Micelles characteristic properties

Principal micelle characteristics. The structure of the casein micelles has attracted the attention of scientists for a considerable time. Knowledge of micelle structure is important because the stability and behaviour of the micelles are central to many dairy processing operations, e.g. cheese manufacture, stability of sterilized, sweetened-condensed and reconstituted milks and frozen products. Without knowledge of the structure and properties of the casein micelle, attempts to solve many technological problems faced by the dairy industry will be empirical and not generally applicable. From the academic viewpoint, the casein micelle presents an interesting and complex problem in protein quaternary structure. 

One characteristic property of surfactants is that they spontaneously aggregate in water and form well-defined structures such as spherical micelles, cylinders, bilayers, etc. (review Ref. [524]). These structures are sometimes called association colloids. The simplest and best understood of these is the micelle. To illustrate this we take one example, sodium dode-cylsulfate (SDS), and see what happens when more and more SDS is added to water. At low concentration the anionic dodecylsulfate molecules are dissolved as individual ions. Due to their hydrocarbon chains they tend to adsorb at the air-water interface, with their hydrocarbon chains oriented towards the vapor phase. The surface tension decreases strongly with increasing concentration (Fig. 3.7). At a certain concentration, the critical micelle concentration or... 

Bioaccumulation All classes of surfactant are active surface tension depressants. At the critical micelle concentration (CMC) abrupt changes occur in the characteristic properties of surfactants such that surface and interfacial tensions in an aqueous system are at their minimum while osmotic pressure and surface detergent properties are significantly increased. The CMC for most surfactants is reached around 0.01% (18, 19). These effects have an impact on the potential for bioaccumulation of the pesticide, and in the organisms monitored the presence of Dowanol and nonylphenol increased the accumulation of fenitrothion and aminocarb at least 20-300% respectively, over the accumulation obtained in their absence (20). In effect, these adjuvants... 

A characteristic property of surfactant molecules is their tendeney to aggregate at interfaces. Examples are adsorptions onto solids and monolayer formation at an air-water interface. Surfactants sometimes ereate their own interface by forming very small aggregates like mieelles or vesieles to remove a portion of their structure from direct contact with a solvent. In ease of a mieelle formed with a surfactant such as Triton X-IOO, the hydroearbon ehains are in closer contact in the center and form a hydrophobic microenvironment. The ethylene oxide moieties are exposed to water with mueh greater frequeney. If a hydrophobic species is added into this micellar system, there will be a tendeney for the hydrophobic molecules to be concentrated inside a mieelle. At low concentration, the micelle system and the added hydrophobic additives ean reach a thermodynamic equilibrium, which is often called microemulsion system. At high concentration, the hydrophobic additives form their own separate phase and the surfactant molecules serve only as a decorative layer... 

The metachromatic reaction of heparin and heparinoids with dyes is an important key to the riddle of their chemical nature. A similar reaction is the starch-iodine reaction. This is due to the fixation of the iodine atoms in the starch micelle in an orderly array and is a well-known example of a clathrate, in which atoms or molecules are held in channels of larger molecules by strong, non-polar forces— hydrogen bond and London forces. It is the possession of a similar structure but with highly polar groups (NH SO4, O SO3, COO ) in close proximity, which endows the mucopolysaccharides and heparinoids with their highly specific, characteristic properties. 

Thus, micelle characteristics depending on pH and IPrOH water ratio play a crucial part in the catalytic properties as they may control the substrate and product transport towards active centers and their modification. 

Although they are not micelles, microemulsions and cyclodextrin (CD) derivatives have also been introduced as PSs for MEKC. Oil-in-water (o/w) microemulsions have been shown to be good PSs for EKC. Microemulsions (o/w) are prepared by mixing oil, water, a surfactant, and a cosurfactant such as a medium alkyl-chain alcohol. They have the characteristic properties of a solvent, such as thermodynamic stability and a high solubilization power. The... 

When the variation of any colligative property of a surfactant in aqueous solution is examined, two types of behavior are apparent. At low concentrations, properties approximate those to be expected from ideal behavior. However, at a concentration value that is characteristic for a given surfactant system (critical micelle concentration, CMC), an abrupt deviation from such behavior is observed. At concentrations above the CMC, molecular aggregates called micelles are formed. By increasing the concentration of the surfactant, depending on the chemical and physical nature of the molecule, structural changes to a more... 

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. 

The most useful characteristic of the micelle arises from its inner (alkyl chain) part (Figure 3.17). The inner part consists of alkyl groups that are closely packed. It is known that these clusters behave as liquid paraffin (Cn H2n+2). The alkyl chains are thus not fully extended. Hence, one would expect that this inner hydrophobic part of the micelle should exhibit properties that are common to alkanes, such as ability to solubilize all kinds of water-insoluble organic compounds. The solute enters the alkyl core of the micelle and it swells. Equilibrium is reached when the ratio between moles soluteimoles detergent is reached corresponding to the thermodynamic value. 

With short chain derivatives, the forces of repulsion are higher than the ones of attraction the curvature is high and spherical micelles are formed at a concentration called the critical micellar concentration (cmc). This concentration can be detected by a change in the physico-chemical properties of the solution (e.g. surface tension, Fig. 3 a). Above a characteristic temperature (referred as Krafft temperature), the tensio-active molecules are infinitely soluble in the form of micelles (Fig. 3 b). 

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