Surface captive drop

The captive drop and captive bubble methods, variations of the sessile drop method, have been developed for the determination of very low values of surface or interfacial tension [140,141], including at elevated temperature and pressure [141]. 

NMR, up to 180 °C by Shinoda et al. [52]. Some work has been reported involving erne determination by calorimetry (measuring heats of dilntion or specific heats). Archer et al. [53] nsed flow calorimetry to determine the erne s of several sulfonate surfactants at up to 178 °C. NoU [5J] determined erne s for dodecyltrimethylammonium bromide and commercial surfactants in the temperature range 25—200 °C using flow calorimetry. Surface tension is the classical method for determining erne s but many surface tension methods are not suitable for use with aqueous solutions at elevated temperatures. Exceptions include the pendant, sessile, and captive drop methods which can be conducted with high-pressure cells [54, 55]. 

There are many methods available for the measurement of surface and interfacial tensions. Details of these experimental techniques and their limitations are available in several good reviews [101-104]. Table 5 shows some of the methods that are used in petroleum recovery process research. A particular requirement of reservoir oil recovery process research is that measurements be made under actual reservoir conditions of temperature and pressure. The pendant and sessile drop methods are the most commonly nsed where high temperatur pressure conditions are required. Examples are discussed by McCaffery [i05] and DePhUippis et al. [J06]. These standard techniques can be difficult to apply to the measurement of extremely low interfacial tensions (< 1 to 10 mN/m). For ultra-low tensions two approaches are being used. For moderate temperatures and low pressures the most common method is that of the spinning drop, especially for microemulsion research [107], For elevated temperatures and pressures a captive drop method has been developed by Schramm et al. [JOS], which can measure tensions as low as 0.001 mN/m at up to 200 °C and 10,000 psi. In aU surface and interfacial tension work it should be appreciated that when solutions, rather than pure liquids, are involved appreciable changes can occur with time at the surfaces and interfaces, so that techniques capable of dynamic measurements tend to be the most useful. 

Some of the commonly used techniques for measuring contact angle [215, 216, 217] are the sessile drop method, captive bubble method and Wilhelmy plate method. These techniques have been extensively used and well documented for characterisation of modified PE surfaces [218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230] for various applications. Whitesides et al. [231 ] studied the wetting of flame-treated polyethylene film having ionisable organic acids and bases at the polymer-water interface. The effect of the size of substituted alkyl groups in amide and ester moieties on the surface hydrophilicity was also studied [232]. The biocompatibility of the polyethylene film surface modified with various water-soluble polymers was evaluated using the same technique [233]. The surface properties of hy-perbranched polymers have been very recently reported [234]. 

With liquid contents beyond the capillary state, liquid completely envelopes the particles (Fig. 2.3D). Only the interfacial tension of the convex surface of a continuous liquid drop tends to hold the particles captive. 

The captive bubble method was applied to quantify the wettability of the resist in contact with water, with surfactant solutions of different concentration and with water after contact with the surfactant solution. The wafer piece is mounted with the photoresist layer down in a cuvette filled with the solution of interest. Through a small hole in the wafer an air bubble is placed under the photoresist surface. The shape of the drop is analyzed while its volume is slowly increased and decreased and the contact angle of the bubble is computed. It has to be converted into the water contact angle by subtracting its value from 180°. 

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. 

Marmur A. (1998) Contact angle hysteresis on heterogeneous smooth surfaces theoretical comparison of the captive bubble and drop methods. Colloids Surf A 136 209-215. 

A number of systems such as sessile drop, captive bubble, hanging, or pendent drop in which a drop or bubble is kept in position on a surface belong to this category. 

An interesting approach for obviating the contact angle problem has been proposed by Padday and Pitt I The method ctm be applied for drops separated from the surface by a thin liquid film, as sketched in fig. 1.14. Depending on the densities of the two fluids, it can be used for surfaces emd interfaces, in the sessile or captive mode. The authors showed that for this situation... 

Three methods are usually used to calculate contact angle—Wilhelmy plate method, sessile drop method [33], and captive bubble method [34]. Sessile drop method is the most commonly used method for biomedical polymers. In this method, about 3 pi of a liquid droplet is placed on the polymer surface and images of the drop are acquired about 30 s of equilibration of the drop. Interface energy between the solid sample snrface and hqnid can also be calculated using the Young s eqnation ... 

Altogether, it may be clear that as long as wetting is not free of hysteresis one should take extrane care in further interpretation and analysis of the contact angle. As an alternative for a sessile drop of liquid, a captive gas (air) bubble may be used to probe the wettability of a solid surface. See Figure 8.5. Analysis and interpretation of the contact angle of the captive bubble are, mutatis mutandis, analogous to those for the sessile drop. 

A distinction can be made among the available methods between static and dynamic contact angle determination methods. In the case of a static determination the contact angle of a drop with an immobile solid/liquid/gas interface is determined microscopically (sessile drop). In the captive bubble method the contact angle of an air bubble, which is located under the solid surface in contact with the liquid, is determined. In contrast to the sessile drop method, in the captive bubble method the contact angle is measured at a completely wet surface. 

J. Drehch, J. D. Miller, and R. J. Good, The effect of drop (bubble) size on advancing and receding contact angles for heterogeneous and rough sohd surfaces as observed with sessile-drop and captive-bubble techniques, J. Colloid Interface Set, 179,37-50 (1996). 

Equilibrium contact angles can be measured very simply from the profiles of liquid drops (Figure 2a) or bubbles (Figure 2b) resting on a plane surface. These methods are known as the sessile drop and captive bubble methods respectively. The contact angle may be measured indirectly by... 

An alternate method frequently mentioned in the literature is the so-called captive bubble technique [42]. Experimentally, an air bubble of known volume is produced at the tip of a microsyringe. This bubble is then injected into a tank containing the test liquid. The test surface is positioned on the top of the test liquid and 2-3 mm above the injected air bubble. A captive bubble is formed when the air bubble floats upward and be captured by test surface. Contact angle 6, formed at the three phase contact line, follows the same Young s equation in Eq. (2.1) and can be calculated from the drop profile of the bubble in a manner similar to the sessile drop method. A schematic of the captive bubble method is shown in Fig. 2.11. 

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