The variation of shearing stress with time at a constant rate of shear has been measured by means of a Weissenberg Rheogoniometer for suspensions of titanate fibers in polyacrylamide solutions. The titanate fibers employed are long thin needles having diameters smaller than 0.5 micron and aspect ratios (L/D) higher than 40. The flow behavior of the suspensions can be divided into three regions depending upon shear rate. In Region I (high rate of shear region) where no structure of fibers exists, flow curves of the suspensions are quite close to that of the medium. Non-Newtonian behavior is most remarkable in Region II (intermediate rate of shear region), which corresponds to the so-called second plateau region of suspensions. The suspensions behave like a Newtonian liquid in Region III (low rate of shear region). The effect of structure on flow behavior of the suspensions is remarkable in Region II and III. When shear rate is lowered instantaneously from a value in Region I or II, the shearing stress at a constant rate of shear increases first and reaches an equilibrium value with increasing time (rheopexy). However, the equilibrium shearing stress obtained by changing shear rate directly from a value in Region I to that in III is higher than obtained by changing shear rate stepwise by a constant factor. This suggests that the strength of structure depends on rheological history of the suspensions.
This paper describes a study of the elimination of crazing by even treatment in polymer coatings on wire. The crazing became invisible under an optical microscope after appropriate heat treatments, leaving some traces observable under an electron microscope. The thermal expansion of the polymer coatings and the enhancement of micro-Brownian motion of polymer segments by heat were found to be main factors affecting the elimination of crazing. The electrical and mechanical properties of enameled wires after the elimination of crazing were measured and compared with those of the original wires. Judging from the breakdown voltage of the treated wires, we found that the perfect elimination of crazing was not realized. However, examination of the stress-strain curve of the polymer coating removed from the wire showed that the crazing was almost perfectly eliminated by the heat treatment. The apparent activation energy for the elimination of crazing was evaluated for a variety of polymer coatings, and it was found that the increased energy was generally accompanied by increased glass transition temperature. The occurrence of crazing in the polymer coatings on wire can be prevented by relaxing the residual stresses by appropriate heat treatment. The time of treatment required for the prevention of crazing was measured at various temperatures, and the apparent activation energy for the process was evaluated. This energy was considerably lower, for all the tested polymers, than the activation energy for the elimination of crazing.
For a cylinder sliding downward in an inclined tube filled with a Newtonian fluid, the translational velocity was measured in the region of low Reynolds number and it was compared with the results of dimensional analysis and Irving's approximate treatment. The resistance to the sliding motion of the cylinder was also characterized on the basis of dimensional analysis. The translational velocity of cylinder V is expressed as V=VM/βV where VM, is the theoretical value derived from the approximate theory and Bv is an unknown function of the dimensionless quantities d/D, l/d, and ρs/ρ: _??_ Here, D is the diameter of tube, ρs is the fluid density, and d, l and ρ are the diameter, length and density of cylinder, respectively. Bv was 1.0±0.2 at d/D≥0.8, l/d=2-10, and ρs/ρ=2-7, respectively, and it decreased with increasing diameter ratio d/D. The resistance characteristic of sliding cylinder was expressed as _??_ in terms of the drag coefficient Ch and the Reynolds number Rh. The characteristic function βD was formulated as _??_ in experimental regions that d/D=0.80-0.93,l/d=2-10, and ρs/ρ=2-7. These equations may be applicable to determination of the viscosity of liquids, and give the basis of the“Sliding Cylinder Viscometer”. The design of Sliding Cylinder Viscometer was discussed and some recommended values of its main dimension were proposed.
The flow properties of concentrated solutions of styrene-isoprene block copolymers have been measured to investigate the effects of solvent, composition of the copolymers, and concentration. The solvents used in this study are n-tetradecane (nTD) and dibutyl phthalate (DBP); the former is a good solvent for the isoprene block and non-solvent for the styrene block, and the latter is the reverse. Apparent viscosity η vs. rate of shear γ curves for solutions of the copolymers show remarkable non-Newtonian character. In the stress relaxation after cessation of steady shear flow, the shearing stress never relaxes to the zero level leaving a residual stress σR. In this study, we defined the relaxed stress as Δσ=σ-σR, and the viscosity corresponding to Δσ asΔη=Δσ/γ. Quantities η, Δη, and σR increase with increasing concentration of the solutions and decrease with increasing the styrene content in the copolymers. σR, is almost independent of γ, while η and Δη depend strongly upon γ. The value of σR agrees very well with that of the yield stress aσy calculated from Casson's equation. These results can be explained by assuming that non-soluble block chains form the aggregates which have cilia of soluble block chains on the exterior. σR and Δη seem to be affected mainly by the stiffness of the aggregates formed and the viscous friction between the aggregates, respectively.
The stress relaxation of poly (isobutylene oxide) (PIBO) in air was measured under UV irradiation. It was found that the relative stress increased remarkably with the UV irradiation time. At the same time, however, the polymer degraded to a considerable extent with increasing irradiation time. The behavior was not observed for other crystalline polymers, such as poly (ethylene). The increment of the relative stress depended on the strain, temperature, and degree of crystallinity, and the relative stress increased with the degree of degradation. In nitrogen atmosphere the dependence was little discernible.