Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Microemulsions cylindrical

In sodium bis(2-ethylhexyl) phosphate microemulsions, which are composed of cylindrical micelles in the dilute region, it has been observed that the formation of micellar clusters is characterized by a branched structure as the volume fraction (<1>) of the aggregates increases. At d> > 0.2, these clusters mutually overlap, forming a network expanded overall [283]. [Pg.496]

Shioi, A., Harada, M., and Tanabe, M. (1995), Static light scattering from oil-rich microemulsions containing polydispersed cylindrical aggregates in sodium bis(2-ethylhexyl) phosphate system,/. Phys. Chem., 99,4750 1756. [Pg.789]

Amphiphilic lipopeptides with a hydrophobic paraffinic chain containing from 12 to 18 carbon atoms and a hydrophilic peptidic chain exhibit lyotropic meso-phases and good emulsifying properties. The X-ray diffraction study of the mesophases and of dry lipopeptides showed the existence of three types of mesomorphic structures lamellar, cylindrical hexagonal and body-centred cubic. Two types of polymorphism were also identified one as a function of the length of the peptidic chain and the other as a function of the water content of the mesophases. The emulsifying properties of the lipopeptides in numerous pairs of immiscible liquids such as water/ hydrocarbons and water/base products of the cosmetic industry showed that small amounts of lipopeptides easily give three types of emulsions simple emulsions, miniemulsions and microemulsions. [Pg.116]

Microemulsions consist of apparently homogeneous transparent systems of low viscosity which contain a high percentage of both oil and water and high concentrations (15-25%) of emulsifier mixture. They were first described by Schulman as disperse systems with spherical or cylindrical droplets in the size range 8-80 nm. They are essentially swollen micellar systems, but obviously the distinction between a swollen micelle and small emulsion droplet is difficult to assess. [Pg.245]

The most reasonable explanation for the increase in apparent hydrodynamic diameter measured by DLS is the enhanced micelle-micelle interactions as the boundary of a two-phase system is approached (i.e., the pressure is lowered). Figure 4 illustrates this concept of micelle-micelle interactions, which is manifested as aggregation (or clustering) of the reverse micelle or microemulsion droplets. Since the solvent environment is essentially unchanged by this "macromolecular aggregation" (Ui) we exclude the possibility of (other than transitory) micelle-micelle coalescence to form stable, larger micelles. The micelles may coalesce briefly to form transitional species (which might be a "dumbbell" or more cylindrical structures), in which the water cores collide and intermix. [Pg.174]

Double Layer Interactions and Interfacial Charge. Schulman et al (42) have proposed that the phase continuity can be controlled readily by interfacial charge. If the concentration of the counterions for the ionic surfactant is higher and the diffuse electrical double layer at the interface is compressed, water-in-oil microemulsions are formed. If the concentration of the counterions is sufficiently decreased to produce a charge at the oil-water interface, the system presumably inverts to an oil-in-water type microemulsion. It was also proposed that for the droplets of spherical shape, the resulting microemulsions are isotropic and exhibit Newtonian flow behavior with one diffused band in X-ray diffraction pattern. Moreover, for droplets of cylindrical shape, the resulting microemulsions are optically anisotropic and non-Newtonian flow behavior with two di-fused bands in X-ray diffraction (9). The concept of molecular interactions at the oil-water interface for the formation of microemulsions was further extended by Prince (49). Prince (50) also discussed the differences in solubilization in micellar and microemulsion systems. [Pg.13]

Interesting effects are observed when a dispersion contains both larger and smaller particles the latter are usually polymer coils, spherical or cylindrical surfactant micelles, or microemulsion droplets. The presence of the smaller particles may induce clustering of the larger particles due to the depletion attraction (see Section 5.4.S.3.3, above) such effects are described in the works on surfactant-flocculated and polymer-flocculated emulsions. Other effects can be observed in dispersions representing mixtures of liquid and solid particles. Yuhua et al. ° have established that if the size of the solid particles is larger than three times the size of the emulsion drops, the emulsion can be treated as a continuous medium (of its own average viscosity), in which the solid particles are dispersed such treattnent is not possible when the solid particles are smaller. [Pg.258]

With appropriate values of the various parameters, this model yielded predictions in good agreement with experiment on such phenomena as the amounts of various pure hydrocarbons solubilized in micelles of sodium dodecyl sulfate SDS as well as the amounts of benzene and -hexane solubilized in the same micelles from various mixtures of the two hydrocarbons. It was also able to predict transformation of rodlike micelles to spherical microemulsion droplets as a result of hydrocarbon solubilization, an effect that has been observed experimentally. In the absence of hydrocarbon, films of these surfactants can attain their preferred curvatures only by forming cylindrical micelles, as micelle radius is limited to the extended length of a surfactant molecule. However, when considerable hydrocarbon is present, this constraint no longer applies, and spherical microemulsion droplets can grow until the preferred curvature is reached. [Pg.524]

Despite the fact that here one has the typical composition of a microemulsion, i.e., surfactant-water-oil, one does not find a low viscosity microemulsion but instead a highly viscous system. The addition of water results in the formation of flexible cylindrical reverse micelles that form a transient network of entangled micelles and has been characterized by means of dynamic shear viscosity measurements [73,74]. Light scattering experiments on systems with cyclohexane as the oil have demonstrated that a water-induced micellar growth occurs and that these systems may be described analogously to semidilute polymer solutions [75-77]. [Pg.367]

Recently, Svergun et al [91] showed that in the system NaAOT/isooctane/ water/NaCl, cylindrical forms increased while spherical forms decreased in amount with increase in temperature. Again, cylinders increased with addition of NaCl up to 0.2% (maximal) but decreased with further increase in the percentage of NaCl. Another theoretical treatment was made by Eriksson and Ljunggren [92] who concluded that for a spherocylindrical shape in a W/O microemulsion with excess water (note that microemulsions, the topic of Chapter 3, are after all derived from micelles), ultralow interfacial tension ( 10 N/m or less) is required in the range of the spontaneous curvature // . Further, the condition stated below should be satisfied ... [Pg.41]

The basic nanoreactor in particle formation is a reverse micelle in most cases, with a generally accepted spherical shape. The particles generated from these micelles transforming into W/O microemulsions are also often spherical in shape. However, other surfactant architectures may also yield particles. Thus, vesicles have been instrumental in the formation of particles in many cases (not discussed in this book) [98] similarly, cylindrical micelles could also generate elongated nanoparticles with the required manipulations in the system. Unfortunately clear-cut evidence on this offshoot procedure of synthesis, i.e. rodlike particle formation from rod-like micelles is apparently not so extensively available. [Pg.42]

Kurumada et al. [86] investigated the structure and percolation of water/oil microemulsions employing sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium bis(2-ethylhexyl) phosphate (SDEHP). The sulfosuccinate-derived microemulsions have produced spherical aggregates, whereas those derived from the phosphate are composed of cylindrical aggregates. But the preparations have shown percolation in conductance the conductance increase with the phosphate system is 10-100 times more than that with the succinate system. Moreover, for the former, (]), 0.06. and for the latter cj), 0.4-0.5. In the region of c >, > 0.2, the electrical conductivity of the phosphate system has been found to be 1000-fold... [Pg.280]


See other pages where Microemulsions cylindrical is mentioned: [Pg.2587]    [Pg.2595]    [Pg.52]    [Pg.399]    [Pg.167]    [Pg.51]    [Pg.207]    [Pg.319]    [Pg.976]    [Pg.170]    [Pg.165]    [Pg.22]    [Pg.331]    [Pg.514]    [Pg.523]    [Pg.524]    [Pg.13]    [Pg.48]    [Pg.135]    [Pg.493]    [Pg.2587]    [Pg.2595]    [Pg.214]    [Pg.249]    [Pg.253]    [Pg.253]    [Pg.222]    [Pg.338]    [Pg.412]    [Pg.144]    [Pg.440]    [Pg.176]    [Pg.229]    [Pg.205]   
See also in sourсe #XX -- [ Pg.251 ]

See also in sourсe #XX -- [ Pg.45 , Pg.104 ]




SEARCH



© 2024 chempedia.info