Surfactant aggregate

We have already seen in Chapter 5, on self-organization, how and why amphiphilic molecules tend to form aggregates such as micelles, vesicles, and other organized structures. 

Equals a surface of a Passport photo Desk Swimming pool Stadium 

It is no surprise then that surfactants are used so extensively in technical applications and of course this large surface area achieved by surfactant aggregates immediately inspires ideas of applications in basic chemistry too if for example the surfactant head had some catalytic properties, these could be extended and developed into an almost incredible dimension. 

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The fonnation of surface aggregates of surfactants and adsorbed micelles is a challenging area of experimental research. A relatively recent summary has been edited by Shanna [51]. The details of how surfactants pack when aggregated on surfaces, with respect to the atomic level and with respect to mesoscale stmcture (geometry, shape etc.), are less well understood than for micelles free in solution. Various models have been considered for surface surfactant aggregates, but most of these models have been adopted without finn experimental support. 

King A D 1995 Solubilization of gases Solubilization in Surfactant Aggregates ed S D Christian and J F Scamehorn (New York Dekker) pp 35-58... 

Christian S D and Scamehorn J F (eds) 1995 Solubilization in Surfactant Aggregates (New York Dekker)... 

Manne S 1997 Visualizing self-assembly Force microscopy of ionic surfactant aggregates at solid-liquid interfaces Prog. Colloid Polym. Sol. 103 226-33... 

S. T. Hyde. Microstructure of bicontinuous surfactant aggregates. J Phys Chem 95 1458-1464, 1989. 

Solubilization in Surfactant Aggregates, edited by Sherril D. Christian and John F. Scamehom... 

Recent development of the use of reversed micelles (aqueous surfactant aggregates in organic solvents) to solubilize significant quantities of nonpolar materials within their polar cores can be exploited in the development of new concepts for the continuous selective concentration and recovery of heavy metal ions from dilute aqueous streams. The ability of reversed micelle solutions to extract proteins and amino acids selectively from aqueous media has been recently demonstrated the results indicate that strong electrostatic interactions are the primary basis for selectivity. The high charge-to-surface ratio of the valuable heavy metal ions suggests that they too should be extractable from dilute aqueous solutions. 

The geometry and surface chemistry of the dendrimer assemblies can be varied through the addition of surfactants. These dendrimer/surfactant aggregates can be tuned to template the formation of the different phases of calcium carbonate [40]. In combination with hexadecyltrimethylammonium bromide (CTAB), small spherical aggregates were formed that induce the formation of vaterite. Over a period of five days, the vaterite was transformed into calcite. The use of the negatively charged surfactant, sodium dodecylsulfonate (SDS), result-... 

The water-soluble calix[n]arenes 6.3 (n = 4, 6 and 8) containing trimethylammonium groups act as efficient inverse phase-transfer catalysts in the nucleophilic substitution reaction of alkyl and arylalkyl halides with nucleophiles in water (Eq. 6.19).40 In the presence of various surfactants (cationic, zwitterionic and anionic), the reactions of different halides and ketones show that the amount of ketone alkylation is much higher and that the reactions are faster in the presence than in the absence of surfactant aggregates.41 The hydrolysis of the halide is minimized in the presence of cationic or zwitterionic surfactants. 

Figure 12.2 Preferred orientation of diene and dienophile at a surfactant aggregate-water interface.

Gauffre, F. and Roux, D. (1999) Studying a new type of surfactant aggregate ( Spherulites ) as chemical microreactors. A first example Copper ion entrapping and particle synthesis. Langmuir, 15, 3738-3747. 

From Chandar et al. (1987) based on the data of Somasundaran and Fuerstenau (1966). Chandar et al. (1987) have shown with the aid of fluorescent probe studies that in region II and above adsorption occurs through the formation of surfactant aggregates of limited size. 

Surfactant solutions critical micelle concentration distribution of reactants among particles surfactant aggregation numbers interface properties and polarity dynamics of surfactant solutions partition coefficients phase transitions influence of additives... 

This paper presents a new finding that the oil solubilization rate is a function of the surfactant aggregate size. This idea originated from Chiu s observation on solubilization phenomena in tertiary oil recovery. 

Although the proposed theory has been used effectively in several practical applications, no experimental proof has been given that the oil solubilization rate is a function of surfactant aggregate size. In view of the importance of solubilization and the existence of practical methods of measuring and controlling surfactant aggregate size, we decided to correlate the solubilization rate with micellar properties for some anionic and nonionic surfactants. 

Light scattering technique was used in determining the oil solubilization rate. Debye s equation ( ) was used in the interpretation. The basic principle involves the measurement of the surfactant aggregate size during the solubilization. As the oil goes into the surfactant micelle, the increased size will be reflected by the turbidity of the solution. 

A Proposed Theory. In earlier publications (1-3), a theory was proposed to correlate solubilization rate, interfacial tension and size of the surfactant aggregate (1) the interfacial tension lowering between the oil-surfactant solution interface is a function of the rate of solubilization of oil, and (2) the rate of solubilization (AS/At) is a function of the effective volume for solubilization ... 

S.D. Christian, J.F. Scamehorn (eds.), Sdubilization in Surfactant Aggregates, Marcel Dekker, New York, 1995. 

Reverse micelles of CTAB in octane with hexanol as cosurfactant were reported to be able to lyse whole cells quickly and accommodate the liberated enzyme rapidly into the water pool of surfactant aggregates [50,51]. In another case a periplasmic enzyme, cytochrome c553, was extracted from the periplasmic fraction using reverse micelles [52]. The purity achieved in one separation step was very close to that achieved with extensive column chromatography. These results show that reverse micelles can be used for the extraction of intracellular proteins. 

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