Superparamagnetic Polymer Nanocomposites with Uniform Fe3O4 Nanoparticle Dispersions

Magnetic nanoparticles embedded in polymer matrices are good examples of functional nanostructures with excellent potential for applications such as electromagnetic interference shielding, magneto‐optical storage, biomedical sensing, flexible electronics, etc. Control over the dispersion of the nanoparticle phase embedded in a polymer matrix is critical and often challenging. To achieve excellent dispersion, competition between polymer–polymer and polymer–particle interactions have to be balanced to avoid clustering of particles in polymer nanocomposites. We report the first deposition of magnetic nanocomposite poly(methyl methacrylate)/polypyrrole bilayers from solution using spin‐coating. Fe₃O₄ nanoparticles have been synthesized using a chemical co‐precipitation route. Using a combination of dissolving the polymer and mixing fatty acid surfactant coated Fe₃O₄ nanoparticles, we have demonstrated the formation of nanocomposites with uniform nanoparticle dispersion. Cross‐sectional scanning electron microscopy, transmission electron microscopy, and magnetic measurements confirm the excellent dispersion and superparamagnetic response. Low‐frequency impedance measurements on these bilayers are also presented and analyzed.     

Magnetic Multi‐Functional Nano Composites for Environmental Applications

A novel concept is proposed to synthesize a new class of composites featuring magnetic, molecular sieve and metallic nanoparticle properties. These multi‐functional materials have potential applications as recyclable catalysts, disinfectants and sorbents. The magnetic property enables effective separation of the spent composites from complex multiphase systems for regeneration and recycle, safe disposal of the waste and/or recovery of loaded valuable species. The zeolite molecular sieve provides a matrix which supports a remarkably new, simple, efficient and economical method to make stable, supported silver nanoparticles by silver ion exchange and controlled thermal reduction. The silver nanoparticles generated in this way have excellent properties such as high reactivity and good thermal stability without aggregation, which act as nano reactors for desired functionality in a wide range of applications. Magnetic component (Fe₃O₄), molecular sieve matrix (zeolite) and silver nanoparticles generated by ion exchange followed by controlled reduction, together form this unique novel composite with designed functions. It represents a practically operational, economical, sustainable and environmentally friendly new advanced functional material. This paper focuses on the novel synthesis and characterization of the composite, with an example of applications as sorbents for the removal of vapor‐phase mercury from the flue gas of coal‐fired power plants.     

TiO2-poly(4-vinylphenol) nanocomposite dielectrics for organic thin film transistors

We report on the fabrication of organic thin film transistors (OTFTs), which operate at low voltages, by incorporating a nanocomposite gate insulator material consisting of titania (TiO₂) nanoparticles used as fillers and poly(4-vinyl phenol) (PVP) used as matrix. The surface of the nanoparticles was modified by the ligands, 4-hydroxybenzoic acid, to enhance their compatibility with the polymer. The structure of the ligand is similar to that of the repeat units in the polymer. Once the nanoparticles were homogeneously dispersed in the polymer matrix, they were immobilized by cross-linking PVP with poly(melamine-co-formaldehyde) methylated/butylated (cross-linker). Consequently, no significant aggregation of the nanoparticles, even at a concentration of 31 wt%, was found in the nanocomposites, as observed by transmission electron microscopy (TEM). As a result, the nanocomposite exhibited a low leakage current density (∼10⁻⁸ A/cm⁻²). With an increase in the concentration of TiO₂ nanoparticles added, the dielectric constant of the nanocomposites also increased proportionately as compared to that of pristine PVP. The performance of the OTFTs in terms of the charge carrier mobility, on/off ratio, threshold voltages, and hysteresis was evaluated. In addition, the relationship between the concentration of TiO₂ nanoparticles and the device performance is discussed in detail.     

Novel Method of Preparation of Gold‐Nanoparticle‐Doped TiO2 and SiO2 Plasmonic Thin Films: Optical Characterization and Comparison with Maxwell–Garnett Modeling

SiO₂ and TiO₂ thin films with gold nanoparticles (NPs) are of particular interest as photovoltaic materials. A novel method for the preparation of spin‐coated SiO₂–Au and TiO₂–Au nanocomposites is presented. This fast and inexpensive method, which includes three separate stages, is based on the in situ synthesis of both the metal‐oxide matrix and the Au NPs during a baking process at relatively low temperature. It allows the formation of nanocomposite thin films with a higher concentration of Au NPs than other methods. High‐resolution transmission electron microscopy studies revealed a homogeneous distribution of NPs over the film volume along with their narrow size distribution. The optical manifestation of localized surface plasmon resonance was studied in more detail for TiO₂‐based Au‐doped nanocomposite films deposited on glass (in absorption and transmittance) and silicon (in specular reflectance). Maxwell–Garnett effective‐medium theory applied to such metal‐doped nanocomposite films describes the peculiarities of the experimental spectra, including modification of the antireflective properties of bare TiO₂ films deposited on silicon by varying the concentration of metal NPs. The antireflective capabilities of the film are increased after a wet etching process.     

Observation of Magnetic‐Switching and Multiferroic‐Like Behavior of Co Nanoparticles in a C60 Matrix

A novel magnetoelectric effect is found to appear in a C₆₀‐Co nanocomposite. Although Co is well‐known as a ferromagnet, its nanoparticles embedded in a C₆₀ matrix can exhibit multiferroic‐like behavior, i.e., an electric field controls magnetic alignment of the nanoparticles and a magnetic field controls their charged states. This novel effect enables a strong magnetic switching effect for which the on/off ratio is ca. 10⁴. Such an effect has been expected to exist and these findings show this magnetoelectric coupling for the first time.     

Versatile Nanocomposite Coatings with Tunable Cell Adhesion and Bactericidity

TiO₂‐Ag nanocomposites are known for their bactericidal effect during exposure to appropriate UV radiation. While involving hazardous radiation, and limited to accessible areas, the bactericidity of these coatings is not persistent in the absence of UV light, which impedes their commercial application. Herein it is shown that TiO₂‐Ag nanocomposites can be made highly bactericidal without the need of irradiation. Beyond this, bactericidity can even be mitigated in the presence of pre‐irradiated coatings. Biocompatibility and cell adhesion are also negligibly small for the as‐processed, non‐irradiated coatings, and become fairly high when the coatings are irradiated prior to testing. This opens the possibility to pattern the coatings into areas with high and low cell adhesion properties. Indeed by irradiating the coating through a mechanical mask it is shown that fibroblast cell adherence is sharply confined to the irradiated area. These properties are achieved using TiO₂‐Ag thin films with high silver loadings of 50 wt%. The films are processed on stainless steel substrates using solution deposition. Microstructural characterization by means of X‐ray diffraction, Raman, and X‐ray photoelectron spectroscopy, high‐resolution scanning electron microscopy, and atomic force microscopy show a highly amorphous TiO₂‐Ag_xO nanocomposite matrix with scattered silver nanoparticles. UV irradiation of the films results in the precipitation of a high density of silver nanoparticles at the film surface. Bactericidal properties of the films are tested on α‐haemolyzing streptococci and in‐vitro biocompatibility is assessed on primary human fibroblast cultures. The results mentioned above as to the tunable bactericidity and biocompatibility of the TiO₂‐Ag coatings developed herein, are amenable to silver ion release, to catalytic effects of silver nanoparticles, and to specific wettabilities of the surfaces.     

Synthesis and Fabrication of Multifunctional Nanocomposites: Stable Dispersions of Nanoparticles Tethered with Short,Dense and Polydisperse Polymer Brushes in Poly(methyl methacrylate)

This paper presents a melt‐processable multifunctional nanocomposite material that shows highly controlled tunability in refractive index, glass transition temperature (T_g) and energy bandgap. ZnO quantum dots tethered with polymer brushes are melt‐blended into the matrix polymer, giving rise to multiple functionalities in the nanocomposites. Brush–matrix polymer interactions are important in determining the ability of polymer‐grafted nanoparticles to disperse in a polymer melt, of which graft density (σ), brush (N) and matrix (P) polymer lengths are the critical parameters. It is generally assumed that long polymer brushes (N > P) and an optimum graft density are necessary to achieve a good dispersion. Here it is demonstrated that nanoparticles tethered with short, dense and polydisperse polymer brushes via radical copolymerization can exhibit a stable, fine dispersion in the polymer melt. The quality of the dispersion of the nanoparticles is characterized by measuring physical properties that are sensitive to the state of the dispersion. This synthesis method presents a general approach for the inexpensive and high‐throughput fabrication of high quality, melt‐blendable nanocomposites that incorporate functional nanoparticles, paving the way for wider application of high performance nanocomposites.     

A probabilistic model and electrodynamic analysis of the resonance interaction of electromagnetic waves with magnetic 3D nanocomposites

A probabilistic model of the resonance interaction of electromagnetic waves with magnetic 3D nanocomposities is developed. It is assumed that the field of the ferromagnetic resonance (FMR) of nanoparticles located in cavities of the dielectric matrix is a random variable distributed according to the normal law. The mathematical expectation of the random values of the real and imaginary parts of the diagonal and off-diagonal components of the tensor effective permeability of a 3D magnetic nanocomposite based on the opal matrix containing Ni_0.7Zn_0.3Fe₂O₄ nanoparticles is calculated. The experimental and calculation data of the probabilistic model are compared.     

Stable Blue Emission from a Polyfluorene/Layered‐Compound Guest/Host Nanocomposite

In this study a blue‐light‐emitting conjugated polymer, poly(9,9‐dioctylfluorene), is confined to the interlayer space of inorganic, layered metal dichalcogenide materials, metallic MoS₂, and semiconducting SnS₂. The nanocomposites are prepared through Li intercalation into the inorganic compound, exfoliation, and restacking in the presence of the polymer. X‐ray diffraction and optical absorption measurements indicate that a single conjugated polymer monolayer, with an overall extended planar morphology conformation, is isolated between the inorganic sheets, so that polymer aggregation or π–π interchain interactions are significantly reduced. Photoluminescence (PL) measurements show that the appearance of the undesirable green emission observed in pristine polymer films is suppressed by incorporating the polymer into the inorganic matrix. The blue emission of the intercalated polymer is stable for extended periods of time, over two years, under ambient conditions. Furthermore, the green emission is absent in the PL spectra of nanocomposite films heated at 100 °C for 7 h in air with direct excitation of the keto defect. Finally, no green emission was observed in the electroluminescence spectrum of light‐emitting devices fabricated with a polymer‐intercalated SnS₂ nanocomposite film. These results support the proposed hypothesis that fluorenone defects alone are insufficient to generate the green emission and that interchain interactions are also required.     

Artificial Magnetic Bacteria: Living Magnets at Room Temperature

Biogenic magnetite is a fascinating example of how nature can generate functional magnetic nanostructures. Inspired by the magnetic bacteria, an attempt is made to mimic their magnetic properties, rather than their structures, to create living magnets at room temperature. The non‐magnetic probiotic bacteria Lactobacillus fermentum and Bifidobacteria breve are used as bioplatforms to densely arrange superparamagnetic nanoparticles on their external surfaces, thus obtaining the artificial magnetic bacteria. Magnetic probiotic bacteria can be produced by using superparamagnetic maghemite nanoparticles assembled at their surfaces. They present a collective ferromagnetic phase at room temperature. The blocking temperature of these maghemite nanoparticles increases more than 100 K when assembled at the artificial magnetic bacteria.     

Synthesis of Interfacially Active and Magnetically Responsive Nanoparticles for Multiphase Separation Applications

A novel interfacially active and magnetically responsive nanoparticle is designed and prepared by direct grafting of bromoesterified ethyl cellulose (EC‐Br) onto the surface of amino‐functionalized magnetite (Fe₃O₄) nanoparticles. Due to its strong interfacial activity, ethyl cellulose (EC) on the magnetic nanoparticles enables the EC‐grafted Fe₃O₄ (M‐EC) nanoparticles to be interfacially active. The grafting of interfacially active polymer EC on magnetic nanoparticles is confirmed by zeta‐potential measurements, diffuse reflectance infrared Fourier‐transform spectroscopic (DRIFTS) characterization, and thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) images show a negligible increase in particle size, confirming the thin silica coating and grafted EC layer. The magnetization measurements show a marginal reduction in saturation magnetization by silica coating and EC grafting of original magnetic nanoparticles, confirming the presence of coatings. The M‐EC nanoparticles prepared in this study show excellent interfacial activity and highly ordered features at the oil/water interface, as confirmed using the Langmuir–Blodgett technique and atomic force microscopy (AFM). The magnetic properties of M‐EC nanoparticles at the oil/water interface make the interfacial properties tunable by or responsive to an external magnetic field. The occupancy of M‐EC at the oil/water interface allows rapid separation of the water droplets from emulsions by an external magnetic field, demonstrating enhanced coalescence of magnetically tagged stable water droplets and a reduced overall volume fraction of the sludge.     

Facile Single‐Precursor Synthesis and Surface Modification of Hafnium Oxide Nanoparticles for Nanocomposite γ‐Ray Scintillators

Inorganic nanoparticles/polymer nanocomposites provide a low cost, high performance alternative for gamma scintillation. However, inorganic nanoparticles used thus far suffer from either moderate atomic numbers or low band gaps, limiting the gamma stopping power and photoelectron production in these systems. Here, a highly efficient, facile single‐precursor synthesis protocol is reported for hafnium oxide nanoparticles with an average diameter of 5 nm. The nanoparticle surface is further functionalized for the fabrication of highly transparent bulk‐size nanocomposite monoliths (2 mm thick, transmittance at 550 nm >75%) with nanoparticle loadings up to 40 wt% (net hafnium wt% up to 28.5%). Using poly(vinyltoluene) as the matrix, 2‐(4‐tert‐butylphenyl)‐5‐(4‐biphenylyl)‐1,3,4‐oxadiazole and 1,4‐bis(5‐phenyl‐2‐oxazolyl)benzene as the cascade fluors, and hafnium oxide nanoparticles as the gamma sensitizer, the nanocomposite monolith of 1 cm diameter and 2 mm thickness is fabricated capable of producing a full energy photopeak for 662 keV gamma rays, with the best deconvoluted photopeak energy resolution <8%.     

Innovative impregnation process for production of γ-Fe2O3–activated carbon nanocomposite

An immobilized superparamagnetic nanocomposite comprising γ-Fe₂O₃ and activated carbon was synthesized via a facile thermal decomposition route. To prepare the magnetically functionalized nanocomposite, treated activated carbon (TAC) loaded with lepidocrocite (γ-FeOOH) nanoparticles (MAC-1) was first produced via a wet chemical method. Then magnetic activated carbon (AC/γ-Fe₂O₃, MAC-2) was fabricated by thermal decomposition of MAC-1 at 250 °C under argon gas for 1 h. Characterization analyses confirmed that superparamagnetic spherical maghemite nanoparticles of 21±2 nm in size were homogeneously dispersed on the TAC. The specific surface area was 643.8 m² g⁻¹ for TAC, 289 m² g⁻¹ for MAC-1, and 303.5 m² g⁻¹ for MAC-2. The industrially friendly nanocomposite was applied as an adsorbent for pollutant removal from aqueous solution.     

A Three Component Self‐Assembled Epitaxial Nanocomposite Thin Film

A self‐assembled three phase epitaxial nanocomposite film is grown consisting of ≈3 nm diameter fcc metallic Cu nanorods within square prismatic SrO rocksalt nanopillars in a Sr(Ti,Cu)O_3‐δ perovskite matrix. Each phase has an epitaxial relation to the others. The core–shell‐matrix structures are grown on SrTiO₃ substrates and can also be integrated onto Si using a thin SrTiO₃ buffer. The structure is made by pulsed laser deposition in vacuum from a SrTi_0.75Cu_0.25O₃ target, and formed as a result of the limited solubility of Cu in the perovskite matrix. Wet etching removes the 3 nm diameter Cu nanowires leaving porous SrO pillars. The three‐phase nanocomposite film is used as a substrate for growing a second epitaxial nanocomposite consisting of CoFe₂O₄ spinel pillars in a BiFeO₃ perovskite matrix, producing dramatic effects on the structure and magnetic properties of the CoFe₂O₄. This three‐phase vertical nanocomposite provides a complement to the well‐known two‐phase nanocomposites, and may offer a combination of properties of three different materials as well as additional avenues for strain‐mediated coupling within a single film.     

Multimodal Magnetic Nanoclusters for Gene Delivery,Directed Migration,and Tracking of Stem Cells

This study develops multimodal magnetic nanoclusters (M‐MNCs) for gene transfer, directed migration, and tracking of human mesenchymal stem cells (hMSCs). The M‐MNCs are designed with 5 nm iron oxide nanoparticles and a fluorescent dye (i.e., Rhodamine B) in the matrix of the Food and Drug Administration approved polymer poly(lactide‐co‐glycolide) using a nanoemulsion method. The synthesized M‐MNCs have a hydrodynamic diameter of ≈150 nm, are internalized by stem cells via endocytosis, and deliver genes with high efficiency. The cellular internalization and gene expression efficiency of the clustered nanoparticles are significantly higher than that of single nanoparticles. The M‐MNC‐labeled hMSCs migrate upon application of a magnetic force and can be visualized by both optical and magnetic resonance (MR) imaging. In animal models, the M‐MNC‐labeled hMSCs are also successfully tracked using optical and MR imaging. Thus, the M‐MNCs not only allow the efficient delivery of genes to stem cells but also the tracking of cells in animal models. Taken together, the results show that this new type of nanocomposite can be of great help in future stem cell research and in the development of cell‐based therapeutic agents.     

UV‐vis‐Induced Vitrification of a Molecular Crystal

A charge‐transfer complex of 2,5‐dimethyl‐N,N′‐dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)₂, defined as α) is irreversibly transformed by UV‐vis illumination. Depending on the illumination conditions, three new types of solids (defined as γ, δ, and ?) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid‐state, high‐resolution, cross‐polarization magic angle spinning (CP‐MAS) ¹³C NMR, elemental analysis (EA), mass spectrometry (MS), X‐ray absorption fine structure (XAFS), and powder X‐ray diffraction (XRD). The CP‐MAS, EA, MS, and XAFS results indicate that compound γ is a glass state of Ag(DM)₂. The transformation from crystalline (α) to amorphous (γ) solid Ag(DM)₂ is an irreversible exothermic glass transition (glass‐transition temperature 155.2 °C; ΔH = –126.8 kJ mol^–1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound δ (Ag(DM)_1.5) consists of silver nanoparticles (diameter (7 ± 2) nm ) dispersed in a glassy matrix of neutral DM molecules. The ?N–CN–Ag coordination bonds of the α form are not maintained in the δ form. Decomposition of α by intense illumination results in a white solid (?), identified as being composed of silver nanoparticles (diameter (60 ± 10) nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both δ and ? are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver.     

Multi‐“Color” Delineation of Bone Microdamages Using Ligand‐Directed Sub‐5 nm Hafnia Nanodots and Photon Counting CT Imaging

The early detection of bone microdamages is crucial to make informed decisions about the therapy and taking precautionary treatments to avoid catastrophic fractures. Conventional computed tomography (CT) imaging faces obstacles in detecting bone microdamages due to the strong self‐attenuation of photons from bone and poor spatial resolution. Recent advances in CT technology as well as novel imaging probes can address this problem effectively. Herein, the bone microdamage imaging is demonstrated using ligand‐directed nanoparticles in conjunction with photon counting spectral CT. For the first time, Gram‐scale synthesis of hafnia (HfO₂) nanoparticles is reported with surface modification by a chelator moiety. The feasibility of delineating these nanoparticles from bone and soft tissue of muscle is demonstrated with photon counting spectral CT equipped with advanced detector technology. The ex vivo and in vivo studies point to the accumulation of hafnia nanoparticles at microdamage site featuring distinct spectral signal. Due to their small sub‐5 nm size, hafnia nanoparticles are excreted through reticuloendothelial system organs without noticeable aggregation while not triggering any adverse side effects based on histological and liver enzyme function assessments. These preclinical studies highlight the potential of HfO₂‐based nanoparticle contrast agents for skeletal system diseases due to their well‐placed K‐edge binding energy.     

The Influence of TiO2 Particle Size in TiO2/CuInS2 Nanocomposite Solar Cells

The recently developed CuInS₂/TiO₂ 3D nanocomposite solar cell employs a three‐dimensional, or “bulk”, heterojunction to reduce the average minority charge‐carrier‐transport distance and thus improve device performance compared to a planar configuration. 3D nanocomposite solar‐cell performance is strongly influenced by the morphology of the TiO₂ nanoparticulate matrix. To explore the effect of TiO₂ morphology, a series of three nanocomposite solar‐cell devices are studied using 9, 50, and 300 nm TiO₂ nanoparticles, respectively. The photovoltaic efficiency increases dramatically with increasing particle size, from 0.2 % for the 9 nm sample to 2.8 % for the 300 nm sample. Performance improvements are attributed primarily to greatly improved charge transport with increasing particle size. Other contributing factors may include increased photon absorption and improved interfacial characteristics in the larger‐particle‐size matrix.     

Nanoscale‐Coordination‐Polymer‐Shelled Manganese Dioxide Composite Nanoparticles: A Multistage Redox/pH/H2O2‐Responsive Cancer Theranostic Nanoplatform

Nanoscale coordination polymers (NCPs) self‐assembled from metal ions and organic bridging ligands exhibit many unique features promising for applications in nanomedicine. In this work, manganese dioxide (MnO₂) nanoparticles stabilized by bovine serum albumin are encapsulated by NCP‐shells constructed based on high‐Z element hafnium (Hf) ions and c,c,t‐(diamminedichlorodisuccinato)Pt(IV) (DSP), a cisplatin prodrug. After further modification with polyethylene glycol (PEG), the formed BM@NCP(DSP)‐PEG can simultaneously serve as a radio‐sensitizer owing to the strong X‐ray attenuation capability of Hf to enhance radiotherapy, as well as a chemotherapeutic agent resulting from the reduction‐induced release of cisplatin. Meanwhile, the in situ generated oxygen resulting from MnO₂‐triggered decomposition of tumor endogenous H₂O₂ will be greatly helpful for overcoming hypoxia‐associated radio‐resistance. Upon intravenous injection, BM@NCP(DSP)‐PEG shows efficient tumor homing as well as rapid renal excretion, as illustrated by magnetic resonance imaging and confirmed by biodistribution measurement. Notably, an excellent in vivo tumor growth inhibition effect is observed with BM@NCP(DSP)‐PEG nanoparticles after the combined chemoradiotherapy treatment. Therefore, the NCP‐based composite nanoparticles with inherent biodegradability and no appreciable in vivo toxicity may be a unique type of multifunctional nanoplatform responsive to different parameters in the tumor microenvironment, promising for cancer theranostics with great efficacy.     

Embedding Ag Nanoparticles into MgF2 Nanorod Arrays

Using a unique glancing angle co‐deposition technique, face‐centered cubic Ag nanoparticles have been embedded into aligned polycrystalline MgF₂ nanorods with different topological shapes, such as tilted, zigzag, vertical, and helical nanorods. The optical properties of the artificial nanocomposite materials, such as surface plasmon resonance and polarization absorbance, are determined by the size of the Ag nanoparticles as well as the alignment and shape of the MgF₂ nanorod arrays. The combination of co‐deposition and glancing angle deposition provides a unique way to design novel nanocomposite materials and doped nanorod arrays.