Large stress increase by application of electric fields (ER effect) was found for homogeneous fluids of liquid crystalline polymers based on polysiloxane (LC silicones). LC silicones diluted with dimethyl silicone, which mesogenic groups were introduced as biterminal group (biterminal type) and as side chain group (side chain type) showed much larger ER effect than those introduced as monoterminal group (monoterminal type). ER effect of the side chain type tended to increase with an increase in positive dielectric anisotropy of the mesogenic groups. The LC silicones showed shear thinning at high shear rate while they showed Newtonian flow at relatively low shear rates. Complex dynamic modulus and viscosity of the side chain type measured under an electric field did not depend on strain up to large strain amplitude while those under no electric field depended remarkably on the strain. These tendencies were discussed in relation to the existence of flexible chain spanning liquid crystalline domains.
The complex Young's modulus, E* (ω), and the complex strain-optical coefficient, O* (ω), were simultaneously determined at various temperatures (T) covering from the rubbery to the glassy zone for a series of alkyl methacrylates, poly (methyl, ethyl, n-butyl, and n-hexyl methacrylate). At T above the glass-to-rubber transition temperature, T<TUB>g</TUB>, all samples exhibited a negative peak in the imaginary part of O* (ω) at 2 H<TUB>z</TUB>, O″(ω). The negative peak appeared to be related to polymer chain orientation. At lower T near T<TUB>g</TUB>, a positive O″ peak corresponding to the α dispersion was observed. For the four samples the magnitudes of those negative and positive peaks decreased and increased, respectively, with increasing length of the alkyl-group. With further decreasing T below T<TUB>g</TUB>, the methyl and ethyl esters again exhibited a negative O″ peak, that was attributed to the β dispersion as judged from viscoelastic data.
Flow properties and aging mechanism were analyzed at three different pH, under simple Bingham approximation of steady flow, for complex suspensions containing finely powdered In2O3and SnO2 sol that was in situ precipitated during gridding processes. At pH 5, near isoelectric points of both oxides, gelation was mainly attributed to crosslinking of the pre-existing flocs. In contrast, increase in the viscosity during aging at pH 2 and 9.5 was mainly due to increase in effective floc volume. The total pore volume, median pore size, and Vickers hardness of slip cast body were found to be closely related with the change in the Bingham yield value during aging.
Temperature (T), molecular weight (M), and concentration (C) dependence of zero shear viscosity (η0) was investigated for solutions of poly (acrylonitrile/vinyl acetate=97/3 wt.%) copolymers with various M ranging from 5×104 to 110×104 dissolved in aqueous NaCNS. The results were as follows; 1) In η0 exhibited linear dependence on 1/T. The activation energy of flow was E_??_6 Kcal/mol and was independent on M and C for the solutions studied. 2) Plots of log η0 vs. log C and log η0 vs. log M were represented by two straight lines with different slopes. The C dependence of η0 was described by power-law relationships η0 ∝C5.5(C>Cc) and η0∝C3.5(C<Cc) and the M dependence, by η0∝M3.4 (M>Mc) and η0∝M2.3 (M<Mc). Here Cc and Mc are critical concentration and critical molecular weight for chain entanglement. 3) The M dependence of Cc and C dependence of Mc were commonly described by a power-law relationship, M·Cc1.5=Mc·C1.5=K (constant).
Effects of a 21-wk exercise training on the mechanical properties and density of bone of the tibia ant the femur were evaluated for 9-wk and 63-wk old wistar 40 male rats. Mechanical tests were conducted for tibial bone. Dynamic stiffness and tan δ were measured with a viscoelastic spectrometer, and a three-point bending test was performed with an Instron-type universal testing machine. Bone mineral content was measured by photon absorptiometry at the middle site of the tibia and the femur. For both young and old bones, the exercise training induced differences in mechanical properties and density. The training effects were considerably different for the young and old bones and greater for the former.
Transient stress of a liquid crystalline solution of poly (γ-benzyl-L-glutamate) after flow reversal was examined to prove shear-induced structural changes in mesoscopic domain level of the system. At first, a theoretical prediction for the transient behavior of flow reversal was discussed using recent polydomain theory of Larson and Doi. After obtaining damped oscillatory stresses for the flow reversal, two experiments such as stress relaxation and stress growth were additionally performed at strains at which stress maxima and minima after the flow reversal appeared. Analysis of characteristic relaxation times for the stress relaxation curves at each extremum can prove the damped oscillatory pattern of domain size after the flow reversal. The orientational change of polydomain field after the reversal also oscillates in the damped manner, which can be demonstrated by the phase shifts deviated from the steady state response.