Structure and Dynamics of Nonionic Polyoxyethylenic Reverse Micelles by Time-Resolved Fluorescence Quenching

Abstract

The application of the time-resolved fluorescence quenching method (TRFQ) to study the structure and aggregation behavior of nonionic surfactant polyoxyethylene(4)lauryl ether (C12E4) in reverse micellar systems is presented. Solutions of different concentrations in three nonpolar solvents (cyclohexane, n-decane, and n-dodecane), at different water content and temperature, employing Ru(bpy )a2+-methylviologen, solubilized in the polar core of micelles, as probe-quencher pair, were studied, tiie aggregation number and fluorescence quenching rates were determined and the size and shape of micelles estimated; the dependence of their values on medium was evidenced. Dynamic light scattering was utilized as a complementary method in checking the hypotheses regarding micellar size/shape. It was found that in cyclohexane, at the compositions studied, the micelles can be regarded as spherical, growing with the water content, with a constant area per head group of about 50 Á2. Only at the lowest water content (3 water molecules per surfactant or less) is there a deviation with a larger area per surfactant. The radius of the polar core is then smaller than the length of the EO tail, and there is no free water that could allow the micelle to swell beyond this limit. The micelles in decane and dodecane appear to grow in a nonspherical way and become much larger with water addition.

Micropolarity and Order in the Reverse Micelles of L62 and L64 Pluronic Copolymers, As Studied by Molecular Probe Techniques

“…Pluronic L62 (EO) 6 (PO) 36 (EO) 6 (MW ) 2600) and Pluronic L64 (EO) 13 (PO) 30 (EO) 13 (MW ) 2900) were obtained from BASF and used without purification. The poly-(ethylene oxides) employed for calibration were as follows: Carbowax 200 (poly(ethylene glycol) 200, TEG), average molecular weight 200 (Loba Chemie), triethyleneglycol monomethyl ether (TGMME) (Fluka), tetraethyleneglycol dimethyl ether (TEGDME) (Aldrich), and poly(propylene glycol) (PPO), average molecular weight 2000 (Aldrich).…”

Investigation of the micropolarity in reverse micelles of nonionic poly(ethylene oxide) surfactants using 4-nitropyridine-N-oxide as absorption probe

“…It must be mentioned that the concentrations of the surfactants and polymers in the mentioned solvents have been chosen to form RM [15,[20][21][22][23][30][31][32][33][34]. Solutions of surfactants in solvents with the concentrations (wt/wt) shown in parentheses were homogenized and the runs were conducted 24 h after preparation.…”

Quenching of Pyrene Derivatives' Fluorescence by Nitroxide Radicals in Sodium Dodecyl Sulfate Micellar Solutions

“…The fluorescence measurements supply information about the micellization process and about the microenvironment of the fluorescent probe in terms of polarity (1,2), microviscosity (4,5), aggregation number (6)(7)(8)(9), and micellar size and shape (10,11). One important parameter that can be estimated using either steady-state fluorescence quenching (SSFQ) or time-resolved fluorescent quenching (TRFQ) is the mean aggregation number of the micellar surfactant aggregates, N .…”