Wetting preferential

Koopal and co-workers [186] have extended this thermodynamic analysis to investigate the competitive wetting of a solid by two relatively immiscible liquids. They illustrate the tendency of silica to be preferentially wet by water over octane, a phenomenon of importance in oil reservoirs. 

Froth flotation (qv) is a significant use of foam for physical separations. It is used to separate the more precious minerals from the waste rock extracted from mines. This method reHes on the different wetting properties typical for the different extracts. Usually, the waste rock is preferentially wet by water, whereas the more valuable minerals are typically hydrophobic. Thus the mixture of the two powders are immersed in water containing foam promoters. Also added are modifiers which help ensure that the surface of the waste rock is hydrophilic. Upon formation of a foam by bubbling air and by agitation, the waste rock remains in the water while the minerals go to the surface of the bubbles, and are entrapped in the foam. The foam rises, bringing... 

In pelletizing, the water—carbon slurry is contacted with a low viscosity oil which preferentially wets the soot particles and forms pellets that are screened from the water and homogenized into the oil feed to the gasification reactor (see Size enlargement). 

Flushing a. Dispersion into a SeeondLiquid. If a dispersion in one Hquid is mixed with a second Hquid which is immiscible with the first but which preferentially wets the powder, the powder transfers into and becomes dispersed in the second Hquid. This process, called flushing, is sometimes... 

The use of a water-immiscible Hquid to separate coal from impurities is based on the principle that the coal surface is hydrophobic and preferentially wetted by the nonaqueous medium whereas the minerals, being hydrophilic, remain suspended in water. Hence, separation of two phases produces a clean coal containing a small amount of a nonaqueous Hquid, eg, oil, and an aqueous suspension of the refuse. This process is generally referred to as selective agglomeration. 

Holdup and Flooding At this point it is useful to introduce the concepts of holdup and flooding in column contactors. It is normal practice to select the phase which preferentially wets the internals of the column as the continuous phase. This then allows the dispersed phase to exist as discrete droplets within the column. If the dispersed phase were to preferentially wet the internals, this could cause the dispersion to prematurely coalesce and pass through the column as rivulets or streams which would decrease interfacial area and therefore column efficiency. 

If a hydrophobic solid is suspended in water and a small amount of oil is added to the system, the oil will preferentially wet out the solid. If a sufficient amount of oil is added, the oil films are brought together and coalescence (a first-order reaction) and agglomeration (a second-order reaction) take place. 

An empty vessel may be employed, but horizontal baffles can be used to reduce turbulence and assist the coalescence through preferential wetting of the solid surface by the disperse phase. More elaborate methods to assist the coalescence include the use of mesh pads in the vessel or the use of an electric field to promote coalescence. Chemical additives can also be used to promote coalescence. 

Solvent additives to the melt (Table 3) fall into two categories extractive and reactive. The extractive solvents (decane, perchloroethane, o-dichlorobenzene, and pyrrolidine) had negligible effect on solubility, possibly due to the preferential wetting of the coal by the solvent and exclusion of the ZnCl2 melt. Reactive solvents (anthracene oil, indoline, cyclohexanol, and tetralin) all incorporated strongly. Donor solvents, tetralin and indoline, increase the "corrected solubility, whereas anthracene oil and cyclohexanol have negligible effect. 

Graphs of relative permeability are generally similar in pattern to that shown in Figure 5.10. As shown, some residual water remains in the pore spaces, but water does not begin to flow until its water saturation reaches 20% or greater. Water at the low saturation is interstitial or pore water, which preferentially wets the material and fills the finer pores. As water saturation increases from 5 to 20%, hydrocarbon saturation decreases from 95 to 80% where, to this point, the formation permits only hydrocarbon to flow, not water. Where the curves cross (at a saturation... 

In some applications, there may be simultaneous flow of two immiscible liquids, or of a liquid and a gas. In general, one of the liquids (or the liquid in the case of liquid-gas systems) will preferentially wet the particles and flow as a continuous film over the surface of the particles, while the other phase flows through the remaining free space. The problem is complex and the exact nature of the flow depends on the physical properties of the two phases, including their surface tensions. An analysis has been made by several workers including Botset(12) and Glaser and Litt(13). 

Figure 4.6. Definition of the contact angle 0 for a particle adsorbed at the water-oil interface. Case where the particle is preferentially wetted by (a) water and by (b) oil.

Fig. 6 Illustration of surface energy effects on the self-assembly of thin films of volume symmetric diblock copolymer (a). Sections b and c show surface-parallel block domains orientation that occur when one block preferentially wets the substrate. Symmetric wetting (b) occurs when the substrate and free surface favor interactions with one block B, which is more hydrophobic. Asymmetric wetting (c) occurs when blocks A and B are favored by the substrate and free surface, respectively. For some systems, a neutral substrate surface energy, which favors neither block, results in a self-assembled domains oriented perpendicular to the film plane (d). Lo is the equilibrium length-scale of pattern formation in the diblock system...

The size of the capillary openings must be relatively large (Tl). The fibers must be preferentially wetted by the dispersed phase (R2, Tl). 

Under the conditions just discussed the solid surface is rigid whilst the two liquids are brought into contact with the solid. The effect of preferential wetting of a solid surface by liquids can also be investigated by the examination of the distribution of fine solid particles placed near the interface of two immiscible liquids. 

If cts2 > cTsi + the solid particles will be preferentially wetted by the first liquid and both the second liquid and the interface will be clear and free from solid (i). 

Experiments illustrating these various possible reactions have been carried out notably by Reinders (Z it. Roll. Ghem. xiii, 235, 1913) and by Hofmann (Zeit. Phys. Ghem. Lxxxiii. 385,. 1913). Finely divided calcium sulphate is preferentially wetted by water in the presence of liquids, such as chloroform and benzene which are frequently termed non-polar or slightly polar. Silver iodide suspensions in water will go into the dineric interface in contact with ether, chloroform and benzene, but are removed from the water by preferential wetting in the case of butyl and amyl alcohols, whilst the reverse holds true in the case of aqueous suspensions of arsenious sulphide. 

Comparison of the G/A complex coacervate and supernatant aging curves against lemon oil 2 in Figures 7 and 13 reveals that the G/A complex coacervate phase consistently has an IFT below that of the G/A supernatant phase between 40 and 50°C. This is evidence that the complex coacervate phase will preferentially wet and encapsulate lemon oil 2 at these temperatures. 

The data in Figures 10 and 14 show that the G/P complex coacervate phase gives a lower IFT against lemon oil 1 at 50°C than the supernatant phase. Thus, at 50°C the G/P complex coacervate phase should preferentially wet and encapsulate the lemon oil 1 phase. 

The low IFT value found immediately after formation of the G/P complex coacervate phase/lemon oil 1 interfaces at 45°C also favors preferential wetting of lemon oil 1 by the G/P complex coacervate phase. The G/P complex coacervate phase is too viscous for an IFT measurement at 40°C, and it has gelled at 35°C, so wetting of lemon oil 1 by a G/P complex coacervate phase should not be a problem during a G/P complex coacervation encapsulation process. 

The reverse is true at 45°C. The 40°C IFT data indicate that a G/GA complex coacervate phase will not preferentially wet or encapsulate lemon oil 1 at 40°C while encapsulation will occur at 45°C. This is consistent with the experimental observation that changes in wetting behavior of a G/GA complex coacervate phase occur during G/GA encapsulation processes. Additional IFT data at 35°C are needed to complete the picture. Such data should yield IFT values for the G/GA complex coacervate phase/lemon oil 1 interface below those of the G/GA supernatant phase, since the G/GA encapsulation process has been used to encapsulate lemon oil. 

Eadie, in Ref 69, reports on a considerable amount of work done on the ability of beeswax and paraffin wax to remain coated on HMX surfaces when immersed in liq TNT. Thru measurements of contact angles, a technique used earlier on RDX/wax systems reported on by Rubin in Ref 23, it was determined that the TNT preferentially wets the HMX and the wax is stripped away. He concludes that the most important property of a desensitizing wax is that it should be readily dispersed uniformly thruout the TNT phase. He also suggests that a better desensitizer for investigation for use would be a wax or substituted hydrocarbon having a low interfacial tension with TNT. The smaller the wax droplet size the more efficiently it will be distributed and the more effectively it should desensitize. Williamson (Ref 64) in his examination of the microstructures of PETN/TNT/wax fusion-casts detected that wax is dispersed thru the cast as isolated descrete globules which he refers to as blebs or irregular or streak-like areas, surrounded by TNT (see also Ref 54)... 

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