Particle size analysis, description

A number of methods have been proposed for particle shape analysis these include verbal description, various shape coefficients and shape factors, curvature signatures, moment invariants, solid shape descriptors, the octal chain code and mathematical functions like Fourier series expansion or fractal dimensions. As in particle size analysis, here one can also detect intense preoccupation with very detailed and accurate description of particle shape, and yet efforts to relate the shape-describing parameters to powder bulk behaviour are relatively scarce.10... 

ISO 9276-6, 2008. Representation of results of particle size analysis—Part 6 Descriptive and quantitative representation of particle shape and morphology. 

Within routine studies of new chemical entities, the initial focus is to explicate a comprehensive description of the drug. The aim is to provide specific information on its physical aspects such as morphological form, polymorphism, crystal habit and solvate state. This information is combined with data from other techniques such as dynamic vapour sorption (DVS), particle size analysis, XRPD (x-ray powder diffraction), solid state NMR, IR spectrophotometry and Raman spectroscopy. 

Particle size is one of the principal determinants of powder behavior such as packing and consolidation, flow ability, compaction, etc., and it is therefore one of the most common and important areas of powder characterization. Typically, one refers to particle size or diameter as the largest dimension of its individual particles. Because a given powder consists of particles of many sizes, it is preferable to measure and describe the entire distribution. While many methods of size determination exist, no one method is perfect (5) two very common methods are sieve analysis and laser diffraction. Sieving is a very simple and inexpensive method, but it provides data at relatively few points within a distribution and is often very operator dependent. Laser diffraction is a very rapid technique and provides a detailed description of the distribution. However, its instrumentation is relatively expensive, the analytical results are subject to the unique and proprietary algorithms of the equipment manufacturer, and they often assume particle sphericity. The particle size distribution shown in Figure 1 was obtained by laser diffraction, where the curves represent frequency and cumulative distributions. 

Morphological analysis is concerned with particle characterization in the case of particle size, particle shape and particle texture. Particle texture may deal with the particle surface characteristics and also with the particle microstructure. Particle size and shape influence physical and chemical properties of particulate materials. Morphological analysis is being developed in order to facilitate a more accurate description of the properties and behavior of particulate systems from a fundamental knowledge of the characteristics of the particles of the system [1,2]. 

The applicability of Volmer and van der Waals equations of state for a description of particle monolayers found that the shape described by the van der Waals equation of state is similar to the behaviour observed experimentally for repulsive particles within monolayers.3 Nevertheless, both the Volmer and van der Waals equations give a dependence of surface pressure on particle size unsuitable for a quantitative analysis of experimental data. It has been recently shown28 that for monolayers of nanoparticles, the equations of state should take into account the significant size differences of particles and solvent molecules. 

Monolayers of micro- and nanoparticles at fluid/liquid interfaces can be described in a similar way as surfactants or polymers, easily studied via surface pressure/area isotherms. Such studies provide information on the properties of particles (dimensions, interfacial contact angles), the structure of interfacial layers, interactions between the particles as well as about relaxation processes within the layers. Such type of information is important for understanding how the particles stabilize (or destabilize) emulsions and foams. The performed analysis shows that for an adequate description of II-A dependencies for nanoparticle monolayers the significant difference in size of particles and solvent molecules has be taken into account. The corresponding equations can be obtained by using a thermodynamic model developed for two-dimensional solutions. The obtained equations provide a satisfactory agreement with experimental data of surface pressure isotherms in a wide range of particle sizes between 75 pm and 7.5 nm. Moreover, the model can predict the area per particle and per solvent molecule close to real values. Similar equations were applied also to protein monolayers at liquid interfaces. 

The description of a colloid should include particle size, mobility, charge and their distributions, charge/mass ratio, electrical conductivity of the media, concentration and mobility of ionic species, the extent of a double layer, particle-particle and particle-substrate interaction forces and complete interfacial analysis. The application of classical characterization methods to nonaqueous colloids is limited and, for this reason, the techniques best suited to these systems will be reviewed. Characteristic results obtained with nonaqueous dispersions will be summarized. Physical aspects, such as space charge effects and electrohydrodynamics, will receive special attention while the relationships between chemical and physical properties will not be addressed. An application of nonaqueous colloids, the electrophoretic development of latent images, will also be discussed. 

Structural features of disperse systems, in particular the existence of the electrical double layer (EDL), are responsible for a number of peculiar phenomena related to heat and mass transfer and electric current propagation in such systems. The description of electromagnetic radiation propagation is also included in this chapter. These features are utilized in numerous practical applications and underlie methods used to study disperse systems. These methods include particle size distribution analysis, studies of the surface structure and of near-surface layers, the structure of the EDL, etc. In the most general way the most transfer phenomena can be described by the laws of irreversible thermodynamics, which allow one to carry out a systematic investigation of different fluxes that originate as a result of the action of various generalized forces. 

Transmission electron microscopy (TEM) is a powerful and routinely employed technique for the analysis of particle size and morphology in supported metal catalysts. A more thorough description of its uses and applications is provided in Chapter 3,... 

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