Host Matrix Material Research Articles

Electrical Characterization of Polyethylene oxide -Alumina composite

This study deals with the electrical characterization of polyethylene oxide (PEO) – alumina (Al2O3) composites at several concentrations, 0%, 5%, 10%, and 15% by weight Al2O3. The alternating current electrical properties were studied as a function of frequency in the range from 20 Hz to 1 MHz and studied with filler concentrations. Transmission light microscopy (TLM) and scanning electron microscopy (SEM) revealed that the dispersed Al2O3 particles were randomly distributed within the PEO matrix with some surface contacts between them and also revealed that the ceramic particles are tightly held by the host matrix material. The melting temperature, Tm, was determined for the composites via differential scanning calorimetry (DSC). The AC electrical properties (impedance, real part of impedance, imaginary part of impedance, dissipation factor, dielectric constant, real part of electric modulus, imaginary part of electric modulus, electrical conductivity, and relaxation time) were determined. It was found that the applied frequency and filler concentrations affected the AC electrical properties of the composites. The universal power-law of alternating current conductivity wasobserved in the PEO/Al2O3 composites. The calculated power exponent ( n < 1) is physically acceptable within this applied model.

Metal/polymer nanocomposite thin films prepared by plasma polymerization and high pressure magnetron sputtering

Recently, there is much interest in nanocomposites consisting of metal nanoparticles dispersed in a dielectric matrix due to their novel functional properties. In many cases the formation of metal clusters is affected by chemical reactions of the metal with the host matrix material during deposition. The integration of a magnetron cluster source into a plasma deposition process allows the pre-formation of clusters in the gas phase and subsequent co-deposition with the matrix material. We chose plasma polymerization of HMDSO as deposition method for the matrix in this case. Here we focus on the composition of the nanocomposites generated by high pressure magnetron sputtering combined with a plasma polymer. The influence of magnetron power, total and HMDSO partial gas pressure on the cluster formation as well as nanocomposite film properties were investigated by ex situ X-ray photoelectron spectroscopy. Furthermore optical und morphological properties of the prepared nanocomposites have been characterized.

Physical Aging of Single Wall Carbon Nanotube Polymer Nanocomposites: Effect of Functionalization of the Nanotube on the Enthalpy Relaxation

The glass-transition temperature and enthalpy relaxation of nanocomposites synthesized with low loadings of single wall carbon nanotubes (1 wt %) in poly(methylmethacrylate) (PMMA) have been investigated using differential scanning calorimetry (DSC). The results are compared with pure PMMA, and the effect of carbon nanotubes on the mobility of the polymer chain is discussed. Composites have been synthesized with unmodified nanotubes (SWNT/PMMA) as well as with amino-functionalized nanotubes (a-SWNT/PMMA) to provide a better interaction between the nanotube and the host matrix material. It was found that the glass-transition temperature of the unmodified nanocomposite SWNT/PMMA is the same as the neat PMMA (Tg = 99 °C). A significant increase of 17 °C in the glass-transition temperature of the modified nanocomposite a-SWNT/PMMA is found when compared with the neat PMMA. Glass-transition results indicate that the presence of a-SWNT in PMMA restricts the segmental motion of the polymer chain. No significant change in activation energy of the enthalpy relaxation process or fragility index of PMMA is observed due to the addition of a-SWNT. However, a large broadening of the enthalpy peak is observed with the incorporation of SWNT in PMMA. This broadening leads to difficulty in the calculation of the activation energy and fragility index of SWNT/PMMA. Enthalpy relaxation behavior during isothermal aging is characterized at the same temperature with respect to the respective glass-transition temperatures of the three samples (at Tg and Tg − 2 °C (2 °C lower than the glass-transition temperature of each system)). The equilibrium enthalpy is reached at a shorter aging time in pure PMMA compared with SWNT/PMMA and a-SWNT/PMMA. The results obtained for enthalpy recovery show the signature of the restrictive environment of a-SWNT and SWNT on polymer chain mobility.

Hybrid organic–inorganic spin-on-glass CuCl films for optoelectronic applications

Cuprous halides are among the most studied inorganic materials for excitonic related linear/non-linear optical processes due to their large excitonic binding energies (∼190 and 108 meV for CuCl and CuBr, respectively). In recent years, we have studied CuCl thin films deposited by vacuum evaporation and sputtering techniques on a variety of substrates. We now report on the extension of this research to the deposition of CuCl nanocrystals on flexible substrates via a spin-on technology. In this study, we present the synthesis, deposition and characterization of CuCl nanocrystals embedded in organic polysilsesquioxane (PSSQ) films on a variety of substrates via the spin coating method. The nanocrystals were synthesized by a complexation–reduction–precipitation mechanism reaction of CuCl2 · 2H2O, alpha D-glucose and de-ionized (DI) water with a PSSQ based solution as the host matrix material. The deposited films were heated at 120 °C for durations between 1 and 24 h in vacuo. The room temperature UV–Vis absorption spectra for all hybrid films, except the as-deposited film, showed both Z1,2 and Z3 excitonic absorption features. Room temperature photoluminescence measurements of all heated films reveal very intense Z3 excitonic emission at 3.221 eV. Room temperature x-ray diffraction (XRD) of the as-deposited films gave no evidence of the crystallization of CuCl. However, after heating the films, XRD confirmed the preferential growth of CuCl nanocrystals whose average size is ≈25–45 nm in the ⟨1 1 1⟩ orientation. The CuCl hybrid films showed bright electroluminescent emission at 384 nm when subjected to an ac voltage of about 100 V peak to peak.

Energy dissipation in carbon nanotube composites: a review

In this article we discuss the energy dissipation that occurs when the interfacial slip of nanoscale fillers is activated in a host matrix material. We consider both polymer (such as polycarbonate, PEO, PEG) and epoxy matrices. The nanoscale fillers considered are carbon nanotubes (both singlewalled and multiwalled) as well as fullerenes. The nano-composites are fabricated by using a solution mixing technique with tetra-hydro-furan as the solvent. The interfacial friction damping is quantified by performing uniaxial dynamic load tests and measuring the material storage and loss modulus. We study various effects such as impact of nanotube weight fraction, nanotube surface treatment (oxidation, epoxidation etc.), test frequency, strain amplitude, operating temperature, as well as effect of pre-strain or biased strain. The effect of geometry (i.e., aspect ratio) is also considered by comparing the damping response of fullerene-composites with that of nanotube-composites.

Synthesis of novel light-emitting polymers and application in diodes with red phosphorescent cyclometalated iridium complex

Novel carbazole- and triarylamine-containing polymers, poly[N-(2-ethylhexyl)carbazole-alt-aniline] (PECA), poly[N-(2-ethylhexyloxy-phenyl)carbazole-alt-aniline] (PEPCA), poly[N-(2-ethylhexyl) carbazole-alt-N-(4-aminophenyl)carbazole] (PECAC) and poly[N-(2-ethylhexyloxy-phenyl)carbazole-alt-N-(4-aminophenyl)carbazole] (PEPCAC) showed good physical, optical, and electronic properties. Study on electrochemical properties of these polymers revealed that the band gap and HOMO energy were 2.91 and −5.19eV for PECA, 3.14 and −5.10eV for PEPCA, 2.97 and −5.01eV for PECAC, and 3.25 and −5.17eV for PEPCAC. Results proved that four polymers could be used as hole-transporting and host-matrix materials for phosphorescent PLEDs. Electrophosphorescent devices were fabricated by using a red phosphorescent iridium complex (IR-PIQCH) as a guest and four polymers as hosts, and the device performance was evaluated in terms of polymer structure, EL emission spectrum, luminance, driving voltage, and color coordinate.

Topotactic Intercalation of a Metallic Dense Host Matrix Chalcogenide with Large Electron—Phonon Coupling: Crystal Structures and Electronic Properties of LixMo2SbS2 (0 ≤ x ≤ 0.7).

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Thermal conductivity modeling of compacted nanowire composites

Nanocomposites may realize a similar thermal conductivity reduction and thermoelectric efficiency enhancement observed in superlattices and thus provide a pathway to scale up the benefits of the nanoscale effects to thermoelectric materials in bulk form. If there are two species, nanocomposites can be in the form of nanoparticles or nanowires of one material specie embedded in another host matrix material, or a discrete mixture of two different kinds of nanoparticles/nanowires that are compacted. A nanocomposite in the form of discrete mixtures of nanowires/nanoparticles does not have a continuous phase of material and may yield even lower thermal conductivity than composites with nanowires/nanoparticles embedded in a host material at the same stoichiometry. In this paper, phonon transport in compacted nanowire composites is investigated using the Monte Carlo simulation. Results show that the thermal conductivity of composites in the form of compacted silicon and germanium nanowire mixtures can be further reduced to around half of the previously studied composites with silicon nanowires embedded in a germanium matrix at the same atomic composition and characteristic size of the nanowires.

Synthesis and Optical Properties of Copolymers Containing Carbazole and 1,3,4-Oxadiazole Groups as Blue Host Matrix and Charge Transport Materials for Polymer Light Emitting Devices

Alternating copolymers with N-arylcarbazole as hole injection and transport moieties with blue emission and 1,3,4-oxadiazole as electron transporting and hole blocking moieties were synthesized by Pd-catalyzed polycondensation reaction, and named as poly[N-(4-aminophenyl)-carbazole-alt-N-(2-ethylhexyl)-3,6-carbazole] (P1), poly[N-(4-aminophenyl)-carbazole-alt-2,5-bis(4-phenyl)-1,3,4-oxadiazole] (P2) and poly[N-(4-aminophenyl)-carbazole-alt-2,5-bis(4-methylenephenyl)-1,3,4-oxadiazole] (P3). It was observed that UV-Vis absorption spectra showed two main peaks at 290 ∼ 295 and 310 ∼ 380 nm and maximum photoluminescence peaks of the polymers were all in the range of blue light emission from 418 to 453 nm. It appeared that optical and electrochemical properties of polymers such as HOMO, LUMO levels and band gap energy could be fine tuned by chemical modification of polymer structures.

Topotactic Intercalation of a Metallic Dense Host Matrix Chalcogenide with Large Electron−Phonon Coupling: Crystal Structures and Electronic Properties of LixMo2SbS2 (0 ≤ x < 0.7)

The functionality of the three-dimensional ternary chalcogenide Mo2SbS2 as a host is demonstrated by low-temperature reactions involving lithium-metal−liquid-ammonia reducing solutions. Rietveld analysis of neutron (T = 1.5 and 270 K) and synchrotron X-ray (T = 300 K) powder diffraction data proves that topotactic insertion of lithium in quasi-one-dimensional channels produces an isostructural family of LixMo2SbS2 (0 ≤ x < 0.7) compounds. The optimization of the electronic properties of such a dense host matrix material via intercalation is studied by band structure calculations using the density functional theory (DFT). Mulliken population analysis indicates that a major effect of the presence of Li in the Mo2SbS2 is the filling of the d-holes close to Fermi level and therefore only the p-orbitals give rise to mobile carriers in the LixMo2SbS2. Charge disproportionation at the two Mo nonequivalent crystallographic sites and the favorable electrostatic environment of the Li (which is partially depleted of its charge) point to polaron formation, consistent with partial localization upon Li-doping. The resistivity, ρ(T) (2 ≤ T ≤ 270 K), for all compositions studied is modeled by the Bloch−Gruneisen function. Phenomenologically, a percolation model describes the crossover of ρ(T) to a higher conductivity regime at a critical Li composition of xc ≈ 0.19. As reflected in the small overall modification to its electronic conductivity, the host efficiently accommodates the perturbations due to chemical and physical (P ≤ 17 kbar) pressure. The data analysis finds an enhanced electron−phonon coupling constant for Mo2SbS2 (λt ≈ 2.45) on the basis of the one-electron band-theory model.

Atomic structure of embedded Fe nanoclusters as a function of host matrix material: a synchrotron radiation study

The atomic structure of Fe nanoclusters embedded in a range of matrix materials has been studied using synchrotron radiation. In particular, the effect of embedding the clusters in Ag, amorphous carbon (a-C) and a porous C60 matrix is investigated. The embedded cluster samples were prepared by co-deposition using a gas aggregation cluster source. Samples with both dilute and high-volume-filling fraction of clusters, at 4 and 40% respectively, were prepared. Fe K edge EXAFS measurements were used to probe the structure within the clusters. In a Ag matrix, the Fe clusters retain the b.c.c. structure of bulk Fe while in a-C there is evidence for both b.c.c. and f.c.c. structures in the clusters. These results are independent of cluster volume-filling fraction over the range investigated. When embedded in a porous C60 matrix, the Fe clusters oxidize to Fe2O3.

Rotary atomizer

Fluorescent polymeric coatings can find interesting applications in the field of solar energy as thin-film luminescent solar concentrators (LSCs). At present, polymers such as polycarbonate (PC) or poly(methyl-methacrylate) (PMMA) are commonly used as dye-doped host matrix materials in LSCs. However, LSC devices based on these polymers still present limited lifetimes resulting from the intrinsic poor photostability of the polymeric carrier. In the attempt to achieve high-durability LSC devices, a series of new crosslinked fluoropolymeric systems is presented in this work as potential alternative host matrix coating materials for LSC applications. The chemical, physical and morphological modifications occurring to the crosslinked fluorinated coatings when subjected to long-term UV–vis light exposure (over 1000 h of accelerated weathering) are found to correlate well with the photovoltaic response over long-term operation of functioning LSC devices. In particular, better operational stability compared to reference PMMA-based devices can be obtained with the new crosslinked fluorinated coatings by appropriate selection of crosslinking agent. In addition, the effect of radical scavengers on LSC device operational stability is also investigated and it is found that in the long-term light exposure regime (>600 h) these additives may lead to improvements in LSC device lifetime. The results of this study allow a greater understanding of structure–property relationships in crosslinked fluorinated coatings subjected to long-term weathering and provide useful guidelines for the design of high durability fluorescent coatings for light management and photovoltaics.

Measured in-water acoustic performance of 1-3 piezocomposite materials.

A selection of different 1-3 piezocomposite materials has been fabricated and tested. Each of the 1-3 piezocomposite materials that will be presented was fabricated by the Material Systems Inc. of Littleton, MA. The materials selection includes variations in volume content of piezoceramic, types of piezoceramic, host matrix materials of varying compliances and air-voided microballoon content, as well as the use of types of cover plates on the radiating surfaces. The acoustic measurements were conducted at both the Lake Gem Mary lake facility and the Anechoic Test Facility 1 (ATF1) of the Underwater Sound Reference Detachment in Orlando, FL. The presentation will include comparisons of free-field voltage sensitivities (FFVS) and transmitting voltage response (TVR) as well as directivity patterns. The measurements from ATF1 will also show the effects of hydrostatic pressure and temperatures of 4 ° and 22 °C. The presentation will include a discussion of how specific 1-3 piezocomposite materials can be tailored to meet specific applications. [Work supported by Advanced Research Projects Agency and NSWC/Coastal Systems Station.]

Determination of platinum and rhodium in γ-alumina catalysts by glow discharge atomization atomic absorption spectrophotometry

The technique of glow discharge atomization atomic absorption spectrophotometry (GDA-AAS) is used to determine platinum and rhodium concentrations in automotive catalyst materials. The glow discharge atomizer allows these difficult-to-dissolve samples to be atomized directly from the solid state after the alumina-based catalyst is mixed intimately with a conductive host matrix material. A troublesome and time-consuming dissolution step is therefore unnecessary. Optimization of the major analytical parameters (discharge current, discharge pressure, and the percentage of catalyst to be mixed with host material) is presented, along with actual determinations of platinum and rhodium, via calibration curves. Internal standardization is employed to compensate for differences in sputtering efficiency from sample to sample. Relative sensitivity factors (RSF) are also used for quantitation. The technique is shown to provide accurate determinations with relative errors of 2–3% ( C x/ C known × 100%) with either quantitation scheme, providing a relatively rapid and inexpensive alternative to competing methods of analysis.

Applicability of a radiofrequency powered glow discharge for the direct solids analysis of non-conducting materials by atomic emission spectrometry

Radiofrequency (r.f.) powered glow discharge atomic emission spectrometry is demonstrated to be a potentially useful technique for the elemental analysis of electrically conductive and non-conductive solids. As opposed to the direct current glow discharge, the r.f. glow discharge enables the non-conductive sample to be atomised directly from the solid state without the need for prior mixing with a conductive host matrix material. Data are reported to illustrate the dependencies of emission intensity on gas pressure and discharge power, as well as the stability of the discharge. Representative atomic emission spectra of both an electrically conductive and non-conductive sample are presented to illustrate that the r.f. glow discharge provides good atomisation efficiency for both sample types.

Electroluminescence studies in silicon dioxide films containing tiny silicon islands

Electroluminescence from metal-insulator-semiconductor structures with silicon dioxide (SiO2) layers containing varying amounts of excess silicon (Si) in the form of tiny Si precipitates have been studied in detail. Bulk insulator emission from the Si islands is shown to dominate over emission from either the SiO2 matrix material or the metallic gate material by studies of oxide or metal gate material, voltage polarity, and insulator thickness dependencies. Several distinct spectral peaks are observed in the energy range from 1.5 to 5 eV which cannot be attributed to optical interference effects. The higher-energy peaks show a strong dependence on electric field relative to that at the lowest energy (1.7–2 eV). The entire spectral amplitude shows a strong dependence on high-temperature annealing and excess Si content, decreasing drastically with increasing Si or decreasing annealing temperature. These results are shown to be consistent with light emission during electronic transitions between discrete energy levels associated with Si islands and/or their interface with the SiO2 host matrix material. Quantum size effects, similar to those observed in semiconductor superlattices, are proposed as one possible explanation.