Phase ripening

Figure 10.11 A well-ordered 2D AuS phase develops during annealing to 450 K. (A) The structure exhibits a very complex LEED pattern, which can be explained by an incommensurate structure with a nearly quadratic unit cell. (B) STM reveals the formation of large vacancy islands by Oswald ripening which cover about 50% of the surface, thus indicating the incorporation of 0.5 ML of Au atoms into the 2D AuS phase. The 2D AuS phase exhibits a quasi-rectangular structure (inset) and uniformly covers both vacancy islands and terrace areas. (Reproduced from Ref. 37).

An analogy may be drawn between the phase behavior of weakly attractive monodisperse dispersions and that of conventional molecular systems provided coalescence and Ostwald ripening do not occur. The similarity arises from the common form of the pair potential, whose dominant feature in both cases is the presence of a shallow minimum. The equilibrium statistical mechanics of such systems have been extensively explored. As previously explained, the primary difficulty in predicting equilibrium phase behavior lies in the many-body interactions intrinsic to any condensed phase. Fortunately, the synthesis of several methods (integral equation approaches, perturbation theories, virial expansions, and computer simulations) now provides accurate predictions of thermodynamic properties and phase behavior of dense molecular fluids or colloidal fluids [1]. 

Ostwald ripening consists of a diffusive transfer of the dispersed phase from smaller to larger droplets. Ostwald ripening is characterized by either a constant volume rate [4,5] (diffusion-controlled ripening) or a constant surface rate 22 [6] (surface-controlled ripening), depending on the origin of the transfer mechanism ... 

If the ripening is controlled by diffusion across the continuous phase, then the cube of the diameter increases linearly with time (a = 3) and the ripening rate S23 can be derived using the Lifshitz and Slyozov theory [2,3] ... 

A.S. Kabalnov, A.V. Pertsov and E.D. Shchukin Ostwald Ripening in Two-Component Disperse Phase Systems Application to Emulsion Stability. Colloid Surfaces 24, 19 (1987). 

Under osmotic pressure gradients between the two aqueous phases of W/OAV emulsions, water may migrate either from the internal to the external phase or vice versa, depending on the direction of the osmotic pressure gradient. This process is entropically driven and is another manifestation of compositional ripening. Such... 

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