			Home About us Contact

Micellar Aggregates (micellar + aggregate)

Distribution by Scientific Domains

Polymers and Materials Science	50%
Chemistry	50%

Selected Abstracts

Dediazoniation of 1-naphthalenediazonium tetrafluoroborate in aqueous acid and in micellar solutions

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2008
Carlos Bravo-Diaz
We have measured the rates and product yields of dediazoniation of 1-naphthalenediazonium (1ND) tetrafluoroborate in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by employing a combination of UV,vis spectroscopy and high-performance liquid chromatography (HPLC) measurements. Kinetic data were obtained by a derivatization procedure with product yields were determined by HPLC. HPLC chromatograms show that in aqueous acid and in micellar solutions only one dediazoniation product is formed in significant quantities, 1-naphthol (NOH), and the observed rate constants (kobs) are the same when 1ND loss is monitored spectrometrically and when NOH formation is monitored by HPLC. Activation parameters were obtained both in the presence and absence of SDS micellar aggregates. In both the systems, the enthalpies of activation are high and the entropies of activation are positive. The enthalpy of activation in the absence of SDS is very similar to that in the presence of SDS micelles, but the entropy of activation is lower by a factor of 4. As a consequence, SDS micelles speed up the thermal decomposition of 1ND and increase kobs by a factor of 1.5 when [SDS] = 0.02 M. In contrast, results obtained in the presence of complexing systems such as crown ethers and polyethers show significant stabilization of the parent arenediazonium ions. Kinetic and HPLC data are consistent with the heterolytic DN + AN mechanism that involves the rate-determining fragmentation of the arenediazonium ion into a very reactive phenyl cation that reacts competitively with available nucleophiles. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 301,309, 2008 [source]

Structural effects of macrocyclic compounds and their partition in sodium dodecylsulphate aqueous solutions

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003
Delia Chillura-Martino
The partition of 1,4,7,10,13,16-esaoxacyclooctadecane (18C6), 4,7,13,16-tetraoxa-1,10-diazacyclooctadecane (2.2), 2,5,8,11,14,17-esaoxabicyclo[16.4.0]dicosane (B18C6) and 2,5,8,15,18,21-esoxatricyclo[20.4.0.09.14]esacosane (Cy218C6) in sodium dodecyl sulfate (SDS) aqueous solutions and their effect on the structure of surfactant aggregates has been investigated by small-angle neutron scattering. Results from data analysis have shown that by increasing macrocycle concentration the SDS micelles dimensions reduce for all systems investigated. At the same time information on macrocycles partition between the micellar and the continuous phase have been obtained. It was found that an appreciable portion of macrocyclic compounds is located in micellar aggregates; in particular, the amount of B18C6 and Cy218C6 results larger than that of 18C6 and 2.2. It was found that 18C6 and 2.2 molecules interact with charged surface of SDS micelles only via complexes formation between the sodium ions and the macrocycles. B18C6 and Cy218C6 interact either via complexes formation with the charged surface or with hydrophobic region inside the micelle, as a consequence of the presence of hydrophobic substituents. It was concluded that Cy218C6 fraction present inside the micelles is located in the core, while the B18C6 fraction is located in the palisade. [source]

Breakdown kinetics of aggregates from poly(ethylene glycol- bl -propylene sulfide) di- and triblock copolymers induced by a non-ionic surfactant

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2008
Simona Cerritelli
Abstract We explored the effects of addition of the nonionic surfactant Triton X-100 on the stability of aggregates of poly(ethylene glycol- bl -propylene sulfide) di- and triblock copolymers. Fluorescence spectra of pyrene, used as a probe molecule, elucidated the various stages of transformation from pure copolymeric micelles to surfactant-rich micelles. Turbidity measurements yielded insight into the mechanism of the interaction, the hydrophobicity of the copolymer driving the process. Triton X-100 tends to strongly interact with highly hydrophobic copolymers by inserting into the core of the micellar aggregates. On the other hand, Triton X-100 tends to interact with the corona of micelles formed by less hydrophobic copolymers which, for this reason, are more stable upon addition of this destabilizing agent. Kinetic data give evidence that only monomers, not micelles of surfactant, interact with the copolymer micelles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2477,2487, 2008 [source]

Novel Amphiphilic Degradable Poly(, -caprolactone)- graft -poly(4-vinyl pyridine), Poly(, -caprolactone)- graft -poly(dimethylaminoethyl methacrylate) and Water-Soluble Derivatives

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 9 2008
Benjamin Nottelet
Abstract New amphiphilic graft copolymers that have a poly(, -caprolactone) (PCL) biodegradable hydrophobic backbone and poly(4-vinylpyridine) (P4VP) or poly(2-(N,N- dimethylamino)ethyl methacrylate) (PDMAEMA) hydrophilic side chains have been prepared by anionic polymerization of the corresponding 4VP and DMAEMA monomers using a PCL-based macropolycarbanion as initiator. The water solubility of these amphiphilic copolymers is improved by quaternization, which leads to fully water-soluble cationic copolymers that give micellar aggregates in deionized water with diameters ranging from 65 to 125 nm. In addition, to improve the hydrophilicity of PCL- g -P4VP, grafting of poly(ethylene glycol) (PEG) segments has been carried out to give a water-soluble double grafted PCL- g -(P4VP;PEG) terpolymer. [source]

Synthesis of a Novel Electroactive ABA Triblock Copolymer and its Spontaneous Self-Assembly in Water

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2007
Lihong Huang
Abstract An electroactive triblock copolymer of poly(ethylene glycol) (PEG) and aniline pentamer (AP), PEG- block -AP- block -PEG (PAP), was synthesized via polycondensation in the presence of N,N' -dicyclohexylcarbodiimide (DCC). The UV-vis spectra and cyclic-voltammograms (CV) spectra exhibited an excellent electroactivity of the triblock copolymer. The amphiphilic triblock copolymer self-assembles spontaneously into uniform micellar aggregates when the triblock copolymer was added directly to the aqueous solution. The size of the aggregates can be changed with the oxidation state of the AP segment in the PAP copolymer and the aggregates were pH-sensitive to the surrounding water solution, which provides a potential application in controlled drug release. [source]