Optical properties of core/shell typed PMMA/CdS nanoparticles prepared by in situ and ex situ surfactant-free emulsion polymerization

Core/shell poly(methyl methacrylate)/cadmium sulfide (PMMA/CdS) nanoparticles were prepared by surfactant-free emulsion copolymerization with 2-(dimethylamino)ethyl methacrylate (DMAEMA) auxiliary monomer. According to the addition time of Cd²⁺ ions, the synthesis of the hybrid nanoparticles was conducted in in situ and ex situ techniques. The core/shell PMMA/CdS nanoparticles synthesized by the post-addition (ex situ) of Cd²⁺ ions showed a wide size distribution and interference fringes in the photoluminescence (PL) spectrum. However, these results were improved when the PMMA/CdS nanoparticles were synthesized in the presence of Cd²⁺ ions (in situ method). The in situ method made it possible to obtain monodisperse hybrid nanoparticles and fairly narrow band-gap emission.     

Wormlike morphology formation and stabilization of "pluronic p123" micelles by solubilization of pentaerythritol tetraacrylate

A transition from spherical to wormlike micelles of a poly(ethylene oxide) 20- block-poly(propylene oxide) 70- block-poly(ethylene oxide) 20 triblock copolymer Pluronic P123 induced by solubilization of a tetrafuctional monomer, Pentaerythritol tetraacrylate (PETA), in aqueous media has been studied. The wormlike micelles shape was locked by UV cross-linking of PETA within the micelles resulting in stabilized polymeric micelles (SPMs). The stability of SPMs in a good solvent for both polyether blocks like THF, and upon dilution below the critical micelle concentration (CMC) of P123 in water was confirmed by dynamic light scattering (DLS) and scanning force microscopy (SFM). Formation of cadmium sulfide (CdS) nanoparticles within the wormlike SPMs was carried out via the reduction of Cd (2+) with NaS and analyzed by transmission electron microscopy (TEM) and UV-vis absorption measurements. A stable water-dispersible hybrid system consisting of CdS quantum dots embedded into the wormlike SPMs was obtained.     

The Hybrids of Polystyrene-block-Poly(ethylene Oxide) Micelles and Sodium Dodecyl Sulfate in Aqueous Solutions: Interaction with Rh Ions and Rh Nanoparticle Formation

The interaction of amphiphilic block copolymer, polystyrene-block-poly(ethylene oxide) (PS-b-PEO), with anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous media has been studied by sedimentation in ultracentrifuge. Three well-defined populations of hybrid aggregates corresponding to micelles, micellar clusters, and supermicellar aggregates were detected in the PS-b-PEO/SDS aqueous solutions at various rotation rates. Parameters of all the micellar aggregates were characterized depending on the SDS loading. An increase in the SDS loading was found to result in an increase in block copolymer/surfactant micelle size and weight at the SDS concentration of 0.8x10(-3) mol/L and in a slight decrease of both parameters at critical micelle concentration and at higher concentration. This decrease was caused by incorporation of SDS molecules in block copolymer micelles followed by charging the PS core and repulsion between similar charges. Using dichlorotetrapyridine rhodium(III)chloride hexahydrate ([Rh(Py)(4)Cl(2)]Clx6H(2)O), ion exchange of surfactant counterions in the hybrid PS-b-PEO/SDS system for Rh cations was carried out, which allowed saturating the micellar structures with Rh species. Subsequent reduction of the Rh-containing hybrid solutions with NaBH(4) resulted in the formation of Rh nanoparticles with a diameter of 2-3 nm mainly located in the block copolymer micellar aggregates. Copyright 2000 Academic Press.     

Preparation and electrorheological characteristic of CdS/Polystyrene composite particles

Cadmium sulfide/polystyrene (CdS/PS) hybrid particles were synthesized and their physical characteristics including electrorheology were examined. Monodisperse CdS/PS nanocomposite particles with diameters of 2 μm were obtained via dispersion polymerization. To form cadmium sulfide nanoparticles onto the PS surface, 2-(dimethylamino)ethyl methacrylate was used as a functional monomer for coordinating with Cd²⁺ ions. Finally, cadmium sulfide nanoparticles with size < 10 nm were formed with the release of S²⁻ ions from thioacetamide. The morphology of the as-prepared CdS/PS nanocomposite particles clearly showed that the CdS particles are present on the surface of the PS. The optical properties were also studied. In addition, their electrorheological characteristics were confirmed by using optical microscopy with applied electrical field. Recently, dielectric properties of CdS nanoparticles were already reported; however, electrorheological characteristics of CdS/PS nanocomposite particles were investigated for the first time.     

Zinc ion induced polymorphism in macromolecular self-assembly of diblock copolymers

A novel interconnected cylindrical micellar network was prepared from a diblock copolymer, poly(maleic anhydride-alt-styrene)-b-polystyrene, in ethanol under a self-assembly directing agent: Zn²⁺ ions. The solution containing interconnected cylindrical network is bluish and transparent, which is stable for more than 6 months at room conditions without any observable macroscopic phase separation. In aqueous solution, however, hydrolysis of the anhydride yields hydrophilic carboxyl groups, which result in formation of uniform positive spherical micelles from the same diblock polymer. The nanostructures of both the spherical micelles and cylindrical assemblies are characterized with light scattering and transmission electron microscopy (TEM).     

Microplate electrochemical DNA detection for phosphinothricin acetyltransferase gene sequence with cadmium sulfide nanoparticles

An electrochemical DNA detection method for the phosphinothricin acetyltransferase (PAT) gene sequence from the transgenetic plants was established by using a microplate hybridization assay with cadmium sulfide (CdS) nanoparticles as oligonucleotides label. The experiment included the following procedures. Firstly target PAT ssDNA sequences were immobilized on the polystyrene microplate by physical adsorption. Then CdS nanoparticle labeled oligonucleotide probes were added into the microplate and the hybridization reaction with target ssDNA sequences took place in the microplate. After washing the microplate for three times, certain amounts of HNO₃ were added into the microplate to dissolve the CdS nanoparticles anchored on the hybrids and a solution containing Cd²⁺ ion was obtained. At last differential pulse anodic stripping voltammetry (DPASV) was used for the sensitive detection of released Cd²⁺ ion. Based on this principle a sensitive electrochemical method for the PAT gene sequences detection was established. The voltammetric currents of Cd²⁺ were in linear range with the target ssDNA concentration from 5.0 × 10^− 13 to 1.0 × 10^− 10 mol/L and the detection limit was estimated to be 8.9 × 10^− 14 mol/L (3σ). The proposed method showed a good promise for the sensitive detection of specific gene sequences with good selectivity for the discrimination of the mismatched sequences.     

Spontaneous generation of amphiphilic block copolymer micelles with multiple morphologies through interfacial Instabilities

We introduce a method for the formation of block copolymer micelles through interfacial instabilities of emulsion droplets. Amphiphilic polystyrene-block-poly(ethylene oxide) (PS-PEO) copolymers are first dissolved in chloroform; this solution is then emulsified in water and chloroform is extracted by evaporation. As the droplets shrink, the organic solvent/water interface becomes unstable, spontaneously generating a new interface and leading to dispersion of the copolymer as micellar aggregates in the aqueous phase. Depending on the composition of the copolymer, spherical or cylindrical micelles are formed, and the method is shown to be general to polymers with several different hydrophobic blocks: poly(1,4-butadiene), poly(-caprolactone), and poly(methyl methacrylate). Using this method, hydrophobic species dissolved or suspended in the organic phase along with the amphiphilic copolymer can be incorporated into the resulting micelles. For example, addition of PS homopolymer, or a PS-PEO copolymer of different composition and molecular weight, allows the diameter and morphology of wormlike micelles to be tuned, while addition of hydrophobically coated iron oxide nanoparticles enables the preparation of magnetically loaded spherical and wormlike micelles.     

Morphology of hybrid polystyrene-block-poly(ethylene oxide) micelles: analytical ultracentrifugation and SANS studies

Morphology and structure of aqueous block copolymer solutions based on polystyrene-block-poly(ethylene oxide) (PS-b-PEO) of two different compositions, a cationic surfactant, cetyl pyridinium chloride (CPC), and either platinic acid (H2PtCl6.6H2O) or Pt nanoparticles were studied using a combination of analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), and small angle neutron scattering (SANS). These studies combining methods contributing supplemental and analogous structural information allowed us to comprehensively characterize the complex hybrid systems and to discover an isotope effect when H2O was replaced with D2O. In particular, TEM shows formation of both micelles and larger aggregates after incorporation of platinic acid, yet the amount of aggregates depends on the H2PtCl6.6H2O concentration. AUC reveals the presence of micelles and micellar clusters in the PS-b-PEO block copolymers solution and even larger (supermicellar) aggregates in hybrids (with CPC). Conversely, SANS applied to D2O solutions of the similar species indicates that micelles are spherical and no other micellar species are found in block copolymer solutions. To reconcile the SANS and AUC data, we carried out AUC examination of the corresponding D2O block copolymer solutions. These measurements demonstrate a pronounced isotope effect on micelle aggregation and micelle size, i.e., no micelle aggregation in D2O solutions, revealing good agreement of AUC and SANS data.     

Preconcentration of cadmium by MEUF in sodium dodecylsulphate solutions

The ultrafiltration preconcentration of Cd²⁺ using micellar extraction with 8-hydroxyquinoline (8-HQ), solubilized in anionic micelles of sodium dodecylsulphate (SDS)) were studied. The n-butanol was used as a co-surfactant. Ultrafiltration yields (R, %) on cellulose acetate membranes (wet, 20000 MW-CO) under 400 kPa pressure were determined. Distribution ratios (D) of cadmium between bulk liquid phase and micellar pseudophase were estimated. The constants (app.) for the cadmium-sodium exchange on SDS micelles surface at pH values of 4.8 and 5.3 (3.36 and 3.86, respectively) were determined. It was found, that the values of ultrafiltration yields of the cadmium (at constant concentration of 8-HQ) are influenced not only by the pH and by the concentration values, but also by the ratio of the concentrations of the metal and the anionic surfactant.     

Cadmium sulphide quantum dots in morphologically tunable triblock copolymer aggregates

Cadmium sulfide (CdS) quantum dots (QDs) are formed within poly(ethylene oxide)-block-polystyrene-block-poly (acrylic acid) (PEO-b-PS-b-PAA) triblock copolymer aggregates of different architectures. These structures are obtained starting with the same ionically cross-linked primary micelles consisting of a cadmium acrylate core, a PS shell, and a PEO corona. One morphology is a worm-shaped micelle prepared in tetrahydrofuran (THF) in which the CdS QDs are surrounded by the PAA and aligned as a loose necklace in the PS matrix. The PEO serves as a corona around the PS rod. Another structure is a multicore spherical (ca. 50 nm) water soluble PS micelle, surrounded by PEO chains. The CdS particles within these two latter structures are formed by the reaction of cadmium ions present in the acrylate cores with hydrogen sulfide. In a third structure, the CdS QDs are located on the surface of PS micelles. A fourth spherical single-core micelle structure is postulated to exist in dilute THF solutions. The dimensions in all the aggregates can be controlled by the block length.     

水溶液中Pluronic嵌段共聚物聚集行为的介观模拟

通过介观动力学方法(MesoDyn)研究了低浓度下的三嵌段共聚物PEO27PPO61PEO27 (P104)水溶液的聚集行为, 讨论了聚合物浓度、模拟时间对P104水溶液相行为的影响. 在聚合物浓度较低(φ<35%)的情况下, 可以形成三种不同的胶束聚集体：球形胶束(spherical micelle)、胶束簇(micellar cluster)和盘状胶束(disk-like micelle). (1) 球形胶束(5%-10%, φ), 模拟的胶束结构表明疏水的PPO嵌段形成球形内核(micellar core), 而亲水的PEO嵌段形成核壳(micellar corona), 并有水分子存在内核和核壳之中；(2) 胶束簇(11%-15%, φ), 由于球形胶束之间的缔合, 形成直径明显高于球形胶束的聚集体, 其半径比球形胶束大1 nm左右；(3) 盘状胶束(16%-25%, φ), 胶束簇核壳PEO嵌段之间的相互缠绕, 形成了成串的类似盘状的胶束. 模拟中有序参数随浓度的变化证明了这种结构划分的合理性.     

The Synthesis of Superparamagnetic Pt/Ni Nanohybrids in Direct Micelles of Cationic Surfactants

Pt/Ni nanohybrids were synthesized by the reduction of the corresponding salts with hydrazine hydrate in aqueous micellar 0.005, 0.02, and 0.15 M solutions of cetyltrimethylammonium bromide. The size, shape, particle size distributions, and superparamagnetic properties of the nanohybrids were studied. The spherical and rod-like shapes of the nanoparticles obtained were discussed in terms of the dualistic model of surfactant micelle formation, according to which Ni²⁺ and hydrazine hydrate were solubilized inside hydrated micelles in water, in which molecules were linked by weak H-bonds with each other. Hydrated spherical and rod-like micelles played the role of templates in the synthesis of spherical and rod-like nanohybrids.     

Electrochemical synthesis of free-standing CdS nanoparticles in ethylene glycol

A novel one-step electrochemical method for the preparation of capping-free cadmium sulfide nanoparticles is described. With gold as the working electrode, capping-free CdS nanoparticles are synthesized very conveniently at 70°C in the ethylene glycol (EG) solution of elementary sulfur, cadmium salt, and supporting electrolyte at −0.1 V. By carefully selecting the reductive potential, elementary sulfur is reduced while the reduction of Cd²⁺ is blocked by the formation of a sulfur monolayer on the gold electrode surface. The produced S²⁻ reacts with cadmium cations in the solution to produce CdS. In this method, magnetic stirring can effectively prevent the deposition of CdS on the electrode surface. XRD analysis indicates that the product is pure cubic-phase CdS. The size and morphology of the particles are studied by TEM. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 9, pp. 1060–1064. The text was submitted by the authors in English.     

Concentration controlled multilevel self‐assembly of 3‐armed poly(ethylene glycol)‐b‐poly(ε‐caprolactone) block copolymers investigated by AFM

Concentration dependent morphology of 3‐armed poly(ethylene glycol)‐b‐poly(ε‐caprolactone) copolymer aggregates in aqueous system was investigated by atomic force microscopy (AFM). The AFM results show that, at a low concentration, 4 × 10^?5 g/mL, spherical micelles occur, and unmicellized molecules are not distributed homogeneously in the copolymer aqueous solution. Unequal outspread clusters composed of wormlike aggregates are formed at a moderate copolymer concentration, 4 × 10^?4 g/mL, those wormlike aggregates are orderly packed in the clusters. At a high concentration of 0.05 g/mL, the copolymer aqueous system is indeed a gel at room temperature, outspread clusters of wormlike aggregates join together to forma network structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1412–1418, 2008     

Synthesis of a hybrid material from CdS nanoparticles and carbon nanotubes

A method for synthesis of a hybrid material from CdS nanoparticles and carbon nanotubes (CNT) by the precipitation of CdS nanoparticles on the CNT surface from an aqueous solution containing the Cd^II salt, thiourea, and ammonia was developed. The dependences of the size of particles formed on the CNT on the temperature of the solution and the duration of precipitation were observed. The degree of imperfection of the CNT surface exerts a substantial effect on the density of the precipitated CdS particles.     

Photochemical behavior of nanoparticles of cadmium sulfide in the presence of a reducing agent

Irradiation of colloidal solutions of cadmium sulfide nanoparticles stabilized with polyvinyl alcohol or gelatine in the presence of strong reducing agents (sulfite, hydrazine) causes reduction of part of the Cd²⁺ ions in the CdS lattice to Cd⁰ with a quantum efficiency of about 10^–4.L. V. Pisarzhevskii Institute of Physical Chemistry, Ukraine National Academy of Science, Ukraine, 252039 Kiev, Nauki Prosp., 31. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 2, pp. 102–106, March–April, 1996. Original article submitted July 12, 1995.     

Photochemical synthesis of cadmium sulfide nanoparticles

The formation of cadmium sulfide nanoparticles upon UV irradiation of aqueous solutions of cadmium thiosulfates was established on the basis of spectroscopic and macroscopic data. The yield and size of the cadmium sulfide nanoparticles depend on the ratio of cadmium to thiosulfate ions in solution, the concentration of the solution, and the irradiation duration. The cadmium sulfide nanoparticles with a diameter of 4 nm were obtained by the photolysis of solutions with a concentration of 10⁻³ mol L⁻¹ at the ratio S₂O₃ ²⁻: Cd²⁺ = 2: 1.     

Photocatalysis of the Reduction of Cd2+ Ions by CdS Nanoparticles in Isopropyl Alcohol

The kinetic relationships governing the photocatalytic reduction of Cd²⁺ cations with participation of CdS nanoparticles in isopropyl alcohol solutions were investigated. Quantum-dimensional effects that manifest themselves in an increase in the rate of the process with decrease in the average size of the photocatalyst nanoparticles were observed and interpreted. In the light of published data a scheme that agrees satisfactorily with the experimental results is proposed for the mechanism of the photocatalytic reduction of cadmium ions.     

Synthesis of Y-shaped poly(solketal acrylate)-containing block copolymers and study on the thermoresponsive behavior for micellar aggregates

One novel type of Y-shaped amphiphilic copolymers with two hydrophobic poly(solketal acrylate) (PSA) branches and one hydrophilic monomethoxy poly(ethylene glycol) (MPEG) block was synthesized by atom transfer radical polymerization (ATRP). These Y-shaped polymers can disperse in aqueous media to self-assemble into micellar aggregates with a spherical core-shell structure. The aqueous copolymer solutions exhibited transmittancy transition in the temperature range of 30-60 °C via optical transmittance measurements. An interesting thermo-dependent size of the micellar aggregates was observed by dynamic light scattering techniques and transmission electron microscopy, which showed that the micelle diameters were decreased with temperature increasing. The nile red release from the micelles at 25 °C and 37 °C under various pHs showed that temperature has great influence on release behavior. With good biocompatibility, the micellar aggregates formed from MPEG-block-(PSA)(2) may serve as one promising thermosensitive nanovehicle for targeted drug delivery.     

Drug-loaded and superparamagnetic iron oxide nanoparticle surface-embedded amphiphilic block copolymer micelles for integrated chemotherapeutic drug delivery and MR imaging

We report on the fabrication of organic/inorganic hybrid micelles of amphiphilic block copolymers physically encapsulated with hydrophobic drugs within micellar cores and stably embedded with superparamagnetic iron oxide (SPIO) nanoparticles within hydrophilic coronas, which possess integrated functions of chemotherapeutic drug delivery and magnetic resonance (MR) imaging contrast enhancement. Poly(ε-caprolactone)-b-poly(glycerol monomethacrylate), PCL-b-PGMA, and PCL-b-P(OEGMA-co-FA) amphiphilic block copolymers were synthesized at first by combining ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), and post- modification techniques, where OEGMA and FA are oligo(ethylene glycol) monomethyl ether methacrylate and folic acid-bearing moieties, respectively. A model hydrophobic anticancer drug, paclitaxel (PTX), and 4 nm SPIO nanoparticles were then loaded into micellar cores and hydrophilic coronas, respectively, of mixed micelles fabricated from PCL-b-PGMA and PCL-b-P(OEGMA-co-FA) diblock copolymers by taking advantage of the hydrophobicity of micellar cores and strong affinity between 1,2-diol moieties in PGMA and Fe atoms at the surface of SPIO nanoparticles. The controlled and sustained release of PTX from hybrid micelles was achieved, exhibiting a cumulative release of ~61% encapsulated drugs (loading content, 8.5 w/w%) over ~130 h. Compared to that of surfactant-stabilized single SPIO nanoparticles (r(2) = 28.3 s(-1) mM(-1) Fe), the clustering of SPIO nanoparticles within micellar coronas led to considerably enhanced T(2) relaxivity (r(2) = 121.1 s(-1) mM(-1) Fe), suggesting that hybrid micelles can serve as a T(2)-weighted MR imaging contrast enhancer with improved performance. Moreover, preliminary experiments of in vivo MR imaging were also conducted. These results indicate that amphiphilic block copolymer micelles surface embedded with SPIO nanoparticles at the hydrophilic corona can act as a new generation of nanoplatform integrating targeted drug delivery, controlled release, and disease diagnostic functions.