Critical micelle concentration hydrophilic groups

One of the most important characteristics of the emulsifier is its CMC, which is defined as the critical concentration value below which no micelle formation occurs. The critical micelle concentration of an emulsifier is determined by the structure and the number of hydrophilic and hydrophobic groups included in the emulsifier molecule. The hydrophile-lipophile balance (HLB) number is a good criterion for the selection of proper emulsifier. The HLB scale was developed by W. C. Griffin [46,47]. Based on his approach, the HLB number of an emulsifier can be calculated by dividing... 

In highly diluted solutions the surfactants are monodispersed and are enriched by hydrophil-hydrophobe-oriented adsorption at the surface. If a certain concentration which is characteristic for each surfactant is exceeded, the surfactant molecules congregate to micelles. The inside of a micelle consists of hydrophobic groups whereas its surface consists of hydrophilic groups. Micelles are dynamic entities that are in equilibrium with their surrounded concentration. If the solution is diluted and remains under the characteristic concentration, micelles dissociate to single molecules. The concentration at which micelle formation starts is called critical micelle concentration (cmc). Its value is characteristic for each surfactant and depends on several parameters [189-191] ... 

A positive value of ME means that the insertion of a hetero atom or group makes the molecule more lipophilic. If ME is negative, the hetero surfactant is more hydrophilic. In general, hetero atom insertion hydrophilizes the surfactant molecule as does the shift of the hetero group to the middle of the carbon chain [71]. ME values are temperature-dependent. / and ME values can also be useful to take into account the influence of various cations on the critical micelle concentration. 

A wide structural variation is possible within each class of molecules because both the length of the hydrophobic portion and the nature of the hydrophilic head group, as well as its position along the backbone, may be varied. The properties of the aggregates formed from these surfactants and the conditions under which they are formed depends on all these parameters. As the concentration of the surfactant in an aqueous solution is increased, many of the chemical and physical properties of the solution change rather abruptly (but continuously) over a concentration range known as the critical micelle concentration (CMC). 

Washing and Cleaning Action. The properties of alkyl ether sulfates, due to the good solubility and the special hydrophilic/hydrophobic properties of the molecule, are of particular practical interest. From the investigations described in sections 2 and 3, it can be concluded that, in addition to the decrease in the Krafft Point, favorable properties for practical applications can be expected as a result of the inclusion of the oxyethylene groups into the hydrophobic part of the molecule. As is true for other anionic surfactants, the electrical double layer will be compressed by the addition of multivalent cations. By this means, the adsorption at the interface is increased, the surface activity is raised, and, furthermore, the critical micelle concentration decreased. In the case of the alkyl ether sulfates, however these effects can be obtained without encountering undesirable salting out effects. 

To understand micelle formation quantitatively, critical micelle concentrations (cmc) have to be determined for a large number of surf actants ( 5 ). When the cmc values of the surfactants with the same hydrophilic group (a homologous series) are examined, a nearly 3-fold decrease in cmc is observed for nonlonlc and zwitterionlc surfactants (1,2) upon the addition of a methylene group into the hydrocarbon chain, whereas, a 2-fold or only 1.8-fold reduction in cmc can be observed for univalent (1,2) and blvalent( ) ionic surfactants,respectively. 

The structure and properties of water soluble dendrimers, such as 46, is, in itself, a very promising area of research due to their similarity with natural micellar systems. As can be seen from the two-dimensional representation of 46 the structure contains a hydrophobic inner core surrounded by a hydrophilic layer of carboxylate groups (Fig. 12). However these dendritic micelles differ from traditional micelles in that they are static, covalently bound structures instead of dynamic associations of individual molecules. A number of studies have exploited this unique feature of dendritic micelles in the design of novel recyclable solubilization and extraction systems that may find great application in the recovery of organic materials from aqueous solutions [84,86-88]. These studies have also shown that dendritic micelles can solubilize hydrophobic molecules in aqueous solution to the same, if not greater, extent than traditional SDS micelles. The advantages of these dendritic micelles are that they do not suffer from a critical micelle concentration and therefore display solvation ability at nanomolar... 

In MEKC, the supporting electrolyte medium contains a surfactant at a concentration above its critical micelle concentration (CMC). The surfactant self-aggregates in the aqueous medium and forms micelles whose hydrophilic head groups and hydrophobic tail groups form a nonpolar core into which the solutes can partition. The micelles are anionic on their surface, and they migrate in the opposite direction to the electroosmotic flow under the applied current. The differential partitioning of neutral molecules between the buffered aqueous mobile phase and the micellar pseudostationary phase is the sole basis for separation as the buffer and micelles form a two-phase system, and the analyte partitions between them (Smyth and McClean 1998). 

Molecules which have hydrophilic head groups attached to hydrocarbon chains are surface active but form micelles in water above a certain concentration (the critical micelle concentration, CMC). These micelles are generally spherical or cylindrical and have a positive, neutral or negative surface with a hydrocarbon like interior. 

McBain pointed out that this seemingly anomalous behaviour could be explained in terms of organised aggregates, or micelles, of the surfactant ions in which the lipophilic hydrocarbon chains are orientated towards the interior of the micelle, leaving the hydrophilic groups in contact with the aqueous medium. The concentration above which micelle formation becomes appreciable is termed the critical micelle concentration (c.m.c.). 

The critical micelle concentration (CMC) of Pluronics [121] has been found to be rather sensitive to temperature, which is ascribed to the changes in hydrophilicity of the ethylene oxide moiety with temperature. As shown already, monolayer viscoelasticity is correlated with the hydrophilicity of polymer backbones such as in polyethers, and that of the pendant group in vinyl polymers. It has been shown that PPO acts differently as a polyether... 

A micelle is a colloidal aggregate of amphiphilic molecules (50-100 molecules per micelle) which forms at a specific concentration termed the critical micelle concentration. As illustrated in Fig. 1, in polar media such as water, the hydrophobic part of the amphiphilic molecule tends to locate away from the polar phase while the polar groups of the molecule tend to locate in the water phase, forming the micelle aggregate. Micellar systems are able to solubilize both hydrophobic and hydrophilic compounds. 

Fixation of hydrophilic units as side-groups of a hydrophobic macromolecular chain leads to water-soluble polysoaps [205], exhibiting a similar diversity of self-organized structures like the monomeric analogues. A detailed review can be found in [206]. In contrast to polyelectrolytes and ionomers described above, the association of the amphiphilic groups of polysoaps occurs preferentially intramolecularly. As a consequence the solution viscosity remains low, even for highly concentrated solutions [207] and no critical micelle concentration (CMC) can be found up to extreme dilutions [208,209]. 

The solution behavior of low molecular weight amphiphilic molecules has been intensively investigated in the past (12-16) with respect to the formation of liquid crystalline phases. In very dilute aqueous solutions, the amphiphiles are molecularly dispersed dissolved. Above the critical micelle concentration (CMC), the amphiphiles associate and form micelles (Figure 4) of spherical, cylindrical or disc-like shape. The shape and dimension of the micelles, as a function of concentration and temperature, are determined by the "hydrophilic-hydrophobic" balance of the amphiphilic molecules. The formation of spherical aggregates is preferred with increasing volume fraction of the hydrophilic head group of the amphiphile, because the... 

Surfactants produce micelles. Their amphophilic nature classifies them as detergents, surface-active agents that are composed of a hydrophilic group and a hydrophobic hydrocarbon chain. In addition to what is known as the critical micelle concentration (CMC), individual surfactant molecules (monomers) interact with each other to form aggregates or micelles, establishing a state of equilibrium between a constant monomer concentration and a rapidly increasing micelle concentration. 

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