Ostwald ripening fraction

In Nature, however, we always have a contiiinous distribution of particles. This means that we have all sizes, even those of fractional parentage, i.e.-18.56n, 18.57p, 18.58 p, etc. (supposing that we can measure 0.01 p differences). The reason for this is that the mecheuiisms for particle formation, i.e.- precipitation, embryo and nucleation growth, Ostwald ripening, and sintering, are random processes. Thus, while we may speak of the "statistical variation of diameters", and while we use whole numbers for the particle diameters, the actuality is that the diameters are fractional in nature. Very few particle-size" specialists seem to recognize this fact. Since the processes are random in nature, we can use statistics to describe the... 

S.C. Hardy and P.W. Voorhees. Ostwald ripening in a system with a high volume fraction of coarsening phase. Metall. Trans., 19A(11) 2713-2721, 1988. 

A.D. Brailsford and P. Wynblatt. The dependence of Ostwald ripening kinetics on particle volume fraction. Acta Metall., 27(3) 489—497, 1979. 

P. Stonehart has specialized in methods for the manufacture of particles of a few atoms each. The art concerns less the actual manufacture of such particles than getting them to stay on the surface without undergoing Ostwald ripening, the thermodynamic tendency for small particles to aggregate and grow in size, thus diminishing the fraction of the Pt that can be used in catalytic reactions. 

The term microemulsion, which implies a close relationship to ordinary emulsions, is misleading because the microemulsion state embraces a number of different microstructures, most of which have little in common with ordinary emulsions. Although microemulsions may be composed of dispersed droplets of either oil or water, it is now accepted that they are essentially stable, single-phase swollen micellar solutions rather than unstable two-phase dispersions. Microemulsions are readily distinguished from normal emulsions by their transparency, their low viscosity, and more fundamentally their thermodynamic stability and ability to form spontaneously. The dividing line, however, between the size of a swollen micelle ( 10-140 nm) and a fine emulsion droplet ( 100-600 nm) is not well defined, although microemulsions are very labile systems and a microemulsion droplet may disappear within a fraction of a second whilst another droplet forms spontaneously elsewhere in the system. In contrast, ordinary emulsion droplets, however small, exist as individual entities until coalescence or Ostwald ripening occurs. 

This process was first recognized by Ostwald and is known as Ostwald ripening. The mathematical details were worked out independently by Lifshitz and Slyozov and by Wagner ° and is known as the LSW theory. However, this theory is based on a mean field approximation and is restricted to low volume fraction systems. Voorhees and coworkers extended the LSW theory to finite volume fraction systems and conducted a series of flight experiments designed to test this and similar theories. ... 

The relaxation time may be used as a guide for the state of the dispersion. For a colloidally stable dispersion (at a given particle size distribution), r increases with increase of the volume fraction of the disperse phase, . In other words, the cross-over point shifts to lower frequency with increase in . For a given dispersion, r increases with increase in flocculation, provided that the particle size distribution remains the same (i.e., no Ostwald ripening). 

Dissolution-precipitation models. Dubinina and Lakshtanov (1997) developed a kinetic model that describes isotopic fractionation between a mineral and fluid involved in one of three types of dissolution-precipitation processes (Fig. 11). Type I (mineral synthesis) considers successive dissolution of an unstable phase, A, of uniform isotopic composition and precipitation (crystallization) of phase B. Type II (Ostwald ripening) involves the partial dissolution of phase B which has a non-uniform isotopic composition... 

Just as is the case for the LSW theory of Ostwald ripening, the Langer-Schwartz theory is also valid for quenches close to the coexistence curve. Its extension to non-zero volume fractions requires that such a theory take into account cluster-cluster correlations. A framework for such a theory has been developed [37] using a multi-droplet diffusion equation for the concentration field. This equation has been solved analytically using... 

Table 12.4 Parameters for Calculation of Theoretical Rate Constants for Coarsening by Ostwald Ripening (Evaporation/Condensation) and Coalescence for HDPE (Fraction)/HPB Blend .

In principle, polymerization proceeds in the monomer droplets and the final particle number is close to the initial number of monomer droplets. However, in many cases not all droplets are initiated to become polymer particles, but only a fraction (<20%) of the initial number of monomer droplets. This effect is related to Ostwald ripening and often a hydrophobe is added in the recipes to prevent this from happening. 

Enomoto Y, Kawasaki K, Tokuyama M (1987) The time-dependent behavior of the Ostwald ripening for the finite volume fraction. Acta Metall 35 915-922... 

Marqusee JA, Ross J (1984) Theory of Ostwald ripening—competitive growth and its dependence on volume fraction. J Chem Phys 80 536-543... 

Enomoto Y, Tokuyama M, Kawasaki K (1986) Finite volume fraction effects on Ostwald ripening. Acta Metall 34 2119-2128... 

Brailsford AD, Wynblatt P (1979) Dependence of Ostwald ripening kinetics on particle— volume fraction. Acta Metall 27 489-497... 

Davies CKL, Nash P, Stevens RN (1980) Effect of volume fraction of precipitate on Ostwald ripening. Acta Metall 28 179-189... 

The interfacial properties of colloidal suspensions are determined by the chemical reactions (e.g. protonation) and adsorption of solutes. Additionally, the interface can be affected by the dissolution-precipitation equilibrium of the particle phase. This is because precipitation changes the surface morphology (Vigil et al. 1994) or leads to phase transition (Lefevre et al. 2002 Carrier et al. 2007). In addition, dissolution means degradation of the particles and may result in the loss of the finest particle fractions (i.e. Ostwald ripening). For this reason, it is necessary to understand the factors governing the dissolution of solid particles. 

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