Sessile Configurations

The family of so-called bounded sessile configurations, that is, sessile drops and bubbles centered at the axis, belongs to the one-parameter subfamily... 

Two alternate core structures of the ordinary 1/2[110] dislocation, shown schematically in 1 gs. 2a amd b, respectively, were obtained using different starting configurations. The core shown in Fig. 2a is planar, spread into the (111) plame, while the core shown in Fig. 2b is non-plamar, spread concomitcmtly into the (111) amd (111) plames amd thus sessile. The sessile core is energetically favored since when a shear stress parallel to the [110] direction was applied in the (111) plane the planar core transformed into the non-plamar one. However, in a similar study emplo3dng EAM type potentials (Rao, et al. 1991) it was found that the plamar core configuration is favored (Simmons, et al. 1993 Rao, et al. 1995). 

Let us come back to the case of spontaneous wetting in the sessile drop configuration. The variation of the drop base radius R with time can be easily calculated from equation (2.5) replacing 9 by 4v/ttR3, where v is the drop volume, which is accurate to within 10% for 0 < 45°. Thus integration of equation (2.5) with 0F = 0° between R0 at t = 0 and R leads to ... 

Figure 2.18. Dissolut i ve wetting the approach of local (c) and total (d) equilibrium in the sessile drop configuration. In liquid metal/solid metal systems, the characteristic times of the different stages are ti 10-2s,t 10Jsandt3 10s s. According to the calculations of Warren et al. (1998).

Given the complexity of the real situation in the sessile drop configuration, a simplified analysis has been proposed by Mortensen et al. (1997). This neglects reactions at the interface far from the triple line and assumes that diffusion is the dominating mechanism for solute transport in a small volume near the triple line. Inside this volume, modelled as a straight wedge of angle 9, the velocity u is taken equal to U so that equation (2.21) reduces to... 

Selected results of Bailey and Watkins (1951-52) are given in Table 5.5. These demonstrate that configuration 2.a of Figure 5.7 is achieved with a wide range of couples that form intermetallics compounds or in which the liquid member dissolves in the solid. For Ag/Fe, the drop-forming behaviour accords with the results of sessile drop experiments which identified contact angles of 36°-57° as... 

Figure 10.1. Schematic illustration of the influence of contact angles on the profiles of (a) sessile drops, (b) fillets between T configuration components, (c) the entry of liquid into capillary gaps and (d) the microscopic contact between the liquid and the solid components.

LOCALIZED SURFACE CONFIGURATION CHANGE UNDER A SESSILE DROPLET OF WATER... 

Data shown above clearly show that the surface configuration of polymer changes when the contact medium is changed from air to liquid water. The same phenomenon occurs when a sessile droplet of water is placed on the surface of a polymer. In this case, however, the surface configuration change occurs only on the surface, which is under the sessile droplet. When the surface configuration change occurs, it creates the interaction force between the surface and the sessile droplet and holds... 

The more dramatic demonstration of the creation of interaction force between the surface and a sessile droplet of water can be seen in the measurement of the sessile droplet rolling-off angle, of which principle is depicted in Figure 23.16. If the sessile droplet contact angle is high and no surface configuration change occurs, such... 

An empirical method to estimate the surface tension of a solid is Zisman s plot (cos 9 as a function of yl), which obtains the critical surface tension of wetting. In the absence of specific interaction between the surface and the liquids used for the measurement of contact angles, the critical contact angle of wetting can be accurately estimated and its value used as the surface tension of the surface. However, if a surface interacts with liquids used as the sessile droplet for the contact angle measurement, to the extent that the surface tension is altered, Zisman s plots deviate from the ideal linear relationship. In a strict sense, the plot is applicable only to imperturbable surfaces with which liquid contact does not alter surface configuration, i.e., no surface dynamics applies. 

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