Micellization driving force

Micellar solutions are sometimes called ordered media [12]. The chemical order in a micellar solution seems to be greater than in a classical solution. Equation 2.9 shows ftiat the micellization of surfactant molecules obeys the second principle of thermodynamics. It seems that the surfectant hydrocarbon chains have a much higher freedom of motion inside the micelle core than in the water bulk [13]. The micelle structure minimizes the molecule energy. The large entropy increai of water molecules associated with the removal of nonpolar surfactant tails from the aqueous solution (hydrophobic effect) is the main micelle driving force. Electrostatic forces tend to separate the polar heads that bear the same charge. The whole micelle is an equilibrium between these forces. This equilibrium is very sensitive to any chemical additive or parameter that can act on any of the forces, such as salts, polar or nonpolar solutes, temperature and/or pressure. 

In addition to the degree of hydrophilicity of the solubilizates, their size and structure, the size of the host microregions, or the occurrence of specific processes must be taken into account in order to rationalize the driving forces of the solubilization process and of the solubilization site within water-containing reversed micelles [25,138,139],... 

In the case of Kryptofix 221D, a cryptand able to complex the alkali metal cations [141-143], it has been observed that it is solubilized mainly in the palisade layer of the AOT-reversed micelles. And from an analysis of the enthalpy of transfer of this solubilizate from the organic to the micellar phase it has been established that the driving force of the solubilization is the complexation of the sodium counterion. In addition, the enthalpy... 

The solubilization of amino acids in AOT-reversed micelles has been widely investigated showing the importance of the hydrophobic effect as a driving force in interfacial solubihzation [153-157]. Hydrophilic amino acids are solubilized in the aqueous micellar core through electrostatic interactions. The amino acids with strongly hydrophobic groups are incorporated mainly in the interfacial layer. The partition coefficient for tryptophan and micellar shape are affected by the loading ratio of tryptophan to AOT [158],... 

The heavy-end portions (usually called heavy fractions) of bitumen (e.g. asphaltenes, preasphaltenes) can exist both in a random oriented particle aggregate form or in an ordered micelle form, peptized with resin molecules (16.17). In their natural state, asphaltenes exists in an oil-external (Winsor s terminology) or reversed micelle. The polar groups are oriented toward the center, which can be water, silica (or clay), or metals (V, Ni, Fe, etc.). The driving force of the polar groups... 

Although the notion of monomolecular surface layers is of fundamental importance to all phases of surface science, surfactant monolayers at the aqueous surface are so unique as virtually to constitute a special state of matter. For the many types of amphipathic molecules that meet the simple requirements for monolayer formation it is possible, using quite simple but elegant techniques over a century old, to obtain quantitative information on intermolecular forces and, furthermore, to manipulate them at will. The special driving force for self-assembly of surfactant molecules as monolayers, micelles, vesicles, or cell membranes (Fendler, 1982) when brought into contact with water is the hydrophobic effect. 

Exchange of unimers between two different types of block copolymer micelles has often been referred to as hybridization. This situation is more complex than for the case described above because thermodynamic parameters now come into play in addition to the kinetic ones. A typical example of such hybridization is related to the mixing of micelles formed by two different copolymers of the same chemical nature but with different composition and/or length for the constituent blocks. Tuzar et al. [41] studied the mixing of PS-PMAA micelles with different sizes in water-dioxane mixtures by sedimentation velocity measurements. These authors concluded that the different chains were mixing with time, the driving force being to reach the maximum entropy. 

Thus, in the case B, the repulsion between the alkyl chain and water has been removed. Instead, the alkyl-alkyl attraction (B) is the driving force for micelle formation. The surfactant molecule forms a micellar aggregate at a concentration higher than CMC because it moves from the water phase to the micelle phase (lower energy). The micelle reaches an equilibrium after a certain number of monomers have formed a micelle. This means that there are both attractive and opposing forces involved in... 

No cysteine residues are found for alpha(sl) and P-caseins do. If any S-S bonds occur within the micelle, they are not the driving force for stabilization. Caseins are among the most hydrophobic proteins, and there is some evidence to suggest that they play a role in the stability of the micelle. It must be remembered that hydrophobic interactions are very temperature sensitive. 

Abstract There is a growing demand for hydrolyzable surfactants, i.e., sirnfactants that break down in a controlled way by changing the pH. Environmental concern is the main driving force behind current interest in these sirnfactants, but they are also of interest in applications where sirnfactants are needed in one stage but later undesirable at another stage of a process. This chapter summarizes the field of hydrolyzable sirnfactants with an emphasis on their more recent development. Surfactants that break down either on the acid or on the alkaline side are described. It is shown that the susceptibility to hydrolysis for many surfactants depends on whether or not the surfactant is in the form of micelles or as free unimers in solution. It is shown that whereas nonionic ester sirnfactants are more stable above the CMC (micellar retardation), cationic ester surfactants break down more readily when aggregated than when present as unimers (micellar catalysis). 

The table reveals that the adsorption free energy is dominated by the cmc term. Thus, the dominating driving force of adsorption is of the same origin as for the micellization, i.e. it depends on the... 

Critical micelle concentration in aqueous solutions was determined by fluorescence using pyrene as a probe. The driving force for micelle formation is the strong hydro-phobic interactions between [(R)-3-hydroxybutyrate] block. It was previously determined by this group that terpolymers with longer PHB blocks have much lower critical micelle concentrations because of PHB block aggregation in aqueous solution. Testing results are provided in Table 2. 

The central core is predominantly hydrocarbon. The expulsion of the hydrophobic tails of the surfactant molecules from the polar medium is an important driving force behind micellization. The amphipathic molecules aggregate with their hydrocarbon tails pointing together toward the center of the sphere and their polar heads in the water at its surface. 

One consequence of roughness at the surface of the micellar core is an increased contact between water and hydrocarbon. Figure 8.3b seems unrealistic because the water-hydrocarbon contact is scarcely less than in the bulk solution, a situation that apparently undermines an important part of the driving force for micellization. Figure 8.3c minimizes this effect without eliminating it. At the same time it allows for some water entrapment, which accounts for that part of the micellar hydration that was unexplained by the hydration of ions and charged groups. 

The objective of this portion of the research was to experimentally evaluate surfactant effects on the liquid-liquid separation of hydrophobic oils from a surfactant system. For pump-and-treat subsurface remediation in the absence of surfactant, contaminated ground water would be pumped from the subsurface and through a liquid-liquid extraction column where the contaminant partitions from the aqueous phase into an extraction solvent phase. In the absence of surfactant, the driving force for partitioning is a function of the contaminant hydrophobicity. In the presence of surfactants, the contaminant is subject to competitive partitioning (i.e., into the micelles and into the extracting oil). 

From your understanding of the non-covalent interactions outlined in Chapter 1, discuss the driving force behind the formation of surface monolayers, micelles and other forms of liquid order. 

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