Contact angle Wilhelmy plate technique

Dynamic contact angle Wilhelmy plate technique Banana stem and bunch 26... 

The computer interface system lends itself well to the determination of interfacial tension and contact angles using Equation 3 and the technique described by Pike and Thakkar for Wilhelmy plate type experiments (20). Contact angles for crude oil/brine systems using the dynamic Wilhelmy plate technique have been determined by this technique and all three of the wetting cycles described above have been observed in various crude oil/brine systems (21) (Teeters, D. Wilson, J. F. Andersen, M. A. Thomas, D. C. J. Colloid Interface Sci., 1988, 126, in press). The dynamic Wilhelmy plate device also addresses other aspects of wetting behavior pertinent to petroleum reservoirs. 

This same technique should be helpful in understanding wetting properties important in the oil industry since wetting is very dependent on mineral surface energies. The use of contact angle hysteresis information may allow a better understanding of the effects of surface heterogeneities of natural mineral samples. The dynamic Wilhelmy plate technique is ideally suited for such experiments ... 

These equations may be compared with those for cylinders, see for instance [1.3.21. For flat plates one does not have to worry about complications of the details of the profile, but this advantage is offset by the much lower rise. Typically, h is of order i.e. h = O (mm) and y is proportional to whereas it scales with ah in capillaries. Over the last few decades laser-optical techniques for scanning the meniscus and establishing h down to about 10" mm have become available In a modem variant of the Wilhelmy plate technique, to be described in sec. 1.8a, the force needed to pull the plate out of the liquid is measured as a function of the height above the zero level. In this way the surface tension and contact angle can be determined simultaneously. Alternatively, the method can be used to obtain contact angles, i.e. from [1.3.161 after y has been measured by some other technique. 

Contact Angle Measurement. Dynamic contact angle measurement was performed on the dried hydrogels at 25°C by the Wilhelmy plate technique using equipment manufactured by Shimadzu Inc. (Automated System for Dynamic Contact Angle Measurement, ST-IS type) Water used for the measurement was purified by de-ionization after double distillation. Five measurements on different parts of the film were averaged. The movement rate of the water vessel into which the gel specimen was immersed was kept at 0,3 mm sec , ... 

As soon as the coated slides were removed from the oven and cooled to room temperature, dynamic contact angles were measured by the Wilhelmy plate technique [21], We obtained the wetting curve with an electrobalance (Cahn Model... 

Fig. 11.15. Scheme of the Wilhelmy plate technique for measuring the contact angle, (a) Zero net depth, (b) finite depth. 

Figure 3 Techniques for measuring contact angles on fibres (a) and (b) tensiometric or Wilhelmy plate technique for measurement of advancing and receding angles (a) fibre touching liquid surface (b) fibre after immersion in liquid to depth d and (c) drop on fibre technique for measurement of equilibrium contact angle...

The electron probe microanalysis (EPMA) spectra were obtained with Shi-madzu EMX-SM (Shimadzu, Co. Kyoto, Japan). The EPMA was operated under an excitation voltage of 15 kV and a sample current of 0.003 mA. A spectrometer ESCA 1000 (Shimadzu Co., Kyoto, Japan) was employed to carry out X-ray photoelectron spectroscopy (XPS) [40-42]. The dynamic contact angle of the PASs was measured using the dynamic Wilhelmy plate technique [43] by means of a Orientic DCA-20 (Orientic Co., Tokyo, Japan). 

This method suffers from two disadvantages. Since it measures 7 or changes in 7 rather than t directly, temperature drifts or adventitious impurities can alter 7 and be mistakenly attributed to changes in film pressure. Second, while ensuring that zero contact angle is seldom a problem in the case of pure liquids, it may be with film-covered surfaces as film material may adsorb on the slide. This problem can be a serious one roughening the plate may help, and some of the literature on techniques is summarized by Gaines [69]. On the other hand, the equipment for the Wilhelmy slide method is simple and inexpensive and can be just as accurate as the film balance described below. 

The capillary rise on a Wilhelmy plate (Section II-6C) is a nice means to obtain contact angles by measurement of the height, h, of the meniscus on a partially immersed plate (see Fig. 11-14) [111, 112]. Neumann has automated this technique to replace manual measurement of h with digital image analysis to obtain an accuracy of 0.06° (and a repeatability to 95%, in practice, of 0.01°) [108]. The contact angle is obtained directly from the height through... 

In addition to the sessile drop method which measures the contact angle directly, Neumann and Renzow (1969) have developed the Wilhelmy slide technique to measure it to 0.1° precision. As shown in Fig. 2.20, the meniscus at a partially immersed plate rises to a finite length, h, if the contact angle, 0, is finite. 6 is calculated from... 

The situation shown in Figure 6.2b is one in which surface tension and contact angle considerations pull a liquid upward in opposition to gravity. A mass of liquid is drawn up as if it were suspended by the surface from the supporting walls. At equilibrium the upward pull of the surface and the downward pull of gravity on the elevated mass must balance. This elementary statement of force balance applies to two techniques by which 7 can be measured if 6 is known the Wilhelmy plate and capillary rise. 

For a plate of rectangular cross section having length f and thickness t, P = 2(f + t) these dimensions can be accurately measured. By suspending the plate from a sensitive balance, we can also measure w with considerable accuracy. The apparatus is called a Wilhelmy balance, and the technique the Wilhelmy plate method. Thus, if the contact angle is known from an independent determination by, say, the tilted-plate method, then 7 can be evaluated by Equation (2). 

All the techniques described here are easily conducted, so that both 0a and 0, may be observed. When the tilted plate method is used to evaluate the contact angle, 6r values are obtained if the plate has been pulled out (emersion) from the liquid 0a results if the plate is pushed into the liquid (immersion). Likewise, both values of 0 may be obtained from the Wilhelmy method, depending on whether the liquid is making an initial contact (0a) with the plate or is draining from it (6r). 

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. 

A widely used technique is the Wilhelmy plate method introduced in Section 2.4. If the contact angle is larger than zero, the force, with which the plate is pulled into the liquid, is 27pi cos 0. Here, l is the width of the plate. 

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]. 

Many different techniques have been developed for the measurement of contact angles 17.8). Of these, the three most useful methods are the Wilhelnty technique, the technique of capillary rise at a vertical plate, and the drop shape methods. These techniques require the solid surface to be flat and smooth. Direct measurement of contact angles on fibers (of uniform thickness) can also be performed using the Wilhelmy technique. For nonflat surfaces or particles, indirect methods such as capillary penetration into columns of powders, sedi-... 

In the following subsections, the three most commonly used contact angle techniques, the Wilhelmy technique, capillary rise at a vertical plate, and drop shape methods, are described in detail. 

If a plate is not effectively smooth, it will not be suitable for determination of the contact angle of the liquid on that solid. However, a well-known useful technique for obtaining a zero contact angle, in order to use the Wilhelmy... 

The method is based on Wilhelmy s plate technique for measuring DCAs. The technique involves the measurement of force as a plate is (automatically) immersed into and then emersed from a liquid at a constant rate. The forces (weight) can be plotted as a function of the immersion depth, and, from this, contact angles calculated (Figure 1.29a,b). 

It is hence essential to be able to measure and modify the surface free energy of the solid if criteria other than trial and error are used to predict the wettability (and the colloidal stability, for that matter) of a solid drug, since the surface tension of the liquid is readily measurable by any well-establi.shed method (Wilhelmy plate, du Nouy ring, drop shape analysis, etc. see. e.g. Ref. 37). In the case of solids, only indirect methods are available to estimate Ys and Ysl here we shall give details on the simplest one. contact angle measurements, and the reader is referred to other chapters of this volume for details on other methodologies. The technique is based on Young s equation (37) ... 

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