Vinylidine Fluoride Research Articles

Effects of Carbon Black on Toner Tribocharging in Two-Component Electrophotographic Developers

Carbon black is the most widely used pigment for black electrophotographic toners. In this article the effects of carbon black on tribocharaging of two-component developers reported in the published literature are reviewed and compared to experemental work done recently. Carbon black is found to have the following effects on the triboelectric properties of model toners made from carbon black in a polymer binder: (1) In toners compared at the same carbon black loading, toners containing carbon blacks with greater work function (or surface acidity) charge more negatively. (2) Increasing the carbon black content causes the absolute value of the charge-to-mass of model toners to decrease when the toner is charged either positively or negatively using poly(methylmethacrylate) coated carrier or poly(vinylidine fluoride) coated carrier. (3) Q/m when the toner is charged negatively is a linear function of Q/m when the same toner is charged positively. (4) Increasing the carbon black content causes the absolute value of the slope and the intercept of linear plots of mass-to-charge as a function of the mass ratio of toner to carrier to increase. A steady-state version of the surface state model of tribocharging is developed and compared to experimentally observed tribocharging behavior. In this model, the rate of charging of the toner and the rate of discharging of the toner due to increased conductivity related to the carbon content of the toner are assumed to be equal at steady state. The model predicts all four of the observed behaviors.

The effect of the binder morphology on the cycling stability of Li–alloy composite electrodes

It is demonstrated that the design of the composite electrode, or more precisely the morphology and distribution of the binder poly(vinylidine fluoride) (PVdF) within the composite electrode, has a significant impact on the cycling performance of Li storage alloy (Sn/SnSb) electrodes. Different binder morphologies and distributions have been obtained by using different solvents for the slurry preparation, such as 1-methyl-2-pyrrolidinone (NMP), in which PVdF is dissolved, yielding electrodes with a homogeneously and finely distributed binder, or decane, in which PVdF is only dispersed, yielding electrodes in which the original particle morphology of the binder powder is preserved. In constant current cycling tests carried out in an excess of electrolyte, the electrodes with the ‘dispersed’ binder show far better cycling capacities and stabilities than those with the ‘dissolved’ binder. This is explained by the different binding strengths, swelling behaviour in the electrolyte, electrode porosities, and possible ‘buffer’ effects of the compact and the finely distributed binders.

Advances in theory of equilibrium melting point depression in miscible polymer blends

The crystalline melting temperature of miscible polymer blends, consisting of a semi-crystalline and an amorphous polymer, is considered from a theoretical point of view. The depression of equilibrium melting temperature of the crystalline region is formulated. It is shown that the use of experimental melting temperatures in calculating interaction parameter between the two components could lead to erroneous results. Instead, the equilibrium melting temperatures are required, in conjunction with an equation of state model, to calculate the interaction energy and other thermodynamic properties of the mixtures. The advantages of equation of state model in this respect are highlighted. Results of theoretical prediction are compared with experimental data on equilibrium melting temperatures of miscible poly(methyl methacrylate)–poly(vinylidine fluoride) blends.

Effects of Carbon Black on Toner Tribocharging in Two-Component Electrophotographic Developers

A steady-state version of the surface state model of tribocharging is developed and compared to the effects of carbon black on tribocharaging of two-component developers. In this model, the rate of charging of the toner and the rate of discharging of the toner, because of increased conductivity related to the carbon content of the toner, are assumed to be equal at steady state.Carbon black was found to have the following effects on the triboelectric properties of model toners made from carbon black in a polymer binder:1. Increasing the carbon black content causes the absolute value of the charge-to-mass of model toners to decrease when the toner is charged positively or negatively using poly(methylmethacrylate) coated carrier or poly(vinylidine fluoride) coated carrier.2. The ratio of q/m when the toner is charged positively to q/m when the same toner is charged negatively is a constant.3. Increasing the carbon black content causes the absolute value of the slope and the intercept of linear plots of mass-to-charge as a function of the mass ratio of toner to carrier to increase.The model predictions agree with these observations.

Interaction of supercritical carbon dioxide with polymers. I. Crystalline polymers

Supercritical fluid (SCF) technology involving carbon dioxide is recently receiving wide attention due to its vast potential application in various fields such as cleaning, extraction, synthesis, etc., in addition to its environmental benefits. To fully exploit the use of SCFs in new technologies, it is important to understand how SCFs interact with materials. To this end, we have undertaken a systematic study involving a wide pressure and temperature range to investigate the interaction of supercritical carbon dioxide (SC CO2) with nine different crystalline polymers, namely, substituted and unsubstituted polyethylene (four varieties), polypropylene, nylon 66, poly(ethylene terephthalate), poly(oxymethylene), and poly(vinylidine fluoride). Critical factors such as changes in appearance and weight, temperature, pressure and time of the supercritical fluid treatment, and dimension of samples have been observed. The influence of SC CO2 on the thermal properties of treated polymers has been investigated through TGA analysis. Further, changes in the mechanical properties such as yield strength, ultimate elongation, and modulus of elasticity of the investigated crystalline polymers were also observed. A discussion has been included to show the possible implications of the observed changes in realizing various applications. © 1996 John Wiley & Sons, Inc.

Interaction of supercritical carbon dioxide with polymers. I. Crystalline polymers

Supercritical fluid (SCF) technology involving carbon dioxide is recently receiving wide attention due to its vast potential application in various fields such as cleaning, extraction, synthesis, etc., in addition to its environmental benefits. To fully exploit the use of SCFs in new technologies, it is important to understand how SCFs interact with materials. To this end, we have undertaken a systematic study involving a wide pressure and temperature range to investigate the interaction of supercritical carbon dioxide (SC CO2) with nine different crystalline polymers, namely, substituted and unsubstituted polyethylene (four varieties), polypropylene, nylon 66, poly(ethylene terephthalate), poly(oxymethylene), and poly(vinylidine fluoride). Critical factors such as changes in appearance and weight, temperature, pressure and time of the supercritical fluid treatment, and dimension of samples have been observed. The influence of SC CO2 on the thermal properties of treated polymers has been investigated through TGA analysis. Further, changes in the mechanical properties such as yield strength, ultimate elongation, and modulus of elasticity of the investigated crystalline polymers were also observed. A discussion has been included to show the possible implications of the observed changes in realizing various applications. © 1996 John Wiley & Sons, Inc.

Kerr-effect measurements on poly(vinylidine fluoride), poly(methyl methacrylate) and their blends

The dynamic electro-optical effect of poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA) and their blends is reported. The response of PMMA exhibited one detectable relaxation in the vicinity of the glass transition, the time constant of which revealed that it is due to side-chain rotation. In contrast, two relaxations were detected in the PVDF melt. From the strength of the faster, the orientation correlation coefficients g 1 and g 2 can be calculated to be 0.5 and 15, respectively, indicating an antiparallel arrangement of the individual electric moments of the monomer units. The slow relaxation is suggested to be due to weakening of these correlations by the action of electric-field-injected charges. The kinetics of that distortion are enhanced by blending with PMMA, whereas the other relaxations of both components do not change with blending.

Effect of temperature on the charge-field hysteresis phenomena in lanthanum-doped lead zirconate titanate-poly(vinylidine fluoride) composite

In recent years a lot of work has been done on the development of various types of polymer-ceramic composites for different applications [1-3]. This is due mainly to the fact that composites allow the flexibility to have a resultant product combining the required properties of the two materials to suit the specific application [3]. However, attention is focused more on the preparation of the composite samples, their poling for obtaining net polarization [4-6] and understanding the mechanisms involved. The lead zirconate titanate (PZT)-poly(vinylidene fluoride) (PVDF) system has been found to be a good composite system [7] from the application point of view, but very little attention has been paid to studying the hysteresis phenomenon in these composite systems. In this letter we report the effect of temperature on the charge-field hysteresis phenomenon of a lanthanum-doped PZT (PLZT)-PVDF composite prepared with a weight ratio of 90:10, respectively. The PLZT and PVDF used in the experiment were obtained from Central Electronics Limited (India) and Aldrich (Switzerland), respectively. The composites were made by taking the required weight ratio of PLZT and PVDF (i.e. 90:10 in the present work) and were mixed and ground thoroughly using acetone as a thinner, so that all of the grains of PLZT were covered with PVDF and the powder became dry. This dry powder was pressed in a 1 cm diameter die under a load of 10 t at 160 °C. The die was cooled to room temperature under the applied pressure. The load was released and the pellet was taken out at room temperature. Quick-drying silver paint was used for electrodes. The Sawyer and Tower circuit was used for hysteresis studies and the loops were traced using Philips PM 3055 oscilloscope. The temperature was controlled within an accuracy of _+ 2 °C by using an electronic relay. An a.c. field (50 Hz) was applied through an isolated step-up transformer. Dielectric measurements were done on a Hewlett-Packard impedance analyser (no. 4192A). A representative charge-field hysteresis loop is shown in Fig. 1. The results of the effect of temperature on the coercive field (Ec), total polarization (Pt), which is the sum of saturation polarization (Ps) and induced polarization (Pi), and the remanent polarization (Pr) are given in Table I. It can be seen from the table that Pt and Pr decrease with increasing temperature up to 100 °C and then

Effect of Viscosity Index Improvers on the Elastohydrodynamic Lubrication Characteristics of a Chlorotrifluoroethylene and a Polyalphaolefin Fluid

The film thickness characteristics and traction behavior, two of the more important elastohydrodynamic lubrication (EHL) properties, of two important classes of synthetic lubricants have been studied. The effect of viscosity index (VI) improvers on these properties has been determined for both hydrogenated polyalphaolefin (PAO) base fluids and chlorotrifluoroethylene oligomer (CTFE) base fluids. A polyalkylmethacrylate (PMM) VI improver was studied in PAO and a copolymer of vinylidine fluoride and chlorotrifluoroethylene was studied in CTFE. The VI improvers demonstrated insignificant improvement in the EHL film thickness of both the PAO and CTFE base fluids as determined by comparing the measured film thickness of the VI-improved fluids to the predicted film thickness based on measured pressure-viscosity characteristics and kinematic viscosities determined at low shear rates. Similarly, the traction behavior of VI-improved PAO and CTFE fluids was nearly equivalent to that of the respective base fluids, demonstrating very little effect of the VI improvers on these properties. The minimal contribution is attributed to the non-Newtonian behavior of the VI improved fluids under the high shear rates and stresses found in an EHL contact. Physical properties of the base oil determine the true behavior of a VI-improved fluid under EHL conditions; therefore, the properties of the base fluid should be used in theoretical predictions instead of the properties of the formulated fluid.

Structure and polarization in piezolectric polymers

Poly(vinylidine fluoride) undergoes several structural conversions during electrical poling which contribute in different ways to its pyro- and piezoelectrical properties. These conversions originate from the molecular dipoles of the CF 2CH 2 monomer unit and its interaction with the poling field. Therefore orientation effects play an important part in these structure formation processes. The mechanism of structural conversions of materials with different conformations and crystalline structures has been investigated with regard to dependence on the poling conditions. By means of modified wide-angle X-ray methods it is possible to separate individual effects from each other.

Electrical properties of ceramic/polymer composites

Three types of ceramic/polymer composites were prepared and their electrical, dielectric and pyroelectric properties analyzed. The composite PZT5/VDF-TrFE shows a significantly higher pyroelectric figure of merit than PZT (VDF=vinylidine fluoride, TrFE=trifluoroethylene). The dielectric loss of the ceramic/polymer composites is observed to be dominated by those of the polymer, whereas the ceramic phase has a significant contribution on the steady-state electrical conduction and low-frequency dielectric loss at high temperatures. >

Depth-Profiling Studies of Double-Layer PVF2-on-PET Films by Fourier Transform Infrared Photoacoustic Spectroscopy

Photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR) is used to study films of poly(vinylidine fluoride) (PVF2) and poly(ethylene terephthalate) (PET). It is shown that PVF2 films over PET change the thermal diffusion length such that the sample PVF2-on-PET becomes optically transparent and thermally thick. By changing the mirror velocity of the Michelson interferometer it is possible to obtain spectra at various sample depths. The intensity of the carbonyl band of the lower PET film changes as a function of the mirror velocity. The log-log plot of these quantities gives a slope of −3/2, which agrees with theoretical predictions for thermally thick and optically transparent samples.

Hydrogen bonding in polymer systems

AbstractThe importance of hydrogen bonding interactions in promoting polymer miscibility has been the subject of much recent investigation. In this study, we address the question of the effect of molecular size and geometry on the intensity of the hydrogen bonding interaction. To this end, the interaction of the functional group in various molecules with a variety of acid and base polymer matrices has been monitored using infrared spectroscopy. The “probes” used in this study each contained only one functional group per molecule to prevent intra‐molecular association. The probes were acetone, di‐n‐hexyl ketone, 10‐nonadecanone, cyclohexanone, cyclododecanone, isopropanol, 4‐decanol, 10‐nonadecanol, cyclohexanol, and cyclododecanol. The interactions of the base probes with poly‐(vinyl chloride), poly(vinylidine fluoride), phenoxy, poly(styrene‐co‐allyl alcohol), and a variety of cellulosic polymers were studied. Acid probe interactions were measured in poly(pivalolactone), poly(butanediol‐1,4‐terephthalate), poly‐(acetal), poly(ϵ‐caprolactone), poly(vinyl methyl ether), poly(4‐methoxy styrene) and poly(ethylene oxide). The effect of the presumably inert poly(styrene) and ethylene‐propylene rubber matrices on the probe's functional group was studied for comparison.

Complement activation by plasma separator membranes.

Because of their structural similarity to dialysis membranes, six plasma separator membranes were evaluated for the ability to activate complement, as judged by immunoconversion of the third component of complement in crossed immunoelectrophoresis. A polysulfone and two cellulose acetate membranes were relatively strong alternative pathway activators. Polypropylene, poly[vinylidine fluoride] and polyvinyl-chloride derivative membranes were weak activators in some sera. Membrane activation was inhibited in citrate-anticoagulated but not in heparin-anticoagulated plasma. The results of such in vitro screening should be of value in selecting materials and anticoagulation regimens for membrane plasma separators.

Nuclear magnetic relaxation and molecular motion in poly(vinylidine fluoride)

AbstractPulsed NMR T1, T2, and T1ρ measurements are reported for poly(vinylidine fluoride) (PVF2). The results demonstrate clearly the presence of four relaxation processes, three amorphous and one crystalline. The α relaxation is undoubtedly a crystalline one, while β and γ are both amorphous, in agreement with earlier conclusions from dielectric and dynamic mechanical measurements. The fourth relaxation (β′) observed initially in the mechanical measurements of Kakutani, but undetected in dielectric experiments, has been confirmed in our results and the process is described by an activation energy of 15.1 kcl/mole. Motion of folds on the surface of crystal lamellae is deemed to be the responsible mechanism for the β′ relaxation. Two models have been considered in the interpretation of the α process; rotation of crystalline chains in the vicinity of defects and rotational oscillation of restricted amplitude of all crystalline chains about the main chain axes. Rotation of amorphous chains is a possible mechanism for the γ process while motions of a general nature are responsible for the β relaxation. Our experimental results again indicate that spin diffusion plays an important role in the overall NMR response of the polymer.

Protection against intense light. II. The role of the gaseous decomposition products

AbstractScreening studies have shown that of a series of halogenated vinyl polymers, poly(vinylidine fluoride) gives comparatively good thermal protection when exposed to the intense light energy of the carbon are‐image furnace. Results indicate that this protection is undoubtedly provided by polyenes, (CHCF)n, formed during pyrolysis. Decomposition products containing these structures are expelled by the gases formed into the region between the light source and the target where they intercept photons from about 200 to 500 mμ and dissipate the energy to the air as heat and/or reradiate it. Instrumental evidence for polyene formation is given. The concept of polyene formation clarifies the relative thermal protection offered by a series of vinyl polymers.

The chemistry of xylylenes. X. Some polymers and telomers of spiro‐di‐o‐xylylene

AbstractSpiro‐di‐o‐xylylene polymerizes via a free‐radical mechanism to give high molecular weight poly(o‐xylylene). It reacts with olefinic molecules, such as styrene, acrylonitrile, methyl methacrylate, vinylidine fluoride, and butadiene to give copolymers containing di‐o‐xylylene units in its backbone. Solutions of spiro‐di‐o‐xylylene can be titrated with iodine, and di‐o‐xylylene‐di‐iodide is produced stoichiometrically. Telomers of di‐o‐xylylene are obtained when the spiro compound is allowed to react in the presence of chain transfer agents such as HSR and CBr4.