This report is described mainly about the measuring methods developed and results obtained by the author on the elasticity in water flow and dilute polymeric liquid flow at high strain rates: Jet thrust/reaction was measured for the flow through capillaries or orifices of small size and the elastic stress was calculated and the thrust/reaction was found to decrease significantly both for polymeric liquid flow accompanied with vortices upstream of the orifice and for water flow through micro-orifices. Elongational stress estimated using the measured thrust/reaction was revealed to be correlated with the flow velocity through orifices. This suggests that these fluids posses a property of elastic solid, not of viscoelastic liquid, under the present experimental condition. It was also shown that the pressure drop of the water flow through micro-orifices is much reduced and this was again explained by the elasticity. The model of elastic fluid possessing only elastic property without viscosity was proposed, Bernoulli's theorem was extended to the one including the elastic property, and several experimental phenomena characteristic of viscoelastic fluids were explained by this extended theorem. Additionally, the property of vortices for polymeric liquids was discussed.
Structure-rheology relationships have been studied on polymer blends, block copolymers and polymer composites. The excess shear stress of polymer blends with droplet/matrix structure after application of a large step shear strain is predicted fairly well by the Doi-Ohta theory, when the interface tensor describing the anisotropy of the interface can be evaluated from observation of the deformed interface shape. The frequency dependence of storage G' and loss moduli G" of polymer blends with bicontinuous structure shows a power law behavior with exponent of 0.75 - 0.83. For diblock, triblock and starblock copolymers with lamellar, cylinder and gyroid structures, power law exponents for the frequency dependences of G' are found to be 1/2, 1/3 - 1/5 and 0, respectively. The power law exponent for G' is sensitive to the curved structure in cylinder-forming samples, while the exponent is always 1/2 in lamellar-forming samples. The structure-rheology relationships are investigated for composites in which ceramics particles are dispersed in polymer blends with bicontinuous structure. It has been found that particles enter exclusively into one phase in binary polymer blends, when flexible polymer chains in that phase adsorb onto those particles and better compatibility than other polymer phase is obtained. The dispersed state of particles in the polymer phase is correlated with G' behavior at low and intermediate frequencies.
Ultra-fine particles of titanium dioxide (TiO2) and Zinc oxides (ZnO) are very attractive as UV-protecting ingredients in cosmetic products. The UV-scattering behavior of single TiO2 suspensions and complex ones in a silicone oil is studied in relation to rheological properties. To control the dispersion stability of suspensions, three polyoxyethylene(POE)-modified silicones of branch-type, (AB)n-type, and ABA-type are used as dispersants. Irrespective of molecular structure, the dispersants can stabilize the TiO2 and ZnO particles and the flow of both single suspensions is Newtonian with low viscosity. However, the Newtonian flow profiles and high dispersion states are maintained only for complex suspensions prepared with ABA-type dispersant. Since the POE groups which are incorporated between terminal silicones groups attach to the particle surfaces, the steric stabilization is responsible for low viscosity and high dispersions. Because the UV scattering of suspensions is determined by the sizes of flocculated structures, the high transmittance in the visible ranges and low transmittance in the UVA and UVB ranges can be achieved in the presence of ABA-type dispersant.
The dynamic moduli of cellulose fiber disperse systems showed a strong dependence on fiber concentration. Power law relationships were established between the moduli and concentration. The exponent of the power law was 9/4 for all the suspensions constructed with three-dimensional isotropic fiber networks. In contrast, the exponent was three for wet pulp fiber webs, which have laminated fiber network structures, and five for a bacterial cellulose pellicle, having another laminated structure. This indicates that the exponent itself reflects the intrinsic properties of the fiber network structures. On the other hand, the front factor of the power law varied with the fiber axial ratio and the fiber flexibility. Therefore, the factor reflects the individual fiber characteristics. Solution properties of cellulose from different biological origins were also investigated in terms of rheological properties in LiCl/amide solutions. Bacterial cellulose solutions form liquid crystal phases, unlike the other celluloses solutions. Tunicate cellulose has large molecular weight as Mw = 4.13 × 106. The solution viscosities were proportional to the α-th power of the polymer concentrations. The exponent α were 3, 4, and 7.5 for bacterial, plant, and tunicate cellulose solutions in the semi-dilute regions. The weight fraction dependence of the zero-shear rate viscosity of the blends can be expressed by a linear mixing relation based on Ninomiya theory.
Observation of visualized flow of capillary entry flow of a mobile viscoelastic polymer solution, PAA/W, shows that the appearance of inflow region is quite similar to a Newtonian jet, and influence of the reservoir bottom where the capillary is attached is insignificant as the case of the nozzle wall on the Newtonian jet. The boundary layer approximation is applied to the viscoelastic capillary entry flow in analogy with the Newtonian jet, in order to give a method to predict the contour and growth of inflow region length Lδ. Uni-axial elongational viscosity is estimated by comparing the analytical result of Lδ with the experimental values in steady flow. Prediction of the length and contour of inflow region of PAA/W by the analytical method is shown to agree well with experimental observation.
Surface-active agents (surfactants) have been used in washing, printing, and medical science to improve efficiency in processing but often cause complicated problems that remain unresolved. As these problems have marked effects on the quality of the final product, basic research to determine solutions is necessary. We observed liquids dripping out of an aperture at relatively low Reynolds numbers using a CCD camera, measured mass and velocity of falling drops, and estimated the dynamic surface tension. Several aqueous solutions of surfactants were used: polyoxyethylene (10) lauryl ether, polyoxyethylene (100) stearyl ether, etc. The momentum equation applied to the falling drop was simplified and an equation was obtained for measuring the dynamic surface tension. It was shown that this equation is useful and dynamic surface tensions were measured for several kinds of aqueous surfactant solutions. The dynamic surface tension was found to depend on the molecular weight of the hydrophilic group and the normalized dynamic surface tension is correlated with the parameter (surface age)×(molecular weight of the hydrophilic group).
The striped patterns of moldings formed parallel to the material flow direction in the vicinity of injection gate was investigated for polypropylene (PP)/ethylene-propylene rubber (EPR)/ethylene-butylene rubber (EBR)/talc blends from the viewpoint of morphologies and rheological properties. The trace of material flow generated at the packing stage of injection molding process was observed on the cross section cut in the direction perpendicular to the stripes. The trace is circular in shape, and the area of the trace shows a maximum at a position just under stripes. The morphologies of the blends at the trace were compared with those in the other region of the moldings. It is found that the morphology at the trace appears co-continuous, but the interfaces between two phases is smeared, differing from usual co-continuous morphologies with distinct interfaces. The emergence of the smeared interfaces indicates that the morphology in the trace originates in part from the large deformation of rubber particulates. A large scale of material flow enlarging the deformation of particulates occurs especially in the trace just under stripes. Namely, the force generated by the flow deforms the materials in the thickness direction of molding and the strain gives rise to the stripes on the surface. This mechanism allows that the stripes would not be observed on the surfaces of moldings if the stress relaxation rate is faster than that of crystallization of PP in the blends in the packing and solidification stages. In fact, the moldings of the blends with the shorter longest relaxation time have the excellent surface appearances without any stripes.
The dynamic rheological properties of hydroxyl-terminated polydimethyllsiloxane (PDMS) filled with calcium carbonate (CaCO3) were investigated systematically over a broad temperature range from −40 to 50°C. The results reveal that with an increase of filler volume fraction (φ), the span of the linear viscoelastic region in which dynamic storage modulus (G′) is constant narrows and the relaxation time of the compounds shifts to longer time scales. Beyond the critical φ (φc = 0.069), G′ remarkably increases and exhibits a "pseudo solid-like" behavior in the low frequency (ω) region, meanwhile the width and height of the modulus plateau increase with increasing φ. On the other hand, the "Cole-Cole" plots of G′ against dynamic loss modulus (G″) at different temperatures indicate that the microstructure of compounds with relative high φ is distinct from those of compounds with low φ. The reasons for "pseudo solid-like" behavior are attributed to the agglomeration of filler particles and the formation of percolated filler network structure due to filler-polymer and filler-filler interactions. When φ<φc, the nonhydrodynamic force of polymer matrix is predominant, while particle-particle interactions play an important role when φ>φc.
The flow instability in a flow front during the injection stage of injection molding process was theoretically investigated for polymeric materials. In addition, the relationship between the flow instability and flow mark on the surface of injection moldings was also examined. According to the theory, the flow in the front region becomes unstable when the shear stress exceeds the normal stress. Whether flow marks occur or not is also controlled by the balance between the normal and shear stresses in the region. The validity of this criterion was verified experimentally for the injection moldings of polypropylene (PP)/rubber/talc blends. The surface appearance for the moldings was more excellent for the blends with lower critical shear rates where the shear stress becomes equal to the normal stress; namely, the enhancement of the elasticity of polymer melts at low shear rates effectively prevents the occurrence of the flow marks for the injection moldings.