The von Karman flow of an incompressible Bingham fluid is studied numerically under laminar and steady conditions. Boundary layer theory is used to simplify the equations of motion assuming that the flow is axisymmetric. A suitable similarity parameter is used to reduce the governing partial differential equations into a system of coupled ordinary differential equations. The equations so-obtained are then solved numerically using MATLAB software. The effect of yield stress is investigated on the validity of boundary layer approximation for this particular fluid when compared with known exact solution. It is shown that for Bingham fluids, the boundary layer theory is valid provided that the Reynolds number is sufficiently large and the Bingham number is sufficiently small.

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We examined the relationship between non-oral sensory evaluations, oral sensory evaluations, and the viscosity of solutions measured using a cone-and-plate viscometer. Samples were thickened using thickening agents composed main ingredients of xanthan gum, guar- gum and modified starch, which had different shear rate dependence. We expected to assess the ease of swallowing thickened solutions through non-oral perception to determine the common index of consistency. We found that the extent of resistance during stirring and ease of flow during the tilting of the container were relevant to the viscosity levels at shear rates of 1-40 s^-1 on the basis of viscometer. As for the dripping from the spoon, we found the flow behavior index n effected on it. The results of the study revealed that means to measure viscosity by tilting the contain and stirring with spoon was useful means to know rough viscosity. This approach, which can be used with solutions which had different shear rate dependence.

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The multi-visco-elastic contact model embedded in the Discrete Element Method (DEM), which was developed by authors previous study (Shimizu et al., 2012)¹⁾ is applied to simulations of margarine’s dynamics in a pin machine, in order to improve margarine’s uniformity during manufacturing process. The results are compared with those using the linear contact model. Also, parametric studies are conducted by changing the operational conditions. As a result, it was found that the new developed multi-visco-elastic contact model represents margarine’s dynamics well during manufacturing process. The following results are considered from the numerical simulations, that is, (1) the migration process is slower than that of granular material, which is often modeled by using the linear contact model in the DEM, also the loaded torque on the machine is around 30 % from the case of using the linear contact model, (2) the migration proceeds mainly in the circumferential direction rather than in the radial direction, as movement of the bulk in the circumferential direction is much larger than that in the radial one, (3) performance of migration in the circumferential direction improves by increasing rotational speed, which is not expected in the radial direction though. Further studies to examine load characteristics of the machine are needed to use the model as a design tool for improvement of the machine’s performance and development of new machines.

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Rheology control additives for hydrophobic fluids, so-called organogelators, are frequently utilized within a wide range of industrial and commercial applications. Numerous organogelators are available; however, their uses are normally limited to highly specialized applications. In this study, we synthesized organogelators having different chemical side chains of C6 to C18 derived from 3,3',4,4'-benzophenone tetracarboxylic acid, and evaluated their rheological control effects for several oils. The molecular mechanisms for thickening and/or gelation properties were probed using transmission electron microscopy (TEM), molecular orbital calculation, differential scanning calorimetry (DSC) analysis and infrared absorption spectrum (IR) analysis. We found that some of our synthesized compounds can significantly increase the viscosity of isododecane, and do so by assembling in worm-like structures due to hydrogen bonding among amide groups. An organogelator into which both a 2-ethylhexayl group and oleyl group were introduced also synthesized not only a thickening property but also a significant viscoelastic property for isododecane, a solvent for which none of the commercial organogelators tested was adequate.

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Intrinsic viscosity [η] of nine pullulan samples with different molecular weights and narrow molecular weight distributions are obtained in 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-ethyl-3-methylimidazolium acetate (EmimAc) from the Newtonian viscosities measured by oscillatory and steady shear flow in conventional rheometer for dilute solutions. For low molecular weight M_w samples, [η] in BmimCl and EmimAc almost coincide with that in aqueous solutions compared at the same M_w. The data at M_w < 30 kg/mol can be represented by M_w^0.5 dependence. The excluded volume effects observed in BmimCl and EmimAc at higher M_w are somewhat stronger than in aqueous solutions. Mark-Houwink-Sakurada equations for pullulan in BmimCl and EmimAc are determined in 20 kg/mol < M_w < 100 kg/mol. It is conclude that measurement of [η] by rheometer is a promising method for characterization of polymers in ionic liquids.

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The formation of anti-parallel (dipole) dimers of liquid crystalline phase forming 4-cyano-4’-alkyl biphenyls (n = 5 (pentyl) and n = 8 (octyl)) was examined in isotropic benzene solution. High frequency dielectric relaxation (DR) measurements up to 50 GHz were performed to probe molecular dynamic processes of nCB molecules and to evaluate a Kirkwood factor (g_K), a measure of orientational correlation between dipole moments of cyano (-C≡N) groups sensitive to the formation of the anti-parallel dimers, (nCB)₂, which shows g_K < 1. DR spectra for solutions at intermediate to high concentrations were decomposed into two relaxation modes. A fast dielectric mode with the relaxation time of ca. 100~120 ps was assigned to free rotation of monomeric nCB molecules, while the other slow relaxation mode with the relaxation time of ca. 400 ps tentatively to the dissociation process of (nCB)₂ dimers due to their lifetime. Infrared (IR) absorption spectra for the isotropic solution were also measured in a wavenumber range from 2200 to 2250 cm^-1 corresponding to C≡N stretching vibration mode to evaluate molar fractions of nCB molecules forming the (nCB)₂ dimers, since the stretching band slightly altered the peak wavenumber due to the formation of anti-parallel (nCB)₂ dimers. The results of both the DR and IR measurements revealed that the formation of (nCB)₂ dimers even in isotropic solution and the equilibrium constant of a chemical reaction, 2nCB ↔ (nCB)₂, in benzene solution remarkably increased with increasing concentrations of nCB. Because most of nCB molecules form the anti-parallel dimers at moderate to high concentrations, the formation of the (nCB)₂ dimers is necessary for nCB to undergo a phase transition from isotropic to a nematic liquid crystalline phase in benzene solutions at higher concentrations and also in the bulk state.

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Under elongational flow at strain rates higher than the Rouse relaxation frequency, entangled polymer melts exhibit thinning of their elongational viscosity whereas equally entangled solutions show thickening. Yaoita et al. [Yaoita et al., Macromolecules 2012, 45, 2773] related this difference between the melts and solutions to reduction of segmental friction on enhancement of the stretch/orientation averaged for the components therein (that includes the solvent for the case of solutions). They analyzed the stress relaxation data after cessation of elongational flow to propose an empirical equation describing this friction reduction as a function of the stretch/orientation factor. Multi-chain slip-link (PCN) simulations considering this friction reduction described the thinning of melts and the thickening of solutions consistently and semi-quantitatively. This study further tests the molecular concept of the stretch/orientation-induced friction reduction with the aid of a simple molecular constitutive equation, a toy version of the Mead-Larson-Doi model [Mead et al., Macromolecules 1998, 31, 7895] (MLD toy model) being modified to incorporate this empirical equation of the friction reduction. The modified toy model mimicked the behavior of melts and solutions consistently. This consistency vanished when the friction reduction in the model was artificially switched off, even though the finite extensible nonlinear elasticity was still taken into account. These results lend further support to the molecular concept of the stretch/orientation-induced friction reduction.

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