Fluorescence intensity surfactant solution

Semiconductor nanoclusters trapped in AOT w/o microemulsions are reported to exhibit longer excited state lifetimes (about 10-100 ns) than those in aqueous solution or in monophasic organic solvents [213]. Clearly the surfactant-nanoparticle interaction is very important not only in restricting growth but also in extending the hfetimes of the excited states. Tata et al. [214] have shown that the removal of water from the micelles leads to a strong increase in fluorescence intensity, and the addition of specific quencher, 4-hydroxythiophenol, leads to variations in quenching efficiencies. 

Figure 1 shows the change in fluorescence intensity of ANS in the aqueous surfactant solution. In the case of the hydrocarbon surfactant, the fluorescence intensity of ANS was proportional to the surfactant concentration above the CMC. Since the fluorescence intensity of ANS had a constant value below the CMC, the inflection point appeared at the CMC. The surfactant concentration at the inflection pojnt nearly coincided with the CMC of 6ED and SDS( the CMC was 6x10 mole/1 for 6ED and 8.5x10 mole/1 for SDS). These findings indicate that ANS is solubilized into the hydrocarbon surfactant micelles. Further, above the CMC, the fluorescence intensity of ANS in 6ED solution was about ten-fold larger than in SDS solution. Since both ANS and SDS are anionic, the lower solubility of ANS in SDS micelles is probably due to the electric... 

Fluorescent organic compounds have been widely used as molecular-microscopic probes in biophysical studies of the local environment in micelle-forming surfactant solutions, in phospholipid dispersions, and in membranes. It is assumed that the nature of the probe environment is reflected in its emission characteristics [i.e. position and intensity of emission maxima, vibrational fine structure, quantum yields, excited-state lifetime, polarization of the fluorescence) cf [112, 115, 360] for reviews. 

The description given here is confined to the method developed by Abuin and Lissi demonstrating the use of fluorescence as a method for determining partition coefficients for solutes that are not by themselves fluorescent. The method is based on the observation that an additive changes the characteristics of the fluorescence of a micelle-incorporated probe such as pyrene. It is assumed that the fluorescence intensity of micelle-incorporated pyrene is determined only by the mole fraction of solute in the micellar pseudophase. The probe fluorescence intensity ratio f/I in the absence and presence of a solute is measured as a function of the solute concentration at different surfactant concentrations. From plots of the intensity ratio vs. the solute concentration at different surfactant concentrations we obtain a set of additive concentrations c,o, that corresponds to the same f/I value and thereby the same and K. Ctot is related to the concentration of micellized surfactant, through the following equation ... 

Another extremely useful method for cac determination, especially in the light of high sensitivity, is fluorescence emission spectroscopy [15]. Some aromatic water-insoluble dyes that are present in trace amounts in mixed polyelectrolyte-surfactant solutions have an ability to solubilize within the self-assembled surfactant aggregates and to change their photophysical properties because of the change of environmental polarity. Through this, they offer a very sensitive method for the determination of cac values. A typical and lately frequently used compound is pyrene, which is used as a fluorescence probe to assess various micellar properties. Pyrene exhibits a polarity dependent fluorescence spectrum with the ratio /,//3 (the ratio of the intensity... 

Spectral characteristics and selection of surfactant. Increase in the fluorescence intensity of the carbaryl solution was observed using SDS as surfactant at excitation and emission wavelengths of 281 nm and 349 nm respectively (Fig. 1). As can be seen from Fig. 1, Triton X-100 and dodecyl pyridinium chloride (DPC) decreased the fluorescence. This phenomenon clearly indicates that cationic surfactant (DPC) and neutral surfactant (Triton X-100) have negative effects on the fluorescence intensity for carbaryl while anionic surfactant (SDS) enhances the fluorescence intensity of carbaryl. This surfactant-enhanced phenomenon by SDS was used for the spectrofluorimetric determination of carbaryl. 

Another type of micelle formation has also attracted the attention of researchers, a brief mention of which will be made below. Gravsholt [93], in an early work, reported viscoelasticity in highly diluted aqueous solutions of some cationic surfactants, namely, certain derivatives of the base structure of cetyltrimethylammonium bromide (CTAB), CTA-X (where X=salicylate, m-chlorobenzoate, p-chlorobenzoate). He came to the conclusion that the viscoelastic behavior indicates a micellar shape other than spheres and rods. Later it has been shown [e.g. 94] by fluorescence anisotropy using fluorescent probe molecules that CTAB and sodium p-toluenesulfonate, NapTS (with suitably weak fluorescence) in aqueous solution could produce long, threadlike micelles with network structure in which the cross-points had finite lifetime. Sodium salicylate was another useful additive for synthesis, but the intensity of its fluorescence was found unsuitable for examining the behavior of the probes. 

Among the common metal ions, only aluminum and cobalt gave peaks when complexed with 8-quinolinol and eluted with SDS-acetonitrile mobile phases. However, the peaks appeared very close to each other with spectrophotometric detection (Fig. 12.2). The selective determination of aluminum was only possible with fluorimetric detection. The addition of SDS as well as several other surfactants to the aluminum complex solution, increased the fluorescence intensity. The procedure did not require deproteinization prior to analysis. The most commonly used technique for aluminum in human serum is graphite-furnace atomic absorption spectrophotometry, which is often limited due to serum matrix interference. 

CPE followed by spectrofluorimetry was applied to analyse the concentration of vitamin Bi in samples of urine (Tabrizi 2006). In this method, Triton-XI14 surfactant was used for CPE. The procedure was accomplished by adding an aqueous solution of thiamin, ferricyanide and Triton-X114 in an alkaline medium. The surfactant-rich turbid phase and diluted aqueous phase were attained after centrifugation of the mixture. The surfactant-rich phase was collected and diluted in an ethanol water mixture prior to measurement of the fluorescence excitation and emission intensity. Thiamin was oxidized by ferricyanide under alkaline conditions to form thiochrome, which is a fluorescent species. During the extraction procedure, thiochrome was entrapped in surfactant micelles. Thus, thiamin was separated from the biological matrix after derivatization. The fluorescence intensity responded linearly with the concentration of thiamin under optimized conditions. 

FI GU RE 7.4 Plot of the parameters energy of (a) maximum absorption/ h) fluorescence, (c) fluorescence intensity and (d) steady-state anisotropy (r) of (Va) in the aqueous solution of surfactants as a function of log Cj-. Cj-for the surfactants have been denoted by surfactant. (From Kedia, N. et al., Spectrochim. Acta A, 131, 398, 2014.)... 

Measurements of the bulk solution properties (e.g., surface tension, electrical conductivity, fluorescence, and light scattering intensity) as a function of surfactant concentration can be used to determine the CMC. As shown schematically in Figure 2.2, the point at which the sudden change in surface tension occurs is taken as the CMC of the aqueous surfactant solutions. How to establish the correlation between the CMC data and the molecular structure of surfactants is of great importance in the selection of optimum surfactants for the effective stabilization of various emulsion polymerization systems. This subject will be the focus of the following discussion. 

The Carboxyfluorescein concentration of the vesicle suspension Cv and after destroying the vesicles with the surfactant Triton X 100 C/ were calculated from the fluorescence intensity of the diluted aqueous solutions. The turbidity of the vesicle solution declined within seconds after detergent addition (vesicle busting), and we obtained then a clear, aqueous solution. Typical results of these measurements are summarized in Fig. 12. Due to Ihe self-quenching properties the destruction of the vesicles with a high inner Carboxyfluorescein concentration (0.05-0.2 mol/1) led to an increase of the Fluorophore concentration in the outer phase. This occurred if a large amount of emulsion droplets coalesced with the lower water phase, thus releasing their Carboxyfluorescein content. 

The fluorescence intensity of ammonium l-anilinonaphthaline-8-sulfonate (ANS) in a solution of a hydrocarbon-type surfactant is constant below the cmc of the surfactant but increases linearly with increasing surfactant concentration above the cmc. The concentration dependence of fluorescence intensity indicates that the ANS probe is solubilized in the micelles of the hydrocarbon-type surfactant. In contrast, fluorinated surfactants do not solubilize ANS [251]. The ANS probe is therefore useful for investigating fluorinated surfactant and hydrocarbon-type surfactant mixtures (see Section 7.3). Asakawa et al. [121] studied the micellar environment of mixed fluorinated surfactants and hydrocarbon-type surfactants by fluorescence intensities of ANS, auramine, and pyrene. The ANS fluorescence intensity is shown in Fig. 28 of Chapter 7 as a function of total surfactant concentration. The ANS fluorescence intensity increased with the increase in hydrocarbon-type surfactant (LiDS) concentration Because the ANS probe was not incorporated in LiFOS micelles, the fluorescence intensity increased very little with increasing fluorinated surfactant (LiFOS = lithium perfluorooctane sulfonate) concentration. 

The luminescence of macrocrystalline cadmium and zinc sulfides has been studied very thoroughly The colloidal solutions of these compounds also fluoresce, the intensity and wavelengths of emission depending on how the colloids were prepared. We will divide the description of the fluorescence phenomena into two parts. In this section we will discuss the fluorescence of larger colloidal particles, i.e. of CdS particles which are yellow as the macrocrystalline material, and of ZnS particles whose absorption spectrum also resembles that of the macrocrystals. These colloids are obtained by precipitating CdS or ZnS in the presence of the silicon dioxide stabilizer mentioned in Sect. 3.2, or in the presence of 10 M sodium polyphosphate , or surfactants such as sodium dodecyl sulfate and cetyldimethylbenzyl-ammonium... 

Reversed micelle-entrapped, colloidal CdS showed the characteristic weak fluorescence emission (Figure 2), previously observed in homogeneous solutions (16-19). However, the maximum emission intensity corresponded to full band gap emission (approximately 500 nm) and was not red-shifted as observed in homogeneous solution (17). This discrepancy might arise from the mode of prep>aration (H S instead of Na S), or from the specific effect of surfactant aggregates. 7 lternatively, tras can be the result of a size... 

The rates of diffusion of solutes and surfactants in and out of micelles have been measured using photophysical techniques. The most commonly used method is to measure the deactivation of excited states of the probe by added quenchers, which are only soluble in the aqueous phase. The measurement of either the decrease in emission intensity or a shortening of the emission lifetime of the probe can be employed to determine exit and entrance rates out of and into micelles 7d). The ability of an added quencher to deactivate an excited state is determined by the relative locations and rates of diffusion of the quenchers and excited states. Incorporation of either the quencher or excited state into a surfactant allows one to determine the rates of diffusion of surfactants. Because of the large dynamic range available with fluorescent and phosphorescent probes (Fig. 3), rates as fast as... 

Several papers compare the properties of sulfobetaine (meth)acrylic polymers. NMR spectra and solution properties of 23a and 23b [59,60] are correlated with data from the corresponding polycarbobetaines [26]. The photophysical and solution properties of pyrene-labeled 23c were studied in terms of fluorescence emission. Addition of surfactants induces the formation of mixed micelles in aqueous solution [61]. Excluded volume effects of the unlabeled polymer were measured by light scattering [62], its adsorption on silica was studied by adsorbance measurement and ellipsometry [62,63], and the electrostimulated shift of the precipitation temperature was followed at various electric held intensities [64]. Polysulfobetaines may accelerate interionic reactions, e.g., oxidation of ferrocyanide by persulfate [65]. The thermal and dielectric properties of polysulfobetaines 23d were investigated. The flexible lateral chain of the polymers decreased Tg, for which a linear relationship with the number of C atoms was shown [66,67]. 

In two-phase systems, however, where surfactant and water can partition between a fluid and a liquid phase, significant pressure effects occur. These effects were studied for AOT in ethane and propane by means of the absorption probe pyridine N-oxide and a fluorescence probe, ANS (8-anilino-l-naphthalenesulfonic acid) [20]. The UV absorbance of pyridine A-oxide is related to the interior polarity of reverse micelles, whereas the fluorescence behavior of ANS is an indicator of the freedom of motion of water molecules within reverse micelle water pools. In contrast to the blue-shift behavior of pyridine N-oxide, the emission maximum of ANS increases ( red shift ) as polarity and water motion around the molecule increase. At low pressures the interior polarity, degree of water motion, and absorbance intensity are all low for AOT reverse micelles in the fluid phase because only small amounts of surfactant and water are in solution. As pressure increases, polarity, intensity, and water motion all increase rapidly as large amounts of surfactant and water partition to the fluid phase. The data indicate that the surfactant partitions ahead of the water thus there is a constant increase in size and fluidity of the reverse micelle water pools up to the one-phase point. An example of such behavior is shown in Fig. 4 for AOT in propane with a total fVo of 40. The change in the ANS emission maximum suggests a continuous increase in water mobility, which is due to increasing fVo in the propane phase, up to the one-phase point at 200 bar. 

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