Pendant drop method, surface tension measurement

A number of methods are available for the measurement of surface and interfacial tension of liquid systems. Surface tension of liquids is determined by static and dynamic surface tension methods. Static surface tension characterises the surface tension of the liquid in equilibrium and the commonly used measurement methods are Du Notiy ring, Wilhelmy plate, spinning drop and pendant drop. Dynamic surface tension determines the surface tension as a function of time and the bubble pressure method is the most common method used for its determination. 

The film pressure is defined as the difference between the surface tension of the pure fluid and that of the film-covered surface. While any method of surface tension measurement can be used, most of the methods of capillarity are, for one reason or another, ill-suited for work with film-covered surfaces with the principal exceptions of the Wilhelmy slide method (Section II-6) and the pendant drop experiment (Section II-7). Both approaches work very well with fluid films and are capable of measuring low values of pressure with similar precision of 0.01 dyn/cm. In addition, the film balance, considerably updated since Langmuir s design (see Section III-7) is a popular approach to measurement of V. 

In order to calculate polymer/filler interaction, or more exactly the reversible work of adhesion characterizing it, the surface tension of the polymer must also be known. This quantity is usually determined by contact angle measurements or occasionally the pendant drop method is used. The former method is based on the Young, Dupre and Eowkes equations (Eqs. 21,8, and 10), but the result is influenced by the surface quality of the substrate. Moreover, the surface (structure, orientation, density) of polymers usually differs from the bulk, which might bias the results. Accuracy of the technique maybe increased by using two or more liquids for the measurements. The use of the pendant drop method is limited due to technical problems (long time to reach equilibrium, stability of the polymer, evaluation problems etc.). Occasionally IGC is also used for the characterization of polymers [30]. 

The pendant drop method has been used to measure the interfacial tension at the surface between mercury and cyclohexane solutions of stearic acid at 30 and 50°C. 

To apply the sitting or pendant drop method to measure the surface tension of a liquid the drop must be large enough so that gravitation plays a significant role. Why ... 

Surface Tension Measurement. The surface tension of the surfactant solution was determined by means of the Dynamic Contact Angle Tester FIBRO DAT 1100 (FIBRO Systems, Sweden) using the pendant drop method. It was also an output of the ADSA captive bubble contact angle measurements with surfactant solutions. 

Pendant drop method of measuring surface tension Drop of liquid hangs from pipette the z axis is vertical, the x axis is horizontal, and R is the (maximum) radius of the drop. To obtain / , many values of the radii S S— 0 to R) are measured at heights z (z = 0 to R) above the apex of the drop 4> is the tangent angle at the radius S. 

The pendant drop method (Fig. 4.16) measures the contact angle 6 and drop radius R to determine the surface tension for any liquid surrounded by gas, or the interfacial tension between any two liquids A drop is hung from a syringe tip in air, and the interfacial surface tension J gl is... 

Methods used to measure interfacial tension are reviewed by Drelich, Fang, and White [ Measurement of Interfacial Tension in Fluid-Fluid Systems, in Encyclopedia of Surface and Colloid Science (Dekker, 2003), pp. 3152-3156]. Also see Megias-Alguacil, Fischer, and Windhab, Chem. Eng. Sci., 61, pp. 1386-1394 (2006). One class of methods derives intertacial tension values from measurement of the shape, contact angle, or volume of a drop suspended in a second liquid. These metho(Js include the pendant drop method (a drop of heavy liquid hangs from a vertically mounted capillary tube immersed... 

In theory, every surface tension measurement method can be used to determine the interfacial tension between two liquids. However, the accuracy of these methods is reduced when applied to liquid-liquid interfaces, or when one or both of the liquids is viscous. In practice, the maximum bubble pressure and pendant drop methods are the most suitable, giving consistent and reliable values for interfacial tensions, although there is sometimes the... 

FIGURE 16,3-14 Surface tension of 4 x ICn4 kmol/m3 dodecylamine hydrochloride solution as a function of pH determined by pendant drop method, measured 15 s after Forming drop.9 (After R. W, Smith, personal communication, 1967.)... 

Pendant Drop Method A method for determining surface or interfacial tension based on measuring the shape of a droplet hanging from the tip of a capillary (in interfacial tension the droplet may alternatively hang upward from the tip of an inverted capillary). Also termed the hanging drop (or bubble) method. 

Surface tensions of both the ST copolymers in homopolymers and the PS-PTHF homopolymer blend were measured in argon by the pendant drop method described by Roe (5). 

DSS lowers the surface tension of liquids e.g. water and various electrolyte solutions. The effect of DSS on surface tension may be measured by a variety of methods however, the Pendant Drop Method (12) seems to be most satisfactory for measuring changes in surface tension. The effect of concentration of DSS on surface tension as determined by Pendant Drop Method is shown in Table VII. 

Surface and interfacial tensions of the two liquids were measured with a Kruss DSA 100 drop analyser system by the pendant drop method. The liquid was injected... 

Pendant or Sessile Drop Method The surface tension can be easily measured by analyzing the shape of a drop. This is often done by optical means. Assuming that the drop is axially symmetric and in equilibrium (no viscous and inertial effects), the only effective forces are gravity and surface or interfacial forces. In this case, the Young-Laplace equation relates the shape of the droplet to the pressure jump across the interface. Surface tension is, then, measured by fitting the drop shape to the Young-Laplace equation. Either a pendant or a sessile drop can be used for surface tension measurement. The pendant drop approach is often more accurate than the sessile drop approach since it is easier to satisfy the axisymmetric assumption. Similar techniques can be used for measuring surface tension in a bubble. 

Surface tension was determined via the pendant drop method using a Kruss EasyDrop. The liquid was suspended from an 1832 pm needle with equatorial and neck diameters measured for the largest stable drop. The surface tension was calculated using the relationship ... 

In order to determine the infants lung maturity and the necessity of surfactant therapy it is of great importance to substantiate the functionality of the alveolar surfactant, derived via invasive techniques [13], Several techniques and models have been largely used to investigate inteifacial physicochemical properties in vitro and to assess clinical efficiency of ES in vivo the Langmuir monolayer technique in combination with Wilhelmy plate method for surface tension measurements and black foam film method for determination of the ability of ES for stable film formation [14]. The pendant drop method combined with the Axisym-metric Drop Shape Analysis (ADSA) has been also used for similar purposes [4,15-18]. 

Modern methods of measuring the surface tension include the pendant drop method, the sessile drop method, and others (7,8,15). These methods depend on the shape of a drop of the polymer or a bubble in it, and on the balance of surface tension and gravitational forces see Figure 12.3 (8). 

The shape adopted by a drop stems from a compromise between the effect of surface tension, which favors a sphere, and gravity (or any other force field), which will cause distortions. For any given situation, analyzing the shape of the drop ought to make it possible to extract the surface tension. Several methods currently used to measure surface (or interfacial) tensions are based on this principle, such as the sessile drop method or the pendant drop method. The latter is the most commonly used. ... 

Surface activity at the air-water interface of solutions of the oligomer salt is inferred from measurements of surface tension lowering. Typical data obtained from two refined molecular weight fractions are presented graphically in Figure 1. Surface tension is estimated by the pendant drop method with the aid of tables supplied by Adamson (4). 

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. 

Only methods based on drop profiles are suitable for both surface and interfacial tension measurements. These include the pendant drop method [125-127], the sessile bubble or drop method [128, 129], and the rotating drop or bubble method [130, 131]. These methods are independent of the solid-Uquid contact angle but require accurate knowledge of the density difference across the interface. The demand of accurate density data becomes even greater when the two phases have similar densities. The rotating drop or bubble method is particularly suited for the determination of very low surface and interfacial tensions. 

Other techniques are of interest but will not be covered here. For example, emphasis is put on the pros and cons of the pendant drop technique by Ambwani and Fort [63]. The pendant drop method has been very laborious traditionally. A fas standard instrumentation using computer image analysis has been described by Hansen and Rodsrud [64]. The characterization of monolayers can be carried out by this technique. For example, Li et al. described the required equipment and the application of the pendant drop technique to measure the surface tension of a insoluble monolayer covered onto a water drop surface [65]. 

One of the key variables governing droplet breakup is the interfacial tension between phases. The pendant drop apparatus can be used to measure either the surface tension between a liquid and air or the interfacial tension between two liquids. The pendant drop method should be used in preference to the du Niioy ring, as it is easier to use and gives more reliable results. 

Surface tension can be measured in many ways. The most important and useful methods are illustrated in Figure 2.2. One of the most accurate methods is to measure the rise of the liquid in a capillary (see Figure 2.2a). Another method is to weigh falling drops of a liquid, called pendant drop method... 

The interfacial tension of C02-saturated triglycerides in a triglyceride-saturated CO2 atmosphere was measured using the pendant drop method introduced in 1938 by Andreas et al. [8]. In this method, a drop is suspended on a capillary in a gas or liquid atmosphere. Its shape results from the balance of gravitational and interfacial forces. As the drop minimises its surface by taking on spherical shape, the pressure inside the drop increases as a result of the curved interface. At the same time, the spherical shape is distorted under the weight of the drop. This results in pear-shaped droplets, which are typical for this method. 

Surface tension of SE (OAV) emulsions and its continuous phases, of relevance for the spray drop formation, were measured versus time using the pendant drop method, demonstrated in Fig. 23.7. It was found that the surface tension values of the emulsions were significantly higher than those of their continuous phases including the same surfactant and thickener composition like the related emulsions. It is assumed that the used surfactants were equally active at oil/water interfaces within the emulsions and at the spray drop surface (gas/liquid interface). Consequently, surfactant availability at the gas/liquid interface seemed being restricted in the presence of surfactant-covered emulsion drops. 

Fig. 23.7 Pendant drop method-based measurements of surface tension a of SE (O/W) emulsion and corresponding continuous phase (J) over time, plotted as In (

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