Viscoelastic properties of several types of multi-component polymer systems were studied. For the miscible blends of poly(styrene-co-acrylonitrile) (SAN) with several (co)polymers, the time-temperature superposition principle was applicable over the entire temperature range and the relaxation behavior was similar to that of a blend consisting of homologous polymers. Poly(vinyl chloride) (PVC)/plasticizer systems exhibited a typical critical gel behavior by changing PVC concentration and temperature. For the carbon black (CB) suspensions, three different types of the rheological behavior were observed: highly nonlinear, elasto-plastic feature, sol-gel transition type behavior, and the slow relaxation due to Brownian diffusion, with the affinity of suspending medium toward the CB particles. Similarity between the behaviors of CB suspensions and ABS polymer melts is also discussed.
Flows of polymeric fluids and liquid crystalline polymers (LCPs) were studied in complex flow geometries. In the present paper, however, there is a focus on the flow analysis of the flow of LCPs. Numerical simulations of flows of LCPs were carried out using the modified Doi equation with the quadratic closure approximation. Molecular orientation of LCPs is strongly affected by the velocity field including both the shear and elongational flows in the complex geometry while the velocity distribution is modified by the molecular orientation. Numerical simulations for a flow between parallel plates containing a cylinder and a spinning flow are presented as examples. A novel rubbing-free alignment layer for LCs was proposed as an application of flow-induced molecular orientation of LCPs. The development of wavy texture in startup flows of LCPs through a slit cell was discussed.
Asahi KASEI group developed two types of ER fluid and succeeded in employing them to practical applications. A homogeneous type consisting of liquid crystalline polysiloxane and a diluent was used for an intelligent brake in a caster walker which prevents a patient from stumbling. A heterogeneous (particle dispersion) type was used for a clutch in an upper limb training system with 3D movements and 3D vision. Key points for employing ER fluids in such devices with less trouble were introduced. The ER effect generation mechanisms of the homogeneous type fluids (type A and type B) were proposed.
Mechanical properties of elastomers and their mixtures were investigated with respect to phase transition, that is, strain-induced crystallization of natural rubber. On crystallization of unstretched natural rubber, effect of fatty acids present in the rubber was investigated by polarized light microscopy. The fatty acids were proved to be nucleating agent on the crystallization. The strain-induced crystallization and its effect on the mechanical properties were investigated by measuring tear strength of blend of SBR with natural rubber dispersoid. Despite superposition of tear energy of SBR, the natural rubber/SBR blend showed abrupt increase in tear energy at melting temperature of natural rubber. Since, after removing fatty acids with acetone, the acetone-extracted natural rubber/SBR blend was superposed with temperature shift factor of SBR, fatty acids were suggested to play an important role in not only tear energy but also strain-induced crystallization.
This paper presents our three studies: (1) dynamic heterogeneity in miscible polymer blends, (2) dielectric study on the dynamics of flexible polymer chains in melts and solutions, and (3) stress relaxation of entangled polymer systems in biaxial extension. In the study of (1), we investigated the segmental and global dynamics mainly in miscible polyisoprene (PI) / poly(vinyl ethylene) (PVE) blends. Specifically, we estimated the characteristic sizes of the segmental motion. Furthermore, in order to see the effect of the concentration fluctuation (CF) on the segmental dynamics, we compared the dielectric relaxation spectra of the segmental motion between PI/PVE blend and PI-PVE diblock copolymer based on the fact that the CF amplitude is suppressed in the diblock copolymer system. In the second study, dipole inverted type-A polymers are used to investigate the detailed chain dynamics. In the third study, we determined the damping function in biaxial extensional deformation for polystyrene melts and compared with Doi-Edwards theory.
The studies concerning the influence of particle parameters such as size, shape and concentration on the rheological properties of graphite (GP) filled high-density polyethylene (HDPE) composites were carried out by using two kinds of GP with different shape and size distribution of the particles. Upon the critical concentration of fillers, the dynamic storage modulus G' remarkably increases and exhibits a "pseudo solid-like" behavior within the lower frequency region. These phenomena are assumed the characteristics of percolated network structure formed by the filler particles. The values of the threshold for two kinds of HDPE/GP composites are also evaluated. It is proved that the smaller was the specific surface of particles dispersed in the composite, the lower the thresholds. It is found that there exists correspondence between the morphology and the percolation phenomena of the rheological behavior for these composites. It is suggested that different topological parameters of two kinds of GP particles result in different percolation mechanism.
A flow model consisting of a clear annulus of the suspending layer surrounding a core of the suspension has been proposed for the flow of colloidal suspensions through a capillary tube. In the present study, on the basis of this model, we derived apparent viscosity equations by considering the effects of the slip along the wall of tube and the floc breakup due to shear stress for a coagulated region. The validity of the derived equation was confirmed as follows. For the dispersed region, the derived equation was applied to the experimental data measured by previous authors, in which the apparent viscosity of suspensions of rigid spheres decreased with decreasing capillary diameter. For the coagulated region, the equation was applied to the experimental results obtained by the measurement of apparent viscosity of a montmorillonite suspension. The apparent viscosity decreased with increasing capillary diameter in a region of low electrolyte concentration (0.3, 0.45mol/L NaCl). On the other hand, viscosity decreased with decreasing diameter in a region of high electrolyte concentration (0.8, 1.0mol/L NaCl).
Co-associating polymers (CAP) are new type of polymers carrying two different species of associative groups along the polymer backbone. Transient gels of CAP show many new interesting thermodynamical and rheological properties such as network inversion, reentrant gelation etc. In this paper, we study linear viscoelasticity of physical gels formed by CAP on the basis of transient network theory. Model CAP to be treated here are difunctional (A-B) and trifunctional (A-A-B) linear polymers, where A and B stand for the associative groups. It turns out that the dynamic shear moduli of difunctional (heterotelechelic) A-B polymers behave like a Maxwell fluid with a single relaxation time τAB=1/(βA+βB), where βi(i =A, B) are the dissociation rates of associative groups from the network junctions. On the other hand, shear moduli of trifunctional A-A-B polymers are well described by the two-mode Maxwell model with two relaxation times τAB and τAA=1/(2βA) when A groups are much less frequently dissociated from the junctions compared with B groups. In such case, structural transformations of the network are expected to occur at a characteristic frequency ω≈1/ τAB where two distinct rubbery plateaux meet.
A mesoscopic simulation method is presented to predict the drying behavior of polymer films using a dissipative particle dynamics method (DPD) with a simple model for evaporation. A gas phase is set above the polymer solution, and then evaporation of the solvent particle is calculated with appropriate parameters which lead solvent particles to prefer the gas phase rather than the polymer solution. A solvent particle that moves into the gas phase is considered as a gas particle after being determined as having evaporated. An effective mass is considered, so as to represent the relatively slower motion of the polymer particle compared to the solvent particle and the dependence of solvent diffusivity on its concentration in a polymer solution. A time-dependent profile of solvent concentration throughout the polymer film was successfully calculated, and skin formation, which indicates significant concentration gradients on the surface of the polymer film, was also observed.
This study is concerned with an origin of entry flow instability generated after vortex enhancement in elastic fluid flows. For this purpose flow visualization experiments of shear-thinning aqueous polymer solution were carried out by means of both tracer-particle method and dye-solution injection technique. Local instability in the salient corner vortex, which was observed as non-smooth particle paths, could evolve to globally unstable entry flow as the Weissenberg number increased. The visualization experiments using the dye-solution injection technique demonstrated that the main cause of the local instability was the occurrence and decay of a dip of the vortex boundary at the lip corner and the small amplitude oscillatory phenomenon of the detachment point had a secondary influence. It was, therefore, concluded that the occurrence of the dip at the lip corner was a trigger of the global entry flow instability after vortex enhancement. However, the mechanism of the occurrence of the dip at the lip corner remains to be an open question, thus it will be necessary to measure the transient velocity field near the lip corner using the LDV or PIV technique.