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Droplet approach

It is also possible to simulate liquid droplets by surrouridiu g a solute by a fin ite ii urn ber of water moleeu les an d perform in g the sim -ulalion without a periodic box. The water, of course, eventually evaporates and moves away from the solute when periodic boundary con ditioii s arc n ot im posed. If the water is in itially added via periodic boundary con dition s, you rn ust edit the resu Itin g H IN file to remove th e periodic boti ruiary con ditioii s, if a droplet approach is desired. [Pg.201]

In TFB technique, the thin film radius is typically of the order of 100 pm, far larger than the contact film radius likely to be formed when two micron-sized droplets approach. The magnetic chaining technique overcomes this limitation, allowing the direct measurement of force-distance profiles between liquid colloidal droplets. This technique exploits the properties of monodisperse ferrofluid... [Pg.55]

The state of stability under these conditions can be qualitatively described as follows. As two oil droplets approach each other, the negative charge gives rise to a repulsive effect (Figure 7.4). The repulsion will take place within the electrical double-layer (EDL) region. It can thus be seen that the magnitude of double-layer distance will decrease if the concentration of ions in the water phase increases. This is because the electrical double layer region decreases. However, in all such cases in which two bodies come closer, there exists two different kinds of forces that must be considered ... [Pg.182]

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 ... [Pg.58]

The interfacial film theory is an extended interfacial tension theory, in which the adsorbed surfactant at the interface surrounds the dispersed droplets forming a coherent thin monolayer film (Figure 4.13). As the droplets approach each other, coalescence is prevented. The stability of the emulsions depends on the characteristics of the monolayer film formed at the interface. Monolayer films are classified as gaseous, condensed, and expanded films. [Pg.226]

In the device presented in Fig. 3.120,a the asymmetric film forms when a water droplet approaches the surface of an organic liquid. The thickness of the film obtained is controlled by either lowering the level of the organic liquid or by rising the water level, with the aid of microscrews. In the cell shown in Fig. 3.120,b the film forms in a capillary contacting a porous material. The principle of action of this device is similar to that employed in the study of foam films formed in the porous plate measuring cell of Exerowa-Scheludko (see Chapter 2, Fig. 2.2C). [Pg.320]

Steric hindrance When a nonionic surfactant adsorbs on an interface between oil and water, the hydrophobic part of the molecule wUl orient itself towards the oily phase, while the hydrophUic part will stick out into the aqueous phase. One can envisage the interface, therefore, as having a coat of hydrophihc chains sticking out of the interface. When two oil droplets approach each other, the two coats would first make contact. The only way that the two droplets can coalesce is when the nonionic surfactant molecules move away from the contact point. However, they are strongly adsorbed and therefore impede the coalescence. Hence, when two droplets with such a layer approach each other, the coats will repel each other. Thus, the droplets will move apart again, and coalescence is prevented. [Pg.308]

Figure 13 shows that the core permeability drops over many injected pore volumes and ultimately levels off. The effluent profile (dashed lines) shows that the oil droplets appear after some time, and their concentration rises slowly and levels off at the inlet value of 0.5%. The time at which the permeability reduction stops is about the same time at which the oil droplets approach their inlet concentration. [Pg.239]

Classical theories of emulsion stability focus on the manner in which the adsorbed emulsifier film influences the processes of flocculation and coalescence by modifying the forces between dispersed emulsion droplets. They do not consider the possibility of Ostwald ripening or creaming nor the influence that the emulsifier may have on continuous phase rheology. As two droplets approach one another, they experience strong van der Waals forces of attraction, which tend to pull them even closer together. The adsorbed emulsifier stabilizes the system by the introduction of additional repulsive forces (e.g., electrostatic or steric) that counteract the attractive van der Waals forces and prevent the close approach of droplets. Electrostatic effects are particularly important with ionic emulsifiers whereas steric effects dominate with non-ionic polymers and surfactants, and in w/o emulsions. The applications of colloid theory to emulsions stabilized by ionic and non-ionic surfactants have been reviewed as have more general aspects of the polymeric stabilization of dispersions. ... [Pg.1557]

DLVO-Theory. The mutual approach of two droplets is a requirement for the coalescence process. Larger droplets approach each other on account of gravitational forces. Smaller droplets show interparticular forces with short distance range, which are responsible for their mutual approach. [Pg.382]

Although the use of fossil fuels in Europe is higher in winter than in summer, the concentration of nitrate in the precipitation is higher in summer, because of the higher photochemical activity. The effect is less pronounced for sulphates, because sulphur dioxide also can be oxidized, after absorption in liquid droplets, catalyti-cally by iron or mangenese ions, or by dissolved ozone and hydrogen peroxide. The limiting factor is that the absorption stops, when the acidity of the droplet approaches pH 3. [Pg.7]

Flocculation and coalescence can be avoided by preventing droplets approaching each other. In fact, flocculation (which may lead to coalescence) is the result of the van der Waals forces between two droplets. These forces act at relatively short distances, and are always attractive. There are two ways to counteract these forces electrostatic repulsion and steric repulsion. [Pg.69]

Dillmann, A., and Meier, G. E. A. (1991) A refined droplet approach to the problem of homogeneous nucleation from the vapor phase, J. Chem. Phys. 94, 3872-3884. [Pg.533]

In process the solvent evaporates before the droplets arrive at the surface and the precipitate impinges upon the surface where it reacts. In process C the solvent evaporates as the droplets approach the substrate and the solid precipitate melts then vapourizes or sublimes and the vapour diffuses to the substrate where the heterogeneous reactions occur and finally in process D at the highest temperatures the compound to be deposited vapourizes before it reaches the substrate surface and a homogeneous chemical reaction takes place in the vapour phase. [Pg.135]

The soluble segments of the polymer chains do not mix but are compressed as the droplets approach each other. [Pg.135]

The pushing out of segments into the aqueous phase (formation of loops and tails) could conceivably have two main effects on stability. The interaction between protein segments, as droplets approach, produces a steric barrier ( ), a result of the free energy increase accompanying a rise in concentration of protein in the interstitial liquid. It is also possible that loops and tails can form bridges between droplets (34), thus promoting flocculation. [Pg.177]


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