Micelle steric force

For similar micellas concentrations, the effect of electrolyte will be more severe for the anionic surfactant as it will suppress the electrostatic double-layer repulsive forces acting between the micelles. For nonionic surfactant, the repulsive force between micelles is a steric force rather than an electrostatic force, such that electrolyte has less of an effect. 

The first reason lies in the fact that the interaction between solvent molecules (usually water) is stronger than the interaction between the solvent and the solute. This effect alone would lead to a precipitation of the solute. In the case of amphiphiles which form micelles, however, the head groups are strongly hydrated and repulse each other. The hydration forces and steric forces which are made responsible for this repulsion effect prevent crystallization above the Krafft point and also above the cmc. Where the formation of 3D crystals is impeded, the smallest possible droplet is formed, removing the alkyl chains from the solvent. The interactions between solvent molecules are therefore disturbed to a minimal extent, allowing the head groups to be solvated with a minimal entropy loss. It is irrelevant whether the solvent contains clusters or not. Micelle formation only occurs as a result of a solvation of head groups and non-solvation of a solvophobic core. ... 

Generally, the disjoining pressure consists of the electrostatic repulsion forces between the two overlapping surface double layers, the attractive van der Waals forces among all the molecules of the film, the steric forces due to steric hindrance in closely packed monolayers and, in the presence of micelles, the structural forces. 

The stages of foam film thinning just described are typical for aqueous solutions of most low-molecular-mass surfactants, and the time scale of the process is approximately the same the film thickness becomes on the order of 1 (Jim in a few seconds, about 1 min is needed for thinning of the film down to about 100 mn, and 2 to 4 min are needed until the final equilibrium film thickness is established. The main difference between the various systems is in the number of the stepwise transitions, which depends strongly on the smfactant concentration. Close to the cmc, when the volume fraction of the micelles is low, either there is only one transition from a common black film to a very thin Newton black film or there are no transitions at all because the equilibrium film thickness corresponds to a common black film, stabilized by electrostatic or steric forces. However, when the surfactant concentration is well above the cmc, up to five to seven transitions are... 

Van der Waals forces There has been some success in relating these forces to micellar stability. However, the steric stabilization has been found to be also of some importance. Especially, the hairy layer interferes with the interparticle approach. There are several factors that will affect the stability of the casein micelle system ... 

Casein or egg-yolk proteins are used as emulsifiers in a number of food products, such as O/W food emulsions (Table 13.1) [78,824]. A key difference here is that in caseinate-stabilized oil emulsions, the casein forms essentially monolayers and there are no casein micelles nor any calcium phosphate. Such emulsions are thought to be stabilized more by electrostatic repulsive forces and less by steric stabilization, in contrast to the situation in homogenized milk products [824]. 

Abstract Polyelectrolyte block copolymers form micelles and vesicles in aqueous solutions. Micelle formation and micellar structure depends on various parameters like block lengths, salt concentration, pH, and solvent quality. The synthesis and properties of more complicated block and micellar architectures such as triblock- and graft copolymers, Janus micelles, and core-shell cylinder brushes are reviewed as well. Investigations reveal details of the interactions of polyelectrolyte layers and electro-steric stabilization forces. 

Certain comb-type silicone surfactants have been shown to stabilize emulsions in the presence of salts, alcohol and organic solvents that normally cause failure of emulsions stabilized using conventional hydrocarbon surfactants and a study by Wang et al. [66,67] investigated the cause of this stability. Interaction forces due to silicone surfactants at an interface were measured using AFM. Steric repulsion provided by the SPE molecules persisted up to an 80% or higher ethanol level, much higher than for conventional hydrocarbon surfactants. Nonionic hydrocarbon surfactants lose their surface activity and ability to form micelles in... 

In w/o emulsions the hydrocarbon chains of the adsorbed molecules protrude into the oily continuous phase. Stabilisation arises from steric repulsive forces as described in section 7.2.2. Emulsions are more complex than suspensions, because of the possibility (a) of movement of the surfactant into either the continuous or disperse phase, (b) micelle formation in both phases, and (c) the formation under suitable conditions of liquid crystalline phases between the disperse droplets. 

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