Solid wettability

Binks, B. P. Clint, J. H. Solid Wettability from Surface Energy Components Relevance to Pickering Emulsions. Langmuir 2002, 18,1270-1273. 

Rapid fluid flow cannot be achieved with active metal brazes because of the need to form solid wettable reaction product layers for their liquid fronts to advance. Equations (10.1) to (10.2) relating liquid flow rates to the opposed effects of surface energy imbalances and of viscous drag are not relevant. Actual penetration rates are so slow, usually of the order of 1 pm.s, that the usual practice is to place the active metal braze alloy within the joints rather than expecting it to fill them, and, as explained already, gap width is not the dominant consideration when designing ceramic-metal joints. 

Their data indicate that the flow transition from gas-continuous to pulsed flow occurs at higher- gas and liquid flow rates for nonwettable solids compared to wettable solids. The change in transition condition due to solids wettability occurs because a major fraction of the liquid tends to flow as rivulets over the nonwettable surface and, thus, delays the formation of a liquid film capable of blocking the interstices between the particles. Furthermore, an increase in bed porosity will also move the transition to occur at higher gas and liquid flow rates. 

Physical State Liquid (Solution for infusion) SoUd Solid, wettable powder liquid. Solid below 36 F... 

Both Emf and hence also C/mf (see Fig. 4) can be significantly reduced by pulsing the fluidizing liquid (El-Temtamy and Epstein, 1986). On the other hand, neither is affected significantly by changes in solids wettability (Mitra and Epstein, 1978). For non-Newtonian liquids that can be represented by the power-law model, an approach analogous to Eq. (17) has been successful in predicting f/mf for liquid-solid fluidization of monosize spheres (Miura and Kawase, 1997, 1998). 

Bhatia, V.K., K.A. Evans and N. Epstein. "Effects of Solids Wettability on Expansion of Gas-Liquid Fluidized Bed" lEC Process Des. Develop 11(1972)151-152. 

An "entropy analysis of the liquid flow through the percolation structures allow us to derive a theoretical expression of flow distribution. This expression may be used as the basis of averaging formula of various hydrodynamic mecanisms. The resulting models involve both parameters characterizing the mechanism modeled at the particle scale and a parameter defining the effective solid wettability, i.e. the minimum liquid velocity u. The various models analysed in this paper and compared with experiments yield logical variations of the parameter u with the operating conditions (solid wettability, liquid viscosity). 

The effect of solid wettability on the shape of adsorbed aggregates was first proposed to explain the formation of hemicylindrical SDS micelles on graphite [40]. The strong correlation between the crystallographic axis and the axis of the adsorbed micelle suggests that, for graphite, the main effect causing hemimicelle formation is actually the epitaxial adsorption of alkyl chains (see Section lll.A). However, the effect of wettability has also been tested on a substrate that does not direct epitaxial adsorption. 

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). 

Fig. 21. Performance cut diameter prediction for typical sieve plate operation on wettable particulates at foam densities F solid line, F = 0.4 g/cm, dashed...

Solids separation based on density loses its effectiveness as the particle size decreases. For particles below 100 microns, separation methods make use of differences in the magnetic susceptibility (magnetic separation), elec trical conductivity (electrostatic separation), and in the surface wettability (flotation and selec tive flocculation). Treatment of ultrafine solids, say smaller than 10 microns can also be achieved by utilizing differences in dielectric and electrophoretic properties of the particles. 

Mixed liberated particles can be separated from each other by flotation if there are sufficient differences in their wettability. The flotation process operates by preparing a water suspension of a mixture of relatively fine-sized particles (smaller than 150 micrometers) and by contacting the suspension with a swarm of air bubbles of air in a suitably designed process vessel. Particles that are readily wetted by water (hydrcmhiric) tend to remain in suspension, and those particles not wetted by water (hydrophobic) tend to be attached to air bubbles, levitate (float) to the top of the process vessel, and collect in a froth layer. Thus, differences in the surface chemical properties of the solids are the basis for separation by flotation. 

Flotation is a physical process involving relative interaction of three phases solid, water, and air. An understanding of the wettability of the solid surface, physical surface, and chemical phenomena by which the flotation reagents act and the mechanical factors that determine particle-bubble attachment and removal of particle-laden bubbles, is helpful in designing and operating flotation systems successfully. 

Albertsson (Paiiition of Cell Paiiicle.s and Macromolecules, 3d ed., Wiley, New York, 1986) has extensively used particle distribution to fractionate mixtures of biological products. In order to demonstrate the versatility of particle distribution, he has cited the example shown in Table 22-14. The feed mixture consisted of polystyrene particles, red blood cells, starch, and cellulose. Liquid-liquid particle distribution has also been studied by using mineral-matter particles (average diameter = 5.5 Im) extracted from a coal liquid as the solid in a xylene-water system [Prudich and Heniy, Am. Inst. Chem. Eng. J., 24(5), 788 (1978)]. By using surface-active agents in order to enhance the water wettability of the solid particles, recoveries of better than 95 percent of the particles to the water phase were obsei ved. All particles remained in the xylene when no surfactant was added. 

There are numerous techniques which provide information related to the surface energy of solids. A large array of high-vacuum, destructive and non-destructive techniques is available, and most of them yield information on the atomic and chemical composition of the surface and layers just beneath it. These are reviewed elsewhere [83,84] and are beyond the scope of the present chapter. From the standpoint of their effect on wettability and adhesion, the property of greatest importance appears to be the Lifshitz-van der Waals ( dispersion) surface energy, ys. This may be measured by the simple but elegant technique of... 

The main purpose of pesticide formulation is to manufacture a product that has optimum biological efficiency, is convenient to use, and minimizes environmental impacts. The active ingredients are mixed with solvents, adjuvants (boosters), and fillers as necessary to achieve the desired formulation. The types of formulations include wettable powders, soluble concentrates, emulsion concentrates, oil-in-water emulsions, suspension concentrates, suspoemulsions, water-dispersible granules, dry granules, and controlled release, in which the active ingredient is released into the environment from a polymeric carrier, binder, absorbent, or encapsulant at a slow and effective rate. The formulation steps may generate air emissions, liquid effluents, and solid wastes. 

Sec. Ill is concerned with the description of models with directional associative forces, introduced by Wertheim. Singlet and pair theories for these models are presented. However, the main part of this section describes the density functional methodology and shows its application in the studies of adsorption of associating fluids on partially permeable walls. In addition, the application of the density functional method in investigations of wettability of associating fluids on solid surfaces and of capillary condensation in slit-like pores is presented. 

Roy et al. (R3) define the critical solids holdup as the maximum quantity of solids that can be held in suspension in an agitated liquid. They present measurements of this factor for various values of gas velocity, gas distribution, solid-particle size, liquid surface tension, liquid viscosity, and a solid-liquid wettability parameter, and they propose the following two correlations in terms of dimensionless groups containing these parameters ... 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

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