Uniaxial elongational flow behavior was examined for polystyrene(PS)/styrene-butadiene-styrene(SBS) triblock copolymer by using a Meissner type rheometer under uniaxial elongational flow at constant strain rates. The mixtures of PS and SBS were prepared by means of a solution blending method. Pure PS did not exhibit strain-hardening. Elongational viscosity was quite similar among the mixtures of PS/SBS without heat treatment. However, large enhancement of strain-hardening was observed for PS/SBS blends treated at temperatures higher than 220 °C, and the magnitude of enhancement reached ten times or more. To analyze the cause of the enhancement of strain-hardening, we examined pure SBS itself using a combination of uniaxial elongation and FT-IR spectroscopy. Change in uniaxial elongational flow behavior, i.e., from strain-softening to strain-hardening, was observed corresponding to heat treatment temperatures. From FT-IR spectroscopy of SBS treated at various temperatures, the correlation between enhancement of strain-hardening and crosslinking of butadiene was obtained. From shear stress relaxation measurement of PS/SBS(90/10) treated at 260 °C for 60 min, convergence of relaxation modulus was observed in a strain range of γ ≥ 2 at long times. Thus, the increase of strain-hardening of PS/SBS blends treated at high temperatures is likely to result from affine deformation of crosslinked SBS component.
Simultaneous observation of morphological change and measurement of shear stress in an immiscible polymer blend of a liquid crystalline polymer (LCP) and a methyl phenyl silicone oil (MPS) were carried out in electric and shear flow fields by using a system combining a rheometer and a confocal scanning laser microscope (CSLM). Under shear flow and no electric field a thin MPS layer with low viscosity was formed between two parallel plates of the rheometer, which reduced the apparent viscosity. When subjected to an electric field the layer was broken, resulting in the viscosity increase. The relationship between the morphology and the rheology was studied in detail.
Designs of flow channel in a slot die are often required to achieve the uniform thickness of coated films for non-Newtonian fluids having nonnegligible yield stress. In previous studies we have proposed a designing method for deriving the optimum geometries of flow channel from a flow distribution model for Bingham fluid. However, it is hard to provide the optimum geometries precisely without manufacturing burden. Therefore, it is useful to substitute simplified asymptotic curves for complex optimum geometries in designing flow channel. But in that case the deviation of outflow from uniformity due to such approximations needs to be checked whether it is within an allowable range or not. In this work we propose a method for predicting the outflow deviation in given geometories of flow channel using Bingham fluid. The usefulness of the method is confirmed by an experiment conducted using a corresponding fluid.
To achieve uniform thickness of coated films using non-Newtonian fluids, we are often required well-designed geometries of flow channel in a slot die. This is the case especially for fluids with the properties of both shear thinning and yield stress which is non-negligible in a range of low shear rate such as in an intermittent die coating. In the present work, flow in the slot die has been studied using Herschel-Bulkley fluid expressing both shear thinning and yield stress. The Herschel-Bulkley fluid includes power-law and Bingham fluid models comprehensively. This fluid model is applicable to many real fluids. We derive simplified equations for the outflow distribution as functions of power-law index, yield stress and the geometry parameters of the die. Furthermore, we propose a useful designing method for predicting the optimum geometry so as to guarantee uniformity of outflow from the die slot, based on the Herschel-Bulkley fluid. The value of this method is confirmed by comparing it with experimental results and with previous theoretical results for the power-law and Bingham fluid models.
Rheological properties and spinnability of chitosan concentrated solutions in aq.organic acids were investigated. The result of the dynamic viscoelasticity of the concentrated solutions indicated the existence of molecular association in the solution. This association tended to be weaker in the solutions with a strong acid. When an ultrasonic apparatus was used to dissolve the chitosan in the aq.organic acids, the size of the associated structure seems to be smaller. The concentration of the chitosan and the kind of acids added in the solution affect the spinnability of the concentrated solutions.
It is known that the CTAB/NaSal aqueous solution forms wormlike micelles when the concentration is higher than a certain value and shows the flow-induced structure change when both the shear rate and shear strain exceed respective critical values. In the present work, the start-up behavior of this surfactant solution in a two-dimensional abrupt contraction channel driven by a constant pressure was investigated. At a low driving pressure, the flow rate increases gradually and reaches an equilibrium state. When the driving pressure is higher than a certain value, the flow rate rises at a certain elapsed time. The elapsed time showing increase in flow rate shortens with increasing driving pressure. In the entry area of the narrow channel, a pair of wedge shape opaque regions appears. From the comparison with the observation in Couette flow of the same solution, it is found the opaque regions are caused by shear induced structure and the viscosity of the regions is higher than the other region. The regions grow up and make the other region with low viscosity narrower. The opaque regions suddenly break and disappear when the flow rate changes. Flow instability is induced by a sudden change of flow states. These phenomena are characteristic of the fluid showing the flow-induced structure change, whereas ordinary polymer solution do not exhibit such behavior.
Effect of static strain on thermal deformation in foamed plastics was investigated in terms of the time dependence of compression dynamic modulus for polyvinyl chloride and closed-cell polyethylene based foams. In all foams, except for closed-cell polyethylene based foams subjected to 30 % static strain, the logarithm of time t at which the compression dynamic modulus decreased to 50 % of its initial value has been found to be a linear function of reciprocal absolute temperature T−1, and the correlation coefficient for the foams was more than 0.91. Because the stiffness of foam skeletons is influenced by inner pressure in closed-cells of polyvinyl chloride based foams, thermal endurance of the foams is improved by larger static strain.
To examine application feelings of skin care creams onto damaged skin, we accomplished sensory evaluation of application feelings of skin care creams before and after treatment with SDS (sodium dodecyl sulfate) aqueous solution which is one of surfactant. Friction coefficient, water content of stratum corneum, sebum content and TEWL (transepidermal water loss) of normal skin and SDS damaged skin were also measured. The results showed that sensory values of application feelings of skin care creams for damaged skin were lower than those for normal skin. It means that application feeling was worsen by SDS treatment. It results from the change of the fluidity of skin care creams on the skin surface due to decrease of hydrophobicity of skin surface caused by SDS treatment removing sebum and stratum corneum lipid from the skin surface.