1,721,315 research outputs found
ELECTRON-SPIN-RESONANCE SPECTRA OF NORMAL-ALKYL NORMAL', NORMAL'-DIMETHYLCARBAMOYL AND N-TERT-BUTYL N-CARBOBENZYLOXY AMINYL RADICALS
No full textTHE CRITICAL HYDROPHOBIC INTERACTION CONCENTRATION FOR AQUEOUS TETRA-NORMAL-BUTYLAMMONIUM BROMIDE
No full textA SEARCH FOR A RELATION BETWEEN AGGREGATE MORPHOLOGY AND THE STRUCTURE OF 1,4-DIALKYLPYRIDINIUM HALIDE SURFACTANTS
No full textA detailed study of the relation between the aggregate morphology and the molecular shape of 27 1-alkyl-4-(or 2-)alkyl(or n-alkoxycarbonyl)pyridinium halide surfactants is described. This shape can be expressed in a molecular packing parameter (P) as suggested by Israelachvili. For unbranched 1-methyl-4-n-alkylpyridinium iodides, the packing parameter does not depend on the length of the alkyl chain (n(c)). Spherical micelles formed from these surfactants grow into rodlike micelles. The critical rod concentration (crc) is, however, dependent on n(c). This originates from the dependence of the aggregation number of spherical micelles on n(c), in agreement with predictions based on the ladder model. Alkyl chain branching in 1-methyl-4-(C12-alkyl)pyridinium iodides affects the shape of the surfactant. Branching near the headgroup decreases P and dramatically lessens the propensity of the spherical micelle to grow. Branching near the chain end increases P and decreases the crc. Highly branched surfactant monomers associate into bilayers, which can be transformed into vesicles. The overall results indicate that the morphology of the aggregate is mainly dependent on the shape of the surfactant. The possibility for backfolding of the 1-alkyl chain of 1-alkyl-4-n-dodecylpyridinium iodide surfactants directly affects the preferred morphology of the aggregate. Bilayers are formed if backfolding occurs; otherwise spherical micelles are formed, which, on increasing surfactant concentration, grow into rodlike micelles. Interestingly, 1-methyl-4-(n-alkoxycarbonyl)pyridinium iodides associate into bilayers, independent of the length of the alkyl chain (n(c) = 10-16). This aggregation behavior probably stems from a special kind of interdigitation, which changes the geometrical constraints for packing into a bilayer.</p
INDUCTION OF AGGREGATE FORMATION OF CATIONIC POLYSOAPS AND SURFACTANTS BY LOW CONCENTRATIONS OF ADDITIVES IN AQUEOUS-SOLUTION
No full textThe induction of aggregate formation of cationic polysoaps ((CL)-Copol C1-12), cetyltrimethylammonium bromide (CTAB), n-dodecyltrimethylammonium bromide (DTAB), and n-dodecylmethyldiallylammonium bromide (DMDAAB) by low concentrations of Methyl Orange (10(-5)-10(-4) M) and anionic surfactants (concentrations below their cmc's) in aqueous solutions was studied using UV-vis absorption and fluorescence spectroscopy. Reduced viscosities were also investigated as a function of polysoap concentration in the presence of low concentrations of the same additives. It was found that the cationic polysoaps, CTAB, DTAB, and DMDAAB aggregate far below their normal cmc in the presence of Methyl Orange in aqueous solution. The cationic polysoaps exhibited an about 5-fold decrease of the reduced viscosity in the presence of the hydrophobic anionic additives but no decrease of the reduced viscosity was found in the presence of hydrophobic nonionic additives and cationic additives (CTAB, DTAB). Depending on the length of the alkyl chains of the organic anionic additives, a conformational transition of the cationic polysoaps was indicated by changes of the reduced viscosity. Pyrene was used as a fluorescence probe to investigate the conformational state of the cationic polysoap CL-Copol C1-12 in the presence of low concentrations of additives. Pyrene fluorescence spectra revealed the formation of hydrophobic microdomains in the presence of the hydrophobic anionic additives depending on the length of alkyl chains. These domains were not observed in the case of hydrophobic cationic additives and nonionic additives
PREFERENTIAL SOLVATION OF NONELECTROLYTES IN MIXED AQUEOUS SOLVENTS - A QUANTITATIVE APPROACH FOR BETA-DISULFONES IN 1,4-DIOXANE WATER, 1,3-DIOXANE WATER, AND DIMETHOXYETHANE WATER IN TERMS OF THE COVINGTON THEORY
No full textSYNTHESIS AND CATALYTIC PROPERTIES OF CROSS-LINKED HYDROPHOBICALLY ASSOCIATING POLY(ALKYLMETHYLDIALLYLAMMONIUM BROMIDES)
No full textCross-linked, hydrophobically associating homo- and copolymers were synthesized by free-radical cyclo(co)polymerization of alkylmethyldiallylammonium bromide monomers with a small amount of N,N'-methylenebisacrylamide in aqueous solution using ammonium persulfate as the initiator. The cross-linked homo- and copolymers showed a increase of their reduced viscosity in water and intrinsic viscosity in 1.0 M sodium chloride solutions upon the controlled introduction of crosslinking N,N'-methylenebisacrylamide into their chemical structure. Depending on the hydrophobic group content of the cross-linked copolymers, a conformational transition was revealed by viscosity measurements which is accounted for by intramolecular micelle formation and intermolecular aggregation. The hydrophobic microdomains of the cross-linked polysoaps were characterized by hypsochromic shifts of the long-wavelength absorption band of methyl orange as a solvatochromic probe, noncovalently bound to the macromolecule. Catalysis of the unimolecular decarboxylation of 6-nitrobenzisoxazole-3-carboxylate by the cross-linked copolymers was investigated in aqueous solution at pH 11.3 and 30 degrees C. The cross-linked polysoaps exhibited higher catalytic activities for decarboxylation than the corresponding non-cross-linked copolymer analogues. A maximum in rate constant was found at about 0.2% (w/w) of cross-linking agent in the cross-linked copolymers.</p
PARTITIONING OF ORGANIC SOLUTES BETWEEN THE MICELLAR AND THE AQUEOUS PHASE AS STUDIED WITH AN ARTIFICIAL-KIDNEY
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