Contact line displacement

Fig. 11 Effect of nanoparticle diameter on contact line displacement...

Fig. 12 Effect of nanoparticle volume fraction on contact line displacement at high interfacial tension...

In the heterogeneous wetting regime, air can instead be trapped inside the features underneath the liquid drop, which ideally stands on the top of the nanostructures. This situation (schematized in Figure 4.8c) is described by the Cassie-Baxter model. The free energy variation following the contact line displacement is ... 

The effect of the nanoparticle volume fraction on the displacement of the contact line becomes pronounced only at higher volume fractions. For example, the displacement of the contact line is 10 times the nanoparticle diameter or approximately 0.2 im for a nanoparticle volume fraction of 0.25, while there is no appreciable change in the contact line position when the volume fraction is 0.2. This non-linear dependence of contact line position on nanoparticle volume fraction is consistent with the form of Eq. 10, where the film energy contribution due to structural disjoining pressure is subtracted from the surface energy contribution. The extent of displacement of the con-... 

We have considered the case of a fluid wedge that can deform under the action of the disjoining pressure. Our simulations show that the extent of deformation of the meniscus (or fluid interface) increases with increase in the volume fraction of nanoparticles/micelles, when a decrease in the diameter of micelles and with a decrease in the capillary pressure resisting the deformation is smaller. The resulting deformation of the meniscus causes the contact line to move so that it displaces the fluid that does not contain the micelles (oil) in favor of the fluid that contains it (aqueous surfactant solution). 

When two droplets - one of surfactant solution and the other of oily soil - are set on a solid surface, on the basal plane two wetting tensions jA and jB will act [3]. When the two droplets approach each other, so that a common interface is formed, at the contact line the difference of the wetting tension will act. This parameter is called oil displacement tension ... 

Hysteresis is a static phenomenon, but its measurement requires displacement of the contact line (fig, 5.4). Immediately the question is raised as to what are the... 

It is important to remember that many dynamic wetting processes act in the presence of wetting agents as a special type of surfactants. In contrast to very low displacements of the contact line where no shear stresses exist and the adsorption equilibrium is established, at higher speeds the modelling of the process (overlap of surface energetic and hydrodynamic forces) becomes very difficult and a lot of boundary conditions must be simplified. 

Consider the case where the substrate is perturbed in a periodic manner in the y direction. In a region of size D in the vicinity of each defect, the substrate is perturbed with a strength wq and is unperturbed outside that region. Using Eq. (4.38) and the appropriate representation of the defect free energy, calculate the displacement of the contact line at x = 0. 

Sheng P, Zhou M (1992) Immiscible-fluid displacement contact-line dynamics and the velocity-dependcmt capillary pressure. Phys Rev A 45 5694-5708... 

A key factor in the consideration of the interfacial movement is the mechanism by which the three phase line moves. The easiest mechanism to envisage is when the displacing phase moves over a thin film of the displaced phase, i.e., the three phase line is only apparent, as in the definition of completely water wet introduced above. For a real three phase contact line, molecular pictures have been attempted (22). Still uncertain is whether the displacement of the three phase contact line results in a resistance to the flow. Measurements reported by Jacobs (21) have suggested that the presence of surfactants is associated with me-niscal resistance to flow, although the mechanism is obscure. 

Note that equation (5.40) neglects the viscous dissipation associated with the displacement of the contact line—a topic to be discussed in chapter 6. We will see then that this simplification assumes 2 to be rather large [Z > lOR/0e) ... 

The velocity potential ip is the field variable, and the free surface y may be expressed in terms of p> by the free surface boundary conditions and the contact line conditions at the vertical sidewalls.h The velocity potential ip and the free surface displacement r] are assumed to be linear combinations of the progressive wavemaker wave and the parametrically excited cross wave given by the following ... 

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