Structure of reversed micelles in the cyclohexane/polyoxyethylene(4)nonylphenol/water system, as studied by the spin probe technique

Abstract

3) Weast, R. C. Hondbook of Chemistry ond Physics, 70th ed.; CRC (4) Conway, B. E. Electrochemicol Doto; Elsevier: Amsterdam, 1952; pp p 760-1 (note that B requires p).The cyclohexane/polyoxyethylene(4)nonylphenol (E0(4)NP)/water system (2.8% EO(4)NP) with [H20] 1 [EO(4)NP] molar ratios between 0.1 and 6.9, has been investigated by electron spin resonance (ESR) spectroscopy using the following nitroxides: 3-carboxy-2,2,5,5-tetramethylpyrroIine-lsxyl (I), 2,5-dihydr~2,2,5,5-tetramethyl-3-[(triethylammonio)methyl]pyrrole-1-oxy1 bromide (11), and 5-doxylstearic acid (IV) as spin probes. For radicals I and I1 the nitrogen hyperfine splitting, aN, and the rotational correlation time, T~, have been analyzed, yielding information about the polarity and viscosity of their locations.At [H20]/[EO(4)NP] 6 0.3, the presence of "waterless" micellar aggregates in fast exchange (v, > 106 s-') with the monomer surfactant is evident. At [H20]/[EO(4)NP] = 0.6, the core viscoSity is at its maximum value and the exchange rate decreases below the limit of slow exchange (vex < lo6 s-I). Upon further increasing the water content, the core becomes more polar and less viscous, with these parameters approaching their values in bulk water. The effect of Cu(I1) ion (in an oil-soluble complex) on the spectra of radical II-confined to the water-pool-has been interpreted by using Leigh's theory, and the 'distance of closest approach" between these two paramagnetic species has been evaluated. This distance is considered to represent a measure of the penetrability of the micellar shell. Radical IV yielded anisotropic spectra in the aggregates with slow exchange. From their ESR parameters the order degree of the surfactant chains in the micellar shell has been evaluated. All results are consistent, indicating reduced penetrability and increased order with increasing dimensions of the water-pool.

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.…”

“…It should have its proper location within the aggregate, and it should be sensitive enough to relevant changes in the system to be able to provide meaningful information. The polarity profile of the nonionic RM has been evidenced by absorption, fluorescence, and spin probe techniques [15,[20][21][22][23].…”

“…The nonionic surfactants of the alkyl ether and alkyl-aryl ether types may form micelles in nonpolar solvents, and water addition plays a very important role in micellization [15,[20][21][22][23][27][28][29]. The colloidal behavior of triblock copolymers of the PEO-PPO-PEO type (Pluronics) in nonaqueous media could be similar, but the information available in the literature is scarce.…”

The structure of gelatin–water/oil microemulsion sols and gels. An EPR spin-probe and spin-labelling study

“…Ethylene diaminetetraacetic acid as the disodium salt (EDTA) and the copper(II) salt (CuEDTA), potassium ferricyanide, (Aldrich), all of them water soluble, and 20 which is soluble only in organic solvents were used as paramagnetic line-broadening agents. 21 The series of CAT n (4-[N,N-dimethyl-N-(methylene) n ]iodide, where n \ 1, 4 2,2,6,6-tetramethyl-piperidine-1-oxyl and 16) were obtained from Molecular Probes, Inc. 5-Doxyl stearic acid (5-DSA) was purchased from Aldrich and TEMPO-laurate was prepared according to the (C 12 -NO) general procedure described by Waggoner et al 22 The nitroxide used for gelatin labelling, 4-(amino-dichloro-triazine)-2,2, 6,6-tetramethyl-piperidine-1-oxyl (SL) was prepared as previously described.…”

Solubilization in nonionic reverse micelles in carbon dioxide

“…Methyl orange penetrates to the center of such aggregates and finds a compatible polarity. However, as water is added, it gathers at the center of the reverse micellar structure, near the -OH terminus of the ethylene oxide chains (Caldararu et al, 1992). The methyl orange is gradually forced into the regions of lower polarity near the hydrocarbon end of the ethylene oxide chain, as indicated by A, , , .…”