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Epoxy-based copolymers were synthesized with N,N-diglycidyl aniline (DGA) and aniline (An), called poly(DGA-co-An), where azo coupling reactions were performed using amino benzonitrile (ABN) and nitro aniline (NA). Two azopolymers were dissolved with both tetrahydrofuran (THF)/dioxane complex solvent and THF to compare the diffraction efficiencies according to solvent. The thin films spin-cast with THF/dioxane showed the better diffractive efficiency than with THF due to the high boil point of the residual dioxane. The azopolymers of two azo bonds were spin-coated at 800 and 1300 rpm where the thicker film showed the better diffractive efficiency. The epoxy-based copolymers synthesized with diglycidyl ether of bisphenol A (DGEBA) and aniline (An) or 3-hydroxyl aniline (HAn) were coupled with hydroxyl nitro amino benzene (HNAB). Hydroxyl groups in chromophores helped to form hydrogen bonding with the nitrogen atoms in the azo bonds and prevented photoisomerization, showing no surface relief gratings under a normal laser intensity of 100 mW/cm2. Polyurethane-based azopolymers were synthesized with disperse orange 17 (DO17) and toluene-2,4-diisocyanate (TDI), which were no hydroxide groups in the main chains, and showed the better diffractive efficiency than the epoxy-based azopolymers with nitro substituents.
Piezopolymer PVDF and P(VDF-TrFE) based diaphragms were fabricated. The diaphragm can be used as a high performance sensor platform for employing in liquid. The microelectronic process for fabricating microdiaphragm and its array is established. The performance of the PVDF based diaphragm in air and liquid was tested. It is found that the diaphragm works well in liquid.
Owing to their low acoustic impedance, high elastic energy density, and relatively high electromechanical conversion efficiency, the electroactive polymers have begun to show the potential for energy harvesting or mechanical to electrical energy conversion. In addition, due to the electromechanical coupling in these materials the electric and mechanical properties of these polymers will depend on the imposed electrical and mechanical conditions. This paper discusses how to utilizing this unique property to maximum the energy conversion efficiency and the harvested electrical energy density in the electrostrictive polymers. As an example, we demonstrate that when a properly phased and externally applied electric AC field is superimposed on the mechanical cycle, an output electrical energy density of 39mJ/cm3 and mechanical-to-electrical conversion efficiency of about 10% can be obtained from the electrostrictive P(VDF-TrFE) based polymers.
Electrospinning is a simple method of obtaining polymer fibers with nanometer diameter. The increase in the ratio of surface area to volume in the case of such fibers, make them attractive in applications such as sensors, etc. It is difficult to electrospin Polypyrrole (PPy) directly to form fibers. Hence electrospinning is attempted with a composite formed with PPy and any other insulating polymer such as Polyethylene oxide (PEO), Polystyrene (PS), etc. The concentration of PPy can be varied to improve the electrical or sensing properties of the resulting composite. In the present report, the PEO-PPy composite fibers with different weight percentages (10% to 50% w/w) are prepared by electrospinning process. The fibers obtained are characterized using SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscopy). I-V Characteristics are studied for single and multiple aligned fibers obtained on gold electrodes. The variation of electrical conductivity with different concentration of PPy is discussed.
Complex impedance and conductivity were measured for regioregular poly(3-hexylthiophene) (P3HT) at alternating current (AC) voltages using a waveform technique. The waveforms were Fourier transformed from time domain to frequency domain and analyzed at fundamental and higher order harmonic frequencies. It was found that the impedance of the semi-conducting P3HT decreases with increasing electric field strength. The non-linear charge transport is dominated by a third harmonic response that originates from extended polarizability of π-type electronic states. The third order non-linear conductivity can be used to quantify the effect of an electric field on the conduction mechanism and to correlate the intrinsic charge carriers mobility with molecular structure.
In this paper, the influence of interface between electrode and polymer or polymer and polymer on space charge dynamics has been studied. Planar samples of low density polyethylene (LDPE) were subjected to high dc electric stresses for extended periods of time and space charge measurements were taken using the pulsed electroacoustic (PEA) technique. Common electrode materials used in either laboratory or power cable industry were selected (i.e. aluminium (Al), gold (Au) and carbon loaded XLPE (Sc)). Experimental results demonstrated that charge injection processes take place in all cases once the applied electric stress has exceeded a threshold value. However, the amount of charge and polarity of the dominant injected charges showed significant dependence on the electrode materials (under the same applied electric stress). Having establishing the influence of electrode materials on charge accumulation, our attention was then focused on the effect of polymer/polymer interface on charge dynamics. Unlike our previous approach where two different polymeric materials were used, this time the polymer/polymer interface was formed by using two layer of LDPE films cut from the same sheet. Sc and Al were used as electrodes to form different combinations. The results clearly indicated that the interface between two layers of LDPE acts as traps for electrons but not for positive charge carriers. The charge distribution in the bulk of the sample strongly depends on the electrode materials.
Since the first reports of charge storage in the gate dielectrics of organic semiconductors, several groups have proposed charge-storing dielectrics that become polarized through varied mechanisms, and have offered various explanations for observed charge storage phenomena. These groups were concerned either with nonvolatile memories as an application, or with controlling hysteresis in conventional OFETs. This manuscript describes measurements of surface charging and OFET threshold voltage shift for a case where charge is clearly stored in the dielectric. The magnitude and stability of the charge storage depend on the hydrophobicity of the dielectric and the charge deposition process. We focus on SiO2 as the dielectric and use a thiophene oligomer or hexadecafluoro-copper phthalocyanineas semiconductor. In one case, the phthalocyanine was inverted from electron- to hole-carrying, enabling a complementary device to be made from a single semiconductor.
An advanced leakage current model combining the electronic carrier injection /ejection at the electrode interfaces (described by thermionic emission) with the film conduction properties of a thin dielectric film (modelled as wide band gap semiconductor) is used to describe the current-voltage (I-V) curve of a flash-like resistive switch memory cell. Such a cell consists of a metal-insulator-metal capacitor structure with some embedded charge storage elements within the dielectric, e.g. a floating electrode (like in the gate of a “Flash”) or some metallic ions or clusters, which can be charged or discharged by an applied voltage or current. The resulting different conductance levels can be used for a resistive switching memory cell. This contribution presents calculated simulation results on I-V curves in dependence on polarity and concentration of the stored charge as well as on other parameters such as dielectric constant, background homogeneous defect densities in the dielectric and electrode properties. These parameters show a large influence on the switching ratio S = R(high) / R(low), an important parameter for the application in a device.
Present study aims to develop a clear insight on factors that influence space charge dynamics in solid dielectrics through a numerical simulation. The model used for the simulation is proposed by Alison and Hill  which describes charge dynamics as a result of bipolar transport with single level trapping. In this model, a constant mobility and no detrapping have been assumed. The simulation results show that carrier mobility, trapping coefficient and Schottky barrier have a significant effect on the space charge dynamics. Many features of space charge profiles observed by experiments have been revealed in despite of over simplistic model. More importantly, the simulation allows us to study the role of each individual parameter in the formation of space charge in solid dielectrics, so that the experimental results can be better understood.
Experiments have shown that a thin polymer film subjected to an electrostatic field may lose stability at the polymer-air interface, leading to uniform self-organized pillars emerging out of the film surface. This paper presents a three dimensional dynamic model that accounts for the behavior. Attention is focused on the interplay of the thermodynamic forces and the kinetic processes. The coupled diffusion, viscous flow, and dielectric effect are incorporated into a phase field framework. The semi-implicit Fourier spectral method and the preconditioned biconjugate-gradient method are applied in the simulations for high efficiency and numerical stability. Numerical simulations reveal rich dynamics of the pattern formation process.
By incorporating dielectrics with stored electric fields and organic semiconductors, new organic electronic components such as circuits with controlling voltages “restored” for transistor tuning can be developed. We have successfully used excellent electret materials including charged and surface-treated silicon dioxide (SiO2) and silsesquioxane (SSQ) polymers as the dielectric layer in organic field-effect transistors (OFETs). Charge injection and quasipermanent charge storage induce threshold voltage shifts and current modulation, which results from the built-in electric fields in the conduction channels. Static and dynamic characteristics of organic thin-film transistors (OTFTs) such as charging conditions and voltage/current retention were evaluated. In addition, self-assembled monolayers (SAMs) of dipolar molecules have been utilized in the dielectric layer, with different mechanisms but similar effects compared to charged dielectrics. We also present new OFET unipolar inverters, comprised of only two simple OTFTs with enhancement-mode driver and depletion-mode load to implement full-swing organic logic circuits for process simplification of electronic components in organic electronics.
To date, many processes have been used for the preparation of ionic polymer-metal composite (IPMC) artificial muscle membranes from conductive metals and perfluorosulfonic polymers such as Nafion. The most widely used of these methods is the platinum plating process, which involves chemical reduction of ionic salt solutions. Although these chemical electroding techniques produce IPMCs with outstanding surface electrodes and excellent performance characteristics, they are relatively costly and time-consuming. In this paper, we describe a novel fabrication process for fast preparation of low-cost Ni-Au-Nafion IPMCs. The process involves the formation of an adherent surface layer on prepared Nafion through DC sputter deposition of a fine-grained gold film, followed by electroplating of a thin and ductile nickel layer in a solution of aqueous nickel salts and boric acid. Preliminary results indicate that the Nafion-117-based IPMCs produced using this technique exhibit good surface conductivity and promising actuation performance, with 20 mg, 11.5 mm × 4.7 mm cantilever bending samples showing high displacements and tip forces up to 4 grams at 4 V. Our current research efforts are focused on achieving repeatable synthesis techniques and evaluating the properties and performance characteristics of the Au-Ni-Nafion IPMCs, especially in comparison to the popular platinum IPMCs.
Ionomeric polymer transducers consist of an ion-exchange membrane plated with conductive metal layers on the outer surfaces. Such materials are known to generate large bending strain (> 9% is possible) at low applied voltages (typically less than 5 V). The main disadvantage of ionomer–ionic liquid transducers is the slow speed of response. The speed of response in such actuators has been correlated to the ionic liquid content and the conductivity of the membrane. To increase the conductivity of the transducers a Nafion™ mat is hydrated with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) ionic liquids and high surface area RuO2 electrodes are attached using the Direct Assembly Process (DAP). The Nafion™ mat is prepared from homogenous solution electrospinning. The solution is prepared by mixing 1 wt % of polyethylene oxide solution in methanol (PEO, Mol. wt 3×106) to 5 wt % Nafion 1100 solution.. The syringe needle is connected to a 15kV power supply and is placed 15cm away from the collecting drum. The measured conductivities of water hydrated Nafion electro-spun fibers are 16.8 mS/cm, which are lower than the nominal 110 mS/cm that of H+ Nafion membranes. The uptake is measured to be around 250 %wt compared to 58 %wt obtained in Nafion films. The ionic conductivity of 110 %wt swollen ionic liquids-Nafion mat composite is computed to be 0.9 mS/cm compared to 0.3 mS/cm in ionic liquid-Nafion membrane composite. The speed of response in actuators with an ionic liquid- Nafion™ mat is 1.34 %/s compared to 0.88 %/s for that in ionic liquid Nafion™ film transducers.
Elongation and contraction of polypyrrole and poly(3-methoxyaniline-5-sulfonate) (PMAS) composite films induced upon electrochemical oxidation and reduction, viz., electrochemomechanical deformation (ECMD) are studied. The composite films were electrochemically prepared in electrolyte solutions of pyrrole and dodecylbenzene sulfonic (DBS) acid with a presence of PMAS acid. The contents of DBS and PMAS were varied. Films which were obtained at higher contents of PMAS, were gel like due to a lot of water content. The change of film length due to ECMD was measured as functions of various electrolytes in either aqueous or organic solvents. The results indicated that films exhibited both cathodic and anodic expansions depending on the bulkiness of cations and anions as well as the content of PMAS.
We consider a theoretical model of a reactive polymer gel in which the reaction can proceed in an oscillatory regime and generate traveling chemical waves accompanied by waves of local swelling-deswelling. This type of gel could be used for fabricating chemo-mechanical devices with self-sustained rhythmic action, and gel-based pumps. We assume that the Belousov-Zhabotinsky (BZ) reaction takes place in the reactive gel. The BZ reaction generates periodic reduction-oxidation (redox) changes of a metal catalyst covalently bonded to a hydrogel that is immersed in a solution containing the rest of the BZ reagents. The redox changes in the metal affect the polymer-solvent interactions, resulting in variations in the gel volume. The self-oscillation of the gel volume, and the traveling waves of local swelling in a hydrogel with the BZ reaction have been experimentally observed by Yoshida and co-workers. To describe the system theoretically, we employ the Oregonator model of the BZ reaction, and the two-fluid model of gel dynamics. Propagation of one-dimensional wave trains through the reactive gel is simulated. The structure of the traveling swelling-deswelling waves is studied.
The Stethoscope (acoustic sensor) is a fundamental tool for the diagnosis of diseases and conditions of the cardiovascular (CV) system. It serves as the most commonly employed technique for diagnosis of such diseases and conditions in primary health care and in circumstances where sophisticated medical equipment is not available, such as remote areas. The piezoelectric sensor was used as an acoustic sensor. The sensitivity of the sensor was improved more than 20 times with our new design. The signal-to-noise ratio was further improved by using unique sensor housing and by using an electronic amplifier in the differential mode.
Poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymers are well known for their excellent ferroelectric and other related properties and they are being exploited as active components in many microdevices such as ferroelectric memory cells and infrared sensors. Compared with conventional photolithography, ink-jet printing provides a low-cost versatile method to fabricate polymer micro-devices. In this paper, the influences of driving waveform at the jet head, ink concentration, substrate chemistry, and the solvent quality on the printed P(VDF-TrFE) dots were investigated. It was found that well-defined P(VDF-TrFE) micro-dots with diameter of less than 30 mm and thickness of ∼1 μm can be printed by using a mixed solvent system, consisting of a good solvent with relatively low boiling temperature and a poor solvent with high boiling temperature, on perfluorinated hydrophobic gold surface. The printed P(VDF-TrFE) micro-dots possess crystallinity comparable to that of the bulk sample, suggesting that ink-jet printing technology is a promising micro-fabrication technology for manufacturing P(VDF-TrFE)-based micro-sensors and other micro-devices.
The synthesis of a polystyrene-b-polyvinylmethylsiloxane-b-polystyrene diblock and triblock copolymer functionalized with liquid crystals exhibiting a smectic C* phase on the PVMS central block is described. The synthetic route is based on the anionic polymerization of styrene and trimethyltrivinylsiloxane monomers and the functionalization of resulting triblock copolymers. The resulting polymer can self assemble into a thermoplastic elastomer where the high Tg styrene blocks serve as physical crosslinks for a low Tg siloxane block. The presence of a smectic liquid crystalline phase and the block copolymer mesophase are observed across various temperature ranges depending on the length of the spacer connecting the liquid crystalline moiety to the polymer backbone. The influence of mechanical deformation upon the morphologies of the liquid crystalline and block copolymer mesophases was investigated. The interactions between the smectic LC and the block copolymer morphologies and their influence upon their respective orientations in response to shear fields are detailed. The parallel-transverse orientation of the hexagonally close packed (HCP) cylinders of the block copolymer morphology and the smectic liquid crystalline phase, respectively, was observed for melt fiber drawn samples. However, the transverse-perpendicular orientation was observed for liquid crystalline block copolymers that experienced oscillatory shear. The transverse orientation of HCP cylinders was observed while shearing took place above the smectic to isotropic transition temperature, indicating that the presence of an isotropic liquid crystalline phase alters the orientation of the block copolymer morphology. Additionally, it was found that the spacer length was a key factor in the clearing points for the smectic liquid crystalline phase, as well as significantly influencing the nanophase segregation of the block copolymer.
Ionomeric polymer actuators based on Nafion membranes exhibit large bending motion (1%) under the application of small voltages (1-5 V). Actuation in these materials is believed to arise from the field-induced motion of mobile charges when a voltage is applied. In order for this charge motion to occur, the material must be swollen with a diluent, typically water. However, dehydration of the water limits the lifetime of these actuators in non-aqueous environments. Recently, highly stable ionic liquids have been demonstrated as viable diluents for these actuators. In the current paper, the physics of transduction in these ionic liquid-swollen Nafion membranes are investigated. Small-angle X-ray scattering reveals that the structure and properties of the ionic liquid have a strong influence on the morphology of the composites. Infrared spectroscopy is used to probe the ion associations within the films and shows that the ionic liquids are able to effectively mobilize the counterions of the Nafion membrane. Nuclear magnetic resonance spectroscopy is also used to investigate the composites and reveals that the mobility of the counterions increases as the content of ionic liquid within the membrane is increased. The results of these characterizations are compared to an experimental investigation of transduction in Nafion / ionic liquid composites to form an interpretation of the mechanisms of actuation. This comparison reveals that the counterions of the Nafion membrane are the primary charge carriers and that it is the motion of these mobile charges that gives rise to the actuation behavior of the films.
A thin film of emeraldine base polyaniline in NMP was cast on an interdigitated electrode and its conductivity investigated by impedance spectroscopy. The thin film responded to carbonic acid solutions of various pHs lower than 5. In general, an emeraldine base (EB) to emeraldine salt (ES) transformation occurs by protonation when the pH is less than 4. In the present case, the stages that occur prior to the onset of changes in total conductivity are detected by impedance spectroscopy. The sensor output was stable and reversible over a period of 3 months of testing.