Contact angle meaning

There are some subtleties with respect to the physicochemical meaning of the contact angle equation, and these are taken up in Section X-7. The preceding, however, serves to introduce the conventional definitions to permit discussion of the experimental observations. 

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... 

The critical surface tension concept has provided a useful means of summarizing wetting behavior and allowing predictions of an interpolative nature. A schematic summary of 7 values is given in Fig. X-10 [123]. In addition, actual contact angles for various systems can be estimated since )3 in Eq. X-38 usually has a value of about 0.03-0.04. 

The terms wetting and nonwetting as employed in various practical situations tend to be defined in terms of the effect desired. Usually, however, wetting means that the contact angle between a liquid and a solid is zero or so close to zero that the liquid spreads over the solid easily, and nonwetting means that the angle is greater than 90° so that the liquid tends to ball up and run off the surface easily. 

Roll-up. The principal means by which oily soil is removed is probably roU-up. The appHcable theory is simply the theory of wetting. In briefest outline, a droplet of oily soil attached to the substrate forms at equiUbrium a definite contact angle at the oil-sohd-air boundary line. This contact angle (Fig. 4) is the result of the interaction of interfacial forces in the three phase boundaries of the system. These interfacial forces, expressed in mN/m(= dyn/cm), or interfacial free energy values expressed in mj/m (erg/cm s) are conveniently designated 1SA iSlj subscripts relate to the Hquid-air,... 

Regardless of which, or which combination, of the above mechanisms is responsible for adhesion in a given case, intimate molecular contact between the adhesive and adherend is required. This means that the contact angle of the liquid adhesive against the adherend surface should be as low as possible, and preferably 0°. For the case of contact adhesion, this is immediately evident, but in cases where mechanical interlocking is the primary mechanism for adhesion it is also the case because the adhesive must first be able to flow or wick into the pores of the... 

The use of the harmonic mean often leads to better predictions of interfacial tensions between polymers and better contact angles between liquids and polymer solids, but the criterion for maximization of the work of adhesion is the same as... 

The contact angles of water and adhesive resin on wood are higher in the case of freshly harvested wood compared to stored chips. This means that the surface of particles from this fresh wood is more hydrophobic. This influences the wetting and the penetration negatively and with this the gluability. Reason for this lower wettability of freshly harvested wood is a higher content of some wood chemical components, or wood extractives, as has been determined by water extraction. This result, however, must not be confused with the better wettability of a freshly cut surface, independently if it is freshly harvested or stored wood. 

Physically, the wetting abdity increases (the contact angle decreases) as the values of the fractal dimension of the electrode increases if the electrode material is same. However, in this study, we could not obtain a good correlation between the fractal dimensions and the wetting abilities as shown in Table 1. It means that not only the physical properties such as the surface irregularity and roughness but also the chemical interaction between electrolyte and electrode were important in wetting ability. 

Contact angle measurements for a water droplet on an asphaltene modified borosilicate surface confirmed that low concentrations of TFSA molecules change the wettability of the surface from fractionally-wet to water-wet. Table II shows the results of the contact angle measurements all reported results are the average of 10 separate measurements, none of which varied from the mean by more than 5° As the concentration of the TFSA... 

The sketch in Fig. 10 shows the equilibrium of forces with an obtuse contact angle in the oil phase (6o). In this case the wetting tension, j, of the aqueous phase is positive, which means that the adhering oil droplet is pushed together by the aqueous phase. With the increase in j the tendency of an oil droplet to be cut off and removed from a solid substrate increases. Because of this, the impeding force for the removal of oil is the interfacial tension oil/water (Yq )> which should be minimized. By minimization of the interfacial tension, moreover, the requirements for emulsification and stabilization of soil in the washing and cleaning liquid will be improved. 

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