Metal-polymer Nanocomposites Research Articles

The microstructure of and charge transfer in thin films based on metal-polymer nanocomposites

Charge transfer in nanostructured metal-polymer composites was studied. The frequency dependences of film conductance and susceptance were obtained at various metal concentrations. The susceptance of samples above the percolation threshold was negligibly small, which corresponded to the purely metallic conductivity type. For samples below the percolation threshold, susceptance and conductance were comparable in magnitude, which was evidence of an important role played by susceptance mechanisms. At low frequencies, the samples behaved as quasi-linear RC circuits and both the active and reactive impedance components increased linearly as the frequency grew. At high frequencies, the dispersion of susceptance, which was inversely proportional to frequency, was observed. The conclusion was drawn that the hopping conductivity mechanism through polymeric matrix surface states prevailed in films below the percolation threshold. At high frequencies, when the applied voltage period was shorter than the characteristic time of surface state recharging, these states began to be eliminated from charge transfer processes. It was suggested that a decrease in the reactive impedance component with an increase in frequency might be the reason for the dispersion observed experimentally.

Synthesis of metal–polymer nanocomposite for optical applications

Thin films of Ag–PET nanocomposite were synthesized by a novel route of atom beamco-sputtering. The nanocomposites were characterized by UV–visible and IR absorptionspectroscopy, Rutherford backscattering spectroscopy and transmission electronmicroscopy. The absorption spectra exhibit features suitable for applications as (i) absorberextending from the visible region to about 2400 nm in the infrared region and(ii) bandpass filter at 320 nm, useful for HeCd laser. The transmission electronmicroscopy observations indicate that the metal fraction is in the form of fractals.

Green approach to bulk and template-free synthesis of thermally stable reduced polyaniline nanofibers for capacitor applications

An extremely simple green approach is described that generates bulk quantities of nanofibers of the electronic polymer polyaniline in fully reduced state (leucoemeraldine form) in one step without using any reducing agent, surfactants, and/or large amounts of insoluble templates. Chemical oxidative polymerization of aniline with acetic acid instead of HCl (conventional synthesis) dramatically changes the morphology of the resulting doped polyaniline powder from nonfibrillar (particulate) to almost exclusively nanofibers of the reduced leucoemeraldine state in the diameter range 20 nm to 50 nm depending on the acetic acid concentration. These reduced leucoemeraldine polyaniline nanofibers undergo a spontaneous redox reaction with noble metal ions under mild aqueous conditions, resulting in deposition of various shapes, such as leaf, particulate, nanowires and cauliflower for Ag, Pd, Au, and Pt, respectively, on the surface of polyaniline nanofibers, affording a facile entry into this technologically important class of metal–polymer nanocomposites. These nanofibers also can act as seed templates to synthesize polyaniline nanofibers by conventional HCl doped synthesis where particulate morphology normally dominates. The ensuing polyaniline nanofibers have a broad final decomposition temperature which is at least 120 °C higher and have a very high dielectric constant ≈3500 at higher frequency when compared to reported reduced polyaniline and HCl based polyaniline.

The microstructure of and charge transfer in thin films based on metal-polymer nanocomposites

Charge transfer in nanostructured metal-polymer composites was studied. The frequency dependences of film conductance and susceptance were obtained at various metal concentrations. The susceptance of samples above the percolation threshold was negligibly small, which corresponded to the purely metallic conductivity type. For samples below the percolation threshold, susceptance and conductance were comparable in magnitude, which was evidence of an important role played by susceptance mechanisms. At low frequencies, the samples behaved as quasi-linear RC circuits and both the active and reactive impedance components increased linearly as the frequency grew. At high frequencies, the dispersion of susceptance, which was inversely proportional to frequency, was observed. The conclusion was drawn that the hopping conductivity mechanism through polymeric matrix surface states prevailed in films below the percolation threshold. At high frequencies, when the applied voltage period was shorter than the characteristic time of surface state recharging, these states began to be eliminated from charge transfer processes. It was suggested that a decrease in the reactive impedance component with an increase in frequency might be the reason for the dispersion observed experimentally.

Teflon AF/Ag nanocomposites with tailored optical properties

Teflon AF/Ag nanocomposites with various metal concentrations were fabricated by an evaporation process. Transmission electron microscopy examination showed that for low metal concentrations, the silver formed isolated individual nanoparticles. At higher metal concentrations, percolating metallic networks within the polymer matrix were formed. Optical absorption measurements showed a transition from individual plasmon absorption peaks for individual Ag nanoparticles to broadband optical absorption for the metallic networks. The absorption profile closely matches the solar radiation spectrum for an intermediate metal concentration of 45%. Thus, these novel polymer-metal nanocomposites have significant potential for photovoltaic applications.

Tuning the microstructure of pulsed laser deposited polymer–metal nanocomposites

Pulsed laser deposition was used to grow complex polymer–metal nanocomposites consisting of Ag, Cu and Nb clusters embedded in a poly(methyl-methacrylate) (PMMA) matrix. During deposition at room temperature, the size and amount of the metal clusters can be tuned in different ways. First, it is controlled by the number of laser pulses hitting the respective targets. In the case of Ag, a bimodal size distribution of the clusters is observed, induced by total coalescence and secondary nucleation processes. For Cu and Nb, much smaller clusters and higher cluster densities are obtained due to a stronger reactivity with the polymer and thus a lower diffusivity in the PMMA. Additionally, the microstructure of the Ag clusters is affected by the degree of cross linking of the polymer and can be influenced by pre-deposition of nucleation seeds in the form of small Cu clusters.

Optical and electrical properties of polymer metal nanocomposites prepared by magnetron co-sputtering

Polymer-metal nanocomposite films were prepared by co-sputtering from two independent magnetron sources as well as from a silver-polytetrafluoroethylene (PTFE) composite target. By sputtering from two magnetrons we prepared both, samples with a metal gradient and homogenous composite films. The dielectric constant depends on the metal filling factor and increases approaching the percolation threshold. The resistivity drops from 10 7 to 10 − 3 Ω cm over a narrow range of metal content. The thin composite films show a strong optical absorption in the visible region and a red shift with increasing silver filling. We have produced Bragg reflectors using multilayer systems of composites and pure sputtered PTFE.

New Approach for Preparation of Silver–Polystyrene Heterogeneous Nanocomposite by Polyol Process

Abstract Silver nanoparticles are homogeneously immobilized onto the polystyrene surface using polyol process for the first time. The formation mechanism of composite materials was discussed briefly. This novel method can be extended to the preparation of other metal–polymer nanocomposites.

Controlled syntheses of Ag–polytetrafluoroethylene nanocomposite thin films byco-sputtering from two magnetron sources

Co-sputtering from two independent magnetron sources was used to prepare polymer–metalnanocomposite films. Both gradient films with increasing metal fraction and homogeneouscomposite films were produced from polytetrafluoroethylene (PTFE) and silver targetsusing a rotatable sample holder. The structure of the pure sputtered polymer as well as thecomposite structure was studied. Electrical properties of the composite material near thepercolation threshold show the expected, sharp change in the resistivity from107 Ω cm atsmall silvercontent to 10−3 Ω cm after percolation. The optical absorption in the visible region due to surface plasmonresonances also has a strong dependence on the metal content, showing a red shift ofthe absorption peak from 405 nm to more than 500 nm at higher silver content.

Structural organization and thermal transformations of various Ni(II) complexes as precursors of polymer-metal nanocomposites

Peculiarities of thermal transformations of metal-containing monomers and polymers prepared by various synthetic routes are analyzed. It is shown that the thermal stability of metalcarboxylate groups is determined by the spatial organization of the nearest environment and the microstructure of polymer chains formed as a result of thermal transformations. Main paths of thermal transformations of studied compounds are considered. Qualitative and quantitative compositions of the gaseous and solid-phase products at the end of transformations and some properties of forming polymer-metal nanocomposites are studied.

Structural organization and thermal transformations of various Ni(II) complexes as precursors of polymer-metal nanocomposites

Structural organization and thermal transformations of various Ni(II) complexes as precursors of polymer-metal nanocomposites

Structural organization and thermal transformations of various Ni(II) complexes as precursors of polymer-metal nanocomposites

Structural organization and thermal transformations of various Ni(II) complexes as precursors of polymer-metal nanocomposites

Optical properties of metal-polymer nanocomposites based on iron and high-pressure polyethylene

The optical reflectance and absorption spectra of nanocomposite materials based on iron and highpressure polyethylene (with different percentages of iron) were measured at room temperature in the visible and near-infrared regions. Oscillations of the absorption coefficient related to the optical transitions between minibands of the quantum well are revealed in the electronic spectrum of a metal nanoparticle. The experimental and theoretical data on the absorption coefficient are compared. It is shown that, with an increase in the iron concentration in the dielectric matrix, the discrepancy in the theoretical and experimental results decreases significantly.

Development of a novel polymer–metal nanocomposite obtained through the route of in situ reduction for integral capacitor application

AbstractMetal nanoparticles exhibit a number of interesting characteristics, including unique physical, chemical, optical, magnetic, and electric properties. Numerous investigations have exploited their properties in a readily usable form by incorporating them into polymers. The current focus of interest is the behavior of such polymer nanocomposites near the percolation loading levels of the metal nanoparticles. This material is particularly suitable for the new integral passive technology. Discrete capacitors are used in many applications, such as noise suppression, filtering, tuning, decoupling, bypassing, termination, and frequency determination, and they occupy a substantial amount of surface area on a substrate. Thus there are limitations in the number of capacitors that can be placed around the chip. Integral passive components are gradually replacing discrete components because of the inherent advantages of improved electrical performance, increased real estate on the printed wiring board, miniaturization of interconnect distance, reduced processing costs, and efficient electronics packaging. For integral capacitors, polymer composite material has emerged as a potential candidate because it meets the requirements of low processing temperature and reasonably high dielectric constant. Yang and Wong, whose patent was filed in 2001, demonstrated novel integral passive component materials with extraordinarily high dielectric constants (K > 1000) and high reliability performance. These materials are characterized by high dielectric constant based on the mechanism of interfacial polarization, although they need precision filler concentration control. The current study overcomes this drawback and produces the composite through an in situ reduction in an epoxy matrix. Material characterization was done through TEM, SEM, X‐ray analysis, and energy‐dispersive analysis for X rays. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1531–1538, 2004

Effect of laser-ablated copper nanoparticles on polymerization of 1,1,3,3-tetraphenyl-1,3-disilacyclobutane

We have studied the effect of copper nanoparticles produced by laser ablation on the ring-opening polymerization of 1,1,3,3-tetraphenyl-1,3-disilacyclobutane (TPDC). The particle size and distribution of laser-ablated, copper nanoparticles were controlled by laser-ablation conditions such as ambient pressure, laser fluence, and distance between target and substrate. Laser-ablated, copper nanoparticles induced polymerization of TPDC effectively, resulting in formation of poly(diphenylsilylenemethylene) (PDPhSM) thin films. The polymerization efficiency depended mainly on the particle size and the surface concentration of copper nanoparticles deposited on the TPDC films by laser ablation. No clear tendency was observed between oxidation of Cu nanoparticles and polymerization efficiency. This technique enables us to easily fabricate PDPhSM thin films and may become a new method for fabricating polymer–metal nanocomposites.

Kinetics and Mechanism of in situ Simultaneous Formation of Metal Nanoparticles in Stabilizing Polymer Matrix

The kinetic peculiarities of the thermal transformations of unsaturated metal carboxylates (transition metal acrylates and maleates as well as their cocrystallites) and properties of metal-polymer nanocomposites formed have been studied. The composition and structure of metal-containing precursors and the products of the thermolysis were identified by X-ray analysis, optical and electron microscopy, magnetic measurements, EXAFS, IR and mass spectroscopy. The thermal transformations of metal-containing monomers studied are the complex process including dehydration, solid phase polymerization, and thermolysis process which proceed at varied temperature ranges. At 200–300°C the rate of thermal decay can be described by first-order equations. The products of decompositions are nanometer-sized particles of metal or its oxides with a narrow size distribution (the mean particle diameter of 5–10nm) stabilized by the polymer matrix.

Nanoparticle architecture in carbonaceous matrix upon swift heavy ion irradiation of polymer–metal nanocomposites

Distinct nanoparticle self-organization in the nanocomposites (∼100 nm) of Teflon AF containing different metallic clusters is reported upon swift heavy ion irradiation of 120 MeV Au beams at different ion fluences ranging from 1 × 10 11 to 3 × 10 12 ions/cm 2. Two dimensionally distributed Au clusters are found to be transformed into long cluster chains of seemingly helical pattern in the organic matrix like pearls on a string. Comparatively diluted three dimensionally arranged Ag nanoparticles are observed to be concentrated in the formed mesh of carbon-enriched nanoregions upon irradiation. The nanoparticle self-organization in such carbonaceous nanowires (diameter ∼ 25 nm) finally leads to a quasi-one-dimensional distribution at the highest fluence with several particles apparently being aligned. It appears most probable that a high Au cluster concentration in the polymer matrix leads to direct ion–cluster interaction. This probably initiates irradiation-enhanced and thermally assisted diffusion of the clusters coupled with intermixing in the polymer layers. Moving clusters are assumed to be trapped in the ion beam induced additional free volume leading to a long string of helical-type nanoscale configuration. On the other hand, with diluted clusters arrangement, irradiation induced electronically excited inter-cluster organic regions are interpreted to act as trapping centres for the nanoparticles that self-organize along the ion damaged zones. Transmission electron microscopic investigations have been applied to analyse the irradiated and pristine nanocomposites.

Self-Organized Metal-Polymer Nanocomposites

A new approach for obtaining matrix-stabilized nanosized particles of metals and their oxides (size less than 50 nm) which are synthesized in one stage by chemical reaction within a condensed phase are elaborated. Such processes are realized by (co)poly merization of metal- containing monomers which include a metal ion chemically bonded with an organic part of a molecule. The molecular and supramolecular organization of such nano-composites is formed in the course of controlled thermal conversion of metal-containing monomers in an inert or self- generating atmosphere. The main stages of this conversion are (a) dehydration, (b) thermal (co)polymerization including self propagation frontal polymerization, (c ) controlled pyrolysis of formed products. Variation of synthesis and pyrolysis conditions leads to formation both of nano- particles with given size and necessary particle size distri butions and of a stabilizing polymeric matrix with controlled composition and thickness.

Synthesis and Characterization of Metal Nanoparticles and the Formation of Metal-Polymer Nanocomposites

ABSTRACTMetal nanoparticles are highly prone to oxidation due to their high surface energy and affinity for oxygen which can lead to the complete oxidation of the particles. Studying and utilizing the unique properties of metal nanoparticles requires minimizing their interaction with the atmosphere. We have used the co-condensation technique to synthesize suspensions of metal nanoparticles in isopropanol. The solvent protects the nanoparticles from the atmosphere and minimizes agglomeration of the nanoparticles. The particles showed a lognormal distribution and the average particle size was below 20nm. Polymer-metal nanocomposites were made by dispersing the metal nanoparticles in PMMA matrix by spin coating and solution casting. Adherent films, fibers and free standing films could be obtained by varying the process conditions. The SEM images show that the nanoparticles in the spun coated films were non-agglomerated and well dispersed over a wide area. Morphology of the spun coated films was different from the solution cast films. Electrically conducting films having interconnected silver particle network could be obtained. Cytotoxicity studies show that the silver nanoparticles and the PMMA-Ag nanocomposite films are antibacterial in nature. We have also dispersed the nanoparticle into pump oil and measured the thermal conductivity of the resultant mixture. The thermal conductivity of the oil could be increased by over 50% by adding an extremely small fraction of the silver nanoparticles.

Magnetic properties of iron-polyethylene nanocomposites prepared by high energy ball milling

Metal-polymer nanocomposites in the system iron-polyethylene have been prepared by high energy ball milling. Minimum average grain size obtained is of the order of 9 nm. Enhanced coercivity of 230 Oe at room temperature and 510 Oe at 5 K have been obtained for the sample containing 0.1 volume fraction of iron in polyethylene after milling for 200 h. This high value of the coercivity could be ascribed to the presence of a fraction of single-domain particles in the sample as evidenced from the thermal dependence of the magnetization and ac susceptibility measurements.