Contact angles interactions

Contact angle Interaction to a liquid probe, three-phase angle Surface tension Type of liquid, roughness, chemical heterogeneity Static and dynamic experiments... 

Equations II-12 and 11-13 illustrate that the shape of a liquid surface obeying the Young-Laplace equation with a body force is governed by differential equations requiring boundary conditions. It is through these boundary conditions describing the interaction between the liquid and solid wall that the contact angle enters. 

The surface film or sprea ding pressure, FI, is used to account for the change in gas—soHd interaction caused by adsorption of vapor evaporated from the Hquid. A Hquid is called wetting if the contact angle from soHd to Hquid through gas, 65 0 nonwetting if > 90°. Because it is easier to... 

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,... 

A requirement underlying the validity of Zisman plots is that there be no specific interactions, such as acid-base interactions, between the solid surface and the probe liquids. Such interactions, however, can, in principle, be taken into account by Young s equation, provided the contact angle remains finite. Their... 

Wetting and capillarity can be expressed in terms of dielectric polarisabilities when van der Waals forces dominate the interface interaction (no chemical bond or charge transfer) [37]. For an arbitrary material, polarisabilities can be derived from the dielectric constants (e) using the Clausius-Mossotti expression [38]. Within this approximation, the contact angle can be expressed as ... 

The change in surface wettability (measured by the contact angle) with concentration for the three surfactants is plotted in Fig. 2.54 (Zhang and Manglik 2005). The contact angle reaches a lower plateau around the CMC where bilayers start to form on the surface. Wettability of non-ionic surfactants in aqueous solutions shows that the contact angle data attains a constant value much below CMC. Direct interactions of their polar chain are generally weak in non-ionics, and it is possible for them to build and rebuild adsorption layers below CMC. The reduced contact an-... 

The decrease in the contact angle and corresponding increase in the work adhesion of the modified surfaces are due to the generation of polar carbonyl (C=0) and ether (C=0=C) groups on the surfaces formed through interaction of macroradicals on EPDM backbone with atmospheric oxygen. The results have been confirmed from IR (Figure 31.4) and X-ray photoelectron spectroscopic (XPS) observation (Table 31.5). 

For aq.KOH on mica, the dependence of the effective contact angle on droplet height is mnch weaker than that for the aq.KOH-graphite system. The estimated Hamaker constant of the van der Waals interaction for this system is -1.9 X 10 ° J (repnlsive), and the fitting gives ... 

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. 

The predominant form of released petroleum products is a liquid that is immiscible with water this is called the free product (in this section it will be referred to as oil). The behavior of water and oil in soil depends on the interaction of the three phases water, oil, and soil. The affinity of water or oil with the soil can be estimated by establishing the contact angle of oil/water/soil triple line. 

A solid is not wetted if k < -1, partly wetted for -1< k< 1 and fully wetted for k > 1. Wetting is favoured when the difference (yss - ysl) approaches and becomes larger than o s. In this case the interaction between the droplet and the substrate increases and the contact angle decreases. It follows that materials with high surface energy are better substrates for deposition of another phase than substrates with low surface energy. One consequence is that metal surfaces are often readily wetted while polymeric surfaces often are not. 

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