We present here a review about our recent studies on relationship between viscoelastic responses and ordered structure, order-disorder transition, and thermal concentration fluctuations (critical fluctuations) of block polymers in condensed state. Brief reviews were first given on order-disorder transition and its characterization by using small-angle X-ray scattering (SAXS) in section 2, and on a relationship between the order-disorder transition and crossover of the flow behavior of block polymers in bulk or concentrated solutions with a neutral solvent in section 3.1. The block polymer solutions with a selective solvent were also discussed in section 3.2 where the two kinds of the thermal transitions (superlattice-ordering or -disordering and the order-disorder transition), their stabilities, and their effects on viscoelastic behavior were discussed. The stability, modulus, and yield stress of the superlattice was proposed to originate from the“entropy elasticity of the confined chains”. In section 4, we discussed the microdomain structure and viscoelastic response in the strong segregation limit, especially the effects of mixing of unlike segments in the domain-boundary region (“domain-boundary mixing”) and in the domains themselves (“mixing-in-domain”) on the viscoelastic behavior in time and temperature scales between the two primary transitions of the block polymers. The domain-boundary relaxation mechanism was proposed and its interpretation was given both from phenomenological and molecular view points. Finally in section 5 was briefly presented a new class of rheo-optical study to elucidate rheology and phase-transition of polymers in condensed state.
We review recent studies of dielectric relaxation and dynamical structure in solutions and melts of cis-polyisoprene (cis-PI) which exhibit dielectric normal mode process due to the fluctuation of end-to-end distance as well as the local segmental mode process. The influences of varying molecular weight, concentration, and solvent quality on the relaxation time for the normal mode process are discussed based on the bead-spring model and the tube model. The dielectric and mechanical relaxation spectra in bulk cis-PI are compared over a wide time scale covering both the wedge and box type spectral region. The relationship between the monomeric friction coefficient and the dielectric relaxation time for the segmental mode process is also discussed.
The purpose of this study is to clarify the relationships among raw material, molding conditions, supermolecular structure of the product and its mechanical property in the injection molding of particulate filled polypropylenes. Flexural specimens were prepared by injection-molding at the cylinder temperature of 200-320°C from polypropylenes filled with talc (flaky) and calcium carbonate (spherical) at the level of 0-60 wt%. We investigated supermolecular structures, such as the dispersion state of fillers, skin/core structure, and degree of crystal orientation and mechanical properties, such as flexural modulus, flexural strength, and mold shrinkage. The thickness of skin layer and the degree of crystal orientation decreased with increasing cylinder temperature, and increased with increasing filler content. For each sample a linear relationship between the thickness of skin layer and the degree of crystal orientation was found. The mechanical properties, such as flexural modulus, flexural strength, and mold shrinkage, also decreased with increasing cylinder temperature and increased with increasing filler content. In all cases studied, these properties correlated linearly with the thickness of skin layer or the degree of crystal orientation irrespective of filler content level. The results were interpreted as due to high degree of molecular orientation in the injection molded specimens of particulate filled polypropylenes.
The molecular orientation process during the injection molding of particulate filled polypropylenes was analyzed from the viewpoint of the growth of melt orientation (recoverable shear strain) at the gate and its relaxation in the mold cavity, based on rheological and thermal properties. The estimated variation of degree of orientation along the thicknesswise and the flow directions was well in accord with the experimental results of thickness of skin layer and degree of crystal orientation. Irrespective of differences in kind of filler, filler contents, and molding conditions, high correlation was obtained between the calculated average degree of molecular orientation and observed thickness of skin layer, or degree of crystal orientation. The observed increases of the thickness of skin layer and the degree of crystal orientation by the particulate filling were interpreted as due to i) long relaxation time of recoverable shear strain, ii) high thermal diffusivity, and iii) high crystallization temperature.
A steady laminar flow of an incompressible non-Newtonian fluid (inelastic power-law fluid; n<1) in pipelines with an axisymmetric sudden contraction was studied by experiments on pressure drops and a theoretical analysis using the finite difference methods. The main results obtained are as follows: (1) The sudden contraction loss decreases with increase in Reynolds number. The effects of the power-law index and the diameter ratio are small in the laminar flow and within experimental error in the range of the present experiments. (2) The present numerical method based on Kawamura's finite difference scheme and curvilinear grid points developed by Thompson et al. is useful for the contraction pipe flow in the range of 102-103 of Reynolds number. (3) The pressure at pipe wall has a minimum right after the sudden contraction section and through the recovery process, it becomes to decrease monotonously. In this monotonous region, the pressure under the same Reynolds number increases with decrease of the power-law index. (4) The pressure at pipe axis varies approximately as the pressure at pipe wall does. As Reynolds number becomes sufficiently small, the minimum right after the sudden contraction section disappears. (5) The velocity profile does not have a monotonous shape in the corner region of upstream side and in the separation region of downstream, and the maximum velocity at non-axial position appears in the downstream side of contraction pipe. (6) The vortex region in the corner of upstream side becomes larger with increase in Reynolds number. As Reynolds number becomes sufficiently large, the separation vortex region appears in the downstream side.