Surfactant micellization

Micelles. Surfactant molecules or ions at concentrations above a minimum value characteristic of each solvent-solute system associate iato... 

FIG. 1 Representation of a reversed micelle ( surfactant molecules are obtained by combining rubber pipette bulbs and magnetic stir bars). 

K Binding constant of solute based on concentration of micellized surfactant... 

In Scheme 2 D denotes micellized surfactant detergent, S is substrate, subscripts W and M denote aqueous and micellar pseudophases respectively, and /fyj and k are first-order rate constants. The binding constant, Ks, is written in terms of the molarity of micellized surfactant, but it could equally be written in terms of the molarity of micelles. The two constants differ in magnitude by the aggregation number of the micelles. 

The concentration of micellized surfactant is that of total surfactant less that of monomer which is assumed to be given by the critical micelle concentration (cmc). The overall first-order rate constant kv is then given by (1). 

Quantitative fits of the rate constant to concentrations of surfactant or reagent are sometimes poor when [surfactant] is close to the cmc. Several factors can be involved here (l) the kinetic cmc can be lower than that in water because the reagents promote micellization (ii) reaction is promoted by submicellar aggregates or (iff) the simplifying assumptions involved in the kinetic equations (2-6) may be invalid when concentrations of substrate and micellized surfactant are similar (Romsted, 1984). 

The functional micellized surfactant contained both imidazole and hydroxyethyl groups and the final products of reaction with p-nitrophenyl alkanoates are acyl derivatives of the hydroxyethyl group. However, these O-acylated products were formed from an acylimidazole intermediate which... 

The rate constants and k represent rate constants for a surface reaction and have units m mol s and s respectively. The accelerative effects are about 10 -10 fold. They indicate that both reactants are bound at the surface layer of the micelle (surfactant-water interface) and the enhanced rates are caused by enhanced reactant concentration here and there are no other significant effects. Similar behavior is observed in an inverse micelle, where the water phase is now dispersed as micro-droplets in the organic phase. With this arrangement, it is possible to study anion interchange in the tetrahedral complexes C0CI4 or CoCl2(SCN)2 by temperature-jump. A dissociative mechanism is favored, but the interpretation is complicated by uncertainty in the nature of the species present in the water-surfactant boundary, a general problem in this medium. 

Addition of further surfactant then dilutes the reactants by increasing the volume of the micellar pseudophase and the observed reaction rate (or reaction rate constant) decreases. This kinetic scheme results in Equation (7) describing the observed second-order rate constant obs,2 as a function of micellized surfactant concentration [8]. ... 

Micelles. Surfactant molecules or ions at concentrations above a minimum value characteristic of each solvent-solute system associate into aggregates called micelles. The formation, structure, and behavior of micelles have been extensively investigated. The term critical micelle concentration (CMC) denotes the concentration at which micelles start to form in a system comprising solvent, surfactant, possibly other solutes, and a defined physical environment. 

Colloidal semiconductor particles were in situ generated and coated by catalysts in reversed micelles, surfactant vesicles and polymerized surfactant vesicles. 

For ionic surfactants micellization is surprisingly little affected by temperature considering that it is an aggregation process later we see that salt has a much stronger influence. Only if the solution is cooled below a certain temperature does the surfactant precipitate as hydrated crystals or a liquid crystalline phase (Fig. 12.4). This leads us to the Krafft temperature1 also called Krafft point [526]. The Krafft temperature is the point at which surfactant solubility equals the critical micelle concentration. Below the Krafft temperature the solubility is quite low and the solution appears to contain no micelles. Surfactants are usually significantly less effective in most applications below the Krafft temperature. Above the Krafft temperature, micelle formation becomes possible and the solubility increases rapidly. 

In the various sections of this chapter, I will briefly describe the major characteristics of FT-IR, and then relate the importance of these characteristics to physiochemical studies of colloids and interfaces. This book is divided into two major areas studies of "bulk" colloidal aggregates such as micelles, surfactant gels and bilayers and studies of interfacial phenomena such as surfactant and polymer adsorption at the solid-liquid interface. This review will follow the same organization. A separate overview chapter addresses the details of the study of interfaces via the attenuated total reflection (ATR) and grazing angle reflection techniques. 

Enormous advances and growth in the use of ordered media (that is, surfactant normal and reversed micelles, surfactant vesicles, and cyclodextrins) have occurred in the past decade, particularly in their chromatographic applications. New techniques developed in this field include micellar liquid chromatography, micellar-enhanced ultrafiltration, micellar electrokinetic capillary chromatography, and extraction of bioproducts with reversed micelles techniques previously developed include cyclodextrins as stationary and mobile-phase components in chromatography. The symposium upon which this book was based was the first major symposium devoted to this topic and was organized to present the current state of the art in this rapidly expanding field. 

Steady-state conversions for VA and MMA polymerizations in a CSTR do not agree with reactor models based on Smith-Ewart Case II kinetics. This is not surprising since such a model does not consider many important phenomena. The particle-formation component of the Smith-Ewart Case II model is based on a simple mathematical relation which assumes that the rate of formation of new particles is proportional to the ratio of free (dissolved or in micelles) surfactant to total surfactant. This equation is based on the earlier concept of particle formation via free radical entry into micelles. 

Total Surface Areas of the Micalira in Solutions of Sodium Alkyl Sulfates Containing 0.012 mol dm Miceller Surfactant... 

Enormous effort is spent on studying complex fluids, more-so than any of the previous topics reviewed above. These fluids include polymer solutions and melts, alkanes, colloidal systems, electrolytes, liquid crystals, micelles, surfactants, dendrimers and, increasingly, biological systems such as DNA and proteins in solution. There are therefore many specialist areas and it is impossible to review them all here. As such, we sample only a select few areas that reflect our own personal interests, and apologise to readers who have specific interests elsewhere. First, we briefly look over some simulations on colloidal systems, alkanes, dendrimers, biomolecular systems, etc, and will then... 

Bunton et al.15 demonstrated catalytic behavior in the spontaneous hydrolysis of 2,4-dinitrophenyl phosphate promoted by alkane a,co-bis(trimethylammonium) bolaphiles. The enhanced rate of hydrolysis followed the greater degree of organization within vesicles from surfactants possessing longer (CX-CY) spacers. Notably, bolaphiles with 12 and 16 methylene spacers did not form micelles, but instead formed small clusters, and showed a lower rate enhancement versus micellizing surfactants. 

Hexadecylpyridinium chloride, cetylpyridinium chloride n-Hexadecyltrimethylammonium bromide (hydroxide) or cetyltrimethylammonium bromide (hydroxide) Stoichiometric concentration of surfactant (detergent) Concentration of micellized surfactant generally [D ] = [D]-cwc... 

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