Captive bubble method

A captive air (or other gas) bubble is formed in the liquid contacting with the solid by means of an inverted micrometer syringe beneath the substrate which is kept in the test liquid. The contact angle is measured by means of a goniometer microscope or video camera. In this method, the solid-vapor interface is in equilibrium with the saturated vapor 

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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°. 

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)...

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 ... 

The octane-in-water contact angle was measured using the captive-bubble method described by HAMILTON. The measurements were carried out with a contact angle goniometer of the Fa. Lorentzen and Wettres (Stockholm),... 

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. 

The determination of the contact angle was carried out by means of the captive bubble method. The influence of the wettability on fibrinogen adsorption... 

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... 

Fig. Zll Schematic of contact angle measurement using the captive bubble method...

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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