Capillary effects

The capillary effect is apparent whenever two non-miscible fluids are in contact, and is a result of the interaction of attractive forces between molecules in the two liquids (surface tension effects), and between the fluids and the solid surface (wettability effects). 

We have described above the main observed phenomena for capillary effects by silver nitrates, however other chemical compounds display a different behaviours as it is described in the next section for lead oxides. 

If there is a large pinhole leak a few inches below tlie liquid surface, it will behave like a leak above the liquid. How ever, a small pinhole leak in the same location may have zero inleakage due to capillary effects. The problem becomes complicated as the depth becomes large, and... 

Capillary phenomena are due to the curvature of liquid surfaces. To maintain a curved surface, a force is needed. In Eq. (8), this force is related to the second term in the integral. The so-called Laplace pressure due to the force to maintain the curved surface can be expressed as, Pl = 2-yIr, where r is the curvature radius. The combination of the capillary effects and disjoining pressure can make a liquid film climb a wall. 

On discs coated with Zdol films 62 A thick or more, droplets with lateral dimensions of tens of micrometers were observed in some areas of the surface, as shown in Figure 16. Apart from that, however, most of the surface was uniform unless disturbed by contact with the SPFM tip. After such contact, a droplet was usually formed due to capillary effects. Once formed, the droplet slowly grows in volume, indicating that the film was in a metastable state. However, no detectable layering in the surrounding region was observed. 

Shale stability is an important problem faced during drilling. Stability problems are attributed most often to the swelling of shales. It has been shown that several mechanisms can be involved [680,681]. These can be pore pressure diffusion, plasticity, anisotropy, capillary effects, osmosis, and physicochemical alterations. Three processes contributing to the instability of shales have to be considered [127] ... 

SPAN module. It was mentioned at the beginning that the special polyacrylonitrile fibers of SPAN have a wall thickness of 30 gm, which is considerably thicker than the 8 gm wall thickness of the SMC modules [19]. As a consequence, the presence of stronger capillary effects from the special porous fiber material of the SPAN module would be a reasonable conclusion. Furthermore, the texture of the special polyacrylonitrile fibers is expected to have better surface properties, supporting the permeation of molecules as compared with synthetically modified cellulose. In conclusion, both convection and diffusion effectively contribute to the filtration efficiency in a SPAN module, whereas for the SMC membrane, diffusion is the driving force for molecular exchange, the efficiency of which is also considerable and benefits from the large surface-to-volume ratio. 

There are three types of mass transport processes within a microfluidic system convection, diffusion, and immigration. Much more common are mixtures of three types of mass transport. It is essential to design a well-controlled transport scheme for the microsystem. Convection can be generated by different forces, such as capillary effect, thermal difference, gravity, a pressurized air bladder, the centripetal forces in a spinning disk, mechanical and electroosmotic pumps, in the microsystem. The mechanical and electroosmotic pumps are often used for transport in a microfluidic system due to their convenience, and will be further discussed in section 11.5.2. The migration is a direct transport of molecules in response to an electric field. In most cases, the moving... 

Fig. 17.12. The determination of typical anions using indirect UV detection. Conditions 10 mM sodium chromate, 2.30 mM cetyltrimethylammonium bromide, 60 cm fused silica capillary (effective length 52 cm) x 75 pm I.D., injection 5 s at 35mbar, 20°C, -15 kV (reversed polarity) resulting in a current of approximately 30 pA, detection UV 254 nm.

Surface tension is responsible for capillary effects and spreading of the NAPL over the water table. At about 20°C, water has a surface tension of 73.05 dyn/cm, whereas CC14 has a surface tension of only 26.95 dyn/cm. Therefore, water will be held in an unsaturated porous media by surface tension to a much greater degree relative to carbon tetrachloride (i.e., the permeability of porous media will be different with respect to each liquid). The ramifications will be important for contaminant transport of mixed wastes. 

Polymerization in microemulsions allows the synthesis of ultrafine latex particles in the size range of 5 to 50 nm with a narrow size distribution [33], The deposition of an ordered monolayer of such spheres is known to be increasingly difficult as the diameter of such particles decreases [34], Vigorous Brownian motion and capillary effects create a state of disorder in the system that is difficult... 

Endohedral doping (encapsulation) of other materials within carbon nanostructures can be carried out by nano-capillary effects or during synthesis (Fig. 4.3(b)). A great variety of halides, oxides, metals and alloys have been encapsulated within CNTs [36-41]. When transition metals are encapsulated, the entire sample can exhibit high magnetic coercivities ca. 0.22 T [42,43]. The encapsulation of C60 molecules can also be accomplished and if the material is heat treated at high temperatures... 

The selective deposition of catalyst particles on the inner or on the outer walls of CNTs is the prerequisite for the investigation or utilization of the confinement effect, as discussed in Section 15.2.3. Wet chemistry methods making use of the capillary effect are most effective however, they depend on surface functionalization and tube diameter. In any case, CNT caps as well as radial carbon sheets and walls blocking parts of the inner CNT cavity have to be removed prior to impregnation, e.g., by mild oxidative treatment. The impregnation of this material with a limited amount of liquid can lead... 

PLATE I Determination of the enantiomeric purity of active pharmaceutical ingredient (main compound = MC, peak I is the enantiomeric impurity). Conditions lOOmM sodium phosphate buffer pH = 3.0, lOmM trimethyl -cyclodextrin, 60 cm fused silica capillary (effective length 50 cm) X 75 pm I.D., injection 10 s at 35 mbar, 25°C, 20 kV (positive polarity) resulting in a current of approximately lOOpA, detection UV 230 nm. The sample solution is dissolved in a mixture of 55% (v/v) ethanol in water. (A) Typical electropherogram of an API batch spiked with all chiral impurities, (B) overlay electropherograms showing the selectivity of method toward chiral and achiral impurities, a = blank, b = selectivity solution mixture containing all known chiral and achiral compounds, c = API batch, d = racemic mixture of the main compound and the enantiomeric impurity. 

Diffusion through pores to the reaction zone will be enhanced by the ultrasonic capillary effect. 

Divisek et al. presented a similar two-phase, two-dimensional model of DMFC. Two-phase flow and capillary effects in backing layers were considered using a quantitatively different but qualitatively similar function of capillary pressure vs liquid saturation. In practice, this capillary pressure function must be experimentally obtained for realistic DMFC backing materials in a methanol solution. Note that methanol in the anode solution significantly alters the interfacial tension characteristics. In addition, Divisek et al. developed detailed, multistep reaction models for both ORR and methanol oxidation as well as used the Stefan—Maxwell formulation for gas diffusion. Murgia et al. described a one-dimensional, two-phase, multicomponent steady-state model based on phenomenological transport equations for the catalyst layer, diffusion layer, and polymer membrane for a liquid-feed DMFC. 

Reynolds excepts from the general validity of Antonow s rule the tension of mercury and amalgams against certain electrolytes and immiscible liquids which react chemically. It is clear that the rule would be difficult to verify satisfactorily in the latter case with mercury in contact with aqueous solutions (or with water) the apparent deviation from the rule is. probably to be accounted for by consideration of the electro-capillary effects (Oh. vn). 

Grimley (Gil) has shown experimentally that for tubes of very small diameter there is an additional capillary effect on the film thickness. 

Benjamin (B5) has given a detailed treatment of the onset of two-dimensional instability in film flow, taking capillary effects into account. The expression for neutral stability found in this work can be given as... 

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