The "ouzo effect" enables one to create a dispersion of small droplets in a surrounding liquid phase without the use of surfactants, dispersing agents, or mechanical agitation: a phenomenon which can be of value in many disciplines. In the quantitative studies presented here, dispersions of oil droplets in water are formed by the addition of water to a solution of the oil dissolved in a solvent. This causes the oil to supersaturate and then nucleate into small droplets. The mean droplet diameter is a function only of the oil-to-solvent ratio at a given temperature. The number density of droplets formed can be controlled independently from the droplet diameter by changing the amount of water added. Smaller droplets are formed by using more hydrophilic cosolvents. The droplet size distribution is typically log-normal. The width of the distribution can be narrowed by mixing the components at an elevated temperature and then allowing the dispersion to cool.

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Theoretical and experimental aspects of homogeneous and heterogeneous bubble nucleation are reviewed. Recent developments in nucleation theory, which include hydrodynamic and diffusion constraints, gas phase nonidealities, and heterogeneous nucleation are discussed. A large number of the measured limits of superheat of pure components are close to 88 to 90% of the critical temperature. Where calculations can be made, these measurements are in agreement with predictions from classical nucleation theory. Measurements of the limits of superheat of mixtures are useful for understanding one proposed mechanism for the dangerous phenomena known as contact vapor explosions.

For every mapping of a perturbed spacetime onto a background and with any vector field ξ we construct a conserved covariant vector density I(ξ), which is the divergence of a covariant antisymmetric tensor density, a "superpotential". I(ξ) is linear in the energymomentum tensor perturbations of matter, which may be large; I(ξ) does not contain the second order derivatives of the perturbed metric. The superpotential is identically zero when perturbations are absent. By integrating conserved vectors over a part Σ of a hypersurface S of the background, which spans a two-surface ∂Σ, we obtain integral relations between, on the one hand, initial data of the perturbed metric components and the energy-momentum perturbations on Σ and, on the other hand, the boundary values on ∂Σ. We show that there are as many such integral relations as there are different mappings, ξ's, Σ's and ∂Σ's. For given boundary values on ∂Σ, the integral relations may be interpreted as integral constraints on local initial data including the energymomentum perturbations. Conservation laws expressed in terms of Killing fields ξ of the background become "physical" conservation laws. In cosmology, to each mapping of the time axis of a Robertson-Walker space on a de Sitter space with the same spatial topology there correspond ten conservation laws. The conformal mapping leads to a straightforward generalization of conservation laws in flat spacetimes. Other mappings are also considered. Traschen's "integral constraints" for linearized spatially localized perturbations of the energy-momentum tensor are examples of conservation laws with peculiar ξ vectors whose equations are rederived here. In Robertson-Walker spacetimes, the "integral constraint vectors" are the Killing vectors of a de Sitter background for a special mapping. [S0556-2821(97)00310-X] PACS number(s): 04.20.Cv, 98.80.Hw

The preparation of polymeric particles and capsules by means of spontaneous droplet formation and subsequent polymer precipitation or synthesis is well-known. However, spontaneous emulsification is a phenomenon that has often been erroneously interpreted. This Minireview provides new insights into the preparation of metastable liquid dispersions by homogeneous liquid-liquid nucleation, and is based primarily on a recent study by Vitale and Katz (Langmuir, 2003, 19, 4105-4110). This spontaneous emulsification, which they named the Ouzo effect, occurs upon pouring, into water, a mixture of a totally water-miscible solvent and a hydrophobic oil--and optionally some water--thus generating long-lived small droplets, which are formed even though no surfactant is present. Herein, we review and reinterpret the most relevant publications on the synthesis of a variety of dispersions (pseudolatexes, silicone emulsions, biodegradable polymeric nanocapsules, etc.), which we believe have actually been synthesized using the Ouzo effect. The Ouzo effect may also become a substitute for high-shear techniques, which, to date have only been of limited utility on industrial scales.