Fluorescence aggregation number

Other solubilization and partitioning phenomena are important, both within the context of microemulsions and in the absence of added immiscible solvent. In regular micellar solutions, micelles promote the solubility of many compounds otherwise insoluble in water. The amount of chemical component solubilized in a micellar solution will, typically, be much smaller than can be accommodated in microemulsion fonnation, such as when only a few molecules per micelle are solubilized. Such limited solubilization is nevertheless quite useful. The incoriDoration of minor quantities of pyrene and related optical probes into micelles are a key to the use of fluorescence depolarization in quantifying micellar aggregation numbers and micellar microviscosities [48]. Micellar solubilization makes it possible to measure acid-base or electrochemical properties of compounds otherwise insoluble in aqueous solution. Micellar solubilization facilitates micellar catalysis (see section C2.3.10) and emulsion polymerization (see section C2.3.12). On the other hand, there are untoward effects of micellar solubilization in practical applications of surfactants. Wlren one has a multiphase... 

Van Paassen [57] describes the CMC of some polyether carboxylates with different fatty chains and EO degrees (Fig. 2). In an extensive study, Binana-Limbele et al. [59] investigated the micellar properties of the alkylpolyether carboxylates of the general formula CnH + OCF CH OCI COONa with n = 8, x = 5, and n = 12 and x = 5,1, and 9, by means of electrical conductivity (CMC, apparent micellar ionization degree) and time-resolved fluorescence probing (micelle aggregation number A7) as a function of temperature and surfactant concentration (Table 1). 

Fluorescence spectroscopy is also particularly well-suited to clarify many aspects of polymer/surfactant interactions on a molecular scale. The technique provides information on the mean aggregation numbers of the complexes formed and measures of the polarity and internal fluidity of these structures. Such interactions may be monitored by fluorescence not only with extrinsic probes or labelled polymers, but also by using fluorescent surfactants. Schild and Tirrell [154] have reported the use of sodium 2-(V-dodecylamino) naphthalene-6-sulfonate (SDN6S) to study the interactions between ionic surfactants and poly(V-isopropylacrylamide). 

Box 4.2 Determination of micellar aggregation numbers by means of fluorescence quenching3 ... 

Fluorescence quenching studies in micellar systems provide quantitative information not only on the aggregation number but also on counterion binding and on the effect of additives on the micellization process. The solubilizing process (partition coefficients between the aqueous phase and the micellar pseudo-phase, entry and exit rates of solutes) can also be characterized by fluorescence quenching. 

The diffusion coefficients obtained with another fhiorophore (NBD derivative) were slightly different. The values of the aggregations numbers were found to be often overestimated because incorporation of the fluorescent probe may require extra surfactant molecules. However, the relative size differences between the micelles are in good agreement with the values reported in the literature. In addition to the size of micelles, FCS can give information on the size distribution. 

Turro and Yekta [142] discussed a simple method for measuring aggregation number by steady-state fluorescence. In this method, the decrease of the fluorescence intensity of a micelle-bound probe is monitored as a function of the quencher concentration and is fitted to the equation [143]... 

Pyrene shown a number of photophysical features that made it an attractive fluorophore to probe the microenvironment in micellar aggregates [19]. For the peaks of pyrene PL, two important peaks at about 373 nm and 390 nm among the five dominant peaks of pyrene fluorescence were numbered as 1 and III, respectively [20]. It has been known that intensity ratio of peak 111 to I (III/I) increased as the polarity at the solubilization site of pyrene decreases. Figure 6 shows fluorescence spectra (A.ex = 310 nm) of pyrene in precursor gel containing TPA and I-IV samples denoted as (a), (b), (c), (d) and (e), respectively. The value of 111/1 of pyrene does not change under silicalite-1 gel due to no formation of micelle. However, in the Fig. 6d (sample II), III/I ratio is rapidly increased, while sample III and IV are decreased slightly again. Previously, Park et al. have reported that 111/1 ratio of pyrene for... 

The probe molecule pyrene (-10"6 M) was used in time-resolved fluorescence quenching experiments using a single photon counting apparatus, cetylpiridinium chloride (CpyC, 10"3 M) being introduced as a quencher of the pyrene fluorescence[ll-13]. All the experiments were performed at 303K. From these fluorescence studies the micelle aggregation number (N) and the pyrene fluorescence lifetime (x) were obtained [14]. 

Systems CTAB/SKVNaOH, CTAC/Si02/NaOH, and CTAB/SiO/TMAOH/MeOH Values of the pyrene fluorescence lifetime (t) and micelle aggregation number (N). ... 

In the presence of D4R species as silica source (second set of experiments Table 1), the aggregation numbers, with and without silica (experiments 11 and 10, respectively), are characteristic of spherical micelles. Moreover, the addition of D4R units has no effect on the pyrene fluorescence lifetime (x), which means that there is no Br /silicate exchange in this micelles-containing system. As it is well known [21], the presence of methanol leads to a decrease of the aggregation number (compare experiments 9 and 10). 

The aggregation numbers Nagg is determined as 27 for C1-(EO)53-C4-VB and 38 for Cr(EO)53-C7-VB micelles by analysis of fluorescence curves. A micelle formation mechanism is proposed for nonionic polymeric surfactants with weakly hydrophobic groups. At low concentrations of PEO macromonomers, large loosely aggregated structures involving the PEO chains are formed. At higher concentrations normal micelles form. These are star-shaped, with a hydrophobic core surrounded by a corona of PEO chains. 

Yekta, A., B. Xu, J. Duhamel, H. Adiwidjaja, and M. A. Wnnik. 1995. Fluorescence studies of associating polymers in water determination of the chain end aggregation number and a model for the association processMacromoleculeS8 956-966. 

Fig. 6. g-micelle volumes ( aggregation numbers = acid residues per aggregate) in ml as determined by fluorescence depolarization measurements versus sulfonate concentration in g-equiva-lents per liter of dinonylnaphthalene sulfonates at 25 °C in benzene saturated with water [J. Colloid Sci. 12, 465 (1957)]... 

A number of experimental techniques by measurements of physical properties (interfacial tension, surface tension, osmotic pressure, conductivity, density change) applicable in aqueous systems suffer frequently from insufficient sensitivity at low CMC values in hydrocarbon solvents. Some surfactants in hydrocarbon solvents do not give an identifiable CMC the conventional properties of the hydrocarbon solvent solutions of surfactant compounds can be interpreted as a continuous aggregation from which the apparent aggregation number can be calculated. Other, quite successful, techniques (light scattering, solubilization, fluorescence indicator) were applied to a number of CMCs, e.g., alkylammonium salts, carboxylates, sulfonates and sodium bis(2-ethylhexyl)succinate (AOT) in hydrocarbon solvents, see Table 3.1 (Eicke, 1980 Kertes, 1977 Kertes and Gutman, 1976 Luisi and Straub, 1984 Preston, 1948). 

Yu, L., et al. (2006), Determination of critical micelle concentrations and aggregation numbers by fluorescence correlation spectroscopy Aggregation of a lipopolysaccharide, Anal. Chim. Acta, 556(1), 216-225. 

The ratio of the slope above to the slope below the cmc provided an estimate of P [7]. The binding constant was also used to estimate the concentration of alcohol in the bulk phase. Time resolved fluorescence quenching of dimethylnaphthalene by cetylpyridinium bromide solubilized in the micelles was used to obtain estimates of the mean aggregation number of the surfactant in the mixed micelles. 

Surfactants are long, we expect each chain to occupy a large patch of the micelle surface, compared to that occupied by a typical small-molecule surfactant. As a consequence, the aggregation number of telechelic micelles should be significantly smaller than that of a small-molecule micelle with a comparably sized hydrophobe. Using fluorescence decay studies, Yekta et al. (1995) have deduced a micelle aggregation number of 18-28... 

Analysis of fluorescence decay curves can be used to determine the mean aggregation number of aqueous micelles. The use of 1-methylpyrene quenching by the immobile quencher... 

Some essential discoveries concerning the organization of the adsorbed layer derive from the various spectroscopic measurements [38-46]. Here considerable experimental evidence is consistent with the postulate that ionic surfactants form localized aggregates on the solid surface. Microscopic properties like polarity and viscosity as well as aggregation number of such adsorbate microstructures for different regions in the adsorption isotherm of the sodium dedecyl sulfate/water/alumina system were determined by fluorescence decay (FDS) and electron spin resonance (ESR) spectroscopic methods. Two types of molecular probes incorporated in the solid-liquid interface under in situ equilibrium conditions... 

The structure of the AOT micellar system, as well as the state of water entrapped inside swollen micelles, have been characterized using different techniques, such as photon correlation spectroscopy (25), positron annihilation (26), NMR (27, 28), fluorescence (29-32) and more recently small angle neutron scattering (33). The existence of reversed micelles has been demonstrated in the domain of concentrations explored by protein extraction experiments. Their size (proportional to the molar ratio of water to surfactant known as wo), shape and aggregation number have been determined. Furthermore, the micelle size distribution is believed to be relatively monodisperse. 

Fluorescence techniques were used to study micelles in clear solutions. Time-resolved fluorescence quenching (recording of the fluorescence decay curves on a single photon counting apparatus) was used to determine the pyrene (used as the probe molecule) fluorescence lifetime (t). Micelle aggregation numbers (N), which correspond to the number... 

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