Critical micelle concentration pyrene

Critical micelle concentration in aqueous solutions was determined by fluorescence using pyrene as a probe. The driving force for micelle formation is the strong hydro-phobic interactions between [(R)-3-hydroxybutyrate] block. It was previously determined by this group that terpolymers with longer PHB blocks have much lower critical micelle concentrations because of PHB block aggregation in aqueous solution. Testing results are provided in Table 2. 

By measuring fluorescence intensity as a function of [Q] at fixed [S], we can find the average number of molecules of S per micelle if we know the critical micelle concentration (which is independently measured in solutions of S). The table below gives data for 3.8 (jlM pyrene in a micellar solution with a total concentration of sodium dodecyl sulfate [S] = 20.8 mM. 

The formation of a ternary complex -CD-13-sodium dodecyl sulfate below the critical micelle concentration (CMC) was indicated by the growth of a new band, peaked at 338 nm, in the absorption spectrum and by the decrease of the R value. Such behavior was not observed in the presence of a-CD. Above the CMC, micelles containing a- or fi-CD were formed [119] in which the CD is located near the micelle surface pyrene is solubilized in the interior core of the mixed micelle. 

The conformations of tethered polyethylene glycol (PEG) chains anchored on styrene polymers (PS) latex particles, labelled with pyrene and mononaphthyl PEG ester, in the presence of an anionic surfactant, dodecyl sulphate (SDS), and Na and K chlorides were studied, using distance-dependent nonradiative energy transfer from the naphthalene moieties to the pyrene ones as a guide. The results indicated a change in acceptor/donor separation distance in response to external stimuli. Analysis of the resnlts snggested considerable polymer chain contraction on interaction with salts and surfactant below the critical micelle concentration of the surfactant. 

Different parameters describing the principal properties of self-assemblies are mentioned in the literature. Critical micellization concentration (CMC) is described using the pyrene fluorescence method. From a stock solution of pyrene dissolved in chloroform, an aliquot is transferred with a micropipette into a series of dry test tubes the solvent is allowed to evaporate under vacuum by protecting it from light to obtain dry pyrene. Then, a series of polymer solutions in buffer solution (pH 7.4) are added to the pyrene. Mixtures are stirred in the dark for 24 h at 25°C and then filtered through a membrane filter for separation of undissolved pyrene crystals. The concentration of solubilized pyrene in the micellar phase is determined spectrofluorometrically at 339 nm wavelengths of excitation and 390 nm of emission. 

Compared to other methods, the advantage of PCS is the ability to detect a very low critical micelle concentration [158, 160-163] (CMC) and a very low critical aggregation concentration [158, 160, 161] (CAC) as they often appear in block copolymer solutions. This could for example be demonstrated by Colombani et al. who could access the CMC of a diblock copolymers by PCS, but only obtained an upper estimate analyzing the absorption band of pyrene which is very sensitive to local polarity of its surrounding [162]. 

Pyrene has been used to investigate the extent of water penetration into micelles and to accurately determine critical micellar concentrations (Kalyanasundaram, 1987). Polarity studies of silica or alumina surfaces have also been reported. In lipid vesicles, measurement of the ratio Ii/Iui provides a simple tool for determination of phase transition temperatures and also the effect of cholesterol addition. 

The pH-induced micellization of a DMAEMA-6-DEAEMA diblock copolymer has been studied in detail using dynamic light scattering, small-angle neutron scattering, and fluorescence spectroscopy [166], The DMAEMA constitutes the corona of the micelle, whereas the DEAEMA forms the core. Pyrene was used as a probe to determine the nature of the DEAEMA blocks. It was shown that the hydrophobicity of the micellar cores increased progressively as the solution pH was adjusted from pH 7 to 9. In the presence of an electrolyte, it was possible to observe both individual chains (unimers) and micelles under certain conditions. The critical micellization pH depended on both the copolymer concentration and also the background electrolyte concentration. 

IJ12 and viscosity measurements were also compared for the above copolymers. Plots of IJI2 and reduced viscosity are shown as a function of concentration (Fig. 2.12). These data indicate that the pyrene probe is in a micelle-like environment at the critical overlap concentration for each polymer, demonstrating that viscosification of the polymer solution occurs through inter-polymer hydrophobic associations. 

Amphiphilic polysaccharide derivatives (APDs) consisting of hydrophilic polysaccharide chains and hydrophobic segments can form micelle structures with hydrophobic inner core and the hydrophilic outer shell in aqueous solutions [40-43]. The critical aggregation concentration (CAC) value, usually determined by pyrene probe fluorescence spectroscopy, is used to evaluate the thermodynamic stability of micelles in aqueous solutions, i.e. the small CAC is, the more stable micelles are [44,45]. Moreover, the formation and properties of the micelles may change with the structures of APDs [46,47]. 

Single polymer micelles were observed at low polymer concentrations in aqueous media whereas at higher concentrations both inter and intrapolymeric aggregation took place. Above the critical solution temperature excimer formation decreased due to disruption of the pyrene aggregates. 

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