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Micellar Structures (micellar + structure)
Selected AbstractsMicellar Structures of Hydrophilic/Lipophilic and Hydrophilic/Fluorophilic Poly(2-oxazoline) Diblock Copolymers in WaterMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 21 2008Ruzha Ivanova Abstract Amphiphilic poly(2-alkyl-2-oxazoline) diblock copolymers of 2-methyl-2-oxazoline (MOx) building the hydrophilic block and either 2-nonyl-2-oxazoline (NOx) for the hydrophobic or 2-(1H,1H,,2H,2H,-perfluorohexyl)-2-oxazoline (FOx) for the fluorophilic block were synthesized by sequential living cationic polymerization. The polymer amphiphiles form core/shell micelles in aqueous solution as evidenced using small-angle neutron scattering (SANS). Whereas the diblock copolymer micelles with a hydrophobic NOxn block are spherical, the micelles with the fluorophilic FOxn are slightly elongated, as observed by SANS and TEM. In water, the micelles with fluorophilic and lipophilic cores do not mix, but coexist. [source] Micellar structure of amphiphilic poly(2-oxazoline) diblock copolymersJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007C. M. Papadakis Amphiphilic diblock copolymers from poly(2-oxazoline)s in aqueous solution can form micelles. By means of small-angle neutron scattering, we have found that poly[(n -nonyl-2-oxazoline)- b -(methyl-2-oxazoline)] {P[(NOx)- b -(MOx)]} diblock copolymers in aqueous solution form micelles of core-shell type. We have determined the core radius and the shell thickness of the micelles. Comparing the values obtained to the stretched lengths of the blocks leads to the conclusion that the P(NOx) core blocks are stretched, whereas the P(MOx) shell blocks are coiled. [source] Injectable Superparamagnetic Ferrogels for Controlled Release of Hydrophobic DrugsADVANCED MATERIALS, Issue 13 2009Jian Qin A ferrogel for magnetically controlled release of drugs is prepared by integration of superparamagnetic iron oxide nanoparticles and Pluronic F127 gels. The hydrophobic drug indomethacin is loaded in the ferrogel owing to the oil-in-water micellar structure. The characteristic sol,gel transition property renders the ferrogel an injectable drug carrier that will be, in principle, free from surgical implant procedure. [source] Amphiphilic Block Polypeptide-Type Ligands for Micellar Catalysis in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Shlomi Elias Abstract Novel amphiphilic block polypeptide ligands were synthesized and showed excellent behavior in the metal-catalyzed organic transformations in pure water. The catalytic activity and/or recycling properties of the catalysts are the result of the micellar structure of the polymeric system in water. [source] Behaviors of self-assembled diblock copolymer with pendant photosensitive azobenzene segmentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2010Jui-Hsiang Liu Abstract A novel monomer, ethyl 4-[4-(11-methacryloyloxyundecyloxy)phenyl azobenzoyl-oxyl] benzoate, containing a photoisomerizable NN group was synthesized. The monomer was further diblock copolymerized with methyl methacrylate. Amphiphilic diblock copolymer poly(methyl methacrylate- block -ethyl 4-[4-(11-methacryloyloxyundecyloxy)phenyl azobenzoyl-oxyl] benzoate (PMMA - b - PAzoMA) was synthesized using atom transfer radical polymerization. The reverse micelles with spherical construction were obtained with 2 wt % of the diblock copolymer in a THF/H2O mixture of 1:2. Under alternating UV and visible light illumination, reversible changes in micellar structure between sphere and rod-like particles took place as a result of the reversible E-Z photoisomerization of azobenzene segments in PMMA - b - PAzoMA. Microphase separation of the amphiphilic diblock copolymer in thin films was achieved through thermal and solvent aligning methods. The microphases of the annealed thin films were investigated using atom force microscopy topology and scanning electron microscopy analyses. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1142,1148, 2010 [source] Synthesis and characterization of core,shell-type polymeric micelles from diblock copolymers via reversible addition,fragmentation chain transferJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2006Ping Zhang Abstract A method was developed to enable the formation of nanoparticles by reversible addition,fragmentation chain transfer polymerization. The thermoresponsive behavior of polymeric micelles was modified by means of micellar inner cores and an outer shell. Polymeric micelles comprising AB block copolymers of poly(N -isopropylacrylamide) (PIPAAm) and poly(2-hydroxyethylacrylate) (PHEA) or polystyrene (PSt) were prepared. PIPAAm- b -PHEA and PIPAAm- b -PSt block copolymers formed a core,shell micellar structure after the dialysis of the block copolymer solutions in organic solvents against water at 20 °C. Upon heating above the lower critical solution temperature (LCST), PIPAAm- b -PHEA micelles exhibited an abrupt increase in polarity and an abrupt decrease in rigidity sensed by pyrene. In contrast, PIPAAm- b -PSt micelles maintained constant values with lower polarity and higher rigidity than those of PIPAAm- b -PHEA micelles over the temperature range of 20,40 °C. Structural deformations produced by the change in the outer polymer shell with temperature cycles through the LCST were proposed for the PHEA core, which possessed a lower glass-transition temperature (ca. 20 °C) than the LCST of the PIPAAm outer shell (ca. 32.5 °C), whereas the PSt core with a much higher glass-transition temperature (ca. 100 °C) retained its structure. The nature of the hydrophobic segments composing the micelle inner core offered an important control point for thermoresponsive drug release and the drug activity of the thermoresponsive polymeric micelles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3312,3320, 2006 [source] Blends of bitumen with polymers having a styrene componentPOLYMER ENGINEERING & SCIENCE, Issue 7 2001A. H. Fawcett The properties of a 100 penetration grade bitumen are modified considerably, and in a number of ways by the addition of 10 to 40 parts per hundred (pph) of a homopolystyrene and graft, block and random copolymers of styrene with butadiene and acrylonitrile. At low temperatures some blends have a similar stiffness to or even lower stiffness than the bitumen, but generally the blends are more than one order of magnitude stiffer, even when a rubber is added. The contrasting behavior is displayed by a polystyrene and a high impact polystyrene, ,3% to 4% of grafted rubber on the latter being sufficient to cause the enhancement, even at the 10 pph level, by two different random styrene-butadiene copolymers, and also by blends consisting of different amounts of SBS block copolymer. Some polymers apparently trigger a Hartley inversion of the micellar structure of the asphaltene micelles. High low temperature stiffness correlates roughly with a lower Tg' as measured by the peak maximum in the E, plots of the dynamic mechanical thermal analysis (DMTA) and by the steps in the differential scanning calorimetry (DSC) curves at temperatures below O°C. Tan , maxima and DSC traces detected the glass transition in the continuous phase and in the dispersed phases, but none of these amorphous polymers formed a crystalline phase, though the DSC traces of the polystyrene and the SBS blends suggested that the polymer-rich phases underwent an aging/ordering process on cooling. Our SBS blends differ in phase inversion behavior and the pattern of loss processes from others that had a smaller asphaltene component. [source] Enantioselectivity of alcohol-modified polymeric surfactants in micellar electrokinetic chromatographyELECTROPHORESIS, Issue 15 2003Jepkoech Tarus Abstract A novel method of modifying sodium undecanoyl- L -leucinate (SUL) micelles employed in chiral separation of analytes in micellar electrokinetic chromatography (MEKC) to enhance selectivity toward specific analytes is discussed. The current study aimed at modifying the SUL micelles by introducing different alcohols into the mono-SUL micelles. The micellar solutions were then polymerized in the presence of alcohols followed by postpolymerization extraction of the alcohols to yield alcohol-free polymeric surfactants (poly- L -SUL). The effects of hexanol (C6OH) and undecylenyl alcohol (C11OH) on micellar properties of this surfactant were investigated by use of surface tensiometry, fluorescence spectroscopy, pulsed field gradient-nuclear magnetic resonance (PFG-NMR), and MEKC. The surface tension and PFG-NMR studies indicated an increase in the critical micelle concentration (cmc) and micellar size upon increasing the alcohol concentration. Fluorescence measurements suggested that alcohols induce closely packed micellar structures. Coumarinic and benzoin derivatives, as well as (±)-1, 1'-binaphthyl-2,2'-dihydrogen phosphate (BNP) were used as test analytes for MEKC experiments. Examination of MEKC data showed remarkable resolutions and capacity factors of coumarinic derivatives obtained with modified poly- L -SUL as compared to the unmodified poly- L -SUL. Evaluation of fluorescence, PFG-NMR, and MEKC data suggest a strong correlation between the polarity and hydrodynamic radii of alcohol-modified micelles and the resolution of the test analytes. [source] Aggregation and membrane permeabilizing properties of designed histidine-containing cationic linear peptide antibiotics,JOURNAL OF PEPTIDE SCIENCE, Issue 4 2008Arnaud Marquette Abstract Members of the LAH4 family of cationic linear peptide antibiotics have been designed to form amphipathic helical structures in membrane environments and switch from alignments parallel to the bilayer surface to transmembrane orientations in a pH-dependent manner. Here the aggregation in aqueous buffer of two members of the family has been investigated by DLS. The peptides form monomers or small oligomers at pH = 5 but associate into nano-sized aggregates at physiological pH. The diameter of these latter complexes can be considerably reduced by sonication. Furthermore, the membrane interactions of the various supramolecular aggregates with POPC or mixed POPC/POPS vesicles have been investigated in calcein-release assays. In all the cases tested, the large preformed oligomeric peptide aggregates of 20,40 nm in size were more active than the structures with the smallest hydrodynamic radii in releasing the fluorescent dye from LUV. In contrast, the relative activity after sonication depends on the specific environment tested. The data suggest that these amphiphiles form micellar structures and support the notion that they can act in a manner comparable to detergents. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] Environmentally responsive micelles from polystyrene,poly[bis(potassium carboxylatophenoxy)phosphazene] block copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2005Youngkyu Chang Abstract Amphiphilic diblock copolymers that contained hydrophilic poly[bis(potassium carboxylatophenoxy)phosphazene] segments and hydrophobic polystyrene sections were synthesized via the controlled cationic polymerization of Cl3PNSiMe3 with a polystyrenyl,phosphoranimine as a macromolecular terminator. These block copolymers self-associated in aqueous media to form micellar structures which were investigated by fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The size and shape of the micelles were not affected by the introduction of different monovalent cations (Li+, K+, Na+, and Cs+) into the stable micellar solutions. However, exposure to divalent cations induced intermicellar crosslinking through carboxylate groups, which caused precipitation of the ionically crosslinked aggregates from solution. This micelle-coupling behavior was reversible: the subsequent addition of monovalent cations caused the redispersion of the polystyrene- block -poly[bis(potassium carboxylatophenoxy)phosphazene] (PS,KPCPP) block copolymers into a stable micellar solution. Aqueous micellar solutions of PS,KPCPP copolymers also showed pH-dependent behavior. These attributes make PS,KPCPP block copolymers suitable for studies of guest retention and release in response to ion charge and pH. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2912,2920, 2005 [source] A New View of the Anionic Diene Polymerization MechanismMACROMOLECULAR SYMPOSIA, Issue 1 2004A.Z. Niu Abstract We investigated the anionic polymerization of butadiene in d-heptane solvent using tert -butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: 1H NMR and small angle neutron scattering (SANS). The time resolved 1H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator --- at about 10% monomer conversion --- signals the onset of the normal ,6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non-polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining 1H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large-scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with Nagg >>1000 and Rg , 1000Å were found. [source] A comparative study of transformation of micellar structures in CTAB and TTAB binary systems using Positron Lifetime SpectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009R. Yadav Abstract The micellar structures of cetyl-tri-methyl ammonium bromide (CTAB) and its homologues have been investigated employing several conventional techniques. However, due to lack of sensitivity inherent in these techniques and the perturbation introduced by the probe, the detailed structures of the aggregates in the so-called single phase regions of these systems are far from being fully understood. Positron has been found to be a useful non-destructive probe for investigating micellar structures in surfactant systems [1-3] The present study is an effort to get a better insight into the micellar structures and their transformations in CTAB and TTAB aqueous binary systems Positron lifetime spectroscopy has been employed to study these systems covering a wide range of surfactant concentrations. A comparative study of the results obtained for the two surfactant systems have been discussed in this paper. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and morphology transformation of amphiphilic diblock polyurethane copolymers in aqueous solutionPOLYMER INTERNATIONAL, Issue 8 2010Qing Miao Abstract Amphiphilic block copolymers possess both hydrophobic and hydrophilic properties and can form versatile micellar structures in aqueous solution. The aim of the research presented was to prepare a series of non-ionic amphiphilic diblock polyurethane copolymers (PUn) based on isophorone diisocyanate, monoallyl-end-capped poly(ethylene oxide) and poly(propylene oxide) (PPO), followed by an investigation of their micellization properties and morphology transformation in aqueous solution. The PUn samples were synthesized by condensation polymerization. These polyurethanes exhibit surface tension as low as 33.7,37.0 mN m,1. There is an obvious decrease in critical micelle concentration as the hydrophobic PPO molecular weight increases. According to transmission electron microscopy, the morphology of aggregates of the copolymers can be tuned by varying the concentration in aqueous solution rather than organic solvent. For example, for PU7, large compound micelles are produced instead of vesicles. For PU17, the concentration can be used to control the size and thickness of vesicles. Vesicle size increases from 60 to 500 nm and vesicle thickness from 40 to 60 nm with concentration ranging from 0.003 to 0.03 wt%. The study shows that the copolymers in aqueous solution have excellent surface activities. In addition, they can self-assemble into large compound micelles or vesicles at certain concentrations. Moreover, the synthesis method described allows one to obtain a desired morphology of aggregates by adjusting the composition of hydrophilic and hydrophobic segments, which provides a novel and simple way to obtain particles on the nanometer scale. Copyright © 2010 Society of Chemical Industry [source] Highly Ordered Mesoporous Carbonaceous Frameworks from a Template of a Mixed Amphiphilic Triblock-Copolymer System of PEO,PPO,PEO and Reverse PPO,PEO,PPOCHEMISTRY - AN ASIAN JOURNAL, Issue 10 2007Yan Huang Abstract A series of highly ordered mesoporous carbonaceous frameworks with diverse symmetries have been successfully synthesized by using phenolic resols as a carbon precursor and mixed amphiphilic surfactants of poly(ethylene oxide)- b -poly(propylene oxide)- b -poly(ethylene oxide) (PEO,PPO,PEO) and reverse PPO,PEO,PPO as templates by the strategy of evaporation-induced organic,organic self-assembly (EISA). The transformation of the ordered mesostructures from face-centered (Fdm) to body-centered cubic (Imm), then 2D hexagonal (P6mm), and eventually to cubic bicontinuous (Iad) symmetry has been achieved by simply adjusting the ratio of triblock copolymers to resol precursor and the relative content of PEO,PPO,PEO copolymer F127, as confirmed by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and nitrogen-sorption measurements. The blends of block copolymers can interact with resol precursors and tend to self-assemble into cross-linking micellar structures during the solvent-evaporation process, which provides a suitable template for the construction of mesostructures. The assembly force comes from the hydrogen-bonding interactions between organic mixed micelles and the resol-precursor matrix. The BET surface area for the mesoporous carbonaceous samples calcined at 600,°C under nitrogen atmosphere is around 600,m2,g,1, and the pore size can be adjusted from 2.8 to 5.4,nm. An understanding of the organic,organic self-assembly behavior in the mixed amphiphilic surfactant system would pave the way for the synthesis of mesoporous materials with controllable structures. [source] | |||||||||||||