Water alcohol mixtures, stabilized

The assertion that a simple solute such as argon stabilizes the component that is fully hydrogen bonded is somewhat counterintuitive. The reason is as follows. Suppose we add large quantities of, say, alcohol to water. It is clear that the very fact that water becomes diluted in the water-alcohol mixture will cause a dissociation of hydrogen-bonded water molecules. At a very high dilution of water in any solvent, we expect very little concentration of fully hydrogen-bonded molecules. Therefore, we can conclude that if such a stabilization effect exists, it must occur only in the range of very dilute solutions of a solute in water. 

Beloedova TV, Kazakova LV, SkorikNA(1972) Stability of rare earth and yttrium citrate complexes in water and water-alcohol mixtures. Zhum Neorg Khim 17 1580-1583 Tripathy KK, Patnaik RK (1973) Citrate complex of yttrium(III). Acta Chim Acad Sci Hung 79 279-288... 

While most vesicles are formed from double-tail amphiphiles such as lipids, they can also be made from some single chain fatty acids [73], surfactant-cosurfactant mixtures [71], and bola (two-headed) amphiphiles [74]. In addition to the more common spherical shells, tubular vesicles have been observed in DMPC-alcohol mixtures [70]. Polymerizable lipids allow photo- or chemical polymerization that can sometimes stabilize the vesicle [65] however, the structural change in the bilayer on polymerization can cause giant vesicles to bud into smaller shells [76]. Multivesicular liposomes are collections of hundreds of bilayer enclosed water-filled compartments that are suitable for localized drug delivery [77]. The structures of these water-in-water vesicles resemble those of foams (see Section XIV-7) with the polyhedral structure persisting down to molecular dimensions as shown in Fig. XV-11. 

Microemulsions are thermodynamically stable, transparent (or translucent) dispersions of oil and water that are stabilized by an interfacial film of surfactant molecules. The surfactant may be pure, a mixture, or combined with a co surfactant such as a medium-chain alcohol (e.g., butanol, pentanol). These homogeneous systems, which can be prepared over a wide range of surfactant concentrations and oil to water ratios (20-80%), are all fluids of low viscosity. 

Microemulsions are macroscopically isotropic mixtures of at least a hydrophilic, a hydrophobic and an amphiphilic component. Their thermodynamic stability and their nanostructure are two important characteristics that distinguish them from ordinary emulsions which are thermodynamically unstable. Microemulsions were first observed by Schulman [ 1 ] and Winsor [2] in the 1950s. While the former observed an optically transparent and thermodynamically stable mixture by adding alcohol, the latter induced a transition from a stable oil-rich to a stable water-rich mixture by varying the salinity. In 1959, Schulman et al. [3] introduced the term micro-emulsions for these mixtures which were later found to be nano-structured. 

One alternative is the Loop process [1-3]. This employs a rather simple principle. A small volume of reaction mixture is recirculated, while streams of monomer and water phase [a stabilizer solution such as aqueous poly(vinyl alcohol)] are pumped into the reactor in the correct proportions. The reactor is fully filled and a balancing volume of product is released through a pressure-sustaining valve. Any unreacted monomer remaining in the outlet stream polymerizes on the way to the cooling tank or over a few hours, prior to packing. The volume of this type of reactor is only 40 to 80 L compared to 3000 to 100,000 L for a batch reactor. 

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