Captive bubble

Fig. 7. The concept of contact angle with a captive bubble in an aqueous medium, adhering to a hydrophobic sofld P is the three-phase contact point. Here, the vector passes through P and forms a tangent to the curved surface of the air bubble. The contact angle 0 is drawn into the Hquid.

Contact angles are commonly measured by the sessile drop, the captive bubble, and the Wilhelmy plate method. To characterize the wetting properties of powders the capillary rise method is used. 

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]. 

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]. 

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. 

Photoresist layers processed at the threshold dose have a thickness of about 5 nm which is too low to show a swelling effect detectable by ellipsometry. However, long-time contact angle measurements using the ADSA captive bubble method revealed a decrease of the contact angle with time as shown in Fig. 7. At the beginning, the water contact angle was 50°. After 50 h a value of only 39° was obtained. It is assumed that the decrease in con-... 

To find out whether a hydrophobizing effect can be obtained by surfactant adsorption, photoresist layers processed with exposure doses between 50% and 120% of the threshold dose have been investigated by the captive bubble method. Their receding contact angle was first... 

Scheme 2 Comparison of the geometries of the receding contact angle responsible for the capillary forces between photoresist lines in the photolithographic process (left image) and the receding contact angle measured by the captive bubble method (right image)...

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. 

The contact angles at the quartz- (or glass) water-air interface were measured using a modified captive-bubble apparatus (1). 

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. 

Figure 1.11. Captive bubble, h is the vertical distanee between the equatorial phase and the apex.

Figure 5.19. Contact angles, measured through the liquid, in sessile drops and captive bubbles. The vapour phase can be replaced by einother liquid.

Abbreviations CB = captive bubble TP = tilting plate WP = Wilhelmy plate SD = sessile drop DCA = dynamic contact angle AFM = atomic force microscopy.)... 

Malcolm, J.D. Elliott, C.D. Interfacial tension from the height and diameter from a single sessile drop or captive bubble. Can. J. Chem. Eng. 1980, 58 (2), 151-153. 

Drops and bubbles are indeed the same mathematical object. However, in marine water studies, the profile analysis of captive (or emerging) bubbles is preferable in respect to the analysis of drops. Actually, from the physical point of view, bubbles exhibit some differences in respect to drops a) diffusion to the air-water interface from a semi-infinite medium (rather than from the small volume confined by the drop) b) limited evaporation c) possibility of observing bubble properties both in quiescent hydrodynamic conditions or in laminar flow regime. Moreover, a captive bubble can be expanded to very large dimensions. 

The advancing and receding contact angle values may decrease with decreaseing drop size (or in the captive bubble method, with the size of the bubble). This decrease is more pronounced in 0, values than in 0a. 

Figure 34-19. The captive-bubble method for measuring contact angle.

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 ... 

There are a variety of simple and inexpensive techniques for measuring contact angles, most of which are described in detail in various texts and publications and will be mentioned only briefly here. The most common direct methods (Fig. 17.4) include the sessile drop (a), the captive bubble (b), the sessile bubble (c), and the tilting plate (d). Indirect methods include tensiometry and geometric analysis of the shape of a meniscus. For solids for which the above methods are not applicable, such as powders and porous materials, methods based on capillary pressures, sedimentation rates, wetting times, imbibition rates, and other properties, have been developed. 

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