Structure and dynamics of three different types of polymer networks are studied using rheological and spectroscopic methods. The self-diffusion coefficient was measured to examine the applicability of the tube model to entanglement network. Formation process of viscoelastic network is investigated for associating polymers. The sol-gel transition of physical gels is discussed based on the fractal concept developed for chemical gels.
Rheological properties of some cooked foods and factor affecting the processability of food ingredients such as the spinnability of soybean proteins for edible fiber, a non-thermally gelation of bovine whey proteins, the gelatinization and retrogradation of starch and starchy foods were investigated. The spinnability of isolated soybean proteins was influenced by the viscoelastic properties of dope, and the frequency dependencies of G' and G" for the dopes were observed for the evaluation of the ability. The non-thermal gelling ability of whey proteins was also discussed. There was a good relationship between the sensory evaluation of firmness and the elastic modulus for starchy food "Dango". The retrogradation process of starch and starchy food during storage could be described by the kinetics using a rheological parameter, and it was strongly suggested that the anti-firming ability of sugars was introduced by the structure-making effect for water.
We have developed an integrated simulation system for soft materials named OCTA. OCTA is developed for the meso-scale simulation, which is important to study the material properties such as rheological properties. OCTA consists of four simulation programs (COGNAC, PASTA, SUSHI, MUFFIN) and a simulation platform (GOURMET), and is designed for collaborative operations of multi programs. Various application studies using OCTA are conducted, e.g. rheological properties of polymer melt, structure and dynamics of polymer melt confined between nano-scale gap, interfacial strength of polymer blends, phase separation of polymer blend under shear flow, and the brief results are introduced in this paper.
Large deformation mechanism of glassy polymers was investigated through examination of stress-strain relations with the aid of a nonlinear single-relaxation model, measurement of dynamic viscoelasticity during deformation, and examination of static fracture properties of well-yielded polymers. A simple mechanical model with variable single-relaxation time as a parameter quantifying strain-induced structural change successfully reproduced stress-strain relations during yielding process. The single relaxation time started to vary at a strain much smaller than the yield strain, and it finally reached low constant values in the post-yield regime of strain. Thus, it was concluded that glassy structures continuously changed in the course of yielding. Variation of dynamic viscoelasticity experimentally observed during yielding process strongly supported this conclusion. Large deformation given at a very low strain rate as well as stress relaxation history after deformation were found to lessen the ductility of glassy polymer. This observation presumably indicates that the mechanism of nonlinear stress relaxation, which provides polymeric glasses with fluidity, also gives brittleness to the glassy system.
Some recent advances in our understanding of the mechanisms governing the flow behaviour of electro-rheological fluids and concentrated particulate suspensions are reviewed. For both systems an overview is presented of theoretical models based on interparticle forces and assumed microstructure, as well as of recent experimental studies which highlight features to be incorporated in future models, such as the effect on electro-rheological fluids of mixing particles with different sizes or electrical conductivities. It is apparent that models based on simplified microstructures can illuminate many of the physical mechanisms of these complex fluid systems.
For an aqueous suspension of poly (methyl methacrylate-co-styrene) (MS) particles, viscosity η and small-angle neutron scattering (SANS) intensity I(q) were measured under steady shear. The MS particles had partially screened surface charges. In the quiescent state, the particle distribution detected through the I(q) profile was isotropic and essentially liquid-like but also exhibited a weak, local order. Under steady shear, this distribution was distorted just moderately, and the η strongly decreased with increasing shear rate γ . Thus, this thinning of η was related to the weak distortion of the particle distribution. Furthermore, the thermodynamic stress σT estimated from the I(q) profile under the shear increased only weakly with increasing γ , and the corresponding viscosity ηT (=σT/ γ ) was close to the η data. These results strongly suggested that the thinning of the MS suspension reflected the nonlinearity of σT.
I have developed a model for porous media suitably implemented to the Real-coded Lattice Gas. In order to accurately detect collisions between moving particles and solid matrices, my model investigates the entire trajectories of moving particles. Behaviour of single phase fluids have been validated by the Darcy's Law. For binary immiscible fluids, the simulation results are in good agreement with the generalised Darcy's Law and the conventional LGA studies.
Rheological properties in steady planar elongational flow of CTAB/NaSal aqueous solutions were investigated using a 4-roll mill flow cell. The planar elongational stress was measured by using a flow-birefringence technique, which is based on the stress-optic rule. On the other hand, the rate of planar elongation was accurately determined by the analysis of the tracer particles in the system. The planar elongational viscosity showed elongational thinning as well as shear thinning. The planar elongational viscosity measured in the 4-roll mill flow cell was compared with that measured in a squeeze flow cell, and both well agreed with each other. Trouton ratio was evaluated to be 4 in both the Newtonian and elongational thinning region. Flow instability is observed in the 4-roll mill flow cell at a planar elongation rate lower than the shear rate at which the shear flow instability takes place.
Rheological measurements were made on aqueous solution of native silk fibroin extracted from the MM part of the silk grand of Bombyx mori silkworm and also on that of regenerated silk fibroin at finite polymer concentration. Steady flow behaviors were found to be distinctly different between two solutions. The native silk fibroin solutions exhibited dynamic viscoelastic properties characteristic of the pseudo plateau modus in the low angular frequency region as well as peculiar thermo rheological behaviors, whereas the regenerated silk fibroin solutions behaved as viscous fluid. Rheological properties of the native silk fibroin solution were interpreted in terms of the protein complex called the elementary unit (EU), which gives rise to development of viscoelastic network even in the dilute regime.
Poly (tetrafluoroethylene) (PTFE) nascent powder was drawn by solid-state extrusion to extrusion draw ratios (EDR) ≤ 100 in the temperature (Te) range of 100~340°C, which covers the Tg(125 °C) and the ambient Tm(334°C). At a given Te, the maximum achievable EDR (EDRmax) increased with increasing shear rate (γ) and hence extrusion rate (Ve), reaching a maximum at a γ of 1 ˜ 4×104/min (Ve of 300 ˜ 600 cm/minjdepending on the Te, and at yet higher γ's, the EDRmax decreased rapidly due to the formation of flaws. At a given γ, the EDRmax increased with increasing Te up to a Te =340°C. At Te's >340°C, the drawability was lost due to melting. The structure and properties of extruded products were complexly affected by the extrusion variables. Thus, the oriented rods having crystalline chain orientation function fc of 0.75˜0.96 and flexural modulus Ef of 7.5 ˜ 15 GPa at 24°C could be obtained by extrusion at an optimum Te of 340°C and a Ve of 1˜1000 cm/min (γ of 1×10˜1×105/min). These results show that nascent PTFE powder could be solid-state extruded at remarkably higher Ve's than other polymers, reflecting the less entangled morphology of the nascent powder and the high ductility of a PTFE crystal due to the week intermolecular interaction.