Charge Of Poly Research Articles

Achievement of high surface charge in poly(vinylidene fluoride) fiber yarns through dipole orientation during fabrication

AbstractElectrospun fiber materials are of scientific interest for use in multiple application areas. Charged fiber structures show enhanced properties as desired for some of these applications. One factor influencing the charge on the fiber structure that has not been explored is fiber alignment. Electrospun fiber structures, such as membranes, typically consist of randomly oriented fibers. Structural properties of the membranes such as mechanical strength are known to be affected by the random orientation of the fibers. It is suspected that fiber orientation may also affect the charge capacity of charged fiber structures. A few approaches to form electrospun yarns have been reported. Some of these approaches can also cause fibers to preferentially align along the yarn axis instead of assembling into a random structure. In this work, a rotating metal cone was used to collect Poly(vinylidene fluoride) electrospun fibers from which stretched yarns were drawn and twisted into yarns. The alignment of the fibers in the yarns was controllable to a degree that allowed exploration of the effect of alignment on charge. Long continuous oriented or random yarns of relatively uniform thickness were produced at a rate of about 10 m/h. The yarns were polarized by methods of heating, stretching, and poling. The results show that the fiber yarn formation process endows more charges to the fibers compared to the normal fiber membrane electrospinning and post polarization. This provides a facile route for the preparation of enhanced charge‐functionalized fiber structures for a wide range of applications.

Recombination of Free Carriers and Space Charges in Poly(3-hexylthiophene), as Revealed by Electrically and Capacitively Detected Magnetic Resonances

Using electrically and capacitively detected magnetic resonance (EDMR and CDMR) techniques, we clarified recombination in regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) films, which is an impo...

The Impact of Carrier Delocalization and Interfacial Electric Field Fluctuations on Organic Photovoltaics

Organic photovoltaic (OPV) devices hold a great deal of promise for the emerging solar market. However, to unlock this promise, it is necessary to understand how OPV devices generate free charges. Here, we analyze the energetics and charge delocalization of the interfacial charges in poly(p-phenylenevinylene) (PPV)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and poly(3-hexylthiophene-2,5-diyl) (P3HT)/PCBM devices. We find that, in the PPV system, the interface does not produce molecular disorder, but an interfacial electric field is formed upon the inclusion of environmental polarization that promotes charge separation. In contrast, the P3HT system shows a significant driving force for charge separation due to interfacial disorder confining the hole. However, this feature is overpowered by the polarization of the electronic environment, which generates a field that inhibits charge separation. In the two systems studied herein, electrostatic effects dominate charge separation, overpowering interfacia...

Generation of photo charge in poly(ethyleneimine)-TiO2-anthocyanin modified papers conditioned at different humidities

The article describes the influence of humidity on the surface photodielectric properties of papers prepared from poly(ethyleneimine)-TiO2 nanoparticles-anthocyanin modified cellulose fibres. The anthocyanins were extracted from purple cabbage, beet-root, plum peel, red wine and red currant juice. The samples were conditioned to various relative humidities (from 9 to 100%) and illuminated with white visible light, λ ≥ 405 nm. The poly(ethyleneimine)-TiO2-anthocyanin modified samples showed similar photodielectric behaviour that can be clearly distinguished from the samples modified solely with poly(ethyleneimine)-TiO2. Generally, an increase in humidity enhances the conductivity of the samples and induces an increase in the amount of photo-induced charge. Also, at higher humidities (above 80%), the samples with anthocyanin showed significantly higher values of photo-induced charges with respect to anthocyanin free samples. The presented results suggest that the presence of water molecules promotes electron-injection processes from the anthocyanin to the semiconductor surface.

Electropolymerization of Ni(salen) on carbon nanotube carrier as a capacitive material by pulse potentiostatic method

The composites of poly[Ni(salen)] and multi-walled carbon nanotube (MWCNT) were synthesized by pulse potentiostatic method. The composites were characterized by field emission scanning electron microscopy, Fourier transform infrared spectra, and electrochemical impedance spectroscopy. The wrapping of carbon nanotubes with poly[Ni(salen)] varied significantly with anodic pulse duration. Variance of structure of poly[Ni(salen)] caused by anodic pulse duration affected the ability of absorption to solvent molecules or solvated ions, which was indicated by ν (C≡N) intensity. The ability to store/release charge of poly[Ni(salen)] caused by redox switching was evaluated in the form of low-frequency capacitance. Correlations of charge-transfer resistance/ionic diffusion resistance with potential and anodic pulse duration were investigated.

Origin of equilibrium charges in poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester solar cell devices

We have clarified the origin of equilibrium charges in poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester devices by using charge extraction by a linearly increasing voltage. By varying the work function of the contacts we find that the equilibrium charges are injected from the contacts due to energy level alignment caused by Fermi-level pinning.

Two-dimensional correlation in cyclic voltammetry and electrochemical quartz crystal microbalance: A complementary tool to conventional techniques

Two new chemometric electrochemical techniques based on generalized two-dimensional correlation are tested and validated. Two-dimensional cyclic voltammetry (2DCV) involves synchronous and asynchronous correlations between two identical sets of cyclic voltammograms; while correlation electrochemical quartz crystal microbalance (CEQCM) is a hybrid correlation between a set of charge vs. potential curves and a set of mass variation vs. potential curves. A model system with two Fe(III)/Fe(II) pairs is set up to evaluate the reliability and advantages of these two techniques. 2DCV analysis indicates that the charging of poly(vinyl ferrocene)/solution interface (non-faradic process) has a negative influence on the heterogeneous electron transfer (faradic process). CEQCM analysis clearly identifies which Fe(III)/Fe(II) pair is responsible for the mass variation of the poly(vinyl ferrocene) network. This is the first attempt that a two-dimensional correlation has been applied to electrochemical methods. We expect more electrochemical techniques will be expanded into two-dimensional analyses.

Comparison of Various Models to Describe the Charge−pH Dependence of Poly(acrylic acid)

The charge of poly(acrylic acid) (PAA) in dilute aqueous solutions depends on pH and ionic strength. We report new experimental data and test various models to describe the deprotonation of PAA in ...

Influence of alkali metal counterions on the charging behavior of poly(acrylic acid)

Charging of poly(acrylic acid) (PAA) in the presence of different alkali metal counterions was studied by precision potentiometric titration. The charging behavior can be described with a novel cylinder Stern model quantitatively. This model is based on the Poisson–Boltzmann equation in the cylinder geometry and a constant Stern capacitance. One finds an increasing cylinder radius with increasing mass of the alkali metal ion and a correspondingly decreasing Stern capacitance. The intrinsic ionization constants for the uncharged polymer are found to decrease with ionic strength, similarly to weak acids of low molecular mass.

Study of thermal aging effect on space charge in poly(methyl methacrylate)

Charges evolution in poly(methyl methacrylate) (PMMA) samples under thermal aging effect has been studied by means of two complementary techniques, thermal step method (TSM) and thermally stimulated depolarization current (TSDC). For the first method, measurements reveal that injected charges, whose quantity is found depending on the number of applied temperature cycles, remain close to the surface sample. TSDC measurements have been carried out for different temperatures ranging from 25 °C to 140 °C. Three distinguishable dipolar relaxations ( β 1 , β 2 and α) have been highlighted. In the same way, the presence of polarization and injected charges has been confirmed. In support of electric characterization, X-ray reflectometry has been used. The obtained results equally emphasized the thermal aging effect on the material.

Magnetic field release of trapped charges in poly(fluorenylenevinylene)s

We have measured the effect of an applied magnetic field on the current through thin films of two different organic conjugated polymers that have previously shown to exhibit magnetoresistance, poly(9,9-dioctyl-1,4-fluorenylenevinylene) and poly(9,9-dioctyl-2,7-fluorenylenevinylene). The results show that the magnetic field releases trapped charges from inside the material and enhances the current. We have also performed optical absorption experiments on these polymer films under applied voltage and magnetic field. The results show that the magnetic field produces a change in the optical absorption in the low-energy range associated with deep traps and only under conditions when these traps are likely charged. These two results provide a strong case for the release of trapped charges caused by the magnetic field as being the cause of the magnetoresistance in these polymers and possibly in other organic materials where magnetoresistance was recently observed.

The storage and its stability of space charge in poly(ethylene naphthalene-2,6-dicarboxylate)

Poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) is an aromatic polyester with molecular structure similar to that of poly(ethylene terephthalate)(PET). In this paper, the space charge storage ability and its stability in corona charged PEN were studied by measurement of surface potential decay under different storage conditions including different temperatures and relative humidities, and analysis of open circuit thermally stimulated discharge (TSD) current spectra and charge TSD curves. The comparison between the charge stability of PEN and PET was carried out. The results point out that the charge stability of PEN is markedly better than that of PET under different environmental conditions. By means of isothermal depolarization program, the space charge lifetimes (effective time constant) t at room temperature of positively and negatively charged PEN are estimated to be 90 y. The results offer theoretical and technical support for the use of PEN as the chip of high quality electret condenser microphone due to its excellent dielectric, mechanical and thermal properties.

Spectroscopic investigations on hybrid nanocomposites: CdS : Mn nanocrystals in a conjugated polymer

We have used electron paramagnetic resonance (EPR) spectroscopy for investigating the properties of spins, such as those carried by polarons which carry both spin and charge in poly (meta/para phenylene) PMPP: CdS doped Mn based nanocomposites. To identify the nature of paramagnetic species in PMPP matrix, we have studied the effect of different physical parameters. It was found that we are in presence of trapped polarons and localized spins which concentration has been estimated. Moreover, spin–spin and spin–lattice relaxation rates have been calculated. Then, we discussed the results of optical and EPR study on the hybrid nanocomposite (CdS nanostructures, doped with manganese (II) ions, incorporated in PMPP conjugated polymer matrix). The optical spectra of these nanocomposites were compared to the existing models of energy levels in quantum dots. Moreover, by the use of electronic paramagnetic resonance, conclusions about the location and the symmetry of Mn 2+ ions have been drawn. The nanocomposite energy gap is in the 3.2–3.3 eV range. The size of the nanoparticle is about 3.3 nm and Mn 2+ ions are located at or near the nanoparticle surface.

Electron-beam charging of poly(methyl methacrylate)

The charging of bulk poly(methyl methacrylate) by irradiation with electrons of ∼2 MeV energy at room temperature in vacuum was studied. The experimental data obtained using the split Faraday cup are compared with the results of numerical simulation assuming one-dimensional geometry with allowance for the spatial distribution of dose rate and injected-electron current, nonlinear properties of radiation-induced conductivity in the prebreakdown electric-field region, and the intrinsic conductivity of poly(methyl methacrylate). It was shown that published data on the electric field strength measured by means of the electro-optical Kerr effect in electron-beam charged poly(methyl methacrylate) agree satisfactorily with the calculation results.

Experimental study and simulation of space charge stimulated discharge

The electrical discharge of volume distributed space charge in poly(methylmethacrylate) (PMMA) has been investigated both experimentally and by computer simulation. The experimental space charge was implanted in dielectric samples by exposure to a monoenergetic electron beam of 3 MeV. Electrical breakdown through the implanted space charge region within the sample was initiated by a local electric field enhancement applied to the sample surface. A stochastic-deterministic dynamic model for electrical discharge was developed and used in a computer simulation of these breakdowns. The model employs stochastic rules to describe the physical growth of the discharge channels, and deterministic laws to describe the electric field, the charge, and energy dynamics within the discharge channels and the dielectric. Simulated spatial–temporal and current characteristics of the expanding discharge structure during physical growth are quantitatively compared with the experimental data to confirm the discharge model. It was found that a single fixed set of physically based dielectric parameter values was adequate to simulate the complete family of experimental space charge discharges in PMMA. It is proposed that such a set of parameters also provides a useful means to quantify the breakdown properties of other dielectrics.

Spatial distribution and dynamics of space charges in poly(2, 5-pyridinediyl)

We present investigations of the spatial distribution of space charges inthin films of conjugated polymers. A thermal wave method, the laserintensity modulation method, has been used to resolve the depth profile ofspace charges and the distribution of the internal electric field in 3–4 μ mfilms of poly(2, 5-pyridinediyl). The dynamics of the space-charge accumulationhas been investigated by means of measurements of the temporal evolution andthe temperature dependence of the pyroelectric response. The results demonstratethat in conjugated polymers, space charges of either sign can be storedpermanently by deep trapping. This charge significantly reduces the internalelectric field in the bulk of the films.

Anomalous thermally stimulated currents and space charge in poly(vinyl pyrrolidone)

To study the mechanisms of charge production and storage in poly(vinyl pyrrolidone) (PVP), short circuit thermally stimulated currents (TSCs) in solution-grown PVP depolarized at 30, 50 and 80 °C with 25, 50 and 100 kV cm−1 have been analysed in the temperature range 30–200 °C. By employing TSC measurements with a conventional ‘contact electrode’ two kinds of charges have been observed. An anomalous TSC flowing in the same direction as the charging current was observed for PVP thermoelectrets poled at 50 and 80 °C with 50 and 100 kV cm−1. The TSCs for samples poled at different temperatures (30, 50 and 80 °C) with 25 kV cm−1 have been found to be normal in the sense that the discharge current flows in the direction opposite to that of the charging current. The TSC thermograms have been found to be characterized by two peaks located at 60–70 °C and 160–170 °C. Various characteristics of thermograms have been explained in terms of the existence of heterocharge due to dipolar orientation and ionic homocharge drift, together with the injection of charge carriers from electrodes and their subsequent localization in surface and bulk traps. © 2000 Society of Chemical Industry

Relation between molecular microstructure and electrical space charges in poly(propylene)

The tacticity-induced molecular microstructure was determined by means of 13C NMR spectroscopy for four distinct poly(propylene) samples. Of these, two polymers are commercial samples of high and middle isotactic content, and two samples were obtained by fractionation with respect to the stereoregularity of the former highly isotactic commercial polymer. The space charge distribution after applying an electric field was studied for every sample by means of the “thermal step”; (TS) method. By comparing the behaviour of the four samples it was demonstrated that both the total space charge accumulation and the type of charges depend strongly on the molecular microstructure.

Further evidence for the role of excitons in photogeneration of charges in poly(phenylene vinylene)s

We have measured the photocurrent action spectra of MEH-PPV and PPV in sandwich cells between indium tin oxide [ITO] and aluminium electrodes. Under different bias conditions, the photocurrent spectra are either symbatic or antibatic to the absorption spectrum. We have investigated several established models which attempt to explain this behaviour and to relate the photocurrent action spectrum to the absorption co-efficient, considering penetration depth of the light and diffusion of excitons or directly photogenerated charges. At a qualitative level, many of these seem to provide an adequate description, although quantitatively none of these models can reproduce the very narrow antibatic photocurrent peak (f.w.h.m. = 0.1 eV) which we observe in both MEH-PPV and PPV, corresponding to the low energy onset of absorption. Enhancement of the photocurrent in air is further evidence for the role of excitons. As the temperature decreases, we observe a progressive red-shift of the absorption edge, although the photocurrent onset undergoes a much smaller red-shift. We propose that the particularly sharp onset of photocurrent at low energy may be due to enhanced intermolecular charge separation within crystallite grains between neighbouring conjugated segments which are more extended and more planar.

Photoluminescence quenching in a polymer thin film field effect luministor

The interaction between photoexcited excitons and field induced charges in poly(3-hexylthiophene) has been studied using photoluminescence. Thin films of poly(3-hexylthiophene) and Langmuir-Blodgett films of poly(3-hexylthiophene)/Arachidic acid show a quenching of the photoluminescence intensity upon charge injection in a field effect device. The quenching is discussed in terms of polarons/bipolarons acting as recombination centra for the excitons, giving non-radiative decay. The rate constant for non-radiative recombination of the excitons is shown to be proportional to the number of injected charges. This field effect luministor device shows the coupling between the optical and electronic properties of excitations in conjugated polymers.