and detach from the capillary tube. 

Fundamental knowledge about the behavior of charged surfaces comes from experiments with mercury. How can an electrocapillarity curve of mercury be measured A usual arrangement, the so-called dropping mercury electrode, is shown in Fig. 5.2 [70], A capillary filled with mercury and a counter electrode are placed into an electrolyte solution. A voltage is applied between both. The surface tension of mercury is determined by the maximum bubble pressure method. Mercury is thereby pressed into the electrolyte solution under constant pressure P. The number of drops per unit time is measured as a function of the applied voltage. 

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. 

A new method of surface tension determination has been developed which is continuous, automated, compatible with computer data acquisition systems, and capable of monitoring flowing process streams. The method is a variant of the well-known maximum bubble pressure technique. To illustrate the principles, we will describe the simplest initial configuration of the instrument here. Further details and a description of a refined version of the instrument will be reported later. 

It is possible to obtain a theoretical calibration curve by precise measurements of the two orifice diameters. This theoretical curve is also shown in Figure 3, and is compared with the theoretical maximum bubble pressure curve to illustrate the differences between the two methods. In this simple configuration, the theoretical calibration calculation involves several approximations and still gives a remarkable a priori fit to the data. 

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. 

The Young-Laplace equation forms the basis for some important methods for measuring surface and interfacial tensions, such as the pendant and sessile drop methods, the spinning drop method, and the maximum bubble pressure method (see Section 3.2.3). Liquid flow in response to the pressure difference expressed by Eqs. (3.6) or (3.7) is known as Laplace flow, or capillary flow. 

For foams, it is the surface tension of the foaming solution that is usually of most interest. For this, the most commonly used methods are the du Noiiy ring, Wilhelmy plate, drop weight or volume, pendant drop, and the maximum bubble pressure method. For suspensions it is again usually the surface tension of the continuous phase that is of most interest, with the same methods being used in most cases. Some work has also been done on the surface tension of the overall suspension itself using, for example, the du Noiiy ring and maximum bubble pressure methods (see Section 3.2.4). 

A better method uses two capillaries of differing radius, at the same immersion depth, and involves measuring the differential maximum bubble pressure between the two capillaries. In this case the two (Apgt) terms cancel out and the differential pressure is the difference between the two (2y/b) terms where b is the radius of curvature at the apex of the bubble. 

---