Ostwald convention

Figure 8.7 Temperature dependences of viscosity for several solvents measured with conventional Ostwald viscometers. Markers exhibit experimental results. Data points were interpolated by polynomial function the calculated curves are drawn with lines.

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]. 

Miniemulsion is a special class of emulsion that is stabilized against coalescence by a surfactant and Ostwald ripening by an osmotic pressure agent, or costabilizer. Compared with conventional emulsion polymerization process, the miniemulsion polymerization process allows all types of monomers to be used in the formation of nanoparticles or nanocapsules, including those not miscible with the continuous phase. Each miniemulsion droplet can indeed be treated as a nanoreactor, and the colloidal stability of the miniemulsion ensures a perfect copy from the droplets to the final product. The versatility of polymerization process makes it possible to prepare nanocapsules with various types of core materials, such as hydrophilic or hydrophobic, liquid or solid, organic or inorganic materials. Different techniques can be used to initiate the capsule wall formation, such as radical, ionic polymerization, polyaddition, polycondensation, or phase separation from preformed polymers. 

Miniemulsion n. A form of emulsion in which an organic liquid is dispersed into a continuous aqueous phase. Unlike a conventional emulsion, where the droplets may be of the order of 10 pm or greater, the droplets sizes are submicron. This is accomplished through a combination of high shear, and surfactant/costabilizer combination. The surfactant prevents emulsion degradation via calescence (as in a conventional emulsion), while the costabilizer prevents diffiisional degradation caused by Ostwald ripening. 

The working portion of the viscometer resembles that of a conventional Ostwald-type viscometer. The complete apparatus consists of a liquid feed reservoir, a capillary, and efflux bulbs in series. The complete unit is submersed in a constant-temperature oil bath. The driving head which forces the liquid through the capillary consists of a controlled nitrogen gas pressure system which is not shown in Figure 1. To initiate an experiment, the fluid reservoir which has a capacity of 200 ml is filled with the solution to be studied, and the fluid reservoir cap with an 0-ring seal is put into place. Stirring is provided to facilitate heat transfer to the sample solution. 

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