ADVANCED ENGINEERING MATERIALS, Issue 3 2009
Zhigang Xie
A facile approach to the preparation of light-responsive copolymer micelles is developed. This approach is based on the attachment of hydrophobic groups to one block of a diblock copolymer via a light-sensitive linkage. The micelles can be dissociated under light irradiation and release the encapsulated pyrene. The obtained polymeric micelles are expected to be of use as drug-delivery vehicles. [source]

Micelle and Solvent Relaxation in Aqueous Sodium Dodecylsulfate Solutions

CHEMPHYSCHEM, Issue 10 2003
Patrick Fernandez Dr.
Abstract Dielectric spectra have been measured for aqueous sodium dodecylsulfate (SDS) solutions up to 0.1 mol,L,1 at 25,°C over the frequency range 0.005,, GHz,1,89. The spectra exhibit two relaxation processes at approximately 0.03 GHz and 0.2 GHz associated with the presence of micelles in addition to the dominant solvent relaxation process at approximately 18 GHz and a small contribution at approximately 1.8 GHz due to H2O molecules hydrating the micelles. Detailed analysis reveals that the micelles bind 20 water molecules per SDS unit, but not as strongly as trimethylalkylammonium halide surfactants do. The relaxation times and amplitudes of both micelle relaxation processes can be simultaneously analysed with the theory of Grosse, yielding the effective volume of a SDS unit in the micelle and the lateral diffusion coefficient of the bound counterions. The findings of this investigation fully corroborate recent molecular dynamics simulations on structure and dynamics of SDS micelles. [source]

Study on the Radius of an Electrical Spherical Micelle: Functional Theoretical Approach

CHINESE JOURNAL OF CHEMISTRY, Issue 4 2004
Zheng-Wu Wang
Abstract For the purpose of eliminating restriction, the Poisson-Boltzmann (PB) equation, which represents the potential of the electrical double layer of spherical micelles, can be solved analytically only under the lower potential condition, a kind of iterative method in functional analysis theory has been used. The radius of the spherical particle can be obtained from the diagram of the second iterative solution of the potential versus the distance from the center of the particle. The influences of the concentration of the ions, the charge number of ions, the aggregation number of the particle, the dielectric constant of solvent and the temperature of system on the radius also have been studied. [source]

Molecular Tailored Histidine-Based Complexing Surfactants: From Micelles to Hydrogels

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2009
Patrick Gizzi
Abstract Novel histidine-based complexing surfactants, designed as AA-His-EOm -Cn, containing trifunctional moduli (peptidic/hydrophilic/hydrophobic) were synthesized by a modular step-by-step procedure, which allowed easy structural changes, and consequently correlations between their molecular structures and their self-assembling properties could be established. Thus, micelles or hydrogels could be obtained by simply modifying the hydrophobic tail lengths or the junction between the different moduli of the designed compounds. At low pH values, all compounds were surface active in aqueous solutions. At higher pH values, in the range 8,10, micellization took place for decyl compounds (n = 10), whereas hydrogelation occurred for longer chain lengths (n = 12, 14), and this, at very-low concentrations of surfactant (<0.3 wt.-%), could thus act as low molecular weight gelator (LMWG). The driving forces for gel formation were noncovalent intermolecular interactions such as ,-stacking and hydrophobic and hydrogen-bonding interactions.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

SN2 Displacement by Bromide Ions in Dichloromethane , The Role of Reverse Micelles

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2006
Lucia Brinchi
Abstract Reverse micellar systems are of interest as reaction media because they are powerful models for biological compartmentalization, enzymatic catalysis and separation of biomolecules. Solutions of ionic surfactants in apolar solvents may contain reverse micelles, but they may also contain ion pairs, or small clusters, with waters of hydration. We studied the bimolecular reaction in CH2Cl2 solutions of cationic tetraalkylammonium bromide salts (onium salts), such as cetyltrimethylammonium bromide (CTABr), cetyltripropylammonium bromide (CTPABr) and tetra- n -butylammonium bromide (TBABr). Methylnaphthalene-2-sulfonate (,-MeONs), its 6-sulfonate derivative (,-MeONsS,) as the 2,6-lutidinium salt and methyl-5- N,N,N,trimethylammonium naphthalene-1-sulfonate (,-MeONsNT+) as the trifluoromethanesulfonate salt react with Br, in CH2Cl2. First-order rate constants, kobs, increase linearly and similarly for the three substrates with increasing concentrations of the onium salts. Reactions are faster with TBABr than they are with CTPABr and CTABr, and the reactivity of the three substrates is in the order: ,-MeONsNT+ >> ,-MeONsS, > ,-MeONs. The reactions are inhibited by the addition of H2O, but CTABr tolerates H2O in large excess. At [H2O]/[CTABr] = w0 , 6, "water-pool" reverse micelles form, and kobs for all three substrates is then independent of w0. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Bionanotechnology: Enhancement of Aggregation-Induced Emission in Dye-Encapsulating Polymeric Micelles for Bioimaging (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2010
Mater.
Amphiphilic block copolymers can form polymer micelles for delivering hydrophobic fluorescent probes with aggregation-induced emission properties, as presented by A. K.-Y. Jen et al. on page 1413. By itself, 1,1,2,3,4,5-hexaphenylsilole (HPS) exhibits dramatically enhanced blue-green fluorescent emission efficiencies when encapsulated within the hydrophobic core of a polymeric micelle. When HPS is co-encapsulated with bis(4-(N -(1-naphthyl) phenylamino)-phenyl)fumaronitrile, effective orange-red fluorescence resonance energy transfer can be demonstrated within live RAW 264.7 cells. Illustration provided by Brent Polishak. [source]

Enhancement of Aggregation-Induced Emission in Dye-Encapsulating Polymeric Micelles for Bioimaging

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2010
Wen-Chung Wu
Abstract Three amphiphilic block copolymers are employed to form polymeric micelles and function as nanocarriers to disperse hydrophobic aggregation-induced emission (AIE) dyes, 1,1,2,3,4,5-hexaphenylsilole (HPS) and/or bis(4-(N -(1-naphthyl) phenylamino)-phenyl)fumaronitrile (NPAFN), into aqueous solution for biological studies. Compared to their virtually non-emissive properties in organic solutions, the fluorescence intensity of these AIE dyes has increased significantly due to the spatial confinement that restricts intramolecular rotation of these dyes and their better compatibility in the hydrophobic core of polymeric micelles. The effect of the chemical structure of micelle cores on the photophysical properties of AIE dyes are investigated, and the fluorescence resonance energy transfer (FRET) from the green-emitting donor (HPS) to the red-emitting acceptor (NPAFN) is explored by co-encapsulating this FRET pair in the same micelle core. The highest fluorescence quantum yield (,62%) could be achieved by encapsulating HPS aggregates in the micelles. Efficient energy transfer (>99%) and high amplification of emission (as high as 8 times) from the NPAFN acceptor could also be achieved by spatially confining the HPS/NPAFN FRET pair in the hydrophobic core of polymeric micelles. These micelles could be successfully internalized into the RAW 264.7 cells to demonstrate high-quality fluorescent images and cell viability due to improved quantum yield and reduced cytotoxicity. [source]

pH-Responsive Flower-Type Micelles Formed by a Biotinylated Poly(2-vinylpyridine)- block -poly(ethylene oxide)- block -poly(, -caprolactone) Triblock Copolymer

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2009
Kathy Van Butsele
Abstract In the present work, a method is proposed to assemble pH-responsive, flower-like micelles that can expose a targeting unit at their periphery upon a decrease in pH. The micelles are composed of a novel biotinylated triblock copolymer of poly(,, -caprolactone)- block -poly(ethylene oxide)- block -poly(2-vinylpyridine) (PCL- b -PEO- b -P2VP) and the non-biotinylated analogue. The block copolymers are synthesized by sequential anionic and ring-opening polymerization. The pH-dependent micellization behaviour in aqueous solution of the triblock copolymers developed is studied using dynamic light scattering, zeta potential, transmission electron microscopy (TEM), and fluorimetric measurements. The shielding of the biotin at neutral pH and their availability at the micelle surface upon protonation is established by TEM and surface plasmon resonance with avidin and streptavidin-coated gold surfaces. The preliminary stealthy behavior of these pH-responsive micelles is examined using the complement activation (CH50) test. [source]

Micellar Effects on the Reaction between an Arenediazonium Ion and the Antioxidants Gallic Acid and Octyl Gallate

HELVETICA CHIMICA ACTA, Issue 1 2008
Losada Barreiro, Sonia
Abstract The effect of sodium dodecyl sulfate (SDS) micelles on the reaction between the 3-methylbenzenediazonium (3MBD) ion and either the hydrophilic antioxidant gallic acid (GA) or the hydrophobic analogue octyl gallate (OG) have been investigated as a function of pH. Titration of GA in the absence and presence of SDS micelles showed that the micelles do not alter the first ionization equilibrium of GA. Analysis of the dependence of the observed rate constant (kobs) with pH shows that the reactive species are GA2, and OG,. Kinetics results in the absence and presence of SDS micelles suggest that SDS aggregates do not alter the expected reaction pathway. SDS Micelles inhibit the spontaneous decomposition of 3MBD as well as the reaction between 3MBD and either GA or OG, and upon increasing the SDS concentration, with kobs approaching the value for the thermal decomposition of 3MBD in the presence of SDS. Our results are consistent with the prediction of the pseudophase model and show that the origin of the inhibition for the reaction with GA is different to that for the reaction with OG; in the former case, the observed inhibition can be rationalized in terms of the micelle-induced electrostatic separation of reactants in the micellar Stern layer, whereas the observed inhibition in the reaction with OG is a consequence of the dilution effect caused by increasing SDS concentration, decreasing the local OG, concentration in the Stern layer. [source]

Stereoselective Aldol Reactions Catalyzed by Acyclic Amino Acids in Aqueous Micelles

HELVETICA CHIMICA ACTA, Issue 1 2007
Dong-Sheng Deng
Abstract The catalytic properties of all proteinogenic, acyclic amino acids for direct aldol reaction in H2O, assisted by various surfactants, were investigated. The basic and neutral amino acids were shown to be efficient catalysts, giving rise to good-to-excellent yields of adducts (up to 95%), with moderate-to-good diastereoselectivities (up to 86%), L -arginine being the most-effective catalyst. The syn/anti diastereoisomer ratio could be readily tuned by proper choice of the amino acid used. Also, the range of substrates that underwent the reaction was extended to less-reactive aldehydes carrying electron-donating Br substituents. [source]

Fabrication of Continuous and Segmented Polymer/Metal Oxide Nanowires Using Cylindrical Micelles and Block Comicelles as Templates

ADVANCED MATERIALS, Issue 18 2009
Hai Wang
Cylindrical micelles were added as templates to sol,gel reaction mixtures to yield highly elongated polymer/inorganic nanostructures with smooth nanothin surface coatings of silica, zirconia, or alumina. Differences in the templating activity of neutral or cationic coronas can be exploited by using triblock comicelles to produce discrete nanocylinders with spatially isolated domains of titania surface deposition. [source]

Effect of self-assemblies of various surfactants in their single and mixed states on the BZ oscillatory reaction

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2010
Muzaffar Hussain Najar
Micelles of different surfactants are well known to affect chemical equilibria and reactivities by selectively sequestering the reagent substrates through electrostatic and hydrophobic interactions. In this article, the effects of micelles of various surfactants on different parameters of the Ce(IV)-catalyzed Belousov,Zhabotinsky (BZ) oscillatory reaction at 35°C in nonstirred closed conditions are studied by employing spectrophotometry and tensiometry. Surfactants used in this study are the cationics hexadecyltrimethylammonium bromide (CTAB) and pentamethylene-1,5-bis(N -hexadecyl- N,N -dimethylammonium)bromide gemini (Gemini), anionic sodium dodecylbenzene sulfonate (SDBS), and nonionic Brij58, whereas the binary surfactant systems used are cationic,nonionic CTAB+Brij58 and anionic,nonionic SDBS+Brij58. The results revealed that the induction period shows a definite variation with increasing concentration of different surfactants above their critical micelle concentration (cmc). The amplitudes of oscillation and absorbance maxima and minima are enhanced in the presence of micelles of CTAB and Gemini surfactants, whereas micelles of SDBS and Brij58 have almost no effect on the nature of the oscillations. However, mixed micelles of CTAB+Brij58 and SDBS+Brij58 binary mixtures show a quite different effect on the overall behavior of the oscillations. The enhanced effect of CTAB and Gemini surfactants on the overall nature of oscillations has been attributed to the positive charge on the surface of their micelles and to some extent on the presence of nitrogen in their head group. The effect of mixed binary micelles may be attributed to their synergistic nature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 659,668, 2010 [source]

Magnetite-Loaded Polymeric Micelles as Ultrasensitive Magnetic-Resonance Probes,

ADVANCED MATERIALS, Issue 16 2005
H. Ai
Increased contrast in magnetic resonance imaging (MRI) is accomplished using polymeric micelles loaded with superparamagnetic iron oxide (SPIO) nanoparticles encapsulated in biocompatible, biodegradable poly(,-caprolactone)- b -poly(ethylene glycol) (PCL- b -PEG) copolymers (see Figure). The loaded micelles show significantly improved T2 relaxivities and remarkable MRI detection sensitivity. [source]

Perceived Creaminess and Viscosity of Aggregated Particles of Casein Micelles and ,-Carrageenan

JOURNAL OF FOOD SCIENCE, Issue 5 2010
Kelly L. Flett
Abstract:, Creaminess, in terms of sensory science, is a very complex and multifaceted term. It is a descriptor often reserved for fat-containing dairy emulsions, however, has also been used to describe nondairy food emulsions. In the food industry, it is a great challenge to decrease fat content while maintaining the original quality and sensory characteristics of a food product. An aggregated particle consisting of casein micelles and ,-carrageenan has the potential to enhance the perceived creaminess of a low-fat food product, due to its colloidal size. In this study, these aggregates were incorporated into nonfat dairy beverages and subjected to sensory studies. In the 1st sensory study, the aggregates, either as a powdered ingredient or a fresh ingredient, were added to thickened dairy beverages and compared to similar beverages containing skim milk powder and either no fat or 2% dairy fat. The panelists found the aggregate-containing beverages to be creamier and more viscous in comparison to the control beverages. In the 2nd sensory study, fresh and powdered aggregates, at 2 concentrations, were added to a sweetened nonfat dairy beverage and compared to a similar beverage containing 2% dairy fat. The results of this panel showed that aggregates, especially at increased concentrations, were perceived as more creamy than the fat-containing beverage. Panelists described the creaminess of the aggregates as more thick and viscous while the dairy fat was described more in terms of mouth-coating. Thus, we have developed a nonfat milk ingredient that can contribute creaminess to a food product. Practical Application:, This study shows potential applications of aggregates of casein micelles and ,-carrageenan as a fat-mimetic or creaminess-enhancing ingredient. These particles may be produced as either fresh aggregates directly formed in a dairy product or as powdered aggregates added to dairy or nondairy products. [source]

Biorelevant dissolution media: Aggregation of amphiphiles and solubility of estradiol

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2006
David Ilardia-Arana
Abstract Biorelevant dissolution media containing bile salt and lecithin at concentrations appropriate for fed and fasted state are useful when testing oral solid formulations of poorly water-soluble drugs. Dilution of amphiphile solutions affects the aggregation state of the amphiphiles because bile salt is partitioned between the aqueous phase and the aggregates. The aim of the investigation was to study the effect of dilution on the size distribution of aggregates and its effect on the solubilization capacity. Clear buffered solutions of four intestinal amphiphiles (sodium glycocholate, lecithin, monoolein, and oleic acid) and a combination of these were prepared at high bile salt concentration. Micelles in the glycocholate solutions decreased in size when diluted. The addition of insoluble amphiphiles led to bigger micelles with no clear correlation between size of the micelles and amphiphile concentration. Dilution of the two- and four component media caused enlargement of the mixed micelles and formation of vesicles. The solubility of estradiol in the buffer solution was increased with addition of the amphiphiles. A good correlation (R2,=,0.987) was found between estradiol solubility and mass concentration of the amphiphiles. The results demonstrate that, in the case of estradiol, the concentration of amphiphiles rather than the aggregation state determines the solubilization capacity of the medium. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:248,255, 2006 [source]

Metathetic Reaction in Reverse Micelles: Synthesis of Nanostructured Alkaline-Earth Metal Phosphates

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007
Purnendu Parhi
For the past few years, hydroxyapatite (HAp) has been identified as a potential biomaterial due to its excellent biocompatibility and bioactivity. The preparation of nanostructured HAp with controlled powder characteristics is a pre-requisite for processing it into useful biocomposites. Here, the synthesis of nanorods of calcium hydroxyapatite (Ca-HAp), strontium hydroxyapatite (Sr-HAp), and barium hydroxyapatite (Ba-HAp) by exploiting the metathetic reaction taking place in reverse micelles in the presence of cetyltrimethylammonium bromide has been reported. Powder X-ray diffraction analysis and thermogravimetric measurements confirm the formation of monophasic Ca-HAp and Sr-HAp. The growth of nanorods was further confirmed using transmission electron microscopy studies. The average lengths of Ca-HAp and Sr-HAp were ,60 and 30 nm, respectively. However, the preparation of Ba-HAp invariably yielded a multiphasic mixture with other competitive phases like BaHPO4 and Ba(H2PO4)2. [source]

Reduction-Sensitive Reversibly Crosslinked Biodegradable Micelles for Triggered Release of Doxorubicin

MACROMOLECULAR BIOSCIENCE, Issue 12 2009
Yanmin Xu
Abstract Reduction-responsive reversibly crosslinked biodegradable micelles were developed and applied for triggered release of doxorubicin (DOX). An amphiphilic block copolymer of poly(ethylene glycol) (PEG) and poly(, -caprolactone) (PCL) that contains two lipoyl functional groups at their interface (PEG-L2 -PCL) has been synthesized. 1H NMR spectroscopy and gel permeation chromatography (GPC) measurements show that the PEG-L2 -PCL block copolymer had a controlled composition (PEG 5 kDa and PCL 5.4 kDa) and a polydispersity index (PDI) of 1.36. PEG-L2 -PCL formed micelles with sizes that ranged from 20 to 150,nm in aqueous solutions, wherein a critical micelle concentration (CMC) of 16,mg·L,1 was determined. The micelles were readily crosslinked by adding 7.6,mol % of dithiothreitol (DTT) relative to the lipoyl groups. Notably, micelles after crosslinking demonstrated a markedly enhanced stability against dilution, physiological salt concentration, and organic solvent. In the presence of 10,×,10,3,M DTT, however, micelles were subject to rapid de-crosslinking. In vitro release studies showed minimal release of DOX from crosslinked micelles at a concentration of 10,mg,L,1 (C,<,CMC, analogous to intravenous injection), wherein less than 15% of the DOX was released in 10,h. In contrast, rapid release of DOX was observed for DOX-loaded non-crosslinked micelles under otherwise the same conditions (,80% release in 0.5,h). In the presence of 10,×,10,3,M DTT mimicking an intracellular reductive environment, sustained release of DOX from crosslinked micelles was achieved, in which 75% of the DOX was released in 9,h. These novel reduction-sensitive reversibly crosslinked biodegradable micelles are highly promising for targeted intracellular delivery of anticancer drugs. [source]

One-Pot Synthesis of Micelles with a Cross-Linked Poly(acrylic acid) Core

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2006
Genhua Zheng
Abstract Summary: Stable micelles with polystyrene (PS) as a shell and cross-linked poly[(acrylic acid)- co -(ethylene glycol diacrylate)] as a core have been successfully prepared by reversible addition fragmentation chain transfer (RAFT) copolymerization of acrylic acid and ethylene glycol diacrylate in a selective solvent with PS-SC(S)Ph as a RAFT agent. For the preparation of stable micelles, the RAFT polymerizations are carried out in different solvents: benzene, cyclohexane, and mixtures of tetrahydrofuran and cyclohexane. The monomer/PS-SC(S)Ph molar ratio and molecular weight of the macro-RAFT agent, PS-SC(S)Ph, influence the RAFT polymerization and the formation of micelles. Block copolymerization in selective solvent with the RAFT agent. [source]

Highly Ordered Hexagonal Arrays of Hybridized Micelles from Bimodal Self-Assemblies of Diblock Copolymer Micelles

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 7 2010
Seong Il Yoo
Abstract We demonstrate the formation of highly ordered hexagonal arrays of hybridized polystyrene,poly(4-vinyl pyridine), PS,PVP, micelles with controllable size by solvent annealing techniques. Because the formation of hybridized micelles was prohibited in the mixture solutions of two different-sized PS,PVP micelles, single-layered films with bimodal self-assemblies of small and large micelles were fabricated from the mixture solutions by adjusting their mixing ratios. When the single-layered films were solvent annealed by saturated vapor of tetrahydrofuran (THF), on the other hand, small and large PS,PVP micelles in the bimodal self-assemblies merged together to form hybridized micelles. In addition, the hybridized micelles arranged themselves in a highly ordered hexagonal array, the diameter and center-to-center distance of which were precisely adjusted by varying the mixing ratio of small to large micelles in the bimodal assemblies. [source]

Sphere-to-Rod Transition of Micelles formed by the Semicrystalline Polybutadiene- block -Poly(ethylene oxide) Block Copolymer in a Selective Solvent

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2010
Adriana M. Mihut
Abstract We present a morphological study of the micellization of an asymmetric semicrystalline block copolymer, poly(butadiene)- block -poly(ethylene oxide), in the selective solvent n -heptane. The molecular weights of the poly(butadiene) (PB) and poly(ethylene oxide) (PEO) blocks are 26 and 3.5,kg,·,mol,1, respectively. In this solvent, micellization into a liquid PEO-core and a corona of PB-chains takes place at room temperature. Through a thermally controlled crystallization of the PEO core at ,30,°C, spherical micelles with a crystalline PEO core and a PB corona are obtained. However, crystallization at much lower temperatures (,196,°C; liquid nitrogen) leads to the transition from spherical to rod-like micelles. With time these rod-like micelles aggregate and form long needles. Concomitantly, the degree of crystallinity of the PEO-cores of the rod-like micelles increases. The transition from a spherical to a rod-like morphology can be explained by a decrease of solvent power of the solvent n -heptane for the PB-corona chains: n -Heptane becomes a poor solvent at very low temperatures leading to a shrinking of the coronar chains. This favors the transition from spheres to a morphology with a smaller mean curvature, that is, to a cylindrical morphology. [source]

Nanometer-Scaled Hollow Spherical Micelles with Hydrophilic Channels and the Controlled Release of Ibuprofen

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2008
De'an Xiong
Abstract PS- b -PAA spherical micelles with a liquid core and a PAA shell are prepared with the assistance of 1,2-dichloroethane. During the process of adding a mixture of PNIPAM- b -P4VP and PEG- b -P4VP, multi-layered micelles with a mixed corona that consists of both PNIPAM and PEG chains are constructed through the electrostatic interaction and hydrogen bonding between the PAA block and the P4VP block. When heating above the LCST, the PNIPAM chains collapse onto the PAA/P4VP complex layer while the PEG chains still stretch into the solution through the collapsed PNIPAM layer, which leads to the formation of hydrophilic channels around the PEG chains. The ibuprofen encapsulated in the hollow space can diffuse through the channels and its release rate can be controlled by changing the ratio of PEG chains to PNIPAM chains in the corona. [source]

Self-Assembly of Large Multimolecular Micelles from Hyperbranched Star Copolymers

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2007
Haiyan Hong
Abstract This work focused on the synthesis and aqueous self-assembly of a series of novel hyperbranched star copolymers with a hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane] (HBPO) core and many linear poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) arms. The copolymers can synchronously form unimolecular micelles (around 10 nm) and large multimolecular micelles (around 100 nm) in water at room temperature. TEM measurements have provided direct evidence that the large micelles are a kind of multimicelle aggregates (MMAs) with the basic building units of unimolecular micelles. It is the first demonstration of the self-assembly mechanism for the large multimolecular micelles generated from the solution self-assembly of hyperbranched copolymers. [source]

Thermo- and pH-Responsive Micelles of Poly(acrylic acid)- block -Poly(N,N -diethylacrylamide)

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 7 2005
Xavier André
Abstract Summary: The bis-hydrophilic block copolymer, poly(acrylic acid)45 - block -poly(N,N -diethylacrylamide)360, was obtained after hydrolysis of poly(tert -butyl acrylate)45 - block -poly(N,N -diethylacrylamide)360, synthesized by sequential anionic polymerization of tert -butyl acrylate (tBA) and N,N -diethylacrylamide (DEAAm) in the presence of Et3Al. The polymer is stimuli-sensitive with respect to both pH and temperature in aqueous solution, reversibly forming spherical crew-cut micelles with PDEAAm-core (,Rh,z,=,21.5 nm) under alkaline conditions for T,>,35,°C as well as inverse star-like micelles with an expanded PAA-core (,Rh,z,=,43.8 nm) under acidic conditions for T,<,35,°C, as indicated by dynamic light scattering. Modes of micelle formation for poly(acrylic acid)45 - block -poly(N,N -diethylacrylamide)360 in aqueous solution depending on the pH and temperature. [source]

The Formation of Biodegradable Polymeric Micelles from Newly Synthesized Poly(aspartic acid)- block -Polylactide AB-Type Diblock Copolymers

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 6 2004
Hidetoshi Arimura
Abstract Summary: A poly(aspartic acid)- block -polylactide (PAsp- block -PLA) diblock copolymer was synthesized through the polymerization of , -benzyl- L -aspartate- N -carboxyanhydride [Asp(OBzl)-NCA] with amino-terminating polylactide (NH2 -PLA) as a macroinitiator. The chain length of the PAsp segment could be easily controlled by changing the monomer/initiator ratio. Dynamic light scattering measurements of PAsp- block -PLA aqueous solutions revealed the formation of polymeric micelles. Changes in the micelles as a function of pH were investigated. The structure and formation of micelles of the poly(aspartic acid)- block -polylactide (PAsp- block -PLA) diblock copolymers synthesized here. [source]

Polycaprolactone- b -Poly(ethylene oxide) Biocompatible Micelles as Drug Delivery Nanocarriers: Dynamic Light Scattering and Fluorescence Experiments

MACROMOLECULAR SYMPOSIA, Issue 1 2005
Cristiano Giacomelli
Abstract Summary: Dynamic light scattering (DLS) and fluorescence experiments were carried out to study PCL44 - b -PEO114 biocompatible micelles used as nanocarriers in drug delivery. Micelles prepared by a simple procedure (THF removal under nitrogen flow) exhibited a narrow size distribution with an average diameter of 100 nm. For micelles containing a hydrophobic model compound (pyrene) within the PCL core, a smaller average micellar size of 80 nm was observed, with a simultaneous broadening in the size distribution profile. In parallel to DLS results, fluorescence experiments showed evidence of pyrene encapsulation, and that the onset of the micellization process occurs at approximately 10/90 (v/v) THF/water mixtures in the case of PCL44 - b -PEO114 polymer. [source]

Exciplex-type Behavior and Partition of 3-Substituted Indole Derivatives in Reverse Micelles Made with Benzylhexadecyldimethylammonium Chloride, Water and Benzene,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2001
Claudio D. Borsarelli
ABSTRACT The fluorescence properties of 3-methylindole (MI), 3-indoleacetic acid (IAA), 3-indoleethyltrimethylammonium bromide (IETA), l -tryptophan (Trp) and tryptamine hydrochloride (TA) were studied in reverse micelles solutions made with the cationic surfactant benzylhexadecyldimethylammonium chloride (BHDC) in benzene as a function of the molar ratio water/surfactant R (=[H2O]/[BHDC]). The fluorescence quenching of the model compound MI by benzene in cyclohexane solutions and by BHDC in benzene solutions were also studied in detail. The fluorescence of MI in benzene is characteristic of a charge-transfer exciplex. The exciplex is quenched by the presence of BHDC, due to the interactions of the surfactant ion pairs with the polar exciplex. In reverse micelle solutions at low R values, all the indoles show exciplex-type fluorescence. As R increases, the fluorescence behavior strongly depends on the nature of the indole derivative. The anionic IAA remains anchored to the cationic interface and its fluorescence is quenched upon water addition due to the increases of interface's micropolarity. For IETA, TA and Trp an initial fluorescence quenching is observed at increasing R, but a fluorescence recovery is observed at R > 5, indicating a probe partition between the micellar interface and the water pool. For the neutral MI, the fluorescence changes with R indicate the partition of the probe between the micellar interface and the bulk benzene pseudophase. A simple two-site model is proposed for the calculation of the partition constants K as a function of R. In all cases, the calculation showed that even at the highest R value, about 90% of the indole molecules remain associated at the micellar interface. [source]

Effect of mixing protocol on compatibilized polymer blend morphology

POLYMER ENGINEERING & SCIENCE, Issue 5 2006
Bin Lin
We investigated the effect of mixing protocol on the morphology of compatibilized polymer blends made with premade compatibilizer and reactively formed in-situ compatibilizer in a custom-built miniature mixer Alberta Polymer Asymmetric Minimixer (APAM). The compatibilized blends show a finer morphology than uncompatibilized blends if the polymers are mixed together in the dry state and then fed into the mixer. It is found that premelting one polymer, and premixing polymers and compatibilizer, both greatly affect the compatibilized blends' morphology. The effects are complex since the dispersed phase particle size and distribution of the compatibilized blends may be smaller or larger when compared with the uncompatibilized system, depending on the material's physical and chemical properties; for example, diblock molecular weight or the preference of copolymer to migrate to a particular phase can change the final morphology. Good mobility of the copolymer to reach the interface is crucial to obtain a finer morphology. Micelles are observed when a high molecular weight diblock copolymer P(S- b -MMA) is used for a PS/PMMA blend. Because of its enhanced mobility, no micelles are found for a low molecular weight diblock copolymer P(S- b -MMA) in a PS/PMMA blend. For PS/PE/P(S- b -E) blends, finer morphology is obtained when P(S- b -E) is first precompounded with PS. Because the block copolymer prefers the PE phase, if the P(S- b -E) block copolymer is compounded with PE first, some remains inside the PE phase and does not compatibilize the interface. In the case of reactive blend PSOX/PEMA, premelting and holding the polymers at high temperature for 5 min decreases final dispersed phase particle size; however, premelting and holding for 10 min coarsens the morphology. POLYM. ENG. SCI. 46:691,702, 2006. © 2006 Society of Plastics Engineers. [source]

Programmable Shape-Shifting Micelles,

ANGEWANDTE CHEMIE, Issue 30 2010
Miao-Ping Chien
Amphiphile DNA-Bürsten-Copolymere bilden Micellen, deren Morphologien durch selektive Wechselwirkungen festgelegt sind, die die sterische und elektrostatische Abstoßung in den Micellhüllen beeinflussen. Die Zugabe einer DNA-Sequenz zu den Micellen induziert deren Phasenübergang von der Zylinder- in Kugelformen (siehe Bild). [source]

Reversible Three-State Switching of Multicolor Fluorescence Emission by Multiple Stimuli Modulated FRET Processes within Thermoresponsive Polymeric Micelles,

ANGEWANDTE CHEMIE, Issue 30 2010
Changhua Li
Micellare Verkehrsampeln: Das im Titel bezeichnete System mit resonantem Fluoreszenzenergietransfer (FRET) nutzt eine Art Donorfarbstoff und zwei Arten Akzeptorfarbstoffe. Das An- und Ausschalten der Fluoreszenz der beiden Akzeptorfarbstoffe kann über den pH-Wert bzw. Licht gesteuert werden. Dieses neuartige vielfarbige lumineszierende Polymersystem kann als ratiometrische Sonde mit einstellbarer Empfindlichkeit für pH-Wert und Temperatur fungieren. [source]

One-Pot Synthesis of Biomimetic Shell Cross-Linked Micelles and Nanocages by ATRP in Alcohol/Water Mixtures,

ANGEWANDTE CHEMIE, Issue 20 2010
Shinji Sugihara Dr.
Ein ABC-Triblockcopolymer wurde für die Eintopfsynthese von Micellen mit vernetzter Schale (SCL) verwendet (siehe Schema; BIEE=1,2-Bis(2-iodethoxy)ethan). Bei deren Dialyse werden die PMPC-Ketten des Kerns solvatisiert. Bei nicht zu starker Vernetzung wandern die Ketten durch die Schale, um zusammen mit den PEO-Ketten die Micellencorona zu konstituieren. [source]