Design and Production of Nanoparticles Formulated From Nano-Emulsion Templates-A Review

Aqueous solutions of certain surfactant micelles exhibit phase separation behavior upon temperature alteration. This phenomenon can be exploited in separation science for the development of extraction, purification, and preconcentration schemes for desired analytes. Since the addition of just a small amount of an appropriate nonionic or zwitterionic surfactant to the aqueous sample solution is required, this approach is convenient and fairly benign, eliminating the need for the use of organic solvents as in conventional liquid−liquid or solid−liquid extraction. The basic features, experimental protocols, and selected recent applications of this alternative extraction approach, termed cloud point extraction (CPE) or micelle-mediated extraction (ME), are briefly reviewed. In addition, the advantages, limitations, and anticipated future directions of this methodology are discussed.

Surfactant-Mediated Cloud Point Extractions: An Environmentally Benign Alternative Separation Approach

Time-resolved fluorescence quenching (TRFQ) and electron paramagnetic resonance (EPR) were employed to characterize micelles of dodecyltrimethylammonium bromide and chloride (DTAB and DTAC) as reaction media. For DTAB, the aggregation numbers, N, and the quenching rate constant of pyrene by hexadecylpyridinium chloride, kq, were measured with TRFQ. Both these aggregation numbers for DTAB and those for DTAC taken from the literature depend only on the concentration of counterions in the aqueous phase, Caq, whether these counterions are supplied by the surfactant alone or by surfactant plus added salt. Both surfactants conform to the power law N = N0(Caq/cmc0)γ where N0 is the aggregation number at the critical micelle concentration in the absence of any additives (cmc0). N0 and γ differ for the two surfactants and vary with temperature in DTAB. EPR is employed to investigate the microviscosity and the hydration of the polar shell using a spin probe. The hydration is expressed by the nonempirical polarity p...

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Characterization of Micelles of Quaternary Ammonium Surfactants as Reaction Media I: Dodeclytrimethylammonium Bromide and Chloride

Product yields measured by high-performance liquid chromatography from chemical trapping of Cl-, Br-, and H2O by an aggregate-bound arenediazonium ion in cetyltrialkylammonium halide {(CTRA)X, R = Me, Et, n-Pr, and n-Bu; X = Cl, Br}, micelles are used to estimate, simultaneously, interfacial counterion, Xm, and water, H2Om, concentrations as a function of [(CTRA)X] and tetramethylammonium halide concentrations, [(TMA)X]. The results are interpreted by using a two-site pseudophase model. Values of Xm and H2Om are estimated by assuming that when the product yields from reaction of a long-tail aggregate-bound arenediazonium ion in micelles are the same as the product yields from reaction of its short chain analogue in an aqueous quaternary ammonium ion salt solution, then Xm = [Xw] and H2Om = [H2Ow] in those solutions. The results show that Xm and H2Om are functions of headgroup size, surfactant concentration, and aqueous counterion concentration and type. Plots of Xm against [(CTRA)X] at a series of salt co...

Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 6. Relationships between Interfacial Counterion and Water Concentrations and Surfactant Headgroup Size, Sphere-to-Rod Transitions, and Chemical Reactivity in Cationic Micelles†

Surface-active amphiphiles aggregate spontaneously in water to form association colloids such as micelles, microemulsions, and vesicles. The hydrophobic effect drives aggregation, but the opposing forces that provide balance and determine equilibrium morphologies are not understood, in particular, how specific ion effects, which often follow a Hofmeister series, affect the properties of association colloids. We have harnessed the competitive trapping of arenediazonium ions by weakly basic nucleophiles such as halide counterions, anionic headgroups, alcohols, urea, and water, to estimate their concentrations in the interfacial regions of association colloids from reaction product yields. In the chemical trapping method, product yields are proportional to the concentrations of water and other nucleophiles within the interfacial region, not their stoichiometric concentrations in solution. Changes in the balance of forces controlling aggregate structure are reflected in changes in interfacial concentrations o...

Do amphiphile aggregate morphologies and interfacial compositions depend primarily on interfacial hydration and ion-specific interactions? The evidence from chemical trapping.

Chemical trapping of water and terminal OH groups in nonionic micelles of hexaoxyethylene monododecyl ether, C12E6, by an aryl cation formed by spontaneous decomposition of an aggregate-bound 4-hex...

Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 4.1-3 Estimation of the Hydration Numbers of Aqueous Hexaethylene Glycol Monododecyl Ether, C12E6, Micelles by Chemical Trapping†

An aggregate-bound long tail arenediazonium ion, 4-hexadecyl-2,6-dimethylbenzenediazonium ion, 16-ArN2+, was used as a chemical trapping reagent to estimate the hydration state and terminal hydroxyl, OH, group distributions within the interfacial region of sets of binary mixed nonionic micelles of oligooxyethylene alkyl monoether, CmEn, surfactants:  C10E4/C12E6, C10E4/C16E8, C10E5/C16E8, C12E6/C16E8, and C10E5/C12E5. 16-ArN2+ decomposes spontaneously to generate an aryl cation that is trapped by water and by the terminal OH groups of the two nonionic surfactants to give phenol and alkyl aryl ethers as products. Quantitative analyses of product yields by HPLC were used to estimate the hydration numbers and relative number densities of the terminal OH groups of the two surfactants in the two inner layers of the interfacial region adjacent to the micellar core. The thickness of one layer is set equal to the length of one ethylene oxide unit. The radial distributions of terminal OH groups and ethylene oxide ...

Arenediazonium salts : New probes of the interfacial compositions of association colloids. 5.1-4 Determination of hydration numbers and radial distributions of terminal hydroxyl groups in mixed nonionic CmEn micelles by chemical trapping

Jihu Yao

Papers

Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 4.1-3 Estimation of the Hydration Numbers of Aqueous Hexaethylene Glycol Monododecyl Ether, C12E6, Micelles by Chemical Trapping†

Arenediazonium salts : New probes of the interfacial compositions of association colloids. 5.1-4 Determination of hydration numbers and radial distributions of terminal hydroxyl groups in mixed nonionic CmEn micelles by chemical trapping