Interfacial tension procedure

Procedure. To form a BLM, a small amount (.— 0.005 ml.) of lipid solution was applied via a Teflon capillary attached to a micrometer syringe. The formation characteristics leading to the black state were observed under reflected light at 20-40 X magnification. Other precautions that should be exercised are essentially those described previously (10). The bifacial tension of BLM was measured as follows. After the membrane had become completely black (except at the Plateau-Gibbs border), the infusion-withdrawal pump was started. The pressure difference across the BLM was continuously monitored and reached a maximum when the membrane was hemispherical. The interfacial tension was calculated from this point using Equation 3. 

Next, procedures for estimating values of the coefficient of isothermal compressibility and oil viscosity are discussed. The chapter ends with methods of estimating hydrocarbon liquid-gas interfacial tension. 

A more complete procedure to compute the average thicknesses of the water and oil layers will be presented below. It is based on eq 3c, mass balances of components, and phase equilibrium equations. The calculations indicated that the interfacial tension of lamellar liquid crystals is very low, of the order of 10 5 N/m. It will be shown that y = 0 is always an excellent approximation of eq 3 c. 

The interfacial tension decay of the three food proteins at the air-water interface at 25°C has been monitored with an apparatus based on the drop volume technique. A full description of the interfacial tension apparatus is given elsewhere (2). The following procedure was used (for details cf. ref. 2)- A drop of a certain volume, corresponding to a certain interfacial tension (y) value, is expelled rapidly, and the time necessary for the interfacial tension to fall to such a value that the drop becomes detached is measured. This procedure is repeated for differing drop sizes, ue. for different values of the interfacial tension. 

Since l is a thermodynamic quantity, the most reliable procedures for its determination are based on a thermodynamic analysis of adsorption data, possibly at low coverages. Adsorption data to be analyzed by the Gibbs adsorption equation can be obtained by measuring the interfacial tension y, the charge density crM or the differential capacity C. Direct y measurements are equilibrium measurements that can only be carried out on mercury. Direct charge measurements are conveniently carried out by the potential-step chronocoulometric technique, which can be... 

Maze and Burnet [61,62] developed a more satisfactory scheme for the determination of contact angle and interfacial tension from the shape of sessile drops both above and below 90. They utilized a numerical nonlinear regression procedure in which a calculated drop shape is made to fit a number of arbitrary selected and measured points on the drop profile. In other words, the measured drop shape (one-half or the meridian section) is described by a set of coordinate... 

Then, scale this value of HETS for the extractor diameter using Equation 6.32.9. A simpler procedure for obtaining HETS, however, is to use the correlation given by Henley and Seader [31], shown in Figure 6.23. the correlation is acceptable for both a low and high interfacial-tension system. The problem, however, is that interfacial-tension data may not be available. 

The initial concentration (0.001 wt% active) was selected from the measurement of surface and interfacial tensions. It lies in the range of CMC value for these measurements, which were performed by using the Wilhelmy plate method in a Rosano surface tensiometer. The standard procedure described in the manual was carefully followed. Surface tension was measured against the air, whereas the interfacial tension was measured against isooctane, which was used to simulate dense CO2. It is well known fact that good foamers are most effective well above the CMC range and in subsequent tests the concentrations were increased well above that range. 

A number of experimental techniques are available to obtain information on some aspects of the structure of liquids near surfaces. It should be realized at the onset that measuring the solid-liquid interfacial tension y " does not belong to this category because it is a thermodynamically inoperable quantity. One cannot Isothermally and reversibly extend interfaces with solids (see sec. 1.2.24). From contact angles one can obtain y but there are no thermodynamically operational procedures to split this difference into its constituents, although models which do this are available (Volume III). 

The choice of chemical is usually based on trial-and-error procedures hence, demulsifier technology is more of an art than a science. In most cases a combination of chemicals is used in the demulsifier formulation to achieve both efficient flocculation and coalescence. The type of demulsifiers and their effect on interfacial area are among the important factors that influence the coalescence process. Time-dependent interfacial tensions have been shown to be sensitive to these factors, and the relation between time-dependent interfacial tensions and the adsorption of surfactants at the oil-aqueous interface was considered by a number of researchers (27, 31-36). From studies of the time-dependent tensions at the interface between organic solvents and aqueous solutions of different surfactants, Joos and coworkers (33—36) concluded that the adsorption process of the surfactants at the liquid-liquid interface was not only diffusion controlled but that adsorption barriers and surfactant molecule reorientation were important mecha-... 

Some interfacial tension measurement techniques are essentially static, i.e. they operate at low Deborah number (De 1) capillary rise, shapes of sessile and pendant drops. Others (drop weight and detachment techniques) require extension of the interface. Then the procedure is static or dynamic depending on the rate of extension relative to the rate of adsorption equilibration, i.e. on De. 

The shapes of these drops and bubbles are governed by the competition between the contractile surface tension and gravity, just as in capillary rise phenomena. The procedure for obtaining interfacial tension normally consists of the following steps ... 

Of the various other methods we mention a few of a more dynamic nature. From wave damping yiw) can in principle be obtained co is the frequency of the applied wave. See sec. 3.6g. Guido and Villone ) proposed a procedure to obtain interfacial tensions from the rate at which shear-deformed droplets retracted to their equilibrium spherical shape. De Hoog and Lekkerkerker ) determined very low interfacial tensions by following the initial state of the Rayleigh break-up of elongated drops. Although these methods are unlikely to develop into routine procedures, they demonstrate how wide the methodical spectrum is. 

The experimental procedure used for the measurement of interfacial tension and the electrophoretic mobility to determine the... 

In order to simulate the conditions of the actual emulsification process, all interfacial tension measurements were made at 65°C, in the following manner. Each aqueous mixed emulsifier solution was pre-emulsified, by mixing for 1.0 hour at 65°C, and then loaded into the capillary tube of the tensiometer. The oil drop was injected into the capillary and the rotation speed increased to the desired level. After allowing time for equilibration, the dimensions of the oil drop were measured in two perpendicular directions using a micrometer in the microscope eyepiece. Multiple oil drops were measured with each surfactant solution by repeating the above procedure. 

Measurement of the partition of the cosurfactant between the oil and the interface is not easy. A simple procedure to select the most efficient cosurfactant is to determine the oil/water interfacial tension as a function of cosurfactant concentration. In this case, the lower the percentage of cosurfactant required to reduce /q/w rn the better is the candidate. 

Although this approximation is not essential to the solution procedures, or to the qualitative physics, it does simplify the analysis by eliminating the need to solve (7-260) for c. We may also note that an additional simplification occurs if r / rfy Langmuir relationship for the interfacial tension, (7-259), can be linearized ... 

An EACN can be defined for any hydrocarbon, hydrocarbon mixture or crude oil by using the following procedure (13). Using surfactants of the same structural type, make up a series of formulations, arranging for each n. value to be different and for these values to span as mucii of the alkane range as possible. Measure the interfacial tensions of each formulation against the oil whose EACN is desired. Make a plot of interfacial tensions vs. n. . If the curve has a minimum, n. for that point define nthe EACN of the oil. 

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