It is a great honor for the author to be given the 1997 SRJ Award for his achievements on Polymer Rheology Research and Services to the Society. He specially appreciates that the subject of the Award includes the “Services” to the SRJ. In the award lecture, his initiation into the polymer rheology, the splendid cooperations of his colleagues to the research, brief comments on the past and future of polymer rheology as well as the SRJ, and finally sincere acknowledgments to his SENSEIs have been told. The award lecture has not include any science except for his recent interests on mechanical properties of canine artery.
This article summarizes our recent studies on rheological properties and structures of polymer blends in miscible and immiscible regions. In the miscible region, viscoelastic properties are quite similar to those of polymer solutions when one of the two components is not entangled and volume fraction of the other component is not so high. That is, viscosity behavior in semidilute region can be explained by the scaling theory and concentration dependencies of elastic parameters are also almost the same as those in solutions. In the immiscible region, shear stress σ and first normal stress difference N1 of equiviscous polymer blends are proportional to shear rate. Plots of rescaled transient stress curves after step change of shear rate vs. strain compose a single curve when shear rate ratio is constant. These results are consistent with the theory of Doi-Ohta. However, an undershoot of σ and an overshoot of N1 which cannot be expressed by the theory are observed after a step increase of shear rate. From direct observation of structural change, it was reported that initial ellipsoidal domains were extremely elongated, then ruptured to shorter ones and gradually changed to the final steady-state structure. The behaviors of transient stresses can be qualitatively explained by the change in the distribution of unit normal vectors of the interface. In the immiscible region close to the phase separation point, a rather sharp change of shear rate dependence of N1 from that in immiscible region to that in miscible region due to shear-induced homogenization was observed.
This paper is composed of two parts. The first part is a brief review of rheological behaviors of viscoelastic cationic surfactant solutions, and the second is a review of viscoelasticity of hard core suspensions. A cationic surfactant, cetyltrimethylammonium bromide (CTAB), forms long and stable thread-like micelles in aqueous solutions with sodium salicylate (NaSal). Then, a CTAB:NaSal/Water system showed pronounced viscoelasticity depending on the concentration of NaSal, CS, when the concentration of CTAB, CD, was kept constant. In the case of CS ? CD, the system exhibited a unique viscoelasticity essentially the same as that of a Maxwell element with only one relaxation time. In this condition, the plateau modulus was proportional to the square of CD. Thus, the origin of the elasticity in the system is entanglement effects between the threadlike micelles as in the concentrated polymer system. On the other hand, the relaxation time in this condition was controlled by the concentration of free Sal-anions, C*S, which could be easily estimated from CS and CD as C*S = CS-CD. A simple model (called the Phantom Network Model) proposed for entangling polymer systems can successfully explain the unique viscoelastic behavior of this CTAB:NaSal/Water system. Suspensions of silica particles dispersed in ethylene glycol possess inter-particle forces very close to the hard core one. Viscoelastic behavior of the monodisperse spherical particle suspension with the hard core inter-particle force was discussed from a series of expeniments of particles with various radii. The zero shear viscosities and the high frequency limiting viscosities were functions of only volume fraction of the particle independent of the particle radius. Relaxation times for the monodisperse suspension were well described with times necessary for dispersed particles to migrate randomly by distance equal to their radii due to Brownian motion. Thus, the origin of viscoelasticity for the monodisperse suspension should be the Brownian motion of the suspended particle. Viscoelastic behavior for bimodal suspensions with the hard core inter-particle force was also investigated to clarify contribution of the distribution of particle radius to their viscoelastic behaviors. When a particle radius ratio was less than 3, shape of relaxation spectra for the bimodal suspension was essentially the same as that of the monodisperse suspension. However, when the ratio was larger than 5, the shape of the relaxation spectrum was much broader than that of the monodisperse suspension. These mean that motions of two kinds of particles are averaged into those of a hypothetical particle with the average radius in the case of the radius ratio less than 3. The zero shear viscosities of the bimodal suspension exhibited minima at compositions dependent on the particle radius ratio, while the high frequency limiting viscosities were essentially independent of the composition in the entire range of the particle radius ratio examined.
Pigment dispersion technology plays an important role in attaining basic coating qualities such as a ”high quality appearance” and ”high durability”. Authors' experiments have quantitatively proved that a basic principle in pigment dispersion was an ”acid-base interaction between pigment and resin” in either non-aqueous or aqueous mediums, by optical and rheological measurements of pigment dispersions. These dispersions were prepared from pigments, acid-base characteristics of which were measured by a new method developed in our laboratory. A conventional pigment dispersing resin, called an ”amphoteric resin”, was also developed using a new idea that any conventional pigment having a variety of acid-base characteristics must be well dispersed, when a resin containing both acid and base functions was used. Pigments with almost no acid and/or base characteristic could be, however, well dispersed when the pigments were surface modified to have either an acid or base characteristic by plasma surface treatment. This result also supported that the ”acid-base interaction” was important in pigment dispersion.
We have developed a new type of fine fiber reinforced composites, prepared from rubber/polyolefin/nylon graft copolymer, named SHP (Super Hybrid Polymer). The fine fibers of nylon with 0.2 μm diameter are uniformly dispersed in matrix polymers composed of rubber and polyolefin, and they are strongly bound with matrix polymers by chemical reaction. The preparation of SHP is carried out by means of reactive processing and in situ fiber formation. SHP contains 33% of nylon fiber and 28% of polyolefin by weight. The rubber composites containing a desirable fiber content can be obtained by addition of NR or synthetic rubber to SHP. In vulcanizates of rubber composites, the fine fibers are uniformly dispersed in matrix rubber and the polyolefin particles are dispersed in size of less than 0.1 μm diameter in rubber phase. It is noticeable that polyolefin crystals grow from surface of fibers. The interfacial adhesion between fiber and matrix rubber becomes stronger not only by chemical bonding, but also by the anchor effect of polyolefin crystals. This strong interfacial adhesion effects give rise to many excellent physical properties of vulcanizates.
This paper discusses dynamics of aqueous suspension of core-shell type carboxylated particle using two characteristic quantities, the critical shear stress σc and the distanceξ. Here σc is the shear stress at which the suspension changes its flow behavior from Newtonian type to shear thinning type, and ξ is the distance between center to center of neighboring particles in flocculated structure of the suspension to be measured with the small angle X-ray scattering method. A finding of the relationship of σc=4kT/3πξ3 between σc and ξ strongly suggests that thermal motion of the particles in the flocculated structure can be regarded as Brownian motion of a free particle with a diameter ξ, and also that the shear-rate dependence of viscosity of the suspension, being related to destruction of the flocculated structure, can be explained by dynamical competition between the thermal motion and the hydrodynamic motion under shear flow. The ξ of the suspension is found to be almost independent of a degree of neutralization of carboxyl groups, indicating that electrostatic repulsion is negligibly small compared with hydrophobic attraction which is considered to play a dominant role for formation of the flocculated structure.
Large deformation of polymethyl methacrylate (PMMA) glass was examined under the condition of simple shear. Post-yield steady plastic flow was observed over a wide range of strain rate. For the post-yield plastic flow, the logarithm of shear viscosity plotted against the logarithm of shear strain rate showed a non-Newtonian behavior quite resembling the shear thinning behavior ob-served in polymer solutions and melts. Rate analysis applied to the non-Newtonian flow showed that the fully annealed equilibrium structure of undeformed PMMA glass has been changed into non-equilibrium meltlike structures in the state of steady plastic flow. Comparison of experimental values of the activation enthalpy ΔH and activation entropy ΔS for the plastic flow in simple shear with those in uniaxial tension and compression led us to the conclusion that the meltlike structures under quite different deformation conditions were uniquely expressed by a single characteristic equation relating the activation enthalpy ΔH to the activation entropy ΔS. Evaluation of shear activation volume in simple shear proved that the experimental functional relation of activation volumes in simple shear, uniaxial tension and uniaxial compression was in good agreement with theoretical relations predicted by the Eyring rate theory.
The effect of shear rate on the reduction in shear stress of electrorheological fluids made from blending of low and high conductivity particles was studied. It was found that while the blend composition corresponding to the dip in shear stress does not depend on the shear rate, the relative magnitude of the dip does depend on the shear rate. At higher shear rates the dip became less pronounced. This behavior cannot be explained by the usual Bingham fluid model, but can be interpreted if we assume that the structures causing the shear resistance change with shear rate.