Surfactant effective packing parameter

Surfactant Effective Packing Parameter g and Physical Chemistry of Assembly and Interface Considerations... 

In the real synthesis systems, the surfactant effective packing parameter, g, are mainly affected by the following factors (1) charge, composition, molecular shape, and structure of surfactant, (2) the interactions between surfactant and inorganic species (e.g., charge-density matching), (3) reaction parameters and conditions concentration, pH, ion strength, temperature, etc. 

III microemulsion system in the presence of water and an appropriate oil, without requiring cosurfactant nor electrolyte. They play a dual role as [1] Oj generating catalyst and as surfactant stabilizing the bicontinuous microemulsion. From a physicochemical point of view, they must have an effective packing parameter close to one [73]. Bis(dimethyldialkylammonium)molybdates are typical examples of such balanced catalytic surfactants, which lead to a three-phase system as shown in Figure 22.6. In such reaction media, 02 is exclusively generated in the aqueous nanodomains of the middle-phase microemulsion where the reaction takes place. Under stirring, the excess oil phase transfers the substrate S to the... 

Effective shape of the surfactant molecule Packing parameter "m.of/r Aggregate morphology... 

It is well known that the aqueous phase behavior of surfactants is influenced by, for example, the presence of short-chain alcohols [66,78]. These co-surfactants increase the effective value of the packing parameter [67,79] due to a decrease in the area per head group and therefore favor the formation of structures with a lower curvature. It was found that organic dyes such as thymol blue, dimidiiunbromide and methyl orange that are not soluble in pure supercritical CO2, could be conveniently solubihzed in AOT water-in-C02 reverse microemulsions with 2,2,3,3,4,4,5,5-octafluoro-l-pentanol as a co-surfactant [80]. In a recent report [81] the solubilization capacity of water in a Tx-lOO/cyclohexane/water system was foimd to be influenced by the compressed gases, which worked as a co-surfactant. 

Different surfactants are usually characterised by the solubility behaviour of their hydrophilic and hydrophobic molecule fraction in polar solvents, expressed by the HLB-value (hydrophilic-lipophilic-balance) of the surfactant. The HLB-value of a specific surfactant is often listed by the producer or can be easily calculated from listed increments [67]. If the water in a microemulsion contains electrolytes, the solubility of the surfactant in the water changes. It can be increased or decreased, depending on the kind of electrolyte [68,69]. The effect of electrolytes is explained by the HSAB principle (hard-soft-acid-base). For example, salts of hard acids and hard bases reduce the solubility of the surfactant in water. The solubility is increased by salts of soft acids and hard bases or by salts of hard acids and soft bases. Correspondingly, the solubility of the surfactant in water is increased by sodium alkyl sulfonates and decreased by sodium chloride or sodium sulfate. In the meantime, the physical interactions of the surfactant molecules and other components in microemulsions is well understood and the HSAB-principle was verified. The salts in water mainly influence the curvature of the surfactant film in a microemulsion. The curvature of the surfactant film can be expressed, analogous to the HLB-value, by the packing parameter Sp. The packing parameter is the ratio between the hydrophilic and lipophilic surfactant molecule part [70] ... 

Introduction to the variety of types of surfactants, effect of surfactants on aqueous solution properties. Law of mass action applied to the self-assembly of surfactant molecules in water. Spontaneous self-assembly of surfactants in aqueous media. Formation of micelles, vesicles and lamellar structures. Critical packing parameter. Detergency. Laboratory project on determining the charge of a micelle. 

Effective Shape of the Surfactant Packing Parameter Aggregate Morphology Cone <1 /3 P = fj Spherical micelles... 

To date, there are many synthesis recipes for MCM-48 available. The basic concept for these syntheses is to control the effective surfactant-packing parameter g between the limits 1/2 and 2/3 in other words, to increase the palisade-layer volume of micelles. The following are some successful synthesis strategies. 

Fig. 4 Critical packing parameters and characteristic structure typical to mesoporous silica films. The top shows a cross-section of a micelle, displaying the parameters used to calculate the CPP. The spherical head group for the surfactant represents the effective cross-sectional area that the head group occupies. (View this art in color at www.dekker.com.)...

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