Dynamic viscoelasticity is measured for threadlike micelles from cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at temperatures T=25, 33, 40 and 50°C. The CTAB concentration of the solutions is fixed at CD=0.01M and a ratio of NaSal concentration CS to CD, CS/CD, is varied from 1 to 41. Effects of both CS/CD and T on frequency dependence of storage and loss shear moduli, G′(ω) and G″(ω), are described in this paper in detail. Characteristic features of this micelle system may be summarized as (1) at 25 and 33°C, the steady viscosity η and the mechanical relaxation time τM both show a minimum at CS/CD~4 that is followed by a maximum at CS/CD~10 as CS/CD increases. (2) The η and τM monotonically decrease with increasing T in the range of CS/CD from 1 to 20, but the maximum itself gradually disappears as T increases. (3) The steady state compliance Je is independent of T and decreases at lower CS/CD. A rapid increase in Je is observed at higher T and CS/CD ends. (4) An additional viscoelastic relaxation process is observed at the high frequency side. This mode appears in the same ω range independent of the salt concentration and exhibits the T dependence such as a type of the local friction factor, ηs/T. The discussion is mainly devoted to the applicability of a couple of models proposed so far.
Non-Newtonian characteristics of boundary layer flow passing a flat external surface with zero incident angle were studied using Phan-Thien Tanner (PTT) type constitutive equation with the network theory. A consideration is given to the shear thickening and the shear thickening-thinning characteristics of fluid in the flow problem. The Von Karman integral equation is solved numerically in order to obtain the boundary layer thickness and associated friction coefficient. Two important parameters in the network theory, the segment number and chain slippage parameter, are discussed to investigate their effects on the boundary layer characteristics. The calculated results indicate that there are large jumps of boundary layer thickness at the leading edge of the plate for small slip parameters when the effect of normal stress is not included in the calculation. On the contrary, the jumps are eliminated, particularly for smaller Reynolds number, with the inclusion of the effect of normal stress.
Normal force is measured which is generated in the flow between two rollers, one rotating and the other fixed. Aqueous glycerin solutions are used as Newtonian fluids, and dilute solutions of polyethylene oxide (PEO) and polyacrylamide (Separan) are used as viscoelastic fluids at concentrations of 50 to 1000 ppm in weight. The force measured for viscoelastic fluids is larger than that for Newtonian fluids. The normal force for Newtonian fluids is evaluated by applying the Cameron's theory with the Reynolds equation and the half Sommerfeld condition. It is found that the calculated force agrees well with the experimental result. The normal force for viscoelastic fluids is predicted using the same assumptions as for Newtonian fluids except the constitutive equation of Coleman-Noll. The predicted expression is in good agreement with the present experimental result for dilute PEO solutions but roughly agree with the data for non-dilute PEO and Separan solutions.
Concentrated suspensions of noninteracting particles show dilatancy at high shear rates, whereas flocculated suspensions are generally pseudoplastic over a wide range of shear rates. The effects of colloidal attraction between particles on the dilatant flow are examined for aqueous suspensions of zinc sulfide (ZnS). The particle-particle interactions are controlled by surface treatment of particles and addition of surfactant. The steady-flow properties were measured for suspensions at concentrations from 40 to 55% by volume and the degree of colloidal stability was evaluated by the particle concentration in the sediment. With decreasing particle concentration in the sediment, i.e., with increasing colloidal interactions, the dilatant behavior becomes less obvious. For the appearance of dilatant flow, the flocs must be broken down to primary particles in shear fields. The hydrodynamic forces required to break the flocs were calculated.
Stress-strain curve was measured for guttapercha point, a dental material, using a tensile testing instrument. Effective strain was calculated with a simple correction based on Hooke's law. All the observed stress-strain curves were in substantial agreement at a low strain range, independent of the initial length. Young's modulus was determined to be 5.6×109dyne/cm2 from the initial slope of the curve in dry state at the humidity of 49~68% at 24°C. Both the yield stress and the yield strain decreased linearly with increasing initial length. In wet state at 20°C in Ringer's solution, the stress-strain curve was remarkably nonlinear and the yield strain in wet state was about twice as large as that in dry state. Increasing the temperature to 37°C at physiological state, the yield stress decreased to a third as large as that at 20°C. Guttapercha plate showed an anisotropic stress-strain behavior depending upon the direction of extension in the manufacturing process. The Young's moduli for the sample stretched in the longitudinal and lateral direction were 8.3×109dyne/cm2 and 13.3×109dyne/cm2, respectively. Both of the moduli increased with the content of the filler in accordance with the theory by Guth. The larger values of the moduli in comparison with that of guttapercha point seem to be due to the difference in molecular orientation caused in the manufacturing process.
The viscosities of liquid dairy foods were measured in a slit rheometer with gap spacings as small as 34 μm. Large positive deviations from the true flow curve and an approach to a constant stress were observed below a critical rate in each material studied. This behavior is indicative of probable agglomeration and“bridging”, most likely in the entrance to the die. In all cases mean particle sizes were an order of magnitude smaller than the slit.
The effect of physical aging on excess enthalpy has been investigated for the amorphous poly (ethylene terephthalate) (PET) glasses prepared by both means of quenching the melt into liquid nitrogen (type I) and casting the melt on a rotating metallic roller at 10°C (type II). The relaxation toward the equilibrium of the enthalpy, monitored by a differential scanning calorimeter (DSC), is described by a relaxation fraction of the excess enthalpy φ as a function of aging time and temperature. On the physical aging in the two PET samples, a plot of φ against log ta gives an essentially straight line for the PET I sample, and the plot for the PET II sample can be divided into three distinct regimes with increasing log ta: a short-time regime where φ linearly decreases with log ta, a middle-time regime where φ takes an almost constant value, and a long-time regime showing a secondary decrease in φ. When the PET II is aged at 60-70°C, two endothermic peaks in a DSC scan arise in the middle and the longer regimes of the aging time. The peak positions as well as their magnitudes considerably vary with the aging time. These results for the PET II suggest that polymer-chain rearrangement during the physical aging process is a dissipative process which results in nonhomogeneous glassy structures consisting of low and high-enthalpy regions.
Finite difference solutions and observations have been presented for the flow of dilute suspensions of rigid, high aspect-ratio fibers in Newtonian Fluids through a 4 : 1 tubular contraction. The effect of flexibility of particles on the flow fields is also discussed from comparison of their configuration and entry flow patterns between rigid fiber suspensions and flexible molecule systems. For rigid fiber suspensions, the main flow patterns become nearly conical and the corner vortex length is almost independent of flow rate under the Reynolds number less than 0.1. On the other hand, for flexible molecule systems, the corner vortex rapidly grows with an increase in flow rate and the wine-glass shaped flow with the convex vortex boundary also presents striking contrast to the fiber suspension flows. Therefore, full discussion of the change in fiber or molecule configuration during flow seems most significant to understand the entry flow kinematics. Furthermore, the computed stress fields clearly indicate that entry flows of rigid fiber suspensions can also exhibit the stress relief phenomenon due to vortex enhancement, which was observed for polymer liquids: the increase in the normal stress difference around the centerline near the entrance of the contraction can be suppressed.