Dispersions, coarse molecular

The defined size ranges and limits are somewhat arbitrary since there are no specific boundaries between the categories. The transition of size ranges, either from molecular dispersions to colloids or from colloids to coarse dispersions, is very gradual. For example, an emulsion may exhibit colloidal properties, and yet the average droplet size may be larger than 1 pm. This is due to the fact that most disperse systems are heterogeneous with respect to their particle size [1-2]. 

Coarse-grained molecular d5mamics simulations in the presence of solvent provide insights into the effect of dispersion medium on microstructural properties of the catalyst layer. To explore the interaction of Nation and solvent in the catalyst ink mixture, simulations were performed in the presence of carbon/Pt particles, water, implicit polar solvent (with different dielectric constant e), and ionomer. Malek et al. developed the computational approach based on CGMD simulations in two steps. In the first step, groups of atoms of the distinct components were replaced by spherical beads with predefined subnanoscopic length scale. In the second step, parameters of renormalized interaction energies between the distinct beads were specified. 

The applicability of this in situ method for the determination of surface areas depends not only on knowledge of the dye s molecular area in the adsorbed state but also on the assumption that the chosen spectral parameter measures the surface concentration of the dye. In order to test the relation between adsorption of dye to silver halide and its spectral characteristics in the bound state, the behavior of Pseudocyanine in a coarse silver halide suspension (Dispersion D) was studied. This particular dispersion was chosen because some of its relevant adsorption characteristics had already been examined (22, 23). Moreover, observations by Boyer and Cappelaere with Pseudocyanine adsorbed on AgBr powders (5) indicated that /-band intensity varied with the amount of adsorbed dye and was not sensitive to the concentration of Ag+ or Br" ions in the range pAg 3.3-8.7. 

Arabinogalactan occurs as a white to yellow-white, coarse or fine powder. It is the dried water extract from the wood of the larch trees Larix occidentalis and Larix laricina (Fam. Pinaceae). It is a highly branched polysaccharide that has a molecular weight of 15,000 to 60,000 daltons and is composed of galactose units and arabinose units in the approximate ratio of 6 1. It is freely dispersible in hot or cold water. It is insoluble in alcohol. 

Aquatic sediments are formed in all surface waters by the settling of coarse and fine inorganic and organic particles. They are present in rivers, in lakes and in the oceans, and radionuclides deposited on the surface of the earth will sooner or later come into contact with these sediments. They may enter the sediments by sorption of molecularly-dispersed species (ions, molecules), by precipitation or coprecipitation, by coagulation of colloids (in particular carrier colloids) followed by sedimentation of the particles formed, or by sedimentation of coarse particles (suspended matter). By desorption, the radionuclides may be remobilized and released again into the water. 

Oil and water are essentially not misdble and coexist as a water phase and an oil phase, with each phase saturated with a trace of immiscible components. A surface active agent (emulsifier or surfactant) is soluble in one or in both phases, but it forms a true molecular solution only at a very low concentration. A mixture of oil, water, and emulsifier can form a milky (coarse) or transparent (fine) dispersion. The resultant dispersion is an oil-in-water (o/w) emulsion when a water-soluble surfactant such as the anionic sodium dodecyl sulfate (SDS) or non-ionic polyethoxylated nonylphenol with an average of 40 ethylene oxide units per molecule (NP40) is used. When the surfactant concentration is above its critical micellar concentration (CMC), these emulsifier molecules aggregate with one another to form micelles. 

Thus, the process of charge redistribution between particles should begin even before their contact, as a result of significant growth of the strength of the electric field in the clearance between them (see Section 12.2). However, because of incomplete equalization of the potentials of the particles and the presence of molecular forces of interaction, it can proceed unnoticed. In coarsely disperse systems, in which the size of particles, R, is around 1-200 pm, the process of charge redistribution can be the main barrier to integration of the dispersed phase. Thus, in... 

The type of dominating interaction forces between drops can vary, depending on particles size, difference in phase densities, external electric field strength, and drop charges. Thus, in case of approaching colloidal particles (I < 1 pm), the basic role is played by forces of molecular and electrostatic interactions (due to charges). For coarse-disperse systems (R > 1 pm) it is necessary to take into account all the forces involved. 

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