Akihiro Nishioka

Description of uniaxial, biaxial, and planar elongational viscosities of polystyrene melt by the K-BKZ model

Abstract The three types of Kaye–Bernstein–Kearsley–Zapas (K-BKZ) equations: Wagner–Demarmels (WD) model, Papanastasiou–Scriven–Macosko (PSM) model, PSM–Luo–Tanner (PSMLT) model have been examined to describe experimental results of uniaxial, biaxial, and planar elongational viscosities of polystyrene (PS) melt. In these equations, the viscosity was calculated from the relaxation spectrum and damping function. The relaxation spectrum was determined by dynamic shear experiment. The damping functions were obtained by stress relaxation experiments under biaxial, planar and shear deformations. The shear and biaxial damping functions were described better by the PSM and PSMLT models than by the WD model. However, the experimental planar damping function was not described well. This poor fitting to the planar damping function came from the result that the planar damping function gave more strain-softening than shear. In the theoretical predictions, the damping function of shear and planar elongations should be identical with each other. Our result is inconsistent with this prediction. The elongational viscosities were calculated from the relaxation spectrum and the damping functions, and then compared to experimental data. Elongational viscosities for planar and biaxial deformations were measured by the lubricated squeezing method. In the case of uniaxial deformation, it was measured by a Meissner-type rheometer. Experimental results of uniaxial and biaxial elongational viscosities agreed with the prediction of the PSMLT model. Although the PSMLT model under-predicted the planar elongational viscosity, it was concluded that this model was the best of three models.

Test of Ferroelectricity in Non-stretched Poly(vinylidene fluoride)/Clay Nanocomposites

We measured of the electric displacement D versus electric field E (D–E) hysteresis loop for non-stretched film samples of poly(vinylidene fluoride) (PVDF)/clay nanocomposites. The film was fabricated by compressing melted pellets followed by rapid cooling. The pellets were prepared by melt-compounding method. For the non-stretched film, we obtained clear D–E hysteresis loops that are clear evidence of ferroelectricity at room temperature. Results of X-ray diffraction pattern analysis indicate that the crystal structure of PVDF in PVDF/clay nanocomposites is similar to the β-form of pure PVDF. We conclude that the crystallization of β-form PVDF in PVDF/clay nanocomposites is induced by the epitaxial growth of the β-form on the surface of clay platelets.

Rheological characterization of ionic bonding in ethylene-ionomer melts with low neutralization degree

The roles of ionic bonding in molten ethylene ionomers without ionic aggregates were rheologically characterized in linear and nonlinear regions under shear. We have measured melt rheology of ethylene-methacrylic acid (EMAA) ionomers by means of dynamic shear, step-shear relaxation, and transient shear viscosity. The studied samples were EMAA copolymer (MAA=5.4 mol %), its sodium and zinc ionomers, in both of which the neutralization degree of total MAA is 20%, where no ionic aggregates exist. The dynamic shear properties revealed that the time-material superposition, i.e., the super-master curve, was applicable among the three samples, suggesting that the ionic bonding only acts as the increase of polymeric chain friction in the linear region. The damping functions from the step-shear relaxation were found to be identical to one another among the three, resulting in that the effect of ionic bonding does not appear. However, the damping property of the zinc ionomer, which was analyzed by the Bernstein–Kea...

Novel method for producing amorphous cellulose only by milling.

The present study investigated a novel method for producing amorphous cellulose by milling without adding water. A new type of milling machine was developed (called a shear and cooling milling machine (SCMM)), which was capable of applying mechanical shear and cooling during the milling process. The SCMM consisted of a pair of mortars attached to a servomotor and a ring cooler. Wide-angle X-ray diffraction (WAXD) analysis was used to determine the cellulose crystallinity in samples produced using the SCMM at different milling temperatures. The results of WAXD for cellulose powder milled at lower temperatures exhibited no diffraction peaks. This experimental result demonstrates that the SCMM produces amorphous cellulose easily by cooled milling without the addition of water. The milling conditions, such as the applied shear and cooling, can be used to control the crystallinity of cellulose.

Electrically excited oscillation and crystalline structure of a nanoclay/poly(vinylidene fluoride) composite film:

This study was conducted to investigate electrically excited oscillation and crystalline structure of nanoclay/poly(vinylidene fluoride) (PVDF) composite films. First, nanoclay/PVDF composite films are fabricated by solvent casting. Second, their PVDF crystalline structure and nanoclay orientation are analyzed using x-ray diffraction. The impedance characteristics of films are then measured. Third, the oscillation excited from films as a result of applied voltage is measured. Thereby, we confirmed the presence of unoriented β-phase PVDF crystals and exfoliated-type nanoclay structure in a composite film. The output oscillation showed monotonic component corresponding to the input sinusoidal voltage at a high frequency range, although its amplitude is low.

Computer simulation of binary mixtures of anisotropic hard particles

We performed isobaric Monte Carlo simulations of binary mixtures of hard disc-like particles called spherical discs. The shape of the spherical discs is determined by a sweep of the centre of a sphere of radius L on a disc of radius D. Simulations of binary mixtures of 370 spherical discs with D/L = 2.5 and 110 spherical discs with D/L = 5 indicated microphase separation of column clusters of larger discs in a fluid of smaller discs.

Surface rheology of rubbed polyimide film in liquid crystal display

The rheological properties of polyimide film surfaces have an important influence on contrast reduction during the in-plane switching mode of liquid crystal displays. To clarify these properties, the slight difference of deviation angles of liquid crystal directors from the rubbing direction were measured during prolonged exposure to alternating electric fields. The results indicate that the data can be well described using the Kelvin-Voigt model. The relation between the in-plane shear modulus G and the strain at the polyimide surface was also investigated based on the torque balance between the energy density of the electric field and the elastic energy density of the polyimide surface. It was found that much smaller G than bulk polyimide materials existed on the polyimide surface in liquid crystal display.

Computing Chemical Potential Using the Phase Space Multi-Histogram Method

We present a new simulation method to calculate the free energy and the chemical potential of hard particle systems. The method relies on the introduction of a parameter dependent potential to smoothly transform between the hard particle system and the corresponding ideal gas. We applied the method to study the phase transition behavior of monodispersed infinitely thin square platelets. First, we equilibrated the square platelet system for different reduced pressures with a usual isobaric Monte Carlo (MC) simulation and obtained a reduced pressure-chemical potential plot. Then we introduce the parametrized potential to interpolate the system between the ideal gas and the hard particles. After selecting the potential, we performed isochoric MC runs, ranging from the ideal gas to the hard particle limit. Through an iterative procedure, we compute the free energy and the chemical potential of the square platelet system by evaluating the volume of the phase space attributed to the hard particles, and then we ...

Critical Phenomena in Ferroelectric Polymers

Vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymers are ferroelectric materials and exhibit ferroelectric to paraelectric phase transitions. In order to understand the ferroelectric phase transition of polymers, we performed Monte Carlo simulations for the three states model which an extra freedom was added to Ising model. The simulations reproduced the characters of the ferroelectric phase transition of VDF/TrFE copolymers. The temperature dependence of the specific heat obtained by MC simulations revealed that the transition changed from a first order transition to a diffuse one and that the critical phenomena existed between them.

Hard Spherocylinders of Two Different Lengths as a Model System of a Nematic Liquid Crystal on an Anisotropic Substrate

In this article, we describe the effects of an anisotropic substrate on the alignment of a nematic liquid crystal. We examine how the substrate affects the alignment of a nematic liquid crystal by Monte Carlo simulation. The liquid crystal on a substrate was described by the phase separation of liquid crystal molecules and substrate molecules, both of which were modeled by hard particles. We used hard rods to represent both the liquid crystal and the substrate. The length of the hard rods representing the substrate was adjusted to represent the degree of substrate anisotropy. The results show that the nematic alignment could either be reinforced or weakened, depending on the length of the substrate rods. Mean field theory is used to analyze the simulation results. We confirmed that the distance over which the substrate affects the bulk liquid crystal is about 3 nm for the present hard-rod-based model.