Particle characterization, indirect

The interactions between colloidal particles (see section C2.6.4) are central to tire understanding of suspension behaviour. Aitlrough most work has had to rely on ratlrer indirect ways to characterize tlrese interactions, novel teclmiques are emerging tlrat access tlrese interactions more directly. 

This technique is the most widely used and the most useful for the characterization of molecular species in solution. Nowadays, it is also one of the most powerful techniques for solids characterizations. Solid state NMR techniques have been used for the characterization of platinum particles and CO coordination to palladium. Bradley extended it to solution C NMR studies on nanoparticles covered with C-enriched carbon monoxide [47]. In the case of ruthenium (a metal giving rise to a very small Knight shift) and for very small particles, the presence of terminal and bridging CO could be ascertained [47]. In the case of platinum and palladium colloids, indirect evidence for CO coordination was obtained by spin saturation transfer experiments [47]. 

Dynamic probe methods Another indirect strategy for emalysis of gel structure is the measurement of the mobility of dynsumic probes whose sizes are well characterized. For example, dynsumic light scattering or any other method for diffusivity determination (for examples, see 37) can be used to measure the motions, through a gel matrix, of a series of spherically shaped particles with varying sizes. To oversimplify greatly, if, as probe size is raised, a dramatic decrease in diffusivity is found, then the "mesh" size of the polymer gel may be estimated. 

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are the techniques most widely used for the characterization of crystallinity and polymorphism of solid lipid particles. Although DSC is usually more sensitive in detecting crystalline material, XRD is much more reliable in determining the type of polymorph present in the dispersions because it provides structural data. In contrast, DSC can detect the type of polymorph only indirectly via the transition temperatures and enthalpies. Because these parameters may be different from those observed in the bulk material, particularly for small colloidal particles [1,62], assigmnent of polymorphic forms in DSC curves should be supported by x-ray data. 

Because of this importance, different techniques have been developed to characterize the droplet size distribution in emulsions, each with its own pros and cons. Light microscopy, for example, is qualitative and only suited for particles larger than about 1 )im. When using electron microscopy, correct sample preparation is crucial to the examination and interpretation of the dispersions. The Coulter method is an indirect method which detects a... 

The indirect climatic impact of aerosol at the ABL is determined by numerous interactions between aerosol and the dynamics of the microphysical and optical properties of clouds. The input to the atmosphere of anthropogenic aerosol particles functioning as CCN favors an increase in cloud droplet number density. As mentioned above, the related increase in the optical thickness and albedo of clouds, with their constant water content, was called the first indirect effect , which characterizes the climatic impact of aerosol. 

Indirect techniques, such as conductivity measurements and the determination of the surface tension were carried out to get more information about the surfactant distribution during the polymerization and were applied to characterize the droplet or particle sizes before and after the polymerization without diluting the system [23]. As a powerful method small angle neutron scattering experiments were applied to characterize the droplet or particle sizes before and after the polymerization without diluting the system [23]. 

Our understanding of miniemulsion stability is limited by the practical difficulties encountered when attempting to measure and characterize a distribution of droplets. In fact, most of the well-known, established techniques used in the literature to characterize distributions of polymer particles in water are quite invasive and generally rely upon sample dilution (as in dynamic and static laser light scattering), and/or shear (as in capillary hydrodynamic fractionation), both of which are very likely to alter or destroy the sensitive equihbrium upon which a miniemulsion is based. Good results have been obtained by indirect techniques that do not need dilution, such as soap titration [125], SANS measurements[126] or turbidity and surface tension measurements [127]. Nevertheless, a substantial amount of experimental evidence has been collected, that has enabled us to estabhsh the effects of different amounts of surfactant and costabihzer, or different costabilizer structures, on stabihty. 

For ferromagnetic cobalt particles in zeolite X, spin-echo ferromagnetic resonance has been used to obtain unique structural information (S6). In addition, study of the catalytic signature of metal/zeolite catalysts has been used by the groups of Jacobs (87), Lunsford (88), and Sachtler (47,73,89). Brpnsted acid protons are identified by their O—H vibration (90,91) in FTIR or indirectly, by using guest molecules such as pyridine or trimethylphosphine (92,93). An ingenious method to characterize acid sites in zeolites was introduced by Kazansky et al., who showed by diffuse reflection IR spectroscopy that physisorbed H2 clearly discerns different types of acid sites (94). Also, the weak adsorption of CO on Brpnsted and Lewis acid sites has been used for their identification by FTIR (95). The characterization of the acid sites was achieved also by proton NMR (96). 

The bulk density of a powder is obtained by dividing its mass by the bulk volume it occupies. The volume includes the spaces between particles as well as the envelope volumes of the particles themselves. The true density of a material (i.e., the density of the actual solid material) can be obtained with a gas pycnometer. The bulk density of a powder is not a definite number like true density or specific gravity but an indirect measurement of a number of factors, including particle size and size distribution, particle shape, true density, and especially the method of measurement. Although there is no direct linear relationship between the flowability of a powder and its bulk density, the latter is extremely important in determining the capacity of mixers and hoppers and providing an easily obtained valuable characterization of powders. 

Particle size characterization techniques can be broadly classified as direct and indirect techniques. In the direct techniques, the characterization is performed directly on the actual particle, whereas in the indirect techniques, the characterization relies on relationships between physical properties and particle size or shape. 

The indirect techniques for particle size characterization include scattering techniques, sedimentation (gravitational or centrifugal), elutria-... 

In the sequence of emission-transport/con-version-deposition, the last phase has been dealt with in detail (Guderian 2000, 2001). Less emission leads to less deposition. Air pollutants exist as dust particles and in gaseous form, and for the effect of air pollutants their concentration in the air (immission) and their quantity deposited on receptors (deposition) is important. In ecosystems, both nutrients and harmful substances are deposited, and air pollutants may act as either acidic or alkaline, and as reductive or oxidative. The impact of immissions on plants may occur either directly (on plant leaves) or indirectly (through the soil), visible or invisible, latent or acute and chronic. Since they serve as sensitive receptors, plants and ecosystems (e.g., crops, forests, natural vegetation), soils and waters are of major interest. In order to characterize the atmospheric pollutant load of a special site in the landscape, it is first necessary to know the concentration situation and the deposited quantity per time and surface unit - the surface load. Concentrations may be measured over shorter or longer (> 24 h) periods. The concentration of gaseous air pollutants is measured in ppm, ppb or jg m. ... 

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