The conductivity behaviour of gamma-irradiated PEO-LiX electrolytes. I

In an attempt to enhance the room temperature ionic conductivity of PEO-LiX films, samples have been exposed to gamma-irradiation at 78°C. The success with which cross-links have been introduced into the amorphous form has been evaluated from d.s.c. analysis and temperature-dependent conductivity data. Retardation of the recrystallisation event, associated with uncomplexed poly(ethylene oxide), does not occur over a range of total doses. Changes in overall conductivity levels for the PEO-LiCF₃SO₃ ([EO units]/[Li] = 9) system, indicate light cross-linking at 2.25 Mrad of exposure. However, higher doses result in a substantial amount of chain scission, leading eventually to poor mechanical properties. A similar study on PEO-LiClO₄ ([EO units]/[Li] = 20) confirms that the above route is an ineffective method to improve room temperature conductivity.     

Measurement of electrolytic conductivity in highly conducting solutions

A new technique, suitable specifically for the determination of specific conductivity in highly conducting solution is described. The technique combines the advantages of four-electrode measurement with those of fast current interruption to yield a clear signal, proportional to the resistivity of the solution and independent of any polarization effects.The conductivity of concentrated aqueous solutions of KOH is measured over a range of temperatures from 25 to 70°C and compared to literature data on the one hand and to measurements with a commercial two-electrode a.c. conductometer on the other. Agreement with literature data is good. Two-electrode a.c. measurements yield consistently lower values because polarization is not eliminated. The technique is simple and easily adaptable for on-line operation in the electrolytic industry where continuous monitoring of the conductivity may be important for process control.     

Thermal properties of rigid polymers. I. Measurement of thermal conductivity and questions concerning contact resistance

Several studies of the influence of contact resistance on the measurement of thermal conductivity of polystyrene using a steady-state device are presented. In each case it is seen that, although this influence can perhaps be minimized, it cannot be eliminated as an experimental complication. A novel technique is then described which does eliminate entirely contact resistance as a variable, and this technique is shown to yield an unequivocal value of thermal conductivity.     

Ion mobility time of flight measurements: effect of experimental parameters on measurements in a non-hydrogen bonded system

An in situ measurement technique that isolates the mobility of charge carriers is described and analyzed. The technique allows significant improvement over conductivity measurements to monitor changes in the physical properties and state of a material as it cures. This is essential in systems where N_i, the number of charge carriers, cannot be assumed constant such as during cure of epoxies, urethanes and polyimides. Currently, there is an assumption made in the literature that the number of charge carriers present in a curing material is constant when conductivity is used as an in situ measurement technique to monitor changes in mobility (and thereby viscosity). This assumption is widely used, for example when dielectric conductivity measurements are correlated with changes in properties such as viscosity. Ion mobility, time of flight (ITOF) measurements, which are described here, are an appropriate technique to isolate and measure particle mobility due to changes in the state of the material. Furthermore, the ITOF technique, coupled with the measurement of σ, the dielectric conductivity, allows one to measure separately changes in the mobility and the number of charge carriers due to curing or changes in temperature. This is possible since conductivity is the product of the number of charge carriers and their mobility. Length of pulse, strength of applied field, sensor geometry, and temperature/viscosity are examined to determine optimum parameters of measurement for a simple, non-curing system: dimethacrylate of tetraethoxylated bisphenol A (D121). This paper seeks to show that with changes in viscosity, the pulse length and magnitude of voltage in relation to the distance between the electrodes should be varied to obtain accurate ITOF information on the changing mobility.     

Electrical conductivity of poly(ethylene terephthalate) modified by titanium plasma

Ion‐implantation‐induced electrical conductivity in a polymer surface is known to have a different mechanism from that of metals and semiconductors. We used a technique called plasma immersion ion implantation and deposition and combined it with a titanium cathodic vacuum arc to modify the surface electrical conductivity of poly(ethylene terephthalate) (PET). The conductivity curve as a function of temperature well fitted the Mott hopping model, which has been proposed for many disordered systems. In addition, we also observed conductivity degradation when modified PET was kept at room temperature. The degradation showed a quasi‐exponential decay as a function of time, that is, an aging effect, which has been seldom reported in the literature to the best of our knowledge. This could have resulted from the unusual structure of PET's surface after ion implantation. A new formula for electrical conductivity in modified PET is proposed that considers both temperature and aging effects. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A new differential scanning calorimetry based approach for the estimation of thermal conductivity of polymer solids and melts

A new concept based on differential scanning calorimetry (DSG) is introduced which enables us to make a rapid estimation of the thermal conductivity of materials. This technique is shown to give reasonable agreement with the literature data and offers unique advantages, e.g. short analysis time, no instrument modification, small thermal radients across the sample, spall sample size requirements, and most importantly it can be applied to polymer melts. Although our data falls within the literature range, it is difficult to comment on its accuracy since the literature itself shows a wide variation. The precision of our measurements is better than ±20 percent which is considered adequate for thermal conductivity evaluation. As a matter of convenience, we have also presented briefly, a background of the thermal conductivity measuring techniques.     

Thermal conductivity and viscosity of normal C2–C6 aliphatic carboxylic Acids

Equipment for measurements of thermal conductivity and viscosity of liquids in the temperature range 273–350 K and at atmospheric pressure is described. The thermal conductivity and viscosity of acetic, propionic, butyric, valeric and hexanoic acids in the liquid state have been measured. The values obtained are compared with published data and the ratio of thermal conductivity, λ, to viscosity, η, is examined in the form of the dimensionless quantities, Mλ/Rη and cpη/λ (Prandtl number).     

Development of a POA/DBS/GOx Biosensor for the Determination of Glucose

In the present work, a simple technique is described for constructing a poly(o-anisidine) (POA)-dodecylbenzene sulphonic acid (DBS)-glucose oxidase (GOx) (POA-DBS-GOx) electrode. The enzyme glucose oxidase (GOx) was immobilized by crosslinking via glutaraldehyde on the POA-DBS film. The POA-DBS films were synthesized electrochemically on platinum substrate. The synthesized films were characterized by using electrochemical technique, conductivity measurement, UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The conductivity of the polymer films was found to be about 7.61 × 10^?2 S/cm. The crosslinking of enzyme and the porous morphology of the polymer film lead to good stability and good response time of the enzyme electrode. The stability and lifetime of the POA-DBS-GOx electrode have been studied. It shows very good stability and response for 3–4 weeks at 4°C. The results of this study reveal that a phosphate buffer gives better response than acetate buffer in amperometric measurements.     

Thermophysical properties of densified pitch based carbon/carbon materials—I. Unidirectional composites

Unidirectional carbon/carbon composites were developed using high-pressure impregnation/carbonization technique with PAN and pitch based carbon fibers of varying microstructure as reinforcements and different types of pitches as matrix precursors. The composites have been given final heat treatment to 2500-2700 °C. Microstructure of these composites has been evaluated using scanning electron microscope and polarized light optical microscope. Thermophysical properties, i.e., thermal conductivity, coefficient of thermal expansion and specific heat have been evaluated. It is found that the type of fibers and matrix present in the composites influences the absorption (specific heat) and transmission (conductivity) of thermal energy. The temperature dependence of thermal diffusion, specific heat, thermal conductivity and coefficient of thermal expansion has been studied and correlated with microstructure of carbon/carbon composites.     

Dielectric analysis of the linear polymerization of an epoxy resin

The dielectric properties of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin and n‐butylamine have been studied in the frequency range 100 Hz to 3 GHz at 25 °C. The unreacted mixture showed a single relaxation which gradually split in two relaxations, the separation of which increased as the reaction progressed. The low and high frequency relaxations are attributed to the structural dynamics of the growing macromolecules and to the motions of the dipoles associated with the monomers, respectively. The increase of the structural relaxation time is described by a phenomenological relationship, similar to the Williams–Landel–Ferry equation, that allows estimation of the conversion at vitrification. A marked decrease of the electrical conductivity has also been observed, as a result of the increasing viscosity of the system. The conductivity and the structural relaxation time are correlated by means of a generalized Debye–Stokes–Einstein model. It has also been found that both components of the complex dielectric permittivity, measured at microwave frequencies, yield information on the advancement of the polymerization process. © 2001 Society of Chemical Industry     

Technique for measuring the electric conductivity of glasses and melts over a wide temperature range covering the glass transition region

The technique for measuring the electric conductivity of glass-forming melts and glasses over a wide temperature range covering the glass transltion region is described in detail. The technique is based on the application of small-sized electrodes that provide the retention of their mutual arrangement in melts and glasses and prevent the appearance of mechanical stresses exceeding the ultimate strength of glasses. The potentialities of the proposed technique are illustrated by the measurement of the electric conductivity for several standard glasses. The coefficients of equations describing the temperature dependences of the electric conductivity above and below the glass transltion range are determined. The technique makes it possible to obtain the hysteresis loops of the electric conductivity at constant rates of cooling and the subsequent heating and also the temperature dependences of the first and second derivatives of the electric conductivity with respect to temperature.     

Technique for measuring the electric conductivity of glasses and melts over a wide temperature range covering the glass transition region

The technique for measuring the electric conductivity of glass-forming melts and glasses over a wide temperature range covering the glass transltion region is described in detail. The technique is based on the application of small-sized electrodes that provide the retention of their mutual arrangement in melts and glasses and prevent the appearance of mechanical stresses exceeding the ultimate strength of glasses. The potentialities of the proposed technique are illustrated by the measurement of the electric conductivity for several standard glasses. The coefficients of equations describing the temperature dependences of the electric conductivity above and below the glass transltion range are determined. The technique makes it possible to obtain the hysteresis loops of the electric conductivity at constant rates of cooling and the subsequent heating and also the temperature dependences of the first and second derivatives of the electric conductivity with respect to temperature.     

The interaction of ozone with bio-fuel, revealed by electrical conduction and infrared spectroscopy

The interaction of ozone with bio-fuel has been investigated. The highly reactive gas promotes accelerated oxidation, along with changes of the electrical conductivity. The materials specific parameter is monitored by a specially designed thin-film resistor sensor, integrated within a micro-fluidic flow cell. Recordings of the ozone induced conductivity (OiC) are presented for bio-diesel samples, processed from cotton seed oil, blended with and without antioxidants, as well as for fuel grade ethanol, and for commercial Petrol-Diesel, serving as a reference. The time delay between onset of ozone induced oxidation and associated increase in the electrical conductivity defines the oxidative stability, usually revealing a time span, ranging from minutes to hours. For comparison, Rancimat tests have been performed for the same samples. Comparable induction times were obtained for the OiC method under low ozone flux conditions. The set-up is an easy to implement proposed test method, and allows for electronic on-line fuel quality monitoring.     

Liquid rubber epoxy blends for Inhibition of Composite Propellants

Liquid rubbers, i.e. polysulphide (PS) and polybutadiene-acrylic acid-acrylonitrile (PBAN) have been blended with Dobeckot E-4 (commercial novolak epoxy resin) in different proportions. These systems have been cured using polyamine/polyamide curing agents and were characterized using gel time, % elongation, tensile strength and bond strength with composite propellants, heat resistance, dioctyl adipate(DOA) absorption, oxygen index, thermal conductivity and brittleness temperature. The data generated for various characteristics indicate that the formulations E-PS-9 and E-PBAN-2 are promising inhibition systems for composite propellants. The inhibition of composite propellants has been done with rayon thread impregnated with the formulations E-PS-9 and E-PBAN-2 using filament winding technique. The successful static evaluation of inhibited composite propellants at ambient, elevated and sub-zero temperatures proves the suitability of these systems for inhibition.     

Electrochemical investigations on the effect of dispersoid in PVA based solid polymer electrolytes

Various compositions of TiO₂ dispersed PVA‐PMMA‐LiBF₄‐EC based electrolytes were prepared using solution casting technique. The prepared electrolytes were characterized using AC impedance, XRD, SEM, FTIR, etc. The ionic conductivity value is increased with the increase in filler content (up to 8 wt %) and then decreased with the increase in filler content. The results are described using Vogel–Tamman–Fulcher theory. The thermal and transport properties of the electrolyte exhibiting maximum conductivity have also been studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3950–3956, 2007     

Thermal conductivity of suspension and emulsion materials

A technique for the prediction of effective thermal conductivity of porous materials previously developed by the authors has been extended to suspension and emulsion systems and its capability is supported by the available experimental data. A nomogram which estimates the effective thermal conductivity for these systems from the knowledge of constituent conductivities and proportions is also provided.     

Dispersion and film properties of carbon nanofiber pigmented conductive coatings

The use of multi-walled carbon nanotubes and nanofibers for coatings applications has been quite limited because of problems associated with obtaining dispersions of individual tubes/fibers. The potential for unique properties associated with these materials, such as obtaining electrical conductivity at very low volume concentrations, is dependent upon exploiting their very large geometric aspect ratios. Therefore, dispersion quality has a direct relationship to performance. We have developed a novel dispersion technique that appears to yield high quality dispersions without significant damage to the nanofiber properties. This technique involves the exfoliation of an aklylamine hectorite clay in the presence of nanofiber agglomerates, forming a stable gel, followed by stabilization with a suitable dispersant. We hypothesize that the size of the clay platelets is appropriate to penetrate the pores of the nanofiber agglomerates to assist in dispersive forces. Several thermoplastic acrylic coating formulations were prepared at various nanofiber volume concentrations utilizing this dispersion method. The onset of DC electrical conductivity was observed at only 4% volume concentration, indicative of high aspect ratios. Conductivity increases as a power law function of nanofiber volume concentration, resulting in 1.0 S/cm values at 12% volume.     

The use of drying experiments in the study of the effective thermal conductivity in a solid containing a multicomponent liquid mixture

The effective thermal conductivity of a porous solid containing multicomponent liquid mixtures has been studied. To achieve this, the liquid composition, liquid content and temperature distributions have been measured in a cylindrical sample dried by convection from the open upper side and heated by contact with a hot source at the bottom side. A quasi-steady state reached at high source temperatures permits to calculate the total heat flux from temperatures measured on the surface and the gas stream. The simulations performed and compared with experimental data made it possible to estimate the adjusting geometric parameter of Krischer's model for the effective thermal conductivity. The effective thermal conductivity has been widely studied for two-phase systems, mostly with regard to thermal insulation elements. The calculation of this transport parameter includes the contribution to heat transfer of the evaporation–diffusion–condensation mechanism undergone by the multicomponent mixture. The influence of liquid composition and temperature on the thermal conductivity due to the evaporation–diffusion–condensation mechanism and the effective thermal conductivity is described. The results reveal that in this case the resistance to heat transfer seems to correspond to a parallel arrangement between the phases.