Surfactant-water system

Another feature of surfactant-water systems is that they can also aggregate into lyotropic liquid crystalline phases when Intermicellar interactions are significant. Typically, non-Newtonian behavior is usually found for these liquid crystalline phases. For the 3LDA0/ISDS mixed system, all evidence suggests that they do form liquid crystalline phase. 

In the remainder of this article, discussion of surfactant dissolution mechanisms and rates proceeds from the simplest case of pure nonionic surfactants to nonionic surfactant mixtures, mixtures of nonionics with anionics, and finally to development of myehnic figures during dissolution, with emphasis on studies in one anionic surfactant/water system. Not considered here are studies of rates of transformation between individual phases or aggregate structures in surfactant systems, e.g., between micelles and vesicles. Reviews of these phenomena, which include some of the information summarized below, have been given elsewhere [7,15,29]. 

The equilibrium in these systems above the cloud point then involves monomer-micelle equilibrium in the dilute phase and monomer in the dilute phase in equilibrium with the coacervate phase. Prediction o-f the distribution of surfactant component between phases involves modeling of both of these equilibrium processes (98). It should be kept in mind that the region under discussion here involves only a small fraction of the total phase space in the nonionic surfactant—water system (105). Other compositions may involve more than two equilibrium phases, liquid crystals, or other structures. As the temperature or surfactant composition or concentration is varied, these regions may be encroached upon, something that the surfactant technologist must be wary of when working with nonionic surfactant systems. 

FIGURE 12.5 Fragment of the phase diagram for surfactant-water system. L, E, and S denotes liquid solution, liquid crystalline, and solid phases, respectively the dotted line is the CMC curve. (Reprinted from Smirnova, N. A. 1995.Fluid Phase Equilibrial 10 1—15. With permission.)... 

The phase diagrams of two-component surfactant-water systems are typically quite different for nonionic and ionic compounds. As exemplified in Fig. 2.22 there are at low temperatures different liquid crystalline phases while at intermediate temperatures there may be a total mutual solubility of surfactant and water98. At higher temperatures, there is, as already noted, a separation into two phases with a very large two-phase region. One of the phases contains very little surfactant, while the other contains appreciable amounts of both components. The cloud-point curve can be described as a liquid-liquid solubility curve with a lower consolute tempera-... 

The phase behaviour can have a significant impact on detergency [21] but, if there is no phase change for the surfactant-water system, a linear dependence of detergency on temperature is observed (Figure 3.19). 

More drastic changes in the CMC and N are observed when additives are present in the micelle-forming surfactant - water systems. The addition of ionic species (i.e. electrolytes) usually results in an increase in the aggregation number and a reduction in the CMC. Table III (and Table II) present some data which illustrate this effect. Depending upon the concentration, the presence of water miscible organic molecules can either enhance or inhibit micelle formation. 

Freeze-fracture TEM combined with nuclear magnetic resonance and quasielastic light scattering was used to study the microstructure of surfactant-water systems and dynamics of o/w and bicontinuous ME systems [41], The authors reported a rather abrupt transition from a discontinuous droplet (o/w) to bicontinuous (oil-and-water) microstructure occurring at low surfactant concentration, close to a three-phase region in the constructed phase diagram of pentaethylene glycol dodecyl ether, water, and octane [41],... 

Analogous results have been reported from the systematic measurements of electrical conductivity and transference numbers of ions (// and tf) in black foam films [336] and parallel measurements of these quantities in highly concentrated surfactant/water system [337], Furthermore, it has been found that while the electrical conductivity of CBF depends on the electrolyte concentration in the initial solution, that of NBF does not. The transference numbers of the ions measured for films and a gel obtained from NaDoS-NaCl-HCl system are given below... 

Whiddon, C.R. Soderman, O. Unusually large deuterium isotope effects in the phase diagram of a mixed alkyl-glucoside surfactant/water system. Langmuir 2001, 17, 1803-1806. 

Imai, M. Teramoto, T. Takahashi, I. Nishiura, Y. Effects of guest hydrophobic molecule on stability or ordered meso structure of a surfactant/water system. Journal of Chemical Physics 2003, 119, 3891-3895. 

Franco, J.M. Munoz, J. Gallegos, C. Transient and steady flow of a lamellar hquid crystalhne surfactant/water system. Langrnuir 1995,11, 669-673. 

Fig. 4 Idealized phase sequence in surfactant-water systems. (From Ref., reproduced by permission of the Royal Society of Chemistry.)...

The present section gives a brief overview of ideas and the physical notions behind self-assembly of surfactant-water systems. 

Possible candidates for aggregates can now be examined. For surfactant-water systems these have been restricted in the past to spherical micelles, non-spherical micelles (globular, cylindrical), vesicles, liposomes, bilayers, and for oil-water-surfactant systems spherical drops, normal or inverted (water in oil) or (oil in water). 

As in binary surfactant-water systems considered previously, two constraints on the geometry of the surfactant interface are active a local constraint, which is due to the surfactant molecular architecture, and a global constraint, set by the composition. These constraints alone are sufficient to determine the microstructure of the microemulsion. They imply that the expected microstructure must vary continuously as a function of the composition of tile microemulsion. Calculations show - and small-angle X-ray and neutron scattering studies confirm - that the DDAB/water/alkane microemulsions consist of a complex network of water tubes within the hydrocarbon matrix. As water is added to the mixture, the Gaussian curvature - and topology -decreases [41]. Thus the connectivity of the water networks drops (Fig. 4.20). 

Most cubic phases in lipid-water systems exhibit unit cell parameters not larger than 20 mn, while the imit cell of cubic membranes is usually larger than 100 nm. Some exceptioi have been apparently found [131, 132] although at this stage such findings should be treated with caution, as the determination of lattice parameters is dependent on the indexing of diffraction patterns, based only on a small niunber of reflections. Further, in lipid-protein-water, lipid-poloxamer-water and lipid-cationic surfactant-water systems, cubic phases with cell parameters of the order of 50 nm have been observed [56,127, 128]. Due to the small number of reports dealing with the... 

A) Use CraTMA as template with necessary organic additives. Polar organic additives are important in the formation of MCM-48 when C/fl MA is used as template. For normal surfactant-water systems, it is widely believed that the role of the alcohol is to prevent the growth of the aggregates into infinite rods (hexagonal)... 

SBA-1 and SBA-6 were synthesized by using different surfactants and from acidic and basic synthesis media, respectively. They have the same structure and show the similar XRD patterns. Their structure is similar with cubic Ij phase, spherical micelles packed in Pm3n symmetry, in lyotropic liquid-crystal phase diagram for surfactant-water systems. 

Blute, I., Effect of hydrotropes on nonionic surfactant/water system. Phase and rheological behavior, manuscript in preparation. 

Surfactants by definition self-organise in water giving rise to micelles of varying size and shape. The core of micelles is non-polar and can solubilise reactants that are insoluble in water. Thus, a simple surfactant-water system at a surfactant concentration well above the critical micelle concentration can be used to overcome the problem of reactant incompatibility the polar reagent will be situated in the bulk aqueous domain, the non-polar reagent will be present in the micelles, and the reaction will occur at the micelle boundary. Organic reactions in micellar systems have been reported more than 40 years ago [1,2]. 

At higher surfactant concentration liquid crystalline phases may be formed. Surfactant liquid crystals can also solubilise appreciable amounts of oil into the non-polar regions made up of the surfactant tails. Thus, both binary surfactant-water systems and ternary systems with oil included can be formulated into liquid crystals. Such systems can also be used as media for organic synthesis. In fact, a reaction in a surfactant liquid crystal often runs very rapidly, considerably faster than in a microemulsion based on the same surfactant [19]. Figure 5.1 shows the reaction profiles of a typical substitution reaction of... 

Shinoda, K. (1970) Thermodynamic aspects of non-ionic surfactant-water systems. /. Colloid Interface Sci., 34,278. 

Table IV. Ultrafiltration (UF) and ultracentrifugation (UC) tests of surfactant solubility and particle size of surfactant-water systems, which were stirred well and allowed to settle for two days at 25°C.

Fig. VI-11. Phase diagram of a micelle-forming surfactant - water system...

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