A rheometer that has an ability of sensitive torque measurement has been developed, which was installed the rheometer functions, such as vibration measurement, based on the coaxial-cylinder rotational viscometer with outer cylinder rotation system that had been developed in our laboratory. The outer cylinder rotation system (Couette style) should be chosen for the rheometry of low viscosity materials. It was necessary to improve the resolution of the motor rotation and the response speed of the torque measurement system. A custom-made stepping motor was employed for the rotation mechanism, which is driven by a high-resolution driving method. As for the torque measurement system, following alternation were made, that is, to decrease the moment of inertia, to improve mechanical strength of the voice coil motor that generates balancing torque against the measuring stress, and to increase the acquisition rate of measurements by using an AD converter. Four modes of driving method, steady flow, vibration, go-and-back rotation, and rectangular wave are programmed for the measurements. As an evaluation of the performance at present from some examination, the torque sensitivity about 3 nNm, and the frequency limit of the vibration measurement mode about 10Hz or higher were found. It was confirmed that this rheometer has advanced elemental abilities.
Structure and viscoelastic properties of aqueous wormlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) were investigated by rheological measurements, flow visualization using small dispersed particles and small-angle neutron scattering under steady shear flows. The concentrations of CTAB and NaSal were respectively fixed at 0.15 mol L−1, so as to show Maxwell type relaxation behavior in the linear mechanical response region. According to the stress response of steady shear flow measurements, shear rate regions were classified into three regions, i.e. (A) a Newtonian region (for γ < γl), (B) a stress plateau region (for γl < γ < γh), which had a characteristic behavior of the shear-banding, and (C) a stress turnup region (for γ > γh) where shear stress increased with γ again. It was revealed that the fraction of the nematic phase flowing at γh was proportional to the shear rate in the region B. The first normal stress difference, N1, was approximately proportional to the shear rate in the region B, while it gradually decreased with increasing shear rates in the region C.
Linear viscoelastic behavior was examined for poly(dimethyl siloxane) (PDMS) gels scarcely crosslinked through the double-liquid reaction. The gel sample after the sol extraction exhibited the fast and slow relaxation processes characterized with the power-law behavior of the dynamic loss modulus, G" ∝ω0.5 and G" ∝ω0.8 at high and low angular frequencies ω. The fast relaxation was essentially the same as that in the gel before the sol extraction and attributed to the constraint release (CR)-Rouse relaxation of individual gel strands having a considerable length distribution. In contrast, the slow relaxation, being related to cooperative CR involving neighboring gel strands, appeared to become faster after the sol extraction than before. This puzzling result may have reflected a spatial heterogeneity of the crosslinking density, although this hypothesis has not been proven yet. For the as-prepared PDMS gels containing the sol chains, an increase of the crosslinking density was found to extend the CR-Rouse relaxation tail to low frequencies compared to the more scarcely crosslinked strands after the sol extraction. Thus, the CR motion of the strands appeared to be more strongly affected by the crosslinking density than by the sol chains.
After application of a large step shear strain, a polymer droplet in an immiscible polymer matrix takes rod-like and spheroidal shapes before returning to the spherical shape. Change in semi axes of those droplets is calculated based on the Cohen-Carriere theory and the extension of the theory by Okamoto et al. From comparison with experimental data, it has been found that retraction of semi axes is well described by the theory using a hydrodynamic factor for the droplet associated with the viscous resistance of the matrix. The excess shear stress for rod-like and spheroidal droplets is predicted based on the Doi-Ohta theory by evaluating the interface tensor from the semi axes calculated. The predicted excess shear stress for the deformed droplet is close to experimental data of a polymer blend with narrow distribution of droplet size after normalization per one droplet with the volume-averaged radius. The effects of polydispersity and interaction with adjacent droplets in the blend are suggested for the remaining difference between the prediction and the data.
Dielectric behavior was examined for an aqueous solution of a two-tail lipid, 1,2 dioleoyl-sn-glycero-3[phospho-L-serine] sodium salt (DOPS Na). At the concentration and temperatures examined (0.02 g cm−3 and 15-60 °C), the lipid molecules formed unilamellar and multilamellar vesicles having a large, correlated fluctuation in curvature. The system exhibited the dielectric dispersion attributable to the electrode polarization of the mobile ion, Na+. The observed dispersion frequency and intensity were higher and smaller, respectively, than those expected for the Na+ ions freely moving between the electrodes. This result suggested that the motion of Na+ in the DOPS-Na system was mostly confined between the vesicle walls. Furthermore, analysis of the dielectric behavior of the DOPS Na system at various T suggested that the spatial confinement for the Na+ motion loosens with increasing T.
Ethylene-propylene block copolymer (EPBC) is mainly composed of two component polymers, polypropylene (PP) and ethylene-propylene rubber (EPR). The dependence of morphologies as well as dynamic moduli of EPBC on the molecular characteristics of the components were investigated for four EPBC samples. From the results of the temperature dependence of dynamic moduli and the morphologies, it was suggested that the samples have heterogeneous structure composed of a dispersed EPR phase and a PP matrix phase in which a part of the EPR component dissolves. The concentration of dissolved EPR in the matrix increases with increasing propylene content of the EPR component. For the melts of the EPBC samples containing the EPR component of higher than about 70 wt% propylene contents, a secondary plateau was observed in the long time region on the dynamic viscoelasticity curves. To clarify the origin of this slow relaxation, the dynamic viscoelasticity were compared with three theories: Palierne's emulsion model, the thermal diffusional model and the blending rule. The comparison suggested that the blending rule can well explain the secondary plateau behavior originated from the existence of the high molecular weight EPR dissolved in the PP matrix.
We examined temperature(T)- and molecular weight(M)-dependent changes of the phase separated structure in immiscible polymer blends. Blend samples used were polyisoprene(PIP-H: Mw = 19.9×103; PIP-L: Mw = 14.4×103) and polydimethylsiloxane(PDMS: Mw = 1.20×105). The blend ratio was PIP/PDMS = 8/2(wt/wt). These blend samples included discrete phases(droplets) of PDMS and showed the relaxation much slower than the component relaxation. This relaxation reflected the shape recovery of the droplets, and the PIP/PDMS interfacial tension can be estimated with Palierne model. The interfacial tension decreased with increasing T, and this decrease was bigger for PIP-L than for PIP-H. These results agreed with the T and M dependencies of the UCST-type polymer-polymer compatibility.