A new pyrene-based fluorescent probe for the determination of critical micelle concentrations
ABSTRACT A new pyrene-based fluorescent probe for the determination of critical micelle concentrations (CMC) is described. The title compound 1 is obtained in five steps, starting from pyrene. Fluorescence spectroscopic properties of 1 are studied in homogeneous organic solvents and aqueous micellar solutions. In a wide range of organic solvents, probe 1 exhibits a characteristic monomer emission of the pyrene fluorophore, with three distinct peak maxima at 382, 404, and 425 nm. The spectra change dramatically in aqueous solution, where no monomer emission of the pyrene fluorophore is detected. Instead, only strong excimer fluorescence with a broad, red-shifted emission band at lambda(max) = 465 nm is observed. In micellar aqueous solution, a superposition of the monomer and excimer emission is found. The appearance of the monomer emission in micellar solution can be explained on the basis of solubilization of 1 by the surfactant micelles. The ratio of the monomer to excimer fluorescence intensities of 1 is highly sensitive to changes in surfactant concentration. This renders 1 a versatile and sensitive probe molecule for studying the micellization of ionic and nonionic surfactants. For a representative selection of common surfactants, the critical micelle concentrations in aqueous solution are determined, showing excellent agreement with established literature data.
SourceAvailable from: Wajih Al-Soufi[Show abstract] [Hide abstract]
ABSTRACT: (Review Article) The systematic description of the complex photophysical behaviour of pyrene in surfactant solutions in combination with a quantitative model for the surfactant concentrations reproduces with high accuracy the steady-state and the time resolved fluorescence intensity of pyrene in surfactant solutions near the cmc, both in the monomer and in the excimer emission bands. We present concise model equations that can be used for the analysis of the pyrene fluorescence intensity in order to estimate fundamental parameters of the pyrene–surfactant system, such as the binding equilibrium constant K of pyrene to a given surfactant micelle, the rate constant of excimer formation in micelles, and the equilibrium constant of pyrene–surfactant quenching. The values of the binding equilibrium constant KTX100 = 3300·103 M− 1 and KSDS = 190·103 M− 1 for Triton X-100 (TX100) and SDS micelles, respectively, show that the partition of pyrene between bulk water and micelles cannot be ignored, even at relatively high surfactant concentrations above the cmc. We apply the model to the determination of the cmc from the pyrene fluorescence intensity, especially from the intensity ratio at two vibronic bands in the monomer emission or from the ratio of excimer to monomer emission intensity. We relate the finite width of the transition region below and above the cmc with the observed changes in the pyrene fluorescence in this region.Advances in Colloid and Interface Science 11/2014; DOI:10.1016/j.cis.2014.10.010 · 8.64 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: The solubilization behavior of nile red dye in aqueous surfactant and micellar solutions was studied by optical spectroscopic techniques, dynamic light scattering, and atomic force microscopy. Nile red exhibits considerable absorption in the submicellar concentration region. When dispersed in aqueous surfactant and/or micellar solution nile red molecules tend to form non-emissive dimers and/or H-type aggregates through π-π stacking interactions. This phenomenon may limit the use of nile red in solubilization studies. In presence of ionic SDS and CTAB micelles, the solubilization of nile red appears to take place primarily at the charged micellar surface within the interfacial region. Similarly, spectra in micellar solution of non-ionic Triton X-100 revealed that nile red dye penetrates the hydrophilic, interfacial poly(oxyethylene) region of the micelles but cannot reach the hydrophobic, innermost core. Our results therefore suggest that nile red dye must be chosen carefully when probing (micellar) hydrophobic environments and (micro)domains.Langmuir 02/2015; 31(9):2639-2648. DOI:10.1021/la504378m · 4.38 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: A water-soluble terpolymer, PAAB, was copolymerized using acrylamide (AM), sodium 2-acrylamido-2-methylpropane-sulphonate (NaAMPS), and a novel macro-monomer, p-vinylbenzyl-terminated octylphenoxy poly(ethylene oxide) (VBE, polymerization degree: 24). This polymer exhibited associating effect and good thickening properties in unsalted and brine solutions, and the effect of salt on apparent viscosity was much weaker than that of the linear associating polymers only containing small hydrophobic monomers. Its brine solution exhibited salt-thickening behavior twice and good resistances to heat because of the incorporation of the functional poly(ethylene oxide) side chains. The PAAB aqueous and brine solutions also displayed obvious shear thickening behavior upon repetitious three-shear cycles. It was found by a scanning electron microscope (SEM) that the polymer chains were extended and large associated structures were formed in brine solutions as well as in water at the PAAB concentrations of 0.05–0.15 g/dL.Chemical Engineering Communications 04/2015; 202(4). DOI:10.1080/00986445.2013.850427 · 0.79 Impact Factor