Contact angle experimental measurements

This is known as the Youx g equation. We shall return to its derivation, intricacies and naming in sec. 5.2, but note in passing that the vertical component sin a is compensated by the tensile strength of the solid. Contact angles are measurable and in a number of methods such measurements run in conjunction with those of interfacial tensions. It follows that [1.1.71 cannot be used to establish the interfacial tension of a solid, cdthough the difference y - is experimentally measurable. 

Contact angle hysteresis measured experimentally may be due to heterogeneities in the composition of the solid surface, surface irregularities, or dynamic effects due to adsorption or desorption phenomena, molecular reorientations, or similar. 

Figure 4. Experimentally obtained relationship between the wetting parameter kb and the (apparent) water contact angle. The measurements refer to a number of different types of rough surfaces with same hydrophobic material properties (all samples were coated with a thin RF sputtered Au layer and a molecular decanethiol film to obtain intrinsic CA about 110 ).

Contact An e Measurements. Advancing contact angles were measured on a Rame-Hart NRL model goniometer at room temperature and ambient humidity. For the measurements, 6 gh of water was put on the surface, followed by adding another 6 gh to the first drop. The contact angle was measured immediately within 1 min. They are 30°, 44°, 60°, and 45° for surfaces Ti, A, MH, and GMH, respectively. The experimental error of this method is estimated to be 3°. 

Experimentally, contact angle is measured based on geometry of the droplet or the interfacial tension across the contact line using various techniques such as tilting plate, sessile bubble and drop, captive bubble, the Wilhelmy method, and so on. Similarly, in simulation, three methods are generally used to find the contact angle. 

The purpose of this chapter is to present the LAD performance experiments carried out in room temperature liquids. Bubble point and reseal pressure tests for a 325x2300, 450 X 2750, and 510 x 3600 Dutch Twill screen are conducted in storable liquids, methanol, acetone, IPA, water, and binary methanol/water mixtures of various methanol concentrations. First screen pore diameters are estimated based on analysis from scanning electron microscopy and historical data. Experimental results are used to compare methods for determining effective pore diameter. Next, contact angles are measured for both pure and binary mixture fluids using a modified version of the Sessile Drop technique. Then, the equation of state analysis from Neumann and Good (1979) is used to determine the critical Zisman surface tension for stainless steel LAD screens, which... 

However, before these concepts may be of use in adhesives technology the surface and the interfacial free energies need to be evaluated and the kinetics considered. Since this frequently involves measuring contact angles, experimental aspects will be considered next. 

Since both sides of Eq. X-39 can be determined experimentally, from heat of immersion measurements on the one hand and contact angle data, on the other hand, a test of the thermodynamic status of Young s equation is possible. A comparison of calorimetric data for n-alkanes [18] with contact angle data [95] is shown in Fig. X-11. The agreement is certainly encouraging. 

The extensive use of the Young equation (Eq. X-18) reflects its general acceptance. Curiously, however, the equation has never been verified experimentally since surface tensions of solids are rather difficult to measure. While Fowkes and Sawyer [140] claimed verification for liquids on a fluorocarbon polymer, it is not clear that their assumptions are valid. Nucleation studies indicate that the interfacial tension between a solid and its liquid is appreciable (see Section K-3) and may not be ignored. Indirect experimental tests involve comparing the variation of the contact angle with solute concentration with separate adsorption studies [173]. 

A. W. Neumann and R. J. Good, in Techniques of Measuring Contact Angles, Surface and Colloid Science, Vol. II, Experimental Methods, R. J. Good and R. R. Stromberg, ed.. Plenum, New York, 1979. 

Section 4.1 briefly describes some of the commonly employed experimental tools and procedures. Chaudhury et al., Israelachvili et al. and Tirrell et al. employed contact mechanics based approach to estimate surface energies of different self-assembled monolayers and polymers. In these studies, the results of these measurements were compared to the results of contact angle measurements. These measurements are reviewed in Section 4.2. The JKR type measurements are discussed in Section 4.2.1, and the measurements done using the surface forces apparatus (SFA) are reviewed in Section 4.2.2. 

Given the importance of surface and interfacial energies in determining the interfacial adhesion between materials, and the unreliability of the contact angle methods to predict the surface energetics of solids, it has become necessary to develop a new class of theoretical and experimental tools to measure the surface and interfacial energetics of solids. Thia new class of methods is based on the recent developments in the theories of contact mechanics, particularly the JKR theory. 

The hydrophobic gas layer of the air electrode [4] possesses high porosity (ca. 0,9 cm2/g), such that an effective oxygen supply through this layer is obtained. From the experimental porogrames measured by both mercury and 7 N KOH-porometiy the contact angle 0en of the hydrophobic material with water electrolytes is obtained (0eff =116° 118°). Because of... 

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