A cyclic voltammetry study on bi layer and multi layer conducting polymer films

Polypyrrole (PPY) is a prime candidate for a polymer actuator; but has the disadvantage that the electronic conductivity decreases by two or three orders of magnitude as the polymer is reduced. This reduces the actuator performance. A Standard way of overcoming this problem is to add Au or Pt layers as thin patterns or as helices on the polymer. The present work is an attempt to use a second more highly conducting polymer, poly(3,4- ethylenedioxythiophene), (PEDOT), to enhance the electronic conductivity

Strain measurements on polypyrrole actuators in aqueous electrolytes

Polypyrrole films doped with the large immobile dodecylbenzene sulfonate anions, (PPy/DBS) films, have been prepared electro chemically on stainless steel electrode and peeled off to obtain free standing actuator strips. The actuator films operating in aqueous electrolytes of NaCl having concentrations ranging from 0.02 M to 4 M have been characterized by simultaneous cyclic voltmeter driven force-displacement measurements in order to investigate the effect of actuation frequencies of the system on the strain of the films. The mechanism of actuation in this type of actuators is the insertion/expulsion of counter ions, accompanied by a large number of water molecules, as the polymer is redox cycled between the reduced and the oxidized states. The expansion and contraction of the films during the redox process were measured under isotonic conditions at various actuation frequencies. The strain variation as a function of actuation frequency follows the same general pattern in all concentrations used and has three distinct regions. The strain is high and remains constant at low frequencies (0.1 Hz). At mid frequencies, the strain decreases considerably. These strain variations can be explained based on the two categories of water molecules that accompany the cations during the redox process: a smaller number strongly bound to the cation (corresponding to the inner solvation shell) and a larger number entering the film after the insertion of the cations because of forces related to osmotic pressure difference. The two processes have very different time constants: The solvated 1--120 molecules are associated directly with the cations, and are therefore inserted in a faster process, whereas the second type enters the film much more slowly

Strain measurements on multilayer conducting polymer films

The demand for actuators based on conducting polymers is growing due to their highly desirable features such as large mechanical strength, high power density, sufficient maximum strain values, high reversibility and safe. Reportedly, several attempts in various aspects have been made to improve the actuator performances. We report here some strain measurements on actuators of multilayer free standing films prepared with polypyrrole (PPy) and poly (3,4ethylenedioxythiophene) (PEDOT) conducting polymers. These multi-layer films were prepared electrochemically, and The PEDOT is very thin compared to PPy layer in this combination. A force-displacement setup is used to measure the mechanical properties and the length change when multilayer conducting polymer film is oxidized and reduced electrochemically. Typical dimensions of the exposed part of the strips were 5 mm (length) x 3 mm (width). Results were compared that of PPy single film. Bilayer film shows a significant increase in the strain measured at higher scan rate (> 100 mV s'1). The force generation between reduced and oxidized state is much higher for trilayer films and then for bilayer films than single layer PPy. These differences are not linked to the Young's modulus of these films. The addition of a thin PEDOT does not change Young's modulus, but change force generation significantl

UV - Visible optical absorption spectroscopic studies on PEDOT and PPY conducting polymer Multilayer films

The energy gap of the conjugated polymer determines the intrinsic optical properties. The colour changes elicited by doping are due to the modification of the electronic band structure of the polymers. A polymer with a band gap in the UV range, is being transparent in its neutral state. When the polymer is doped, new electronic states in the band gap are induced and absorption of light in the visible range occurs. This means that the polymer becomes opaque, or heavily colored, upon doping. Accordingly, the UVVisible technique is crucial in studying the optical properties of conducting polymer. Single and multi layer polymer films were formed galvanostatically on optically transparent ITO coated glass with poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) . The active area of the ITO glass in contact with the solution was 3.14 cm-2 . The thickness of films corresponded to a charge of 40 mc cm-2 consumed during the film formation. The absorption spectra were measured in the range of 311-1100 nm (1.13 — 4.00 eV) with a UV-visible spectrometer during the oxidation and reduction of the films. An aqueous I M NaCl solution was used as the cycling electrolyte. The two polymer PEDOT and PPy films show slightly different optical absorption behaviour. In the reduced state, while the PEDOT film has the main peak at 2.1 eV, the PPy film has it at 3.0 eV. These peaks which can be assigned to It-it electronic transitions correspond to the band gaps of the polymers. Thus, the PEDOT film appears to have lower band gap compared to that of the PPy film. The characteristic features in the spectra for both bilayer and trilayer films are a combination of the features from the spectra of the pure constituents. This means that these multilayer films behave like a combination of the pure components

A study of electrochemical behaviour of polypyrrole films in highly concentrated aqueous electrolytes

Polypyrrole polymer films doped with large surfactant anions, dodecyl benzene sulfonate, (PPy/DBS) can be used as soft actuators and their performance and stability depend on the type of the cycling electrolytes and their concentrations. In an attempt to discover suitable electrolytes for such actuators, the diffusion of counter ion into PPy/DBS films in various aqueous electrolytes has been investigated in this work. The PPy/DBS films were cycled at different scan rates in various alkali halide aqueous electrolytes having concentrations ranging from 0.1-1 M in order to determine the diffusion coefficients of alkali halide ions. The effective diffusion coefficients were found to increase with the concentration of the electrolytes and decrease with the increase in size of cations. Since the effective diffusion coefficient of counter ions is a direct measure of the speed of response when such films are used as electrodes in artificial muscles or in batteries, this finding is especially useful for the design of fast actuators based on PPy/DBS polymers

A study on electro chemical stability of polypyrrole films in concentrated LiCl aqueous electrolytes

Polypyrrole (PPy) conducting polymer films operating in aqueous electrolytes have a shorter cycle life and such a system has, therefore, limited use as far as applications are concerned. This can be rectified to some extent when ionic liquids are used as cycling media. However, the cost involved is prohibitive. The aim of this study is to investigate the possibility of using concentrated alkali halite electrolytes to improve the cycle life of PP y films Polypyrrole films doped with large surfactant anions, dodecyl benzene sulfonate, (PPy/DBS), were formed on quartz crystals using the galvanostatic electropolymerization technique. The redox behavior of the films up to 300 cycles in LiCl aqueous electrolytes of selected concentrations ranging from 0.1 - 8 M, was investigated using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. During the first cycle, while large water movement was observed along with the counter ions in dilute electrolytes, such water transport in concentrated electrolytes was found to be very low. On continuous cycling the shape and capacity of the cyclic voltamograms changed significantly in dilute electrolytes. But in highly concentrated electrolytes the cyclic voltammograms remained unchanged with the number of cycles indicating that the PPy/DBS films had stable cycle life in such electrolytes

Bovine Parasitic Gastroenteritis and Bronchitis: Control vs Immunity

This thesis comprises a series of studies carried out (1) to review the literature on parasitic gastroenteritis and bronchitis with special emphasis on epidemiology, immunity and control methods (2) to determine the influence of anthelmintic prophylaxis in calves on their subsequent immunity to Ostertagia, Cooperia and Dictyocaulus as yearlings (3) to assess the parasitological status of adult dairy cattle and (4) to compare the efficacy of several techniques used in these studies

Characterisation of plasticised PVDF–HFP polymer electrolytes

This study focuses on the preparation and characterisation of sodium ion conducting polymer electrolytes. Poly(vinylidenefluoride-co-hexafluoropropylene) has been used as the host matrix and hydrated sodium sulphide (Na2S.9H2O) salt as the source of charge carriers in the polymer electrolyte system. To the highest conducting polymer–salt electrolyte, different concentrations of equal weight of propylene carbonate and diethyl carbonate mixture have been added, and the electrolytes have been characterised by X-ray diffraction, Fourier transform infrared spectrometry, scanning electron microscopy and electrochemical impedance spectroscopy. The room temperature ionic conductivity of 1?3461024 S cm21 for the unplasticised electrolyte with a composition of 65 wt-% poly(vinylidenefluoride-co-hexafluoropropylene)–35 wt-%Na2S increased to 3?4961024 S cm21 when 30 wt-% propylene carbonate/diethyl carbonate (w/w51) plasticisers were added

Induction of innate immune response following infectious bronchitis corona virus infection in the respiratory tract of chickens

AbstractInfectious bronchitis virus (IBV) replicates in the epithelial cells of trachea and lungs of chicken, however the mechanism of generation of innate immune response against IBV infection in these tissues has not been fully characterized. Our objective was to study innate responses induced early following IBV infection in chickens. Initiation of the transcription of selected innate immune genes such as TLR3, TLR7, MyD88, IL-1β and IFN-β, as well as recruitment of macrophages, were evident following an initial down regulation of some of the observed genes (TLR3, IL-1β, and IFN-γ) in trachea and lung. This initial down-regulation followed by the induction of innate immune response to IBV infection appears to be inadequate for the control of IBV genome accumulation and consequent histopathological changes in these tissues. Potential induction of innate immunity before infection occurs may be necessary to reduce the consequences since vaccine induced immunity is slow to develop