The dependence of piezoelectric constants on measuring frequency and temperature has been observed for a variety of polymers. The characteristic features of piezoelectric relaxation different to elastic and dielectric relaxations are that the sign of piezoelectric constants is either positive or negative and that the phase angle in dynamic measurements is either in lag phase or in lead phase. For an oriented film of amylose, the instantaneous polarization at low temperatures is negative and the relaxational polarization at high temperatures is positive. The relaxation is related to the internal rotation of CH2OH polar bonds. An elongated film of copolymer of poly-β-hydroxybutyrate and poly-β-hydroxyvalerate displays a piezoelectric relaxation at its glass transition temperature, obeying WLF equation. Based on the theory of spherical dispersion model, the piezoelectric constants in the piezoelectric phase have been estimated. The calculated piezoelectric constants show no relaxation at the glass temperature, indicating that the apparent piezoelectric relaxations are caused by the influence of elastic and dielectric relaxations in nonpiezoelectric amorphous phase. For poly-β-hydroxybutyrate, the similar analysis shows that the piezoelectric relaxation is present even in the piezoelectric phase. The oriented noncrystalline phase, which is also piezoelectric, may show the piezoelectric relaxation. The piezoelectric relaxation in poled films of polyvinylidene fluoride in the glass temperature is mainly influenced by elastic relaxation.
This paper gives a review on extensional and fractural properties of monodisperse polystyrenes at elevated temperatures investigated by the present author and his coworkers. The extensional and fractural properties were measured for monodisperse linear and star polystyrenes over wide ranges of extension rate and temperature. From stress-strain curves, failure parameters such as failure stress σf and failure strain γf, and fractural parameters such as breaking stress σb and breaking strain γb were evaluated. Effects of molecular weight, polymer concentration, molecular weight distribution and branching on these parameters were discussed.
A capillary rheometer to achieve an extremely high shear rate was developed and applied to homogeneous polymer systems, polymer blends and solid particle filled polymer systems. Two non-Newtonian regions and a Newtonian region between them were observed in the wide range of shear rates up to 107 s-1. The flow behavior in high shear rate results from high orientation and scission of macromolecular chains. For the calculation of the viscosity-shear rate curves of blends, a concentric multilayer model was proposed. The model was proved to be useful not only for immiscible polymer systems, but also for miscible polymer blends in which some amount of macromolecules of each component could behave independently. The extremely high shear rate processing was applied to the immiscible blends to investigate a modification by the microstructure development in polymer blend by shear. Incompatible blends of SAN and PC were extruded with extremely high shear rate. Compatibility of SAN with PC was enhanced in extremely high shear rate processing. Fibrillation of PA-6 phase was obtained for HDPE-PA-6 blends by injection molding under extremely high shear at a temperature between the melting points of HDPE and PA-6. Flow analysis program for injection molding was developed by using the Flow Analysis Network Method (FAN). Flow behavior of polymer melts at the high shear rates was applied to the flow analysis program to improve the accuracy of the analysis.
Applicability of the Leonov constitutive model was investigated based on reliable experimental data on steady shear flow and stress relaxation after cessation of the flow for several concentrated polymer solutions and polymer melts. The following conclusions were obtained : (1) Analytical solutions for stress components in steady shear flow and stress relaxation after cessation of the flow were derived from basic equations of the Leonov model in different ways from those of Leonov et al. (2) Discrete relaxation time spectra were determined based on the dynamic viscoelastic data, assuming constant ratio τn/τn+1 for adjacent relaxation times and variable relaxation strength Gn. (3) When the discrete relaxation time spectra were determined properly in wide range of time scales, the Leonov model could predict quantitatively the shear stress and the first normal stress difference in steady shear flow for all samples investigated. (4) When the steady shear rate was high, the Leonov model gave much smaller stresses than experimental data at long time end of the stress relaxation. Since the first normal stress difference is underestimated in stress relaxation process, evaluation of flow birefringence and molecular orientation should be very careful when it is made based on the predicted stresses.
Steady shear and elongational flow characteristics have been measured for polystyrene melts filled with CaCO3 particles. The particle contents are 20, 40, 60 wt% and the average size of particles is 3 μm. The normal stress difference N1 at a fixed shear stress σ decreases as the particle content increases. There is a relationship between N1 and σ, N1 ∝ σ2, which is independent of particle content. The shear compliance Js at a fixed shear rate γ decreases with increasing particle content but is almost independent of γ for each content of particles. The extrudate swell ratio of polymer melt decreases with increasing particle content, suggesting a reduction of elasticity. Mixing of the solid particles also increases the elongational viscosity and the extent of viscosity increase depends on the particle content. At small strains, the transient elongational viscosity ηE+ of CaCO3-filled systems is independent of strain rate. After the strain exceeds a critical value, ηE+ increases with strain rate and strain. When the strain rates are low, ηE+ of the unfilled polymer has a tendency to approach to a steady value, while the filled samples still exhibit an increase of ηE+ with strain.
The mechanism of drag reduction caused by injection of concentrated polymer solutions into a turbulent pipe fllow was investigated by a tracer particle method, and the results were compared with those obtained by the previous LDV measurements. The conclusions obtained in this study are summarized as follows; (1) In a middle range of concentration of polymer, the multi-fine polymer threads (“MPT”) are mainly contained in the high speed large eddies of pipe flow. Both the radial fluctuation and the Reynolds stress for injected polymer threads are significantly suppressed, even at the center of pipe. (2) For the injection of a high concentration polymer solution, a single polymer thread (“SPT”) is relatively stable, and does not divide into fine threads. The highly viscoelastic polymer thread flowing mainly at the center of pipe is non-turbulent but shows a wave-like motion. The injected polymer thread has a rather uniform velocity which is lower than the medium (water) velocity at the center. A significant suppression of the radial fluctuation was observed. The Reynolds stress shows almost the same distribution as that of a Newtonian fluid flow in the relatively wide central region but reduces strongly near the wall. It was suggested that the wall turbulence structure could be controlled by suppressing the large eddy motion in the turbulent core region.
Microphase separation in segmented polyurethaneureas prepared from poly (oxyethylene)-poly (oxypropylene)-poly (oxyethylene) triblock copolyether was investigated, and their mechanical and blood-compatible properties were discussed in relation with microphase-separated structures. Elemental analysis and infrared spectroscopic measurements showed a regular chemical structure for the present polyurethaneureas having various hard-segment contents. Thermal analysis, dynamic mechanical analysis, and small-angle X-ray scattering (SAXS) measurements confirmed the microphase separation between hard-segment domains and soft-segment martices for all the samples. Hard-segment content little influenced the glass-transition temperature of soft segments, suggesting a well-defined phase separation. On the other hand, the physical properties of the segmented polyurethaneureas were much dependent on the hard segment content, for example, the tan δ peak became broader with increasing hard-segment content, and the SAXS peak shifted to the longer distance of the Bragg spacing. These results suggest that the interface between hard-segment domain and soft-segment matrix becomes thicker with increasing hard-segment content. This might be one of the reasons why the antithrombogenicuty lowered with the increase of hard-segment content.