Micellar discontinuous

Block copolymers at high styrene contents behave similarly, with no break around the micellar region. Two of the block copolymers are shown separately in Figure 7c. The low M.W. BC 90 moves from an apparently adequate stabilization in CCI4 to a new level of modest protection at higher CyH g volume fractions. The block polymer of 42% styrene gives a hint of a discontinuity at the non-solvent content for micelle formation, but thereafter stabilizes the silica until the conditions approach those for phase separation. 

In the micellar region the trend to decreasing colloid stability is arrested and a partial improvement, in line with the enhanced level of polymer adsorption, is noted until the conditions for gross phase separation are reached. Only the intermediate block copolymer BC 42 shows indications of discontinuities in behavior at the solvent composition for micelle formation. The results presented here do not show the sharp transition from stability to instability found experimentally (4,8,17) by Napper and generally expected on theoretical grounds. However, there are important differences in experimental methodology that must be emphasised. 

What characterizes surfactants is their ability to adsorb onto surfaces and to modify the surface properties. At the gas/liquid interface this leads to a reduction in surface tension. Fig. 4.1 shows the dependence of surface tension on the concentration for different surfactant types [39]. It is obvious from this figure that the nonionic surfactants have a lower surface tension for the same alkyl chain length and concentration than the ionic surfactants. The second effect which can be seen from Fig. 4.1 is the discontinuity of the surface tension-concentration curves with a constant value for the surface tension above this point. The breakpoint of the curves can be correlated to the critical micelle concentration (cmc) above which the formation of micellar aggregates can be observed in the bulk phase. These micelles are characteristic for the ability of surfactants to solubilize hydrophobic substances in aqueous solution. So the concentration of surfactant in the washing liquor has at least to be right above the cmc. 

As the temperature of a mixed surfactant system is increased above its cloud point, the coacervate (concentrated) phase may go from a concentrated micellar solution mixed ionic/nonionic systems, it would be of interest to measure thermodynamic properties of mixing in this coacervate as this temperature increased to see if the changes from micelle to concentrated coacervate were continuous or if discontinuities occurred at certain temperatures/compositions. The similarities and differences between the micelle and coacervate could be made clearer by such an experiment. 

In subsequent work, ordering in solutions of the same matched diblock and triblock spanning a broader range of volume fractions, 0.1 < < 0.4, was explored (Hamley et al. 1997). For liquid-like and SAXS showed that there was no inter-micellar order in the liquid. Above a crossover concentration 0.2, ordering of micelles was shown by the presence of a structure factor peak. The ordered micellar structure, identified as hexagonal-packed cylinders for more concentrated solutions, persisted up to an order-disorder transition located from a discontinuity in the... 

Micellar cubic (OD), hexagonal columnar (ID), lamellar (2D), and bicontin-uous cubic (3D) nanostructures are formed by self-assembly of 13. For the complexes with IiC104, the ionic conductivities show discontinuous changes following the phase transitions with change of temperature or molecular structure of the dendritic moiety. For example, the conductivity of the complex of 13 with LiC104 drops from 4.6 x 10 6 to 1.2 x 10 9 S cm, along the phase transition from crystalline lamellar to micellar cubic phases. 

In contrast to the bicontinuous cubes, the less studied micellar cubic phases have positive Gaussian interfacial curvatures and are discontinuous, consisting of discrete micellar aggregates [164]. The structure of four micellar cubic phase has so far been established. 

Figure 4.11 Schematic representation of spherical reverse micellar structure formed in discontinuous cubic (b) phase. The radius of the micelle is r, the radius of the hydrophilic...

In an additional study by Yuli-Amar et al., in order to achieve low-viscosity reverse hexagonal phases at room temperature, ethanol and diethylene glycol monoethyl ether (Transcutol) were added to the ternary GMO/TAG/water mixture [29], These studies were based on findings showing that alcohols can destroy liquid-crystal phases, and ethanol and PEG were shown to form discontinuous micellar cubic and sponge phases instead of bicontinuous phases (49-51). It was shown that the addition of Transcutol or ethanol to the GMO/TAG/water mixture enabled the formation of a room temperature fluid Hn phase. 

The MEUF process is based on the formation of micelles and on the increased solubility, in a micellar solution, of an organic, which is sparingly soluble in water. The overall result is a two-phase system (a) the dispersed or discontinuous phase consisting of micelles, and (b) the continuous or aqueous phase consisting of surfactant monomers. Both these phases exist in a dynamic equdibrium. This concept of phase separation suggests that the permeate concentration should be constant. Experimental data show that this is indeed the case [57, 58]. 

Entrapment and mobilization mechanisms at low flow rates and low interfacial tension can also control the recovery obtained by tertiary methods. In micellar flooding, for example, high ratios of viscous to capillary forces arise at field flow rates when interfacial tensions are very low. Development of a continuous oil bank having significant mobility requires that discontinuous oil be mobilized to form a continuous bank which gathers more residual oil as it advances. Interfacial tensions may exist or develop between the micellar bank and the oil, or between the micellar fluid and the aqueous polymer bank used to push the micellar fluid. Entrapment of oil by the micellar bank, or of micellar fluid by the polymer bank would eventually cause the process to fail. 

The formation of micellar aggregates from ionic surfactants in water causes sharp discontinuities in conductivity and surface tension. Water-soluble surfactants form spherical or globular micelles at concentrations near the CMC (Fig. 2). Micelle formation is thermodynamically favored in water for water-soluble surfactants such as cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Brij 35, and is driven by hydrophobic interactions between the tails [10]. The charged or polar head groups face the water phase and the hydrocarbon tails reside in the interior of the micelle. For ionic surfactants in water, the head group region is only partly neutralized by counterions, setting up an interfacial... 

These self-assembled systems include lamellar (La) and non-lamellar (two and three dimensional bicontinuous and discontinuous nanostructures) phases, and inverted type micellar solution (L2). 

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