Dispersions, sohd

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

This is because the effect of the dispersed soHd, rather than the dispersing medium, is usually more significant. However, the latter should not be ignored. Many industrial problems involving unacceptably high viscosities in dispersed systems are solved by substituting solvents of lower viscosity. 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

Creams tend to be invisible on the skin. The same is true for ointments, although the oiliness of ointments causes them to glisten to an extent. Whatever opacity creams and ointments have is due primarily to the presence of insoluble soHds. These often imbue applications with a powdery or even crusty appearance. Dispersed soHds are usually functional, as in calamine lotion, zinc sulfide lotion, zinc oxide paste, and so on, and are an implacable feature of these preparations. However, at times insoluble soHds are added as tints to match the color of the skin and to impart opacity. Since individual skins vary widely in hue (pigmentation) and texture, tinting to a single color and texture is generally unsuccessful. 

Chibowski, S., Zeta potential and thickness of a polymer adsorbed layer in the system dispersed sohd-electrolyte, Pol. J. Chem., (H. 1137, 1993. 

EP 1319706 06/2003 Ramcharen et al.l Unilever Dispersed sohd in a hquid detergent in a water-soluble pouch... 

Fagerquist CK, Lightfleld AR, Lehotay SJ, Confirmatory and quantitative analysis of fS-lactam antibiotics in bovine kidney tissne by dispersive sohd-phase extraction and liquid chromatography-tandem mass spectrometry. Anal. Chem. 2005 77 1473-1482. 

For the mechanical high-shear devices, there is quite a bit of empirical and proprietary data on how these devices disperse sohds, liquids, and gasses in a continuous medium. It turns out that many types of these devices have become inherent tools in a particular industry and that the performance is empirically studied and correlated to give the resulting final product. 

Solid-Phase Components. Dispersed sohds are vital ingredients in commercial antifoam formulations. Much of the cmrent theory on antifoaming mechanism ascribes the active defoaming action to this dispersed solid phase with the liquid phase primarily a carrier fluid, active only in the sense that it must be surface-active in order to carry the solid particles into the foam films and cause destabilization. For example, PDMS, despite its considerable effectiveness in nonaqueous systems, shows little foam-inhibiting activity in aqueous surfactant solutions. It is only when compounded with hydrophobic silica [7631-86-9] to give the so-called silicone antifoam compounds that highly effective aqueous defoamers result. The three main solid-phase component classes are hydrocarbons, silicones, and fluorocarbons. 

Uvarov N, lusupov V, Sharama V, Shukla K (1992) Effect of morphology and particle size on the ionic conductivities of composite solid electrolytes. Solid State Ionics 51 41-52 Uvarov NF, Ponomareva VG, Lavrova GV (2010) Composite solid electrolytes. Russ J Electrochem 46(7) 722-733 Vaidehi N, Akila R, Shukla A, Jacob KT (1986) Enhanced ionic conduction in dispersed sohd electrolyte systems CaFj-AljO, and CaF -CeO. Mater Res Bull 21 909-916... 

These metal hydrogenation catalysts do not dissolve in organic solvents. The catalytic hydrogenation of alkenes is a heterogeneous reaction, and the solution of the alkene must be stirred or shaken vigorously so that the reactants remain in contact with the dispersed sohd phase. Solvents commonly used are ethanol (CH CH OH) and methanol (CHjOH). 

All liquid—polymer mixed-mattix membranes have liquid polymer encapsulated in the continuous polymer matrix. The long-term stabUity of these membranes for industrial gas separation processes is stUl a critical issue because of the undesirable leakage of the liquid from the membrane. To stabilize the hquid in the polymer membrane, a new type of mixed-matrix membranes, solid—hquid—polymer mixed-matrix membranes, has been developed most recentiy. The sohd, such as activated carbon impregnated with liquid polymer such as PEG, functions as a stabilizer of the hquid polymer in the continuous polymer phase. These hybrid sohd—hquid—polymer mixed-matrix membranes combine the properties of the continuous polymer phase, the dispersed sohd filler phase, and the impregnated liquid phase. 

Horio M, Kuroki H Three-dimensional flow visualization of dUutely dispersed sohds in bub-bhng and circulating fluidized beds, Chem Eng Sd 49 2413—2421, 1994. http / dx.doi. org/10.1016/0009-2509(94)E0071-W. 

Magnetorheological materials (fluids) are the magnetic equivalent of electrorheological fluids. In this case, the particles are either ferromagnetic or ferrimagnetic sohds that are either dispersed or suspended within a Hquid and the apphed field is magnetic (14). 

X-rays are collected and analy2ed in ema in one of two ways. In wds, x-rays are dispersed by Bragg diffraction at a crystal and refocused onto a detector sitting on a Rowland circle. This arrangement is similar to the production of monochromati2ed x-rays for xps described above. In the other approach, edx, x-rays are all collected at the same time in a detector whose output scales with the energy of the x-ray (and hence, Z of the material which produces the x-ray.) Detectors used for ema today are almost exclusively Li-drifted Si soHd-state detectors. 

Fig. 19. Correction factor for axial dispersion as a function of NTU. SoHd lines are rigorous calculations broken lines, approximate formulas according to hterature (61). (a) Numbers on lines represent Pe values Pe = 20 /Lj = 0.8. (b) For design calculations. Numbers on lines represent Pep u ...

In order to maintain a definite contact area, soHd supports for the solvent membrane can be introduced (85). Those typically consist of hydrophobic polymeric films having pore sizes between 0.02 and 1 p.m. Figure 9c illustrates a hoUow fiber membrane where the feed solution flows around the fiber, the solvent—extractant phase is supported on the fiber wall, and the strip solution flows within the fiber. Supported membranes can also be used in conventional extraction where the supported phase is continuously fed and removed. This technique is known as dispersion-free solvent extraction (86,87). The level of research interest in membrane extraction is reflected by the fact that the 1990 International Solvent Extraction Conference (20) featured over 50 papers on this area, mainly as appHed to metals extraction. Pilot-scale studies of treatment of metal waste streams by Hquid membrane extraction have been reported (88). The developments in membrane technology have been reviewed (89). Despite the research interest and potential, membranes have yet to be appHed at an industrial production scale (90). 

Many substances used in modem processing industries occur in a mixture of components dispersed through a soHd material. To separate the desired solute constituent or to remove an unwanted component from the soHd phase, the soHd is contacted with a Hquid phase in the process called Hquid—soHd extraction, or simply leaching. In leaching, when an undesirable component is removed from a soHd with water, the process is called washing. 

Aqueous Dispersions. The dispersion is made by the polymerization process used to produce fine powders of different average particle sizes (58). The most common dispersion has an average particle size of about 0.2 p.m, probably the optimum particle size for most appHcations. The raw dispersion is stabilized with a nonionic or anionic surfactant and concentrated to 60—65 wt % soHds by electrodecantation, evaporation, or thermal concentration (59). The concentrated dispersion can be modified further with chemical additives. The fabrication characteristics of these dispersions depend on polymerization conditions and additives. 

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