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a characteristic of particle dimensions in disperse systems; it is inversely proportional to the average particle diameter and is determined by the specific surface—that is, the ratio of the total particle surface to the unit volume (or sometimes mass) of the dispersed phase. The specific surface is the average dispersity index. A more complete representation of dispersity is provided by the volume or mass distribution curve for the dispersed phase according to particle dimensions (see Figure 1). With increasing poly dispersity of the system—that is, with increasing difference in particle sizes—the maximum on the distribution curve decreases and becomes broader, but the area bounded by the curve and the x-axis remains constant. In the rare case of a monodisperse system, when the dimensions of the particles are almost identical, the curve has a sharp peak with a narrow base. Systems with two or more maximums on the distribution curve exist. In the case of finely porous materials, such as adsorbents and catalysts, the concept of dispersity is replaced by the equivalent concept of porosity, which is the characteristic of the channel or pore size in the materials.

Figure 1. Distribution curves of the volume (weight) of particles according to size: (1) monodisperse system, (2) polydisperse system; δmin. δmax. and δ0 τ(δ) are the minimum, maximum, and most probable particle size, respectively, and t(δ) is a distribution function, the proportion of the volume or weight of the dispersed phase made up of particles within a given size interval divided by the magnitude of the interval

In the chemistry of macromolecular compounds, the size characteristic of the linear or branched (chain) polymeric molecules, which is determined by the molecular weight, is often called the dispersity. The poly dispersity of polymers may be expressed by the distribution function of the molecules according to their molecular weights (so-called molecular-weight distribution). This function is graphically represented by the curves shown in Figure 1. The molecular weights are plotted along the x-axis, and the proportions of polymeric fractions, with the corresponding molecular weights, are plotted along the y-axis.

Dispersity is an important technological index in the production and use of pigments, various plastic fillers, mineral binders, fertilizers, pesticides, pharmaceuticals, and many other powdered and fine-grained products. It is determined by the methods of dispersion analysis.

References in periodicals archive ?
f,"k"] makes preconditions to reduce numerical experiment sizes for droplets heated up by conduction ("k" heating case): enough to create a phase transformation cycle [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] for freely chosen diameter droplet, to define its heat and mass transfer parameters P relatively dimensionless forms [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and according to them define P([tau]) functions for wanted droplets dispersity [16].
Control experiments were performed with Au329 which shows fixed composition, to verify the size dispersity of the 115 kDa mass range.
It is also clear that there is a good correlation between the glass transition temperature and the average molecular weights and polydispersity of the polymer, indicating that the noncrystallinity of the material increases with the average molecular weight and the dispersity of the chains size.
Contributions on emulsified systems and dispersity analysis lead into treatment of cellular response to small particles, surfaces, and functionalizations.
Projects working on the network layer cover new routing methods, such as dispersity routing.
The degradation of the polymer in this work on the examples with varying molecular dispersity (monodisperse, with the most probable dispersion and a polydisperse) has considered.
The effects of additional factors such as the size variation, shape or dispersity of the SeNPs on the recovery of WBC counts in BM suppressed mice or normal animals have not been investigated in the current study and merit further investigation.
This brings out the necessity of researching about the behavior and constitutive modeling using the critical state and unsaturated soil mechanics, to avoid the dispersity of the results and have consistency into a more coherent framework.
Among the main parameters that affect growth by sedimentation are: i) material size, ii) mono dispersity, iii) density of particles in the solvent, iv) surface charge density of the spheres, v) rate of evaporation of the solvent, and vi) settling velocity of the particles (12,13).
Transpec-WideWavelength uses the UV-Vis-NIR reflectance spectrum, which means it can pick up information on colour and dispersity as well as the molecular structure.
High dispersity of oil shale particles reduces to minimum the change of primary pyrolysis products under their passing through particles pores.
2007; Karlov & Shakhov, 2001) as technology of their production and covering allows regulation of basic coating characteristics providing their biological compatibility as follows: 1) regulation of mechanical characteristics and biological activity right up to bio-inertness by means of change of mass fraction of in-organic filling; 2) control of elemental composition and rate of biological degradation of composite by means of selection of correspondent forms of calcium-phosphate compounds; 3) regulation of morphometric characteristics of composite by means of change of filling dispersity.