Keiji Minagawa

Direct observation of the biphasic conformational change of DNA induced by cationic polymers

The interaction between T4 DNA and basic polypeptides was observed using fluorescence microscopy. Free DNA molecules exhibited random Brownian motion accompanying the conformational change. With the addition of polycation, such as histone and polyarginine. DNA molecules tended to shrink to become spherical shapes. The persistent lengths and the distributions of long axis lengths of DNA‐polyarginine complexes were determined from the video images at various polyarginine concentrations. It is demonstrated that the conformation of DNA changes in a biphasic manner in the presence of polyarginine.

Nanocomposites of 2-arylpropionic acid drugs based on Mg–Al layered double hydroxide for dissolution enhancement

Naproxen (NP) and flurpibrofen (FB) as non-steroidal anti-inflammatory drugs (NSAIDs) of 2-arylpropionic acid derivatives have been used as host organic drugs to be intercalated into layered double hydroxide (LDH) applying reconstruction and co-precipitation techniques. The obtained NP-LDH and FB-LDH nanocomposites were characterized by X-ray powder diffraction, infrared and thermogravimetric analyses. From drug loading, thermal analysis and X-ray measurements we can decide that coprecipitaion technique is better than reconstruction technique to obtain intercalated monophase nanocomposites. In acidic medium LDH dissolved and the intercalated drug starts to release in a molecular form which is suitable for adsorption. The drug solubility has been investigated before and after intercalation. It has been found that LDH improves the drug solubility and its dissolution rate.

Effect of Pressure and Shear Stress on Crystallization Behaviors in Injection Molding

Abstract We studied in detail the effects of pressure and shear stress on the crystallization behaviors during injection molding process. Crystallization of isotactic-polypropylene (iPP) was simulated for various injection flow rates. The crystallization started during the filling stage under long filling condition. Moreover, the crystallization in some layers showed two -step growth behavior, while in other layers the crystallization does not progress during the packing -cooling stage. Since pressure becomes very high during molding process under long filling time condition, the change of pressure is the most important factor governing the crystallization.

Simulations of polymer crystallization under high pressure

High pressure crystallization of polypropylene was studied by means of PVT measurements and computer simulations. The isothermal crystallization behaviour were described by using a model which takes into account the effect of pressure on the temperature dependence of nucleation rate and linear growth rate. The agreement between the simulation and the experiments was seen in the tendency that the crystallization was accelerated by the high pressure. The non-isothermal crystallization behavior was also simulated by applying a generalized Avrami equation. The simulation curves well reproduced the experimental values below relative crystallinity 0.5 and below 100 MPa.

Effect of ionic interaction on elongational viscosity of ethylene-based ionomer melts

The effects of ionic interaction on the uniaxial extensional flow of polymer melts were investigated using poly(ethylene- co -methacrylic acid) and its metal (Zn, Na, Mg) salts. The presence of ionic bonding enhanced the elongational viscosity in the linear region and the degree of non-linearity. Both the linear and non-linear elongational viscosities were increased more by zinc ions than by sodium or magnesium ions. The order of elongational viscosities was in agreement with the order of activation energies obtained from dynamic shear measurements. It was concluded that the increase in both linear elongational viscosity and non-linearity is determined by the degree of ionic interaction. The different flow properties between zinc and magnesium ionomers indicated that the ionic cluster formation weakens the ionic interaction. A Bernstein-Kearsley-Zapas constitutive analysis revealed that the effect of ionic interaction under elongational deformation in the linear region is similar to that under dynamic shear deformation.

A reaction kinetics model of water sonolysis in the presence of a spin-trap

The time development of the concentration of a spin-trapped OH radical was studied by electron spin resonance at various sound intensities and various 5,5-dimethyl-1-pyrroline N-oxide (DMPO) concentrations in water sonolysis. The lifetime of the spin-trapped OH radical was also studied, and factors governing sonolysis are discussed. We found that the production of spin-trapped OH radical increases with increasing ultrasound intensity. The lifetime of a spin-trapped OH radical decreases linearly with increase in sonication time. This result suggests that an unknown scavenger is produced by ultrasound. Based on the above results, we suggested a model of the reaction kinetics and estimated the production rate of OH radical from this model.

Electro-magneto-rheological effects in parallel-field and crossed-field systems

Rheological measurements of electro-magneto-rheological (EMR) fluids were carried out by use of modified parallel-plate rheometers equipped with electrodes and magnetic coils. The electric field and magnetic field either parallel or perpendicular to each other were applied to a suspension of spherical iron particles under a constant shear flow. The EMR effects, evaluated as the stress increase induced by these fields, were compared. It was found that the parallel field gives a marked EMR effect in the spherical iron suspension and that the crossed field also results in an EMR effect though the increase of stress value under the crossed field is not so large. The difference in these EMR effects has been interpreted in terms of the different orientations of the dispersed particles toward the field directions. Similar experiments using a suspension of needle-like iron particles have also indicated that particle orientation plays a major role in the EMR effects.

Effect of ionic interaction on linear and nonlinear viscoelastic properties of ethylene based ionomer melts

The effect of ionic interaction on linear and nonlinear viscoelastic properties was investigated using poly(ethylene-co-methacrylic acid) (E/MAA) and its ionomers which were partially neutralized by zinc or sodium. Dynamic shear viscosity and step-shear stress relaxation studies were performed. Stress relaxation moduli G(t, y) of the E/MAA and its sodium or zinc ionomers were factorized into linear relaxation moduli G°(t) and damping functions h(y). The relaxation modulus at the smallest strain in each ionomer agreed with the linear relaxation modulus calculated from storage modulus G′ and loss modulus G″. In the linear region, the ionic interaction shifted the relaxation time longer with keeping the same relaxation time distribution as E/MAA. In the nonlinear region, the ionic interaction had no influence on h(y) when the ion content was low. At higher ion content, however, the ion bonding enhanced the strain softening of h(y).

Opposite electrorheological effects between urethane-based polymers having different terminal groups

Electrorheological (ER) measurements have revealed that a solution of a urethane-based polymer having a cyanoethoxy terminal group exhibits an increase in the elastic modulus under an electric field. In contrast, the elasticity of a similar polymer with a methoxy terminal group is decreased by the field. The opposite ER effects are discussed in terms of the induced segmental behaviour of the polymers.

A novel apparatus for rheological measurements of electro-magneto-rheological fluids

Abstract A parallel-plate rheometer equipped with electrodes and magnetic coils was developed for rheological measurements of electro-magneto-rheological (EMR) fluids which respond to both electric and magnetic fields. The effects of electric and magnetic fields perpendicular to the direction of shear flow were examined. It has been found that the shear stress of the fluid depends not only on the strength of the fields but also on the order of application. The apparent viscosity of the EMR fluid under shear flow increased when the electric and magnetic fields were applied simultaneously. The increase in viscosity was lower when only an electric or magnetic field was applied. The dependence of EMR fluid behavior on the external field conditions is discussed in terms of the difference between cluster structures induced by electric and/or magnetic fields.