Micelles formation driving force

Surface-active agents also aggregate in solution forming micelles. The driving force micelle formation (or micellization) is the reduction of contact between the hydrocarbon... 

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. 

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... 

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. 

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. 

The driving force for formation of rod shaped SDS micelles is the elimination of water from die micellar core/water interface (31). The reduction in average headgroup area reflects the removal of water molecules between the SDS headgroups, and should affect the bands due to the asymmetric S-O stretching vibrations, as indicated in the discussion of the transition moment vectors above. 

Surfactants are classified on the basis of the charge carried by the polar headgroup as anionic, cationic, nonionic, and amphoteric. Surfactant headgroups are dipoles, especially ionic ones that exist as ion pairs in hydrocarbon solvents. Electrostatic dipole-dipole attraction between headgroups in hydrocarbon solvents is the driving force for the formation of reverse micelles, or micellar aggregates, see Fig. 3.1 and Fig. 3.2. 

Some fundamentals of micelle formation and of the solubilization of water-insoluble substances by micelles are reviewed. The accelerating effect of micellization upon the rate of dissolution and of transport of solubilizate through bulk liquid is then considered. Membranes present an obstacle to transport. A larger fraction of the total driving force can be brought to bear upon this obstacle as other resistances are reduced by solubilization. Hence, transport across a membrane will, in general, be accelerated whether micelles are effective within the membrane or not. It is now possible to determine also this contribution of micelles to the transport within the membrane. In a specific case it was found to be negligible. 

The driving force for the formation of the hpid bilayer structure is the amphiphiUcity of the component molecules one part of the molecule is soluble in a particular solvent while the other has a low affinity to the solvent. If this concept is extended, the use of water as a medium is not a necessary condition of bilayer structure formation. Reversed micelles are formed in organic solvents. Are bilayer structures also formed in organic solvent This is an important question regarding the fundamental nature of amphiphilicity and the abihty to extend the applicability of amphiphile assembhes to various fields. The answer to this question is yes . Some compounds with a fluorocarbon part and a hydrocarbon part can form bilayer-like assemblies in organic solvent. The fluorocarbon part has a low affinity to the organic solvent and has a solvophobic nature, hi contrast, solvophilic characteristics are exhibited by the hydrocarbon parts. As shown in Fig. 4.30, these amphiphilic molecules assemble in order to expose the solvophilic part to the solvent and to hide the solvophobic part inside the assembly. If there is a good structural balance between the solvophilic part... 

So. at the minimum, where ln]c.m.c.] is - independent of T, AH(mic) = 0. Below this temperature, AH(mic)>0 (micelle formation endothermic), above it, AH(mic) < 0 (exothermic). Both the low magnitude and the sign change are in line with hydrophobic bonding as the main driving force. For cationic surfactemts not so many detailed studies are available, but the same trend is expected. In order to observe the minimum, careful measurements are required over a long temperature... 

Micelles form at the critical micelle concentration, which has a characteristic value for a particular surfactant under a given set of conditions. The main driving force for the formation of micelles is the increase of entropy that occurs when the hydro-phobic regions of the surfactant are removed from water and the ordered stmcture of the water molecules around this region of the molecule is lost. 

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