Zirconium oxide (ZrO2) particles are dispersed in polystyrene (PS)/poly(butyl methacrylate) (PBMA) and PS/poly(methyl methacrylate) (PMMA) blend melts with bicontinuous structure. ZrO2 particles enter exclusively into PBMA phase in PS/PBMA blend, while the particles exist in both phases in PS/PMMA blend. The main cause for the exclusive localization in PBMA phase is the lowest entropy loss of the most flexible PBMA chains among the three polymers due to adsorption onto ZrO2 particles. In PBMA phase, spherical aggregates of ZrO2 particles are formed at a concentration of 11 vol%, while ZrO2 particles make linear arrays at 21 vol% and branches at 29 vol%. These arrays and branches give very high second-plateau in G' at low frequencies. In PS/PMMA blend melt, linear arrays and branches appear in both phases even at 4.4 vol%, and network structure is formed at 11 vol%. Due to the structural difference, the PS/PMMA/ZrO2 composite gives much higher second-plateau than that of PS/PBMA/ZrO2, when compared at the same vol% of ZrO2. A peculiar network structure is observed in PS/ZrO2 composite at a low concentration of 4.4 vol%. The low value of G' close to that of the matrix at intermediate frequencies with a small number of spherical aggregates indicates very weak adsorption of PS chains to ZrO2 particles.
Linear viscoelastic behavior was examined for a series of binary blends of linear polyisoprenes (PI). These blends contained high molecular weight (M) component chains (probe chains) that were dilute and entangled only with the lower-M matrix chains. The PI probe exhibited the Rouse-like constraint release (CR) relaxation in the matrix chains much shorter than the probe, but this CR-dominance vanished on a moderate increase of the matrix molecular weight because of the competition with other mechanisms (such as reptation). These features are qualitatively similar to, but quantitatively different from, those noted for binary blends of linear polystyrenes (PS): The CR-dominance was more easily achieved in the PI/PI blends than in the PS/PS blends, which suggests that the entanglement dynamics is not uniquely determined by the number of entanglement segments per chain and the relaxation time within this segment but is affected by additional molecular factors such as the local CR gate number considered by Graessley (Adv Polym Sci, 47, 67 (1982)).
The objective of this study is to examine the property of pressure loss under the flow of surfactant solutions in a packed bed of particles. Three mixtures of CTAB and NaSal in distilled water were used as test fluids. The flow property of surfactant solution in the packed bed was expressed by a wall shear stress and an apparent shear rate, which were defined in a model channel for a packed bed. The flow curve, a plot of the shear stress versus the shear rate, shows a sigmoidal shape. The first bending point in flow curve occurs because of the sudden increase in shear stress, which looks like the shear-thickening in shear viscosity. However, the surfactant solutions in the packed bed was affected by a stretch deformation due to a converging-diverging flow. We estimated an apparent elongational viscosity by means of the difference in pressure loss between the packed bed and the capillary flow data. As a result, it is found that the obtained elongational property demonstrates a significant change, that is the transition from a stretch-thickening property to stretch-thinning one with the increase in stretch rate. It is considered that the property of elongational viscosity for surfactant solutions is closely related to the transition of micellar network structure.
Associating polymers which consist of hydrophilic long-chain molecules containing a small amount of hydrophobic groups(hydrophobes) behave as flocculants in aqueous suspensions. The effects of surfactant on the rheological behavior are studied for latex, silica, and mixed suspensions flocculated by associating polymer. Because the hydrophobes are adsorbed onto hydrophobic surfaces and water-soluble chains onto hydrophilic surfaces, two single suspensions are highly flocculated by a bridging mechanism. In latex suspensions, the surfactant molecules force to desorb the polymer chains from the particles and at the same time enhance the micellar formation between the adsorbed chains. As a result, the flow becomes shear-thickening due to the elastic forces generated in extended multichain bridges under shear fields. In silica suspensions, the additions of surfactant cause the viscosity increase which may be attributed to enhancement of micellar formation between the adsorbed chains. By mixing the silica and latex suspensions, the viscosity is substantially reduced and the flow becomes nearly Newtonian. The associating polymer in complex suspensions acts as binder between the silica and latex particles. The hetero-flocculation which leads to the formation of composite particles may be responsible for the viscosity reduction of complex suspensions.
The importance of rheological study in food and health is discussed in relation with the texture and mouthfeel of foods. Concepts of elastic modulus for solid foods, and viscosity for liquid foods are not sufficient to describe diverse textures of foods, and it is necessary to measure viscoelasticity and fracture behaviour of foods. The reason why the texture is more important in solid foods than in liquid foods is discussed. Rheological behaviours of inhomogeneous foods such as cooked rice and carrots are also described. The rheology of hyaluronan, the main component of synovial fluid, is introduced because elderly persons have serious problems such as arthritis. Then, the typical frequency dependence of complex modulus in foods is explained, and rheological monitoring in food processing such as gelling processes of tofu and konjac as well as retrogradation of starch are described. Since the diversity of foods is necessary to improve the quality of life in ageing society, the texture control is urgently required. Some examples of rheological control of texture by hydrocolloids mainly by polysaccharides are discussed. Temperature dependence of food gels is discussed. Rheological change of foods in mastication and deglutition process is discussed and rheological control of digestion and absorption process using hydrocolloids is also described.