Stress relaxation behavior was investigated under large step shear strains γ for polyisobutylene/poly(dimethyl siloxane) blends with different average droplet-size. The interfacial contribution to the relaxation modulus, Gint(t,γ), was evaluated by subtraction of the matrix contribution from the relaxation modulus of the blend, assuming the linear additivity rule for the relaxation modulus. The interfacial modulus Gint(t,γ) for the blends with different average droplet-size obtained at the same strain can be superposed in a reduced form, Gint(t,γ)/(Γφ/rV) vs. t/τD, where Γ is the interfacial tension, φ the volume fraction of the droplet phase, rV the volume-averaged radius of droplets, and τD is the linear viscoelastic relaxation time of the droplets (interface). Superposition can be applied for the blends with φ = 0.108 and 0.214. The superposition is developed from consideration on the theoretical expression for the stress tensor which includes both contributions from the interface velocity term and Laplace pressure term. It is suggested from the good superposition that contribution from droplet-droplet interactions to the stress can be neglected in the present blends with φ ≤ 0.214 or that the contribution is also reduced by the same factors as (Γφ/rV) and t/τD.
An experimental study was conducted on the flow of aqueous solutions of detergent through mesh screens to mimic cloth washing. Pressure losses across the mesh screens were measured for water, dilute polymer and several aqueous detergent solutions. A reduction of pressure losses was observed for the flow of aqueous solutions of low molecular weight surfactants such as Laurylether (AE), Laurylbenzene-sulfonic acid-sodiumsalt (LAS), Benzalkonium-chloride (BC) Sodium-dodecyl-sulfate (SDS), and Hexadecyltrimetyl-ammonium-bromide (CTAB), but not for the high molecular weight polymers like Polyethylene-oxide (PEO18) and Polyacrylamide (PAA), through mesh screens. A flow visualization experiment was carried out to observe the flow pattern upstream and downstream of the mesh screen. Photographic images revealed that, instead of an expected large converging flow from the upstream section into the screen opening as in orifice flow, the bulk of the liquid entering the screen aperture took the form of a liquid column of similar diameter as the inlet tube. Based on this observation, a flow model, which led to a new set of definitions of Reynolds number and drag coefficient, was proposed. Good correlations of drag coefficient and Reynolds number were obtained for all test solutions, and the drag reduction phenomenon was manifested for detergent aqueous solutions.
Draw resonance, known to govern the onset of instability occurring in extension-dominant polymer processes, has been investigated using the bifurcation analysis method. Time-periodic trajectories of draw resonance along the drawdown ratio over the onset point or Hopf point, have been directly obtained by Newton's method implemented with pseudo arc-length continuation scheme. Floquet multipliers of the monodromy matrix to determine the stability of limit cycles have been also computed by time-integration during one period of the oscillation. It has been revealed that the limit cycles over the onset are more stable when drawdown ratio rises for both Newtonian and viscoelastic fluids, so draw resonance is a stable supercritical Hopf bifurcation.
Aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) were made to flow through two-dimensional slots and a capillary, and pressure losses ΔP were measured under various conditions to investigate its flow properties. In the results with slot flow, the flow curves relating ΔP to the apparent elongational rate consisted of three characteristic regions. In the first region of low flow rate, the flow curve showed a gentle slope with the pressure loss increasing with elongational rate. In the second region of intermediate flow rate, ΔP increased sharply, which was thought to be caused by flow induced structure (FIS). In the third region of relatively high flow rate, the slope of the flow curve became gentle again. Here, it should be noted that ΔP in the third region was much higher than that in the first region; for example, the third region provides one order of magnitude larger ΔP than the first region for the concentration of CTAB (Cd) = 3×10-2 mol/L solutions, and it gives two or three orders of magnitude larger ΔP than the first region for Cd = 5×10-4 mol/L solutions. Furthermore, the flow field was visualized using reflex powders and a laser light sheet in slot flows. Observations of the flow field indicated that there are three types of flow field corresponding to the three regions of the flow curve. The first region showed a Newtonian-like flow field. The second region exhibited vortices and a contraction flow upstream of the entrance. In the third region, the vortices and the contraction flow fluctuated with increase in elongational rate. On the other hand, experiments regarding the pressure loss in capillary flow for Cd = 3×10-2 mol/L solutions showed the same character as slot flow. For Cd = 5×10-4 mol/L solutions, however, the character of the capillary flow curve was completely different from that of slot flow, and the flow curve of capillary flow was almost a normal type of Newtonian viscous flow. Consequently, we postulated that a considerable FIS is generated in the flow around the inlet of the capillary, but it collapsed in the downstream capillary flow for such dilute solutions as Cd = 5×10-4 mol/L.
Simple shear and Poiseuille flows of liquid crystalline polymers between parallel plates were numerically simulated using the Marrucci-Greco model, which is a constitutive equation that includes long-range elasticity effects. Homogeneous, inhomogeneous decoupled, and inhomogeneous full coupled models [Kupferman et al., J Non-Newtonian Fluid Mech, 91, 255 (2000)] were considered in the present simulation. In the simulation of Poiseuille flows, the relation between the long-range elasticity and the emergence of textures caused by the distribution of orientation angle of directors was investigated. The molecular orientation on the channel plate restricts rotation of directors near the plate through the long-range elasticity, and irregular rotation motions of directors were observed in the inhomogeneous full coupled simulation. Full coupled computations of the velocity field and the director motion predicted the emergence of textures during flows. In addition, the simulation results suggested that a director rotation and the molecular interaction due to the long-range elasticity are necessary for the emergence of textures.
Temperature and frequency characteristics of compression loss tangent of micro-cell polyurethane foams in which bonding tape made by acryl foam was sandwiched, were investigated by dynamic viscoelastic measurements. The larger the thickness of bonding tape or the smaller the storage modulus of the micro cell polyurethane foam, the loss tangent of compound model type sample in normal temperature become to be larger. Therefore, the larger the difference of the storage modulus, the loss tangent of compound model type sample may be larger by the hystereisis of the tension and compression deformation.