Polymer Composite Layer Research Articles

Arrays of hollow out-of-plane microneedles made by metal electrodeposition onto solvent cast conductive polymer structures

Transdermal drug delivery using microneedles is a technique to potentially replace hypodermic needles for injection of many vaccines and drugs. Fabrication of hollow metallic microneedles so far has been associated with time-consuming steps that restrict batch production of these devices. Here, we are presenting a novel method for making metallic microneedles with any desired height, spacing, and lumen size. In our process, we use solvent casting to coat a mold, which contains an array of pillars, with a conductive polymer composite layer. The conductive layer is then used as a seed layer in a metal electrodeposition process. To characterize the process, the conductivity of the polymer composite with respect to different filler concentrations was investigated. In addition, plasma etching of the polymer was characterized. The electroplating process was also studied further to control the thickness of the microneedle array plate. The strength of the microneedle devices was evaluated through a series of compression tests, while their performance for transdermal drug delivery was tested by injection of 2.28 µm fluorescent microspheres into animal skin. The fabricated metallic microneedles seem appropriate for subcutaneous delivery of drugs and microspheres.

Heat generation in 1–3 piezoceramic—polymer composites

This paper describes the mechanism of heat generation in lossy 1–3 piezoceramic- polymer composite active layer of ultrasonic transducers excited at different voltages at resonance and off-resonance frequencies. The physical parameters controlling the heat generation and dissipation are estimated by least squares fitting the experimentally measured time-temperature profiles to a theoretical model. The theoretical profiles agree well with the measured data. The temperature rise at resonance frequency (250 kHz) and at an off-resonance frequency (30 kHz) is found to be 54 °C at 13.2 Vp-p and 38 °C at 169 Vp-p, respectively. The temperature rise, the total loss and the radiation heat transfer coefficient are found to vary quadratically with driving electric field. The convection heat transfer coefficient is estimated to be in the range (6–10) Wm−2 K−1, validating the free convection in air. Variations in the physical parameters with applied voltage are found to be different at resonance and off-resonance frequencies, indicating that the process of heat generation in piezocomposite transducers depends on the frequency region in which they are operated, with respect to the resonance frequencies.

Effects of Annealing Conditions on ZnO Buffer Layer for Inverted Polymer Solar Cells

A solution-processed zinc oxide (ZnO) thin film as the buffer layer with optimized processes especially the annealing conditions for inverted polymer solar cells (PSCs) has been demonstrated. Firstly the thickness of ZnO buffer layer was optimized, and different annealing conditions including temperature and time have also been taken into consideration. And the best Power Conversion Efficiency (PCE) 3.434% was observed when the ZnO buffer layer was spin–coated at 1500 rpm and annealed at 275℃ for 5 min, and AFM results showed that morphology of this ZnO film has the best uniformity which was beneficial to form high quality polymer composite active layer.

A novel carbon–PEDOT composite counter electrode for monolithic dye-sensitized solar cells

The development of a new counter electrode structure for monolithic dye-sensitized solar cells (DSCs) is reported. A conducting polymer, PEDOT, is selectively electrodeposited throughout the carbon layer of the counter electrode, as confirmed by SEM. The formation of this composite allows reduced electrical resistivity, thus improving the fill factor and efficiency of devices. The improved mechanical stability of the carbon/conducting polymer composite layers makes these more suitable for use with flexible substrates, which is advantageous for the development of monolithic DSCs on plastic substrates that can be produced using roll-to-roll processes.

Organic Field-Effect Transistor-Based Nonvolatile Memory Devices Having Controlled Metallic Nanoparticle/Polymer Composite Layers

Nonvolatile memory devices based on the pentacene film and controlled gold nanoparticle (Au np )/polymer composite layers were developed. Organic field-effect transistor-based nonvolatile memory devices having self-assembled Au np exhibited controllable and reliable current level differences (on- and off-states) according to the applied gate voltages (programming/erasing operations). The memory devices showed large memory windows as well as good data retention properties by adopting charge storage layers of controlled Au np separated by insulating polymer layers. The process for fabricating nonvolatile memory devices was based on the solution processes and organic semiconductor layers, so it has a potential use in flexible nonvolatile memory applications.

Efficiency Enhancement and Color Stabilization in Organic Light-Emitting Devices Utilizing a Fullerene–Polymer Composite Layer Acting as a Hole Transport Layer

The electrical and optical properties of organic light-emitting devices (OLEDs) utilizing a nanopolymer composite layer consisting of fullerene (C60) and poly(2-methoxy-5-[2'-ethylhexyloxy]-p-phenylenevinylene) (MEH-PPV) were investigated. The current density of devices with a C60/MEH-PPV composite hole transport layer (HTL) was larger than that of devices without a composite HTL owing to the enhancement in the hole injection and transport. The luminance efficiency of the OLEDs utilizing a C60/MEH-PPV composite layer was significantly enhanced owing to an increase in the conductivity of the C60/MEH-PPV composite HTL. The recombination region in the center of the emitting layer for the device with a C60/MEH-PPV composite layer decreased the variation of color coordinates and enhanced the color stability, resulting in the realization of the highly efficient device.

Fluoropolymer composites of triboengineering purposes

The effect of polymer filler F-4MB on the properties of a composite based on polytetrafluoroethylene (PTFE) and magnesium nanospinel has been studied. The filler was found to exert a plasticizing effect on the polymer system. This promotes the formation of mobile interfacial layers, intensifies interfacial interaction between the composite components, and initiates a strong effect of nanospinel on strength and triboengineering characteristics of the composite. To provide adaptation of the polymer composite surface layer to frictional conditions, a plasticizing additive F-4MB is introduced during friction.

Stress analyses of a smart composite pipe joint integrated with piezoelectric composite layers under torsion loading

In order to improve the joint failure strength, an adhesively bonded smart composite pipe joint system has been developed by integrating electromechanical coupling piezoelectric layers with the connection coupler. It has been validated that the integrated piezoelectric ceramic layers can smartly reduce stress concentration in the adhesive layer bond-line under bending or axial tension loads. In this study, piezoelectric particle/fiber reinforced polymer composite was utilized to construct adhesively bonded smart composite pipe joint systems, in order to overcome the brittle characteristic of the piezoelectric ceramic layers and to facilitate joint construction. Since torsion is one of the dominating loading conditions in practice, the behavior of the newly developed smart pipe joint system subjected to torsion loading was investigated in-detail to evaluate the effect of the integrated piezoelectric reinforced polymer composite layer on the joint performance. Firstly, based on the first-order shear deformation theory, the fundamental equations with relevant boundary and continuity conditions were developed to theoretically model the smart pipe joint system subjected to torsion loading. Further, the analytical solutions for the mid-plane displacements and the shear and peel stresses in the adhesive layer were obtained by using the Levy solution and the state-space method. Finally, some numerical examples were presented to evaluate the detailed effect of the stacking sequence and thickness of the integrated composite piezoelectric layers in the connection coupler on reducing the stress concentration in the adhesive layer; the effect of the applied electric fields on shear and peel stresses in the adhesive layer was also illustrated.

Tribology of a novel UHMWPE/PFPE dual-film coated onto Si surface

A novel wear resistant polymer composite layer is coated onto the Si surface. The first layer consists of ultra-high molecular weight polyethylene (UHMWPE) film and the second top layer is made of perfluoropolyether (PFPE). These two layers are coated onto Si using a simple dip-coating technique. This particular combination of dual-film has reduced the coefficient of friction by at least 6 times and increased the wear resistance of the Si surface by at least 1000 times with very minimum to no sign of wear debris formation. The tribological tests are carried out using ball-on-disk tribometer employing 4 mm diameter Si 3N 4 ball as the counterface at a nominal contact pressure of ∼370 MPa. The UHMWPE/PFPE dual-film provides hydrophobic surface with very high water contact angle (134°). Finally, this dual-film may find applications in reducing wear and stiction of micro-components (such as micro-electro-mechanical systems) made from Si.

Hydrogen evolution on nickel incorporated in three-dimensional conducting polymer layers

The paper discusses results on the development of nickel/conducting polymer composite layers used as catalysts in the hydrogen evolution reaction (HER). Conducting polymers (CP), polypyrrole (PPY), and polyaniline (PANI) are used as three-dimensional pattering templates (matrices) for electrodeposition of nickel on an inert glassy carbon surface. It is shown that Ni/CP layers offer a significantly higher overall electrocatalytic activity in the HER than Ni electrodeposited on a flat two-dimensional substrate. This is a result of favorable Ni/CP morphology which yields an increase in the active surface area of the catalyst. The overall best catalyst is a Ni/PANI layer formed by incorporation of small amounts of Ni into a thick pre-deposited PANI layer. The resulting porous layer is composed of ca. 3 μm interconnected spherical Ni particles, with an almost complete surface absence of PANI. The increased porosity of the layer is of a great benefit at high HER overpotentials, where accumulation of produced molecular hydrogen inside the catalyst layer is prevented. Due to a lower porosity, all the Ni/PPY catalytic layers studied are susceptible to the surface blockage (hydrogen accumulation) at high overpotentials. However, in the lower overpotential region, a Ni/PPY catalyst formed by incorporating a larger amount of Ni into a thin porous pre-deposited PPY layer offers an electrocatalytic HER activity comparable to the best Ni/PANI catalyst. When PPY and Ni are electrodeposited simultaneously (co-deposition method), a substantial decrease in a diameter of Ni islands, down to 100 nm, and an increase in the island surface density are obtained.

Optical properties of metal nanoparticles synthesized in a polymer by ion implantation: A review

Polymer composite layers irradiated by 30-keV Ag+ ions with doses from 3.1×1015 to 7.5×1016 cm−2 and an ion current of 4 µA/cm2 are investigated. The composites were examined using Rutherford backscattering (RBS), transmission electron microscopy (TEM), and optical spectroscopy. As follows from electron microscopy and electron microdiffraction data, ion implantation is a promising tool for synthesizing silver nanoparticles in the surface region. The optical density spectra taken of these composites demonstrate that the silver nanoparticles exhibit unusually weak plasma resonance. The formation of silver nanoparticles in layers carbonized by ion implantation is considered. Based on the Mie theory, optical extinction spectra for silver particles in the polymer and carbon matrices are simulated and optical spectra for complex silver core-carbon sheath nanoparticles are calculated. The physics behind the experimental optical spectra of the composite is discussed.

A one-dimensional stress wave analysis of a lightweight composite armour

Existing work in the literature has addressed the synthesis and analysis of lightweight composite armour, consisting of ceramic, polymer composite and metal foam layers. The aim of this paper is to apply classical one-dimensional stress wave theory to the analysis of the behaviour of the armour, due to an impact from a fragment simulating projectile. Good agreement between the results from the literature and the stress wave model, discussed here, is achieved, and the developed model is then used to gain insight into the effect of the variation of various parameters, e.g. layer material, layer thickness and impact velocity.

Flexible ceramic-polymer composite films with temperature-insensitive and tunable dielectric permittivity

BaTiO3–polymer composite layers have been produced by the spin-on technique (thickness 3–10 μm). The dielectric permittivity of the layers at room temperature can be tuned from 2.8 to approximately 33 by varying the ceramic filling from 0 to 60% by volume. The dielectric properties of the films are almost insensitive to temperature variations in the range 20–180 °C. Free-standing composite layers with ceramic content ≤50% are flexible without noticeable change of permittivity after repeated mechanical bending.

On the fracture mechanical behaviour of fibre reinforced metal laminates (FRMLs)

Fibre reinforced metal laminates (FRMLs) are hybrid composite materials consisting of thin metal sheets adhesively bonded together with fibre reinforced polymer composite layers. This combination results in composite laminates having some unusual fracture mechanical characteristics, which are described and analysed in this paper. Experimental results are obtained for a carbon fibre reinforced aluminium laminate (CARE) on the in-plane mechanical properties, notched and post-impact residual strengths, and the effects of fibre–matrix interfacial bond strength and adhesion between metal and fibre composite layers. Microscopy, C-scan, and chemical removal techniques are used to reveal the inter-layer delamination mechanism and the failure behaviour of CARE. A new analytical model for notched residual strength was developed based on a global equilibrium approach. The residual strengths predicted by this model agree well with experimental data of several FRMLs (e.g., CARE and ARALL) containing either a central crack or a circular hole. The effects of metal layer stiffness, fibre types, and fracture toughness of fibre composite layer on notched residual strength are also investigated. Finally, limitations of the proposed crack growth model are discussed and areas of future research presented.

Tensile fracture of fibre reinforced metal laminates containing a circular hole

Fibre reinforced metal laminates (FRMLs) are a new family of aerospace structural materials developed for fatigue critical applications. These materials are laminated sheets of thin and high strength metal layers, usually aluminium, and alternating plies of fibre reinforced polymer composite layers, viz, aramid/epoxy, carbon/epoxy, glass /epoxy, etc. Afaghi-Khatabi and Ye have considered the fracture data existing on various ARALL (aramid reinforced aluminium) laminates containing a circular hole for evaluation of notched tensile strength, using the effective crack growth model (ECGM), point stress criterion (PSC) of Whitney and Nuismer and damage zone criterion (DZC) of Eriksson and Aronsson. It is noted that ECGM overestimates, whereas PSC and DZC underestimate the notched tensile strength of FRMLs. This note highlights briefly the two different criteria of Whitney and Nuismer known as ‘point stress criterion (PSC)’ and ‘average stress criterion (ASC)’, and suggests a modification in the criteria for accurate evaluation of the notched tensile strength.

Morphological Observations of lead ore (Galena) Grafted Between Polymer Composite Layers and Formulated of Styrenated Methacrylate Vinyl Ester System

Abstract Composites based on styrenated methacrylate vinyl ester, quartz, and fused alumina were prepared in a lab model Sigma blender and polymerized at room temperature by catalysis. Lead ore galena was grafted in between as two layers, wetted with the monomer, and compression molded. After complete curing the specimen was cut with a slow-speed diamond cutter and observed at the interfaces for morphology. SEM studies revealed excellent compatibility and some compounding at the interphases.