Dissipative particle dynamics (DPD) was used to simulate the formation and stabilization of gold nanoparticles in poly(ethylene
oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymer micelles. Primary gold clusters that were
experimentally observed in the early stage of gold nanoparticle formation were modeled as gold bead in DPD simulation. It
showed that gold beads were wrapped by the block copolymer and aggregated into spherical particles inside the micelles and
forming stable Pluronic–gold colloids with two-layer structures. Increasing Pluronic concentration, molecular weight, and
PPO block length led to the formation of more uniform and more stable gold nanoparticles. Density profiles of water beads
suggested that the micelles, especially the hydrophobicity of the micellar cores, played an important role in stabilizing
gold nanoparticles. Dynamic process indicated that the formation of gold nanoparticles was controlled by the competition between
aggregation of primary gold clusters and the stabilization by micelles of block copolymers.. The DPD simulation results of
gold–copolymer–water system agree well with previous experiments, while more structure information on microscopic level could
be provided. 相似文献
In this study, acrylic polymer–nanogold nanocomposites and their cast films were prepared from an acrylic copolymer and 3-mercaptopropyltrimethoxysilane
(MPS) stabilized gold nanoparticles by a sol–gel reaction. The acrylic copolymer was synthesized from methyl methacrylate
(MMA) and 3-(trimethoxysilyl)propyl methacrylate (MSMA). The Si–OMe groups of MPS on the surface of gold nanoparticles (MPS–Au)
provided the further reaction with the same groups of MSMA, hence the covalent bonds between polymers and MPS–Au nanoparticles
were formed. FE-SEM images show MPS–Au nanoparticles are dispersed well in the prepared nanocomposites, and no large aggregation
is occurred. TGA results indicate that the decomposed temperatures (Td) of low Au-content (0.1 wt.%) nanocomposites are higher than these of the acrylic copolymer and high Au-content (1.0 wt.%)
nanocomposites. The temperature of maximum decomposed rate (Tp) of each prepared nanocomposite is higher than that of the acrylic copolymer. The hardness of the cast film increases with
increasing the Au content. The results show the improved thermal stability and application potentials of the prepared acrylic
polymer–nanogold nanocomposites. 相似文献
The effects of the block copolymer composition and the solvent selectivity on the micellar morphologies of poly(styrene- b-4-vinylpyridine)s (PS- b-P4VPs) and their functionalizations with gold were studied in 10 mg/mL solutions using small-angle X-ray scattering and transmission electron microscopy (TEM). The solvent selectivity for the PS block was controlled by toluene/tetrahydrofuran (THF) mixtures in which toluene and THF are selective for PS and nonselective, respectively. The micellar structure was strongly dependent on phi (wt % toluene in toluene/THF mixture) and the composition of the block copolymers. PS(12K)- b-P4VP(11.8K) (symmetric) showed spherical micelles in the entire range of phi except phi = 0 (THF, nonselective solvent). PS(3.3K)- b-P4VP(18.7K) (asymmetric, longer P4VP) showed multiple morphologies with transitions from spheres to cylinders and finally to vesicles with an increase in phi. PS(19.6K)- b-P4VP(5.1K) (asymmetric, longer PS) showed spherical micelles only at the narrow ranges of 90 wt % 相似文献
A series of poly(styrene)/poly(styrene-co-acrylonitrile) core-shell latexes were synthesized by seeded emulsion polymerization. The dried latex was dissolved in toluene and then cast on the surface of water to form a very thin film (60–90 nm). Phase separation in the thin film was studied by transmission electron microscopy (TEM). Electron micrographs of these thin films yielded fine structure and interesting morphology that was unattainable by ultramicrotoming of the corresponding compression-molded specimens. Glass transition temperatures and percent grafted polystyrene were correlated with the TEM results. As grafting increases, mixing of the two phases improves, with the resulting Tg value being between the two Tg's of poly(styrene) and poly(styrene-co-acrylonitrile). 相似文献
Polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymer chains form aggregates with bimodal distribution in toluene. The introduction of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) chains leads to the formation of mixed micellar cluster due to the hydrogen-bonding complexation between PAA and PEO. By using laser light scattering and transmission electron microscopy, we have investigated the structural evolution of the mixed micellar cluster. As the standing time increases, the cluster split into regular complex micelles composed of PS-b-PAA and PS-b-PEO chains. Our results reveal that the hydrogen-bonding complexation between PAA and PEO in the core and the repulsion between PS chains in the corona as a function of the molar ratio (r) of PEO to PAA manipulate the evolution. 相似文献
CdS nanoparticles of 4.5 nm diameter were synthesized in poly(2‐vinylpyridine) micellar cores which were obtained by solvating a polystyrene‐block‐poly(2‐vinylpyridine) block copolymer in polystyrene‐selective toluene. Then, a C60‐toluene solution was dispersed into the CdS micelle solution with stirring. This led to the well‐defined organization of two different nanoparticles; specifically: a CdS NP decorated by several/dozens of C60 molecules, because C60 molecules were strongly coordinated with pyridine molecules in the micellar cores by charge‐transfer complexation C–P2VPδ+. A harmoniously organized CdS/C60 micellar structure was clearly verified by transmission electron microscopy. Fluorescent quenching of CdS nanoparticles, which was strongly affected by neighboring C60 molecules, was observed.
We report on a simple procedure to tune the hydrophilicity of hybrid gold nanoparticles. The nanoparticles have been prepared in the core of a poly(ethylene glycol)-block-poly(epsilon-caprolactone) (PEG-b-PCL) five-arm star block copolymer. A hydrophilic corona was then added to these hybrid gold nanoparticles by direct chemisorption of trithiocarbonate-containing poly(acrylic acid) chains. These polymers were synthesized by RAFT polymerization with a trithiocarbonate as the chain-transfer agent. The efficiency of the grafting was evidenced by TEM, AFM, and DLS and by the successful transfer of these nanoparticles from organic solvent to water. 相似文献
In this paper we present the effect of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer micelles and their hydrophobicity on the stabilization of gold nanoparticles. Gold nanoparticles were prepared by a method developed by Sakai et al. (Sakai, T.; Alexandridis, P. Langmuir 2004, 20, 8426). An absorption centered at 300-400 nm in time-dependent UV spectra provided evidence that the very first step of the synthesis was to form primary gold clusters. Then the gold clusters grew in size and were stabilized by block copolymer micelles. The stabilization capacities of the micelles were modulated by tuning the block copolymer concentration and composition and by adding salts. With good stabilization, gold particles were spherical and uniform in size with a diameter of 5-10 nm. Otherwise they were aggregates with irregular shapes such as triangular, hexagonal, and rodlike. The presence of a small amount of NaF significantly increased the stabilization capacity of the micelles and consequently modified the quality of the gold particles. Using FTIR and 1H NMR spectroscopy, micellization of the block copolymers and hydrophobicity of the micelles were proven very important for the stabilization. A higher hydrophobicity of the micelle cores was expected to favor the entrapment of primary gold clusters and the stabilization of gold nanoparticles. 相似文献
Polymerizable rare earth complex Eu(AA)3Phen was synthesized by complexion of europium ion, acrylic acid (AA), and 1,10-phenanthroline (Phen). The structure and fluorescence properties of the complex were studied by elemental analysis, 1H-NMR spectroscopy, and fluorescence spectroscopy. Eu-containing copolymer poly(PEGMA-co-MMA-co-METAC-co-Eu(AA)3Phen) (PPMMEu) was then synthesized by free radical copolymerization of Eu(AA)3Phen and other functional monomers including poly(ethylene glycol) methyl ether methacrylate (PEGMA) and [2-(Methacryloyloxy) ethyl] trimethylammonium chloride (METAC). 1H-NMR spectroscopy and fluorescence spectroscopy were used to characterize the copolymer and the interactions between the copolymer and DNA was investigated by TEM, fluorescence spectroscopy, and agarose gel electrophoresis. The desired luminescent cationic copolymer was successfully obtained. The copolymer can form micelles in water solution and can efficiently bind to DNA molecules through electrostatic interaction. The results suggest the potential use of PPMMEu in bioprobes and gene vectors. 相似文献
The existence of micelles of polystyrene-block-poly(ethylene/propene) in solutions of polystyrene in toluene was investigated. Toluene is a good solvent of both copolymer blocks whereas polystyrene and poly(ethylene/propene) are immiscible polymers. The presence of homopolystyrene at high enough concentration can induce the micellization of polystyrene-block-poly(ethylene/propene) in solution of a good solvent such as toluene. The thermodynamics of this new micelle system at a given polystyrene concentration was studied. Light scattering measurements were carried out in order to determine the critical micelle temperature (CMT) of different micellar solutions. Standard Gibbs energy, enthalpy and entropy of micellization were estimated from CMT and concentration data. The numerical values found were less negative than those found for micelle systems consisting in a block copolymer dissolved in a single selective solvent. 相似文献
An amphiphilic heteroarm star polymer containing 12 alternating hydrophobic/hydrophilic arms of polystyrene (PS) and poly(acrylic acid) (PAA) connected to a well-defined rigid aromatic core was studied at the air-water and the air-solid interfaces. At the air-water interface, the molecules spontaneously form pancakelike micellar aggregates which measure up to several microns in diameter and 5 nm in thickness. Upon reduction of the surface area per molecule to 7 nm2, the two-dimensional micelles merged into a dense monolayer. We suggest that confined phase separation of dissimilar polymer arms occurred upon their segregation on the opposite sides of the rigid disklike aromatic core, forcing the rigid cores to adopt a face-on orientation with respect to the interface. Upon transfer onto solid supports the PS chains face the air-film interface making it completely hydrophobic, and the PAA chains were found to collapse and form a thin flattened underlayer. This study points toward new strategies to create large 2D microstructures with facial amphiphilicity and suggests a profound influence of star molecular architecture on the self-assembly of amphiphiles at the air-water interface. 相似文献
The phase transition between unimer and micellar phases of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide)
(PEO–PPO–PEO) triblock copolymer Pluronic P105 in aqueous solution has been investigated as a function of temperature using
Fourier transform infrared spectroscopy. The transition of 8 wt% Pluronic P105 in aqueous solution was found to occur at 25 °C.
As temperature increases, PO blocks appear to be stretched conformers with strong interchain interaction, and the formation
of a hydrophobic core in the micellar phase. The EO chains are found to change to a more disordered structure with low-chain
packing density from the unimer phase to the micellar phase. Both the EO and PO blocks exhibit dehydration during the phase
transition.
Received: 17 September 1998 Accepted in revised form: 10 December 1998 相似文献
The effect of additions of hydrophobic dioctyl sulfide (L) on the kinetics of dissolution of gold nanoparticles in the interaction
with a dispersed aqueous hydrochloric solution of H2O2 in Triton N-42 reverse micelles (decane was the dispersion medium) was studied spectrophotometrically. The process consists
of a two-stage oxidation Au0 → AuCl2− → AuCl4− at the surface of gold particles; the first stage occurs in two ways: a spontaneous reaction and an autocatalytic reaction
involving AuCl4− ions. With small additions of L (cL < cAu), only spontaneous oxidation of Au(0) to Au(I) takes place because Au(I) is completely bound in an inert complex AuLCl. When
unbound L is exhausted, the newly formed AuLCl is accumulated in micellar shells, changes the properties of the medium inside
the micelles, and affects the rate constant of the autocatalytic reaction, which increases with increasing cL. At high concentrations of L, the coagulation of particles occurs instead of their dissolution, because of the deterioration
of the protective properties of micellar shells as a result of the ingression and accumulation of dioctyl sulfide molecules
on account of selective adsorption on gold particles. The rate constants of all stages of dissolution and coagulation are
determined. 相似文献