Enhanced Initial Permeability and Dielectric Constant in a Double- Percolating Ni0.3Zn0.7Fe1.95O4–Ni– Polymer Composite

A novel, three-phase, double-percolating composite with NiZn-ferrite particles and nickel particles embedded in a poly(vinylidene fluoride) matrix is prepared by a simple hot-pressing method. Large ferrite particles in the composite not only act as a magnetic phase, thus endowing the composite with a high initial permeability, but also present (in a high volume fraction) a discrete (non-percolating) phase, confining polymer and metallic particles into a continuous double-percolating structure of low volume fraction. In particular, a large enhancement in both the initial permeability and the dielectric constant of the three-phase composites is observed, which is due mainly to the addition of a small number of nickel particles that act as both magnetic and percolative metallic phases. The dielectric and magnetic behavior observed in the three-phase composites can be explained by effective-medium and percolation theories.     

Bonding Polyether onto ZnO Nanoparticles: An Effective Method for Preparing Polymer Nanocomposites with Tunable Luminescence and Stable Conductivity

A series of new polymer nanocomposites, ZnO(PEGME), in which ZnO nanoparticles and poly(ethylene glycol methyl ether) (PEGME) molecules are connected by covalent bonds, have been synthesized by a sol–gel route and purified by a non‐solvent method. Various characterization techniques have been employed to determine the compositions and structures of the ZnO(PEGME)s, and their luminescent properties and ionic conductivities (after dissolving lithium salts to form solid polymer electrolytes) have been measured and compared with their counterparts—polymer nanocomposites prepared by mixing PEGME and ZnO nanoparticles physically. These comparisons prove that ZnO(PEGME) hybrids derived from chemical reactions have much better properties and stabilities than their counterparts. As a result, tunable photoluminescence of ZnO nanoparticles and stable conductivity of solid polymer electrolytes have been realized successfully.     

Preparation of Uniform,Water‐Soluble,and Multifunctional Nanocomposites with Tunable Sizes

Novel, thiol‐functionalized, and superparamagnetic, silica composite nanospheres (SH‐SSCNs) with diameters smaller than 100 nm are successfully fabricated through the self‐assembly of Fe₃O₄ nanoparticles and polystyrene₁₀₀‐block‐poly(acrylic acid)₁₆ and a subsequent sol‐gel process. The size and magnetic properties of the SH‐SSCNs can be easily tuned by simply varying the initial concentrations of the magnetite nanoparticles in the oil phase. By incorporating fluorescent dye molecules into the silica network, the composite nanospheres can be further fluorescent‐functionalized. The toxicity of the SH‐SSCNs is evaluated by choosing three typical cell lines (HUVEC, RAW264.7, and A549) as model cells, and no toxic effects are observed. It is also demonstrated that SH‐SSCNs can be used as a new class of magnetic resonance imaging (MRI) probes, having a remarkably high spin–spin (T₂) relaxivity (r₂* = 176.1 mM ^?1 S^?1). The combination of the sub‐100‐nm particle size, monodispersity in aqueous solution, superparamagnetism, and fluorescent properties of the SH‐SSCNs, as well as the non‐cytotoxicity in vitro, provides a novel and potential candidate for an earlier MRI diagnostic method of cancer.     

Templated Synthesis of Mesoporous Superparamagnetic Polymers

We present a novel synthetic strategy for fabricating superparamagnetic nanoparticles randomly dispersed in a mesoporous polymeric matrix. This method is based on the use of mesoporous silica materials as templates. The procedure used to obtain these mesoporous magnetic polymers consisted in: a) generating iron oxide ferrite magnetic nanoparticles (FMNP) of size ～ 7–8 nm within the pores of the silica, b) loading the porosity of the silica/FMNP composite with a polymer (Polydivinylbenzene), c) selectively removing the silica framework from the resulting silica/FMNP/polymer composite. Such magnetic porous polymeric materials exhibit large surface areas (up to 630 m² g^–1), high pore volumes (up to 0.73 cm³ g^–1) and a porosity made up of mesopores. In this way, it is possible to obtain superparamagnetic mesoporous hybrid nanocomposites that are easily manipulated by an external magnetic field and display different magnetic behaviours depending on the textural properties of the template employed.     

Superparamagnetic Fe3O4 nanoparticles,synthesis and surface modification

Magnetite nanoparticles have been synthesized through a co-precipitation of iron (Fe³⁺ and Fe²⁺), and were characterized using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and superconducting quantum interference device magnetometer (SQUID). The particles have been modified by several types of stabilizers such as polyethylene glycol (PEG 4000), sodium citrate, and ethylenediaminetetraacetic acid (Na₂H₂Y·2H₂O). These nanoparticles are nearly spherical with an average diameter 12 nm. The capping agents have been successfully anchored to the surface, as revealed by the absorption bands in infrared, and the adsorbed quantities are evaluated by TGA analysis. Magnetization of these magnetic nanoparticles was almost zero at room temperature in the absence of an applied magnetic field, indicating their superparamagnetic behavior. Such NPs magnetite could serve as a magnetic core to an eventual core-shell structure when coated with various materials.     

Solvent‐Mediated Plasmon Tuning in a Gold‐Nanoparticle–Poly(Ionic Liquid) Composite

The design, synthesis, and characterization of a hierarchically ordered composite whose structure and optical properties can be reversibly switched by adjustment of solvent conditions are described. Solvent‐induced swelling and de‐swelling is shown to provide control over the internal packing arrangement and hence, optical properties of in situ synthesized metal nanoparticles. Specifically, a gold‐nanoparticle‐containing ionic‐liquid‐derived polymer is synthesized in a single step by UV irradiation of a metal‐ion‐precursor‐doped, self‐assembled ionic liquid gel, 1‐decyl‐3‐vinylimidazolium chloride. Small‐angle X‐ray scattering (SAXS) studies indicate that in the de‐swollen state, the freestanding polymer adopts a perforated lamellar structure. Optical spectroscopy of the dried composite reveals plasmon resonances positioned in the near‐IR. Strong particle–particle interactions arise from matrix‐promoted formation of aggregated 1D clusters or chains of gold nanoparticles. Upon swelling in alcohol, the composite undergoes a structural conversion to a disordered structure, which is accompanied by a color change from purple to pale pink and a shift in the surface plasmon resonance to 527 nm, consistent with isolated, non‐interacting particles. These results demonstrate the far‐field tuning of the plasmonic spectrum of gold nanoparticles by solvent‐mediated changes in its encapsulating matrix, offering a straightforward, low‐cost strategy for the fabrication of nanophotonic materials.     

Density Functional Theoretical Studies on Polyaniline/HNb3O8 Layered Nanocomposites

A theoretical study of polyaniline (PANI)/HNb₃O₈ layered nanocomposites has been performed based on ab initio calculations and experimental data. The Brønsted acidity of the layered niobic acid, and the interaction between the interlayered polyaniline molecules and the inorganic slabs in PANI/HNb₃O₈ nanocomposites, have been investigated. For the intercalation process of organic species into layered niobic acid, it is important to clarify whether the source of Brønsted acidity arises from the interlayered or hydrated protons. Thus, three inorganic layer structures, KNb₃O₈, HNb₃O₈, and HNb₃O₈·H₂O, are evaluated, and the results show that there is only a minor contribution to the total acidity if the hydrogen is tightly bound by the inorganic slab. After the interlayered aniline monomers are polymerized within the acidic inorganic layers, two orientated structures of PANI molecules are calculated in which the interlayered C6 rings are perpendicular and parallel to the inorganic slabs, respectively, based on the experimental results. In comparison, PANI molecules in the latter orientation are placed in a relatively narrower interlayer space, and the hydrated proton cannot simultaneously form two effective hydrogen bonds with the O atom of Nb₃O₈^– and an N atom of the PANI molecule because of the orientation requirement of the hydrogen bond. The interlayered hydrated proton cannot effectively transfer electrons between the PANI molecule and the inorganic slab. A similar conclusion is also reached from a detailed analysis of band structure and density of states (DOS). The calculated results are in good agreement with the experimental fact that a relatively higher conductivity is apparent in the former rather than in the latter.     

Anisotropy and Dynamic Ranges in Effective Properties of Sheared Nematic Polymer Nanocomposites

Nematic, or liquid‐crystalline, polymer nanocomposites (NPNCs) are composed of large aspect ratio, rod‐like or platelet, rigid macromolecules in a matrix or solvent, which itself may be aqueous or polymeric. NPNCs are engineered for high‐performance material applications, ranging across mechanical, electrical, piezoelectric, thermal, and barrier properties. The rods or platelets possess enormous property contrasts relative to the solvent, yet the composite properties are strongly affected by the orientational distribution of the nanophase. Nematic polymer film processing flows are shear‐dominated, for which orientational distributions are well known to be highly sensitive to shear rate and volume fraction of the nematogens, with unsteady response being the most expected outcome at typical low shear rates and volume fractions. The focus of this article is a determination of the ranges of anisotropy and dynamic fluctuations in effective properties arising from orientational probability distribution functions generated by steady shear of NPNC monodomains. We combine numerical databases for sheared monodomain distributions^[1,2] of thin rod or platelet dispersions together with homogenization theory for low‐volume‐fraction spheroidal inclusions^[3] to calculate effective conductivity tensors of steady and oscillatory sheared mesophases. We then extract maximum scalar conductivity enhancement and anisotropy for each type of sheared monodomain (flow‐aligned, tumbling, kayaking, and chaotic).     

碳纳米管/聚苯胺/四氧化三铁复合材料的制备及磁性能研究

通过Fe2+,Fe3+共沉积以及原位聚合的方法制备出了一种新型的碳纳米管/聚苯胺/四氧化三铁纳米复合材料。TEM及XRD结果表明四氧化三铁磁性纳米颗粒均匀地分散在碳纳米管/聚苯胺的表面,且结晶性良好;此外,也研探究了不同硫酸亚铁铵的加入量对复合材料形态及磁性能的影响。当硫酸亚铁铵反应剂的加入量是2.4 g时,复合材料显示出最大饱和磁化强度可达44 A·m2·kg–1的超顺磁行为。这些结果表明所制备的碳纳米管/聚苯胺/四氧化三铁纳米复合材料在电子系统、新型的药物传输系统方面具有潜在应用价值。     

On The Origins of Silicate Dispersion in Polysiloxane/Layered‐Silicate Nanocomposites

We report the first multi‐system study of a layered‐silicate dispersion in polysiloxane/layered‐silicate nanocomposites. A variety of layered silicates (montmorillonite, synthetic fluoromica, laponite, and fluorohectorite) and cationic modifiers (single‐, twin‐, and triple‐tailed surfactants with tails of varying lengths and both primary and quaternary head‐groups) are combined to form organically modified layered silicates, which are then screened for compatibility with low‐molecular‐weight silanol‐terminated poly(dimethylsiloxane) (PDMS). Promising combinations are then selected and studied in greater depth with respect to both molecular weight and polysiloxane end‐group and substituent chemistry. We find that the PDMS backbone is generally incompatible with the layered silicates, regardless of modification type, and that dispersion in PDMS systems results from the presence of polar end‐groups, a result unprecedented in the field of polymer nanocomposites. We go on to quantify the substituent effect, not only with respect to end‐group chemistry, but taking into account changes in the polysiloxane backbone itself. For instance, in the absence of polar end‐groups we observe dispersion in the case of poly(methylphenylsiloxane) but not poly(3,3,3‐trifluoropropylmethylsiloxane). Finally, we apply a new epoxy/amine PDMS curing chemistry to PDMS‐nanocomposite production and show higher levels of layered‐silicate dispersion than observed in comparable silanol‐terminated PDMS‐based systems. Our findings serve as an indication of what is necessary to achieve a layered‐silicate dispersion in polysiloxane/layered‐silicate nanocomposites, and may indicate a more general approach for improving dispersion in systems where the polymer backbone is otherwise incompatible with the layered silicate.     

Preparation and electrical properties in epoxy resin/In2O3:Sn nanocomposites materials for optoelectronics

To characterize the electrical properties of epoxy resin filled with different contents of Indium Tin Oxides (ITO) nanoparticles (In₂O₃ doped with 15% Sn). We study and discuss the Polarization and Depolarization Current tests (PDC). Using the depolarization current obtained at room temperature under several applied electric field, we perform the time to frequency domain transformation. Our results indicate that the transient currents behavior of the epoxy resin is affected by the presence of ITO nanoparticles. The obtained data were first analyzed in terms of the dielectric permittivity and then transformed to electric modulus to highlight conduction process. In the low frequency region, a weak MWS effect is recorded. This relaxation is ascribed to polarization phenomena taking place at the interfaces between the nano-ITO and the epoxy matrix.     

Vapor Sorption and Electrical Response of Au‐Nanoparticle– Dendrimer Composites

Films comprising Au nanoparticles and polyphenylene dendrimers (first and second generation) are deposited onto transducer substrates via layer‐by‐layer self‐assembly and characterized by atomic force microscopy and X‐ray photoelectron spectroscopy. Their sorption behavior is studied by measuring the uptake of solvents from the vapor phase with quartz crystal microbalances (QCMs). The resistance of the films is simultaneously monitored. Both sensor types, QCMs and chemiresistors, give qualitatively very similar response isotherms that are consistent with a combination of Henry‐ and Langmuir‐type sorption processes. The sorption‐induced increase in relative differential resistance scales linearly with the amount of analyte accumulated in the films. This result is in general agreement with an activated tunneling process for charge transport, if little swelling and only small changes in the permittivity of the film occur during analyte sorption (a first‐order approximation). The relative sensitivity of the films to different solvents decreases in the order toluene ≈ tetrachloroethylene > 1‐propanol ? water. Films containing the larger second‐generation dendrimers show higher sensitivity than films containing first‐generation dendrimers.     

Cover Picture: Vapor Sorption and Electrical Response of Au‐Nanoparticle– Dendrimer Composites (Adv. Funct. Mater. 6/2007)

The cover shows chemiresistors and mass‐sensitive vapor sensors coated with Au‐nanoparticle/dendrimer composites. The Au nanoparticles provide the film with electrical conductivity and the dendrimers control the chemical selectivity, as reported by Nadjedja Krasteva and co‐workers on p. 881. Analyte sorption follows a combined Henry–Langmuir model, and measurements reveal that sorption‐induced increase in film resistance scales linearly with the concentration of analyte sorbed in the film. The background shows a silicon wafer with lithographically defined microelectrode structures for chemiresistor fabrication. Films comprising Au nanoparticles and polyphenylene dendrimers (first and second generation) are deposited onto transducer substrates via layer‐by‐layer self‐assembly and characterized by atomic force microscopy and X‐ray photoelectron spectroscopy. Their sorption behavior is studied by measuring the uptake of solvents from the vapor phase with quartz crystal microbalances (QCMs). The resistance of the films is simultaneously monitored. Both sensor types, QCMs and chemiresistors, give qualitatively very similar response isotherms that are consistent with a combination of Henry‐ and Langmuir‐type sorption processes. The sorption‐induced increase in relative differential resistance scales linearly with the amount of analyte accumulated in the films. This result is in general agreement with an activated tunneling process for charge transport, if little swelling and only small changes in the permittivity of the film occur during analyte sorption (a first‐order approximation). The relative sensitivity of the films to different solvents decreases in the order toluene ≈ tetrachloroethylene > 1‐propanol ? water. Films containing the larger second‐generation dendrimers show higher sensitivity than films containing first‐generation dendrimers.     

Exploring Exchange Bias Coupling in Fe3−δO4@CoO Core–Shell Nanoparticle 2D Assemblies

Core‐shell ferro(i)magnetic@antiferromagnetic (F(i)M@AFM) nanoparticles exhibiting exchange bias coupling are very promising to push back the superparamagnetic limits. However, their intrinsic magnetic properties can be strongly affected by interparticle interactions. This work reports on the collective properties of Fe_3–dO₄@CoO core‐shell nanoparticles as function of the structure of their assembly. The structure of nanoparticle assembly is controlled by a copper (I) catalyzed alkyne–azide cycloaddition (CuAAC) “click” reaction between complementary functional groups located at the surface of both substrates and nanoparticles. 2D arrays of nanoparticles with tunable sizes ranging from clusters of few nanoparticles to a dense and homogenous monolayer were prepared. The spatial arrangement of nanoparticles strongly influences the exchange bias coupling which is significantly enhanced for large 2D nanoparticle assemblies and, even more in 3D assemblies such as powder, which favour weak and random dipolar interactions.     

Fe3O4磁性纳米颗粒的制备及性能表征

以Fe_2(SO_4)_3·6H_2O,FeSO_4·4H_2O和NH_3·H_2O为原料,采用化学共沉淀法制备Fe_3O_4磁性纳米颗粒,并通过XRD、FTIR、TEM和VSM手段,研究了反应温度对其结构、形貌和磁性能的影响。结果表明:制备的Fe_3O_4磁性纳米颗粒表面包裹了一层有机物质,呈球形,大小均匀,平均粒径在13nm左右,分散性好,饱和磁化强度Ms最大值可达53.38A·m~2·kg~(–1),且反应温度70℃时其磁性能最佳。     

Magnetic and Temperature‐Sensitive Release Gels from Supramolecular Polymers

Supramolecular gels consisting of trivalent polyisobutylene and bivalent poly(ethylene oxide) are generated. Strong hydrogen bonding interactions, affixed to the end‐group moieties of the respective polymers (binding constant K_assn = 10⁵ M ^–1), serve as molecular glue, leading to the formation of weak gels. Two different gels were prepared: one, with a short telechelic poly(ethylene glycol) (PEG) segment (gel A), and one with a longer PEG segment (number‐average molecular weight M_n = 2000 g mol^–1) (gel B). Both gels show a significant increase in viscosity upon mixing of the two polymeric components, with a lag time of several minutes, indicative of nucleation mechanisms as the formation principle. However, only gel A displays classical gel‐like behavior, with a loss modulus G′ larger than the storage modulus G″ after formation. Both gels display microphase‐separated behavior with a spacing between 4–5 nm as probed via small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) measurements. The incorporation of magnetic nanoparticles (Fe₂O₃; radius r = 3.5 nm) is successfully achieved, generating new magnetic gels with strongly thermoresponsive properties, displaying a strong temperature‐dependent release profile of included dye molecules. Magnetic measurements indicate a superparamagnetic behavior of the incorporated nanoparticles, prospecting the application as magneto‐sensitive delivery gels for pharmaceutical purposes.     

Superparamagnetic Hyperbranched Polyglycerol‐Grafted Fe3O4 Nanoparticles as a Novel Magnetic Resonance Imaging Contrast Agent: An In Vitro Assessment

Hyperbranched polyglycerol‐grafted, magnetic Fe₃O₄ nanoparticles (HPG‐grafted MNPs) are successfully synthesized by surface‐initiated ring‐opening multibranching polymerization of glycidol. Reactive hydroxyl groups are immobilized on the surface of 6–9 nm Fe₃O₄ nanoparticles via effective ligand exchange of oleic acid with 6‐hydroxy caproic acid. The surface hydroxyl groups are treated with aluminum isopropoxide to form the nanosized macroinitiators. The successful grafting of HPG onto the nanoparticles is confirmed by infrared and X‐ray photoelectron spectroscopy. The HPG‐grafted MNPs have a uniform hydrodynamic diameter of (24.0 ± 3.0) nm, and are very stable in aqueous solution, as well as in cell culture medium, for months. These nanoparticles have great potential for application as a new magnetic resonance imaging contrast agent, as evidenced by their lack of cytotoxicity towards mammalian cells, low uptake by macrophages, excellent stability in aqueous medium and magnetic fields, and favorable magnetic properties. Furthermore, the possibility of functionalizing the hydroxyl end‐groups of the HPG with cell‐specific targeting ligands will expand the range of applications of these MNPs.     

Efficient Synthesis of Carbon Nanotube–Nanoparticle Hybrids

A simple and versatile approach has been developed to synthesize different carbon nanotube (CNT)–nanoparticle hybrid materials. The strategy is based on the nondestructive (noncovalent) functionalization of pristine CNTs and the subsequent in situ synthesis of a variety of different nanoparticles, including metal, semiconductor, and insulator particles, on the modified CNTs. This strategy has been demonstrated here with Pt, CdS, and silica nanoparticles. It is believe that this technique will provide a simple and convenient route to efficiently assemble a wide variety of nanoscale particles/clusters on the surfaces of CNTs, and will enable the construction of nanoscale heterostructures with novel functionalities in nanotechnology.     

Bismuth–Ceramic Nanocomposites with Unusual Thermal Stability via High‐Energy Ball Milling

Electrically conducting nanocomposites of bismuth metal and insulating ceramic phases of SiO₂ and MgO were generated via high‐energy ball milling for 24 h using zirconia milling media. The resulting nanocomposites contain Bi nanoparticles with sizes down to 5 nm in diameter. The morphology is a strong function of the oxide phase: specifically, the Bi appears to wet MgO while it forms spherical nanoparticles on the SiO₂. X‐ray diffraction measurements indicate a nominal bismuth grain size of 50 nm, and peak fitting to a simple bidisperse model yields a mixture of approximately 57 % bulk bismuth and 43 % 27 nm diameter crystallites. Nanoparticles as small as 5 nm are observed in transmission electron microscopy (TEM), but may not constitute a significant volume fraction of the sample. Differential scanning calorimetry reveals dramatic broadening in the temperatures over which melting and freezing occur and a surprising persistence of nanostructure after thermal cycling above the melting point of the Bi phase.