Flow property, which is expressed by the relation between wall shear stress and apparent shear rate, is examined in the flows of surfactant solutions through various capillaries. Furthermore, small angle light scattering (SALS) experiments are carried out in the flow through a slit cell. In the present experiments, aqueous solutions of Cetyltrimethylammonium bromide (CTAB) and Sodium Salicylate (NaSal) are used. The flow curve has a break point and its slope below the bending point significantly depends on the ratio of salt concentration CS to surfactant concentration CD. From the experiments on the effect of capillary diameter, it is found that eqimolar solution for CD= 0.03M exhibits a remarkable diameter dependence below the break point while the solution for CD= 0.03M and CS /CD = 7.7 exhibits a diameter dependence only in a narrow region at intermediate shear rates. In the SALS experiments the butterfly pattern is observed for CS / CD=1 and the four-fold symmetry pattern for CS /CD = 7.7. The characteristic scattering pattern is destroyed just after the startup of the flow at high shear rates where the flow curves overlaps regardless of salt concentration and length and diameter of capillary. This fact suggests that micellar network structures are broken at the high shear rates.
Viscoelastic simulations of deformation-induced bubble coalescence in forming process under isothermal condition were carried out. Multi mode PTT model was used in a simplified model for deformation of Polypropylene(PP) melt between bubbles in plane strain. 2-Dimentional Lagrangian FEM was adopted in the unsteady creeping flow simulation. The numerical results demonstrates that the thinnest part between neighboring gas bubbles is easily deformable and consequently coalescence occurs. Still more, creep recovery by elastic residual stress promotes the coalescence. The strain-hardening property is very effective to the coalescence prevention. Furthermore, the relaxation time distribution of polymer melts has significant influence on the behavior. Composition of the relaxation time that is a little longer than the elongational time makes a deformed bubble unstable and causes bubbles to coalesce. The numerical simulation could explain the deference in appearances of foamed sheets made of various PP.
We discuss hysteresis in shear rate dependence of domain size for immiscible polymer blends observed in break-up process of relatively large domains after stepwise increase of shear rates and in coalescence process of relatively small domains after stepwise decrease of shear rates based on the applicability of Doi-Ohta theory. The sample was 7:3 blend of polydimethylsiloxane and a hydrocarbon-formaldehyde resin. Below the critical shear rate, where the theory is not applicable, domain size in the break-up process is not well controlled by the flow resulting in the broad size distribution and poor reproducibility of viscosity. However, shear rate dependence of average domain size is practically the same as that observed above the critical shear rate. On the other hand, the domain size observed in the coalescence process is well controlled by the flow and the viscosity is reproducible but the shear rate dependence of domain size are lower than those observed above the critical shear rate. It is concluded that when the break-up process is first carried out for blend samples containing relatively large domains started from a shear rate lower than the lower critical shear rate and then the coalescence process is carried out, domain size hysteresis is observed.
Micro-capsules composed of poly(methyl metacrylate) (PMMA) or poly(vinyl acetate) (PVAC) as core materials, and silica as wall material were produced by sol-gel process. PMMA or PVAC emulsions were covered with silica derived from tetraethoxysilane by sol-gel process, and microcapsules with diameter of about 10-30 μm were obtained. These micro-capsules were dispersed in silicone oil with concentration of 30 wt% to prepare electro-rheological (ER) fluid. When DC or AC electric fields were applied on these fluids, the shear stress of the system increased, and ER effect was observed. In the case of PMMA micro-capsule, the shear stress of the system under AC electric field increased with shear rate, and higher than that under DC electric field. PVAC micro-capsule/silicone oil fluid showed Bingham flow under DC electric field, and shear stress was higher than that of PMMA system. PVAC micro-capsule/silicone oil system showed the dip behavior under AC electric field at higher shear rate region of 540-600 s-1 caused by destruction and reformation of the structure, and the stress was lower than that of PMMA system above 150 s-1. Organic-inorganic micro-capsules produced by the sol-gel process were effective dispersoids for ER fluid.
We have examined the solid-like behavior of concentrated suspensions with non-Brownian particles in squeezing film flows. The apparent yield stress has been estimated with a very weak squeezing flow between a flat plate and a spherical surface with a large radius of curvature. This instrument allowed us to explore the effect of repeated squeeze flow on these materials. It was found that there was a dramatic increase in solid-like properties as the number of cycles grew, especially for the higher volume fraction samples. This growth appeared to be accelerated if we used irregularly shaped particles, slower squeeze velocities, smaller final gap values or plates with a rougher surface. The fact that this occurred in cyclic squeeze flow, and did not occur in a corresponding cyclic shear flow, suggests that the highly non-uniform nature of the flow field in squeezing contributes to this behavior. Indeed, we suggest that there is a gradual build-up over many cycles of aggregates in the central region which leads to this behavior.
Coalescence process of a immiscible polymer blend having broad distribution of domain size, which is a 1:1 mixture of two pre-sheared polymer blends is compared with those of the two pre-sheared samples having narrow size distributions. Component samples used are polydimethylsiloxane (PDMS: viscosity 27.1 Pa·s) and hydrocarbon-formaldehyde resin (Genelite: viscosity 10.5 Pa·s). The weight ratio of PDMS:Genelite was 7:3 and shear rates of pre-shear are 2.4 and 4 s-1. The coalescence process was observed under steady shear flow with 0.8 s-1. It was observed that the coalescence between large and small domains more frequently occur in the blend sample with broad size distribution than those of similar size domains in the blend samples with narrow size distribution. As a result, initial coalescence rate became faster for the blend with broad distribution than that with narrow size distributions. Moreover, the size distribution after a long time of flow are different for the samples with broad and narrow size distributions, though the average radius are similar, implying that the domain structure of immiscible polymer blends with broad size distribution cannot be well controlled by the flow at low shear rates.
A shape of a bubble in PolyAcrylAmide (PAA) water solution, which is a typical viscoelastic model fluid, is examined with visualization experiment. In order to study the fundamental aspect of the bubble shape attention was given for a single bubble rising upward against the gravity. Range of size of bubble in the present investigation covers from 0.32 mm up to 12.1 mm, small size to intermediate size. To characterize a bubble in the viscoelastic fluid, Newtonian fluid (glycerine water solution), whose shear viscosity is the same as the viscoelastic one, is also used for the sake of comparison. From results of this study, it was observed that the shape of a small bubble can be kept spherical for both viscoelastic and Newtonian fluids. However, when the size of bubble is increased, the shape is largely deformed with a spike in the tale of rising bubble in the case of the viscoelastic fluid.