Copolymers and two-layered composites of poly(<Emphasis Type="Italic">o</Emphasis>-aminophenol) and polyaniline

Electroactive conducting copolymers of aniline (ANI) and o-aminophenol (OAP) and two-layered poly(o-aminophenol) (POAP)/polyaniline (PANI) composites were prepared in aqueous acidic solution by electrode potential cycling. Copolymerization was carried out at different feed concentrations of OAP and ANI on a gold electrode. A strong inhibition of electropolymerization was found at a high molar fraction of OAP in the feed. The copolymers showed good adherence on the electrode surface and gave a redox response up to pH=10.0. Two transitions were observed in the in situ conductivities of the copolymers (as with PANI), but the conductivities were lower by 2.5–3 orders of magnitude as compared to PANI. Electrosynthesis of PANI on POAP modified electrodes showed copolymer formation after reaction initiation and finally formation of a PANI layer at the copolymer/solution interface. The ‘memory effect’ of the bilayer structures of both polymers was discussed in terms of protonation/deprotonation and anion consumption taking place during redox processes of both polymers.     

Role of Bipolar Pulsed DBD on the Growth of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> in Three-Phase Discharge Plasma Reactor

Algae in drinking water supplies often bring about impact on the water treatment. In this study, a bipolar pulsed dielectric barrier discharge system in three-phase discharge plasma reactor was constructed for investigating its ability to control excessive growth of cyanobacteria, Microcystis aeruginosa. Experimental results show there was almost no change in optical density immediately after the interruption of electrical discharge, but the decreasing trend of optical density, cell density and chlorophyll-a content was obvious during the incubation period, indicating a significant residual effect of electrical discharge process on the algal growth inhibition. Scanning electron microscopy investigation of algae revealed surface damage, apparent leakage of intracellular contents and pores formed after electrical discharge process, which showed that algal cells had no potential to survive and grow. Compared with the control sample, it was observed that electrical discharge on the algal extracellular products has almost no residual effect and the growth rate of algae slightly decreased before three days storage. Hydrogen peroxide was produced by electrical discharge in the μM level and showed a first-order decay. But at such level, the external addition of hydrogen peroxide alone is not likely to cause the residual effect. These results implicated that the growth inhibition of M. aeruginosa was mainly caused by electrical discharge process, and it made the algal cells lose ability to survive, demonstrating the considerable potential of such an alternative process for efficient water purification.     

Preparation of conductive polypyrrole (PPy) composites under supercritical carbon dioxide conditions

Electrically conductive composites were prepared via the chemical oxidative polymerization of the pyrrole monomer in polystyrene (PS) and zinc neutralized sulfonated polystyrene (Zn-SPS) films under supercritical carbon dioxide (SC-CO₂) conditions. The strong swelling effect of SC-CO₂ made polypyrrole (PPy) particles not only form on the surface, but also become incorporated into the film, resulting in a homogeneous structure with a relatively higher conductivity. By comparison, the composite prepared in aqueous solutions shows a skin-core structure and a conductivity of 3 to 4 orders of magnitude lower than that of the former due to the diffusion-controlled process of the pyrrole monomer. The percolation thresholds of PS/PPy and Zn-SPS/PPy composites were 6.2% and 2.7% of the volume fraction of PPy, respectively, much lower than the theoretically predicted value of 16%. Moreover, the conductive composites prepared under SC-CO₂ conditions showed higher thermal stability, especially in the high-temperature region. Translated from Chemical Journal of Chinese Universities, 2006, 27(4): 771–774 (in Chinese)     

Curing Characteristics and Tear Properties of Bentonite Filled Ethylene Propylene Diene (EPDM) Rubber Composites

The effect of bentonite clay loading on curing characteristics and tear strength of bentonite filled ethylene propylene diene monomer (EPDM) composite were studied. Compounding was carried out on two-roll mill and vulcanization was done at 150⁰C. Torque values, scorch time and optimum cure time of the prepared rubber compound were assessed by using Mosanto Disc Rheometer (MDR 2000). Results indicated that the maximum torque of EPDM/Bt composite decreases at high bentonite loading. Increasing in values with increasing bentonite loading was recorded for minimum torque and optimum cure time of EPDM/Bt composite. The increase is related with the increase in viscosity due to the increasing of bentonite clay loading in EPDM matrix. Scorch time was found to be decreasing up to 30 phr bentonite clay. Results also show that tear strength of EPDM/Bt composite increased with increasing bentonite loading up to 90 phr. The reason is probably due to agglomeration occur causes the reduction in properties at high loading above 90 phr bentonite clay. The scanning electron microscopy (SEM) of tear fracture surface of EPDM/Bt composite illustrated that with increasing bentonite loading up to 90 phr bentonite clay, a better dispersion of bentonite clay is achieved as compared to lower loading, resulting in high tear strength value for EPDM/Bt composite.     

Pressure‐temperature study of dielectric relaxation of a polyurethane elastomer

The effect of hydrostatic pressure up to 1,361 atms on the dielectric properties of a segmented polyurethane elastomer (Dow 2103‐80AE) is studied at temperatures from 0°C to 80°C. The experimental results show that the relaxation time for both the I–process, associated with the molecular motions in the hard segments, and the α–process, associated with the glass transition, increases with pressure, and this shift is more pronounced for the I–process. Besides the glass transition, it is found that the I–process can be described by the Vogel–Fulcher (V–F) and Williams–Landel–Ferry (WLF) relations. At atmospheric pressure, T_g and T₀ for the I–process are 235.9 K and 4.2 × 10³ K, respectively. Based on the V–F and WLF relations and experimental results, it is found that a parameter, C₁, in the WLF relation is independent of the pressure. Thus, a method is introduced to determine the values of both the characteristic transition temperature (T_g) and activation energy (T₀) for the processes at different pressures. As the pressure increases from atmospheric to 1,361 atms, the increase of T_g for the I–process is about 30°C. The results also show that, for both the I– and the α–processes, T₀ decreases with increasing pressure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 983–990, 1999     

Probing buried carbon nanotubes within polymer-nanotube composite matrices by atomic force microscopy

Multi-walled carbon nanotubes (MW-CNT) inside a polyamide-6 (PA6)-MW-CNT composite were visualized by atomic force microscopy (i) in a field-assisted intermittent contact and (ii) in the tunneling (TUNA) mode. Individual buried MW-CNTs were clearly discerned within the PA6 matrix. An average diameter of 33 ± 5 nm of the MW-CNTs was determined based on field-assisted intermittent contact mode AFM images, which is consistent with the expected size of PA6-coated MW-CNTs. Single well dispersed MW-CNTs that are located in the sub-surface region of the composite were also observed in the TUNA mode. These new AFM approaches circumvent the tedious sample preparation based on ultramicrotoming required for high resolution electron microscopy studies to obtain “in-depth” morphological information and hence are expected to facilitate the analysis of CNT-based and other nanocomposites in the future.     

The dynamic mechanical behavior of random-in-plane short fiber-reinforced epoxy resin composites

In the present paper, the dynamic mechanical properties of random-in-plane short fiber-reinforced epoxy resin composites were studied by using a rheometrics solids analyzer. The three-point bend testing of the four composites (glass fiber/913 epoxy resin, glass fiber/924 epoxy resin, carbon fiber/913 epoxy resin and carbon fiber/924 epoxy resin) was carried out over temperatures from −100°C to 200°C at a frequency of 10 Hz and strain 0.05%. The composites based on 924 epoxy resin, which has been designed specially for high temperature applications, have less energy loss than the 913 epoxy resinbased composites. For the same resin, the carbon fiber-reinforced composites have less energy loss than the glass fiber-reinforced composites. All the composites have less energy loss than their corresponding matrices; the greater the fiber content, the lower the energy loss. The beta transition of 913 epoxy resin has been shifted to a higher temperature after being reinforced. It was shifted from −50°C to −30°C after being reinforced with glass fiber and made a diffuse shoulder-like peak commencing at −30°C after being reinforced with carbon fiber. The 924 epoxy resin has undergone the same change in beta transition as the 913 resin, though to a smaller extent. The phenomenon suggested that interactions between the macromolecules of the epoxy resins and the molecules along the fiber's surface.     

A rigorous comparison of theoretical autocorrelation functions with dielectric relaxation parameters for the alpha process of polymers

Recently, tables of parameters used to represent experimental dielectric relaxation data as well as autocorrelation functions have become available. The experimental and autocorrelation function data were represented with the Havriliak–Negami function using rigorous statistical techniques. These tables include not only parameters and their temperature dependencies, but also the confidence intervals for all of the parameters. The important parameters for this work are the two shape parameters, α and β, which represent the width and skewness of the relaxation process, respectively. A comparison is made between the experimental data and several autocorrelation functions by calculating the minimum distance (in units of standard deviations) between the experimental values of αβ parameters for a specific polymer and the αβ parameters corresponding to the autocorrelation functions reported in these tables. Quantities derived from these minimum distances (a distribution function and an error function) are reported for each of the autocorrelation functions. These results are discussed in terms of the basic assumptions of the mode coupling theory. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1887–1897, 1997     

Correlation of the Dielectric Properties of Dispersed Particles with the Electrorheological Effect

The dc field rheological properties and frequency dependent dielectric properties of a set of electrorheological (ER) fluids composed of oxidized polyacrylonitrile or aluminosilicate materials dispersed in silicone oil were examined in this paper. Our experimental investigations show that there is a complicated relationship between the dielectric properties of dispersed particles and the ER effect. The dielectric loss of dispersed particles, which has not attracted much attention in previous work, was found to play a considerable role in ER response. The large dielectric loss tangent, experimentally around 0.10 at 1000 Hz, is found to be needed for a strong ER effect. A good ER solid material should first have large dielectric loss, and then the higher the dielectric constant, the stronger the ER effect. The large dielectric loss would facilitate the turning of dispersed particles, and the high dielectric constant would maintain the fibrillation structure stable and strong. Two processes, the particle turning process and the particle polarization process, are thought to be involved in ER activity. Our findings, in connection with the Wagner model, can better explain why the strongest ER effect occurs at particle conductivity of 10⁻⁷S/m; why the shear stress of some ER fluids decreases with frequency while with others the shear stress increases with frequency; and why trace water can enhance the ER effect considerably, which would help in understanding the mechanism of the ER effect. Too large a dielectric loss is thought to be unfavorable for the ER effect, and its suitable range is worth further study. The results also present a method of designing high performance ER fluids, which would significantly promote development of electrorheology and its application in industrial areas.     

A new ultrasonic measurement system for the cure monitoring of thermosetting resins and composites

Measurements of the ultrasonic sound speed of thermosetting resins and composites can be used as an in-process cure monitoring technique. Ultrasonic measurements have an advantage over other in-process techniques in that ultrasonic sensors do not make contact with the part (thus leaving no imbedded sensor or witness mark) and can make true bulk measurements of the part. A new commercially available ultrasonic cure monitoring system has been developed which easily enables ultrasonic measurements to be made in compression molding, resin transfer molding, and autoclave processes. Advancements in ultrasonic sensor technology enable the sensor to maintain good coupling to the part during thermal cycling to 260C. Data is presented showing the change in ultrasonic sound speed during the compression molding of a graphite-epoxy prepreg. The data shows a good relationship to the ionic conductivity and resistivity data collected via dielectric cure monitoring.This effort was sponsored by the Manufacturing Technology Directorate, Wright Laboratory (WL/MTX), Air Force Material Command, USAF, under cooperative agreement award(s) to NCMS. The U. S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Wright Laboratory or the U.S. Government.