The 1998 SRJ award winner has concisely reviewed his achievements in both scientific and administrative fields which brought him the great honor. Some brief introductions have been made on a series of simultaneous and/or sequential chemical reactions occurred in binary blend systems which made them to be of high quality or more functional. First, a series of poly (organo aloxane)s were synthesized and solution-blended with polyacrylonitril. The dry spun fibers prepared from the blends of various compositions were subjected to the pyrolysis around 1000°C. The high temperature sintering reaction made the fiber electrically conductive, because the poly (organo aloxane) converted into alumina ceramics while fine continuous conductive carbon phases were generated as a result of the thermal decomposition of distributing polyacrylonitril components. Then in the second part, the role of chain-extender in developing high performance blends has been described: Blends consisted of a thermotropic liquid-crystalline polyarylate (LCP) and a flexible polyester were chemically linked with a bis-oxazoline to give a variety of block copolymers and then were cast into thin films. A dynamic mechanical test revealed that the chemical bonding between both component polymers has significantly been effective to improve the mechanical properties of the resultant films. In the third topic, the polyblending technique has progressively been applied to the environmental protection: It was found that, when immersed in aqueous media, the decomposition rate of polyamide blended with a small amount of polymer having ester linkages was much higher than that of Nylon 6 itself. Analytical studies with GPC, NMR, IR, visible and UV spectroscopes revealed that the carboxylic acids generated by the hydrolysis of ester-linkages might be responsible to the enhancement. By these examples, the author has intended to demonstrate that the introduction of chemical reactivity to polymer blends has possibly led to a development of new polymeric materials with superior function or performance. Finally a brief description has been made on his efforts as the editor of the Journal of SRJ from 1991 to 1997.
This article proposes a new method for dynamic viscoelastic measurements, named Fourier Transform RheoMetry (FT-RM), and proves its versatility using four apparatuses constructed on the basis of this novel idea. In FT-RM, strain is imposed on samples in the form of multi-frequency wave functions with angular frequencies ω=2iω0 (i=1, 2, 3, …) where ω0 is the fundamental frequency, and the storage and the loss moduli at respective w can be simultaneously estimated from Fourier analysis of the response function. This greatly improves a shortcoming of conventional dynamic methods with which the modulus-frequency curve is only obtained from repeated measurements at ten to twenty different frequencies. The method is shown to be particularly useful for studying frequency dependence of the complex modulus of samples whose viscoelasticity continuously changes with time, i. e., being neither in the thermal equilibrium nor in the steady state. Examples are given for four samples; (1) an automobile primer paint in the hardening process; (2)silica dispersion systems for clarification of an effect of preshear history; (3) rice starch through thermal denaturation; (4) epoxy/polyamide resin for examination of chipping performance.
Electrorheological (ER) fluids consist of dielectric particles dispersed in insulating oil. If an electric field is applied to these dispersions, the stress under shear flow is strongly enhanced, and the fluids behave as Bingham plastics. The mechanism of this ER effect is studied by a simple theory and numerical simulations. Under the electric field but no shear flow, the dispersed particles form chain-like clusters which align along the field and connect the two electrodes. The static yield stress of the fluids can be understood as the force necessary to break these clusters. If shear flow is also applied, however, the clusters should break into short segments. Our theory and simulation show that the clusters become shorter as the shear rate γ increases, but the stress due to the clusters remain almost independent of γ, as experimentally observed. It is also found that the strength of the induced stress is mostly determined by, and directly proportional to, the electrostatic attractive force between two particles contacting with each other. Transient response to a step-like electric field under steady flow becomes faster as γ increases. This is because the steady state length of the clusters becomes shorter, and also because the growth of the cluster becomes faster. Behavior of magnetorheological fluids under tilted magnetic fields is also studied.
This paper is concerned with some typical results obtained in our studies on transient flows of polymer solutions and liquid crystalline polymer (LCP) solutions with a view to the industrial applications in fluid engineering. We have mainly clarified the effects of forces generated in liquid films and those mechanisms with flow history for squeezing flows and so on. In examinations of lubrication for polymer solutions, improved transient responses in transmitting force have been obtained in squeezing flows with complex histories. That is, two plates with the polymer solution between them are hard to contact and easy to separate in a reciprocative squeezing flow. Moreover, the polymer solutions generate smaller amplitude of the force in an oscillatory squeezing flow. These phenomena are analytically expressed using a constitutive equation that is helpful to describe flow history effects such as a stress overshoot. An experimental study has been also conducted on a squeezing flow with a pre-shear radial flow for the LCP solutions. The response in the force generated in the subsequent squeezing flow is significantly influenced by the intensity of the pre-shear deformation and the length of the pause time taken after pre-shear flow. The difference in the response of the force is correlated with that in the optical flow pattern observed with polarizers. In a similar visualization of Couette flows with a pre-shear deformation, a rapid tumbling motion of LCP is observed in flow following strong pre-shear flow. The occurrence of the rapid tumbling motion is strongly dependent on the pre-shear rate and well explains a change in the transient fluidity of the LCP solution in the subsequent flow.
The coatings composed of a mixture of NAD/solution acrylic polyol/melamine formaldehyde resin give a typical two-phase structured system, not only in liquid enamel, but also in crosslinked filmes with discrete polymer particles, which brings out specific features in the coatings performance. Especially in the area of automotive metallic finishes, NAD has been used extensively to improve their rheology, mechanical properties and durability. The mechanism of the rheological control of the coatings by NAD particles is mainly discussed.
An investigation is carried out for flow of viscoelatic fluids through a concentric annulus channel converging at the inlet of a pipe, where such a flow configuration is often encountered in a needle part of a stop valve. Experiments are conducted using dilute polyacrylamide water solutions as viscoelastic fluids, with which measurements of pressure and observations with the flow visualization are made. In the experiment, complicated flow patterns which are caused by viscoelastic effects are observed, and the classification of prevailing flow modes is obtaind. By measurement of pressure along the channel wall, it is found that additional pressure loss exists in relation with an appearance of the extra normal stress due to the viscoelasiticity. A correlation is proposed to estimate the pressure characteristic across the entire region of the channel.
An experimental method for shear dynamic birefringence measurement was developed with a tensile oscillatory rheometer to study stress-optical relationship around the glass transition zone. Because of large compliance of the rheometer, the complex shear modulus and the complex strain-optical coefficient were erroneously measured as the modulus increased in the glass-to-rubber transition zone. However, the complex stress-optical coefficient, C*, was found to be precisely measured under the same condition. In order to examine reliability of the method, C* of a polystyrene with MW=270k was measured from the rubbery plateau zone to the glassy zone. The result was in accord with that obtained for tensile deformation as the linear viscoelasticity theory required. The complex strain-optical coefficient could be calculated from the complex shear modulus data measured with a conventional parallel plates shear rheometer.
We propose a theoretical model to explain the dip in shear stress as particles of differing conductivity are blended in an electrorheological fluid, a significant effect that has been experimentally verified and is of great practical importance. We propose that for low concentrations of high conductivity particles φh, clusters of particles are formed due to the enhanced electrostatic forces. The rigid nature of these clusters leads to cavities forming within the stress transferring columns under shearing deformation. These cavities are the reason for the decrease in shear stress, and the minimum is thought to correspond to the formation of a slip plane composed predominantly of cavities. The rise in shear stress as φh is further increased is due to the formation of percolating chains of overlapping clusters through the columns, which will enhance the stress transfer ability of the material. It is found that this model shows good qualitative agreement with the experimental results.