Bubble methods contact angle

The maximum bubble pressure method is good to a few tenths percent accuracy, does not depend on contact angle (except insofar as to whether the inner or outer radius of the tube is to be used), and requires only an approximate knowledge of the density of the liquid (if twin tubes are used), and the measurements can be made rapidly. The method is also amenable to remote operation and can be used to measure surface tensions of not easily accessible liquids such as molten metals [29]. 

The wetting (contact) angle method is used for solid surfaces. If a gas bubble sticks to a metal surface, then the individual interfacial tensions are distributed as shown in Fig. 4.11. It holds at equilibrium that... 

The profiles of pendant and sessile bubbles and drops are commonly used in determinations of surface and interfacial tensions and of contact angles. Such methods are possible because the interfaces of static fluid particles must be at equilibrium with respect to hydrostatic pressure gradients and increments in normal stress due to surface tension at a curved interface (see Chapter 1). It is simple to show that at any point on the surface... 

Provides measuring techniques of contact angle, surface tension, interfacial tension, and bubble pressure. Suitable methods for both static and dynamic inteifacial tension of liquids include du Nous ring, Wilhelmy plate, spinning drop, pendant drop, bubble pressure, and drop volume techniques. Methods for solids include sessile drop, dynamic Wilhelmy, single fiber, and powder contact angle techniques. 

Alternatively, we can measure the contact angle at the edge of a bubble. This method is called captive or sessile bubble. In this case a bubble is positioned usually at the top of a cell which is otherwise filled with liquid. The method is less sensitive to pollution of the interface. In addition, the vapor phase is automatically saturated. 

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 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)...

Another method is to measure the thickness of a drop of liquid resting on a horizontal plate, or of a bubble underneath a plate. If the bubble or drop is large, so that the curvature at the apex can be neglected and this part of the surface treated as flat, the contact angle is given by the equation8... 

Measurements on molten metals. The maximum bubble pressure method has proved one of the most satisfactory, but sessile drops, and drop-volumes have also been used with success.2 The principal difficulty lies in the proneness of metals to form skins of oxides, or other compounds, on their surfaces and these are sure to reduce the surface tension. Unless work is conducted in a very high vacuum, a freshly formed surface is almost a necessity if the sessile bubble method is used, the course of formation of a surface layer may, if great precautions are taken, be traced by the alteration in surface tension. Another difficulty lies in the high contact angles formed by liquid metals with almost all non-metallic surfaces, which are due to the very high cohesion of metals compared with their adhesion to other substances. 

Bubble of size of the order of tens of micrometers floating on the surfactant surface only little deviates from the spherical shape. This fact has been used in the method of diminishing bubble [128,129] which allows to measure the contact angle of the black film, the linear tension of the contact line film/meniscus and the coefficient of the gas permeability through the film. Fig. 2.24 presents the scheme of this device. 

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. 

Another widely used method is the measurement of contact angles from sessile drops or adhering bubbles. Because of its simplicity, various procedures have been developed, as we shall describe below. 

Contact angle measurements provide information on the wettability of the sample, the surface energetics of the solid, and the interfacial properties of the solid-liquid interface. The samples were immersed in water and captive air and octane bubbles were determined by measuring the bubble dimensions. By measurement of both air and octane contact angles the surface free energy (.y) of the solid-vapor ( > ) interface may be calculated by use of Young s equation and the narmonic mean hypothesis for separation of the dispersive and polar components of the work of adhesion. This method for determination of surface and interfacial proper-... 

The bubble injection method of contact angle measurement utilizes a sessile bubble below the surface that is immersed in water. It is nearly impossible to measure the sessile bubble contact angle on top surface of a sample immersed in water, of which contact angle is to be measured, because the buoyancy works in the direction to lift the bubble. Although the two methods should yield the identical contact angle, the values obtained by the two methods could deviate significantly depending on the solubility of air in water and the perturbability of the surface by water as described in the previous chapters. 

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