Wetting meniscus, shape

It should be noted that on the receding cycle the wet plate surface has previously interacted with water molecules for a different period of time depending on the immersion depth of the plate. Therefore, the bottom deeper immersed portions of the plate interact with the water molecules for a longer period than the shallow immersed portions closer to the top of the plate. This causes small but continuous changes in the meniscus shape even after the three-phase contact line starts to move in the advancing and receding processes. 

Figure 2.7 Schematic diagram of the shape of a meniscus for wetting and non-wetting liquids.

A similar technique can be used to study the rheological properties of liquid films. Figure 4 shows the formation of a W/O/W emulsion film with two, identical aqueous phases (such as in water-in-oil emulsions) at the tip of the capillary. A pre-requisite of the experiment is that the surface of the capillary must be well wetted by the film phase, i.e., it should be hydrophobic in this case. First, an aqueous drop is formed inside the oil (film liquid) and the aqueous phase is in the bottom of the cuvette. Then, the level of the aqueous phase is slowly increased. As the oil/water interface passes the drop, a cap shaped oil film, bordered by a circular meniscus, covers the drop. This film can be studied in equilibrium and in dynamic conditions, similar to the single interfaces (See above). The technique can be used to study films from oil or aqueous phase which can be sandwiched between identical or different liquid or gas phases. 

Figure 26.16 Effect of plasma treatment on dynamic hysteresis, which is the difference in the d5mamic first cycle advancing line and the receding line, (AF/L)d (mN/m) = (F/L)D,a,i — (F/T)D,r,i IS a direct result of the changing shape of the meniscus during a wetting cycle.

Kim, I. and Wayner, P., (1996) Shape of an evaporating eompletely wetting extended meniscus. Journal of Thermophy.sics and Heat Transfer, Vol. 10, pp.320-325... 

The meniscus in a tube with triangular cross-section is of complex shape because liquid is held in the comers of the tube (see Fig. 2). We will call these parts of the meniscus arc-menisci (or AM for short) because their cross-section is a circular arc. The three arc menisci are on the dryside (D) and merge into the main terminal meniscus (MTM). The part of the tube filled with wetting liquid is referred to as the wetside (W)... 

An approximate treatment of the phenomenon of the capillary rise can be easily made in terms of Laplace s equation. If the liquid wets the wall of the capillary, the liquid surface is forced to lie parallel to the wall, and the liquid surface has to be concave in shape. The pressure in the liquid below the surface is less than that in the gas phase above the liquid surface. If the capillary is circular in cross section and not too wide in radius, the meniscus will be approximately hemispherical, as is illustrated in Figure 6.5. Such a case is described well by Eq. (6.11). If h denotes the height of the meniscus above the flat liquid surface, then at equilibrium, AP must also be equal to the hydrostatic pressure of the liquid column inside the capillary. Thus AP = Apgh, where Ap is the difference in density between the liquid and gas phases and g is the acceleration due to gravity. Equation (6.11) then becomes... 

An interesting phenomenon based on capillarity is the appearance of a capillary attractive force between particles of moistened solids. As a result of wetting, a meniscus is formed upon the particle contact (Fig. 1-14). This meniscus between two contacting particles of radii r0 has a shape of surface of rotation, and can be characterized at each point by the two curvature radii r, and r2 (in Fig. 1-14, a these radii are of opposite sign, i.e. r,>0 and r2<0), which are related to each other as 1/r, + /r2 = const. If r, r0, both rx and r2 may be considered to be constant. 

Fig. 1-14. The shape of the meniscus is indicative of the strength of the capillary attractive force, F, between two wetted particles...

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