Capillary rise method, surface tension measurement

While determining the liquid height, it is better to measure with a falling (or receding) meniscus, so that the liquid level is initially raised above its equilibrium value by a slight suction above the capillary tube, and then left to equilibrate. On the other hand, two-armed capillary tubes, connected with a cross tube above the liquid level, are also used to ensure that the pressure in both arms of the glass apparatus is the same. An interesting modification of the capillary rise method is to measure the pressure, AP, that is required to force the meniscus down until it is on the same level as the plane surface of liquid outside the capillary tube. This method is useful to compare the surface tension of water and its dilute solutions. 

The capillary-rise method was employed to measure the surface tension of aqueous solutions of disodlum alkyl phosphate at 25 °C. The cmc values of the solutions were obtained from the discontinuity in the surface tension - concentration curves(7). 

Figure 2. Surface tensions of sodium dodecylsulfonate solutions with and without polymer addition as measured by the capillary rise method.

Surface Tension. The surface tension of various ozone-fluorine mixtures was determined by the capillary rise method in the apparatus used for the viscosity measurements (1) using Equation 4. 

For this reason, the surface tension has units of either energy per unit area or force per unit length. The surface tension of a liquid is measured in one of several ways capillary rise, ring detachment, or drop weight. Each method of surface tension measurement is outlined in Figure 9.2. With capillary rise, the fluid is suspended by the surface... 

The surface tension of pure ozone was determined by the capillary rise method in the apparatus used for viscosity measurements. The ratio of the capillary rise of liquid ozone to that of water at 20° C. was measured and zero contact angle was assumed. Results at —183° and —195.5° C. are given in Table III. The parachor for... 

When compared with the other methods, the capillary rise method is the ultimate standard method in terms of the degree of theoretical exactitude, and, although it is the oldest method, it still gives the most precise liquid surface tension results if carefully applied, and when the time of measurement is allowed to be sufficiently long. However, with the improvement in computer-controlled electronic equipment, other methods now also have a very high precision. Some of the surface tension results are summarized in Table 6.1, and the interfacial tension between pure liquids in Table 6.2. 

The capillary rise method is a static method, which measures the tension of practically stationary surfaces that have been formed and equilibrated for an appreciable amount of time. The use of a cathetometer and suitable illumination of the menisci is required during the measurement. The capillary tubes must be very clean, be placed as accurately vertical, and be circular in cross section with an accurately known and uniform radius. The... 

The detachment of a ring or a plate (a Wilhelmy plate) from the surface of a liquid or solution is a static surface tension measurement method, which gives the detachment force of a film of the liquid and its extension from the liquid surface. These methods are less accurate than the capillary rise method, but they are normally employed in most surface laboratories because of their ease and rapidity. 

The precision of surface tension measurements using the capillary rise method can be further increased if the deviation of the meniscus shape from the spherical is taken into account. This correction is especially important when capillaries of large radii are used. Corrections for non-spherical meniscus curvature are based on tabulated numerical solutions of the differential Laplace equation [6]. The capillary rise method yields a values with a precision of up to hundredths of mN/m. 

Up to now we primarily have been considering the interfaces in two-phase systems. The conditions of phase contact in tri-phase systems were only briefly mentioned in relation to the capillary rise and during the description of methods for surface tension measurement (see Chapter I, 3). Within this section we will address this issue in greater detail, but restrict ourselves mainly to consideration of systems that consist of mutually insoluble phases and do not contain any substances that might adsorb at interfaces. 

From Eq. (10.2.4) it is evident that for small capillaries Hg can become relatively large. For example, for water with o- = 73mNmin a 0.1-mm-radius clean glass capillary the liquid will rise to an equilibrium height of about 0.15 m. The capillary rise method is one of the most accurate means for the measurement of surface tension. 

Figure 2.4. Measurement of surface tension by the differential capillary rise method...

Equation 14 therefore represents an equilibrium dominant balance between the gravitational and surface tension forces. Thus, given that p and cos 0 are known for a given fluid, the capillary rise can be determined. It is also evident from Eq. 14 that the capillary rise is dependent on the capillary radius. For small capillaries, H can therefore become relatively large. This capillary rise method is therefore very useful and accurate for measuring the surface tension of liquids. 

FIGURE 6.10. In the capillary rise method of surface tension measurement, surface tension effects canse the wetting hquid to rise in the small capillary to a height that just balances the hydrodynamic force dne to gravity (a). For non-wetting liquids such as mercury, a depressing effect is observed (Z>). 

The capillary rise method was used to measure the surface tension of a liquid that wetted glass. A glass capillary tube of 0.0200 cm diameter was used and a capillary rise of 10.47 cm was measured. The liquid density was 1.000 g cm". What is the surface tension of the liquid What influence do corrections for the weight and nonsphericity of the meniscus have on the surface tension ... 

Jones G, Ray J (1939) A theoretical and experimental analysis of the capillary rise method for measuring the surface tension of solutions of electrolytes. J Am Chem Soc 59 187... 

Surface tension of liquids can be measured by either of the two methods static and dynamic. The static methods are based on the assumption that the liquid has attained surface equilibrium. For pure liquids and solutions of crystalloids the process of attainment of equilibrium is very fast and the static methods are best suitable. But for colloidal solutions a considerable time is required to reach the equilibrium state and therefore the dynamic methods of measuring surfacf tension are preferred. The dynanJc methods measure the tension of a liquid before the surface film has had time to form. TTiere are other methods too which fall between the static and the dynamic methods. Among the static methods, the most commonly used ones are (0 the capillary rise method, (ip the du Nouy ring method, (Up the Wilhelmy balance method, and (iv) the drop-weight method.,... 

Capillary Rise Method In this approach a capillary tube is immersed into the liquid. The surface tension is calculated by measuring the liquid height in the capillary tube via Eq. (9). The capillary rise is also a measure of the vertical component of surface tension. 

The surface tension measurement techniques can be divided into the following three categories (i) Force Methods, which include the truly static methods of the capillary rise and Wilhelmy plate methods, as well as the dynamic detachment methods of the Du Nouy ring and drop weight, (ii) Shape Methods, which include the pendant or sessile drop or bubble, as well as the spinning drop methods, and (iii) Pressure Methods, which are represented by the maximum bubble pressure method. These techniques are summarized in the following sections of this chapter. 

The capillary rise method was the earliest technique by which surface tension was measured and, indeed, was the technique by which the force itself was recognized. If a narrow tube of radius r is partially inserted into a liquid, the liquid rises up inside the tube to some equilibrium position as shown in Fig. 22. This occurs because the attractive interaction of the wetting liquid (aqueous solution) with the solid surface is stronger than that of the gas phase. Gravity opposes the rise, and the equilibrium height H corresponds to the minimum free energy of the system. The treatment is based on the Laplace equation that gives the pressure difference across a curved interface due to the surface or interfacial tension of the liquid [62]. Let us assume that we have a spherical bubble Of gas in a liquid... 

Surface tension can be measured in many ways. One of the most accurate and conceptually simple methods is to measure the rise of a liquid in a capillary (Fig. 4.7a). The surface tension is related to the height of liquid supported by gravity, the tube radius, the contact angle of the liquid meniscus and the density difference between liquid and vapour. The determination of surface tension using this capillary rise method is easiest when the liquid completely wets the capillary wall, i.e. when the contact angle (Section 4.5.1) is near zero. 

Problem 4.2 The capillary rise as a method for measuring the surface tension of liquids The rise of liquids in thin capillaries is a well-known phenomenon (partially) due to smface phenomena and at the same time it represents a very efficient and simple method for obtaining experimentally the surface tension of liquids (upon measuring their rise and knowing the dimensions of the capillary tube). First of all, orient yourself (see, for example, Pashley and Karaman, 2004 Shaw, 1992, etc.) on how the capillary rise method works. 

Measurement of surface tension can be carried out in a variety of ways. Two of the most common, simple, and relatively accurate methods of calculating surface tension are measuring the rise of liquid in a capillary (capillary rise method) and the pull on a thin vertical plate partially immersed in the liquid (Wilhelmy plate method). 

The capillary rise method Ibr measurement of surface tension, which gives most accurate results in absolute terms, is not in common use as it is extremely laborious, time consuming and requires a large amount of liquid. 

Surface tension of uranyl sulfate solutions. The capillary rise method was adapted to conditions prevailing at elevated temperatures and pressures for measurements made at Mound Laboratory by Heiks et al. [51,54]. Briggs [59] has compiled information on the surface tension of aqueous solutions of uranyl sulfate, including the relationships established by Van Winkle. 

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