A slip-link model of entangled polymeric liquid and its applications are presented. The model includes the three major relaxation mechanisms of entangled polymers, i.e., reptation, contour length fluctuation and constraint renewal. It can predict various linear and nonlinear rheological properties of linear and star polymers. Especially, it can quantitatively predict, without any fitting parameters, the enhancement of the strain hardening of uniaxial elongational viscosity by an addition of small amount of a very high molecular weight component. The effect of dynamical tube dilation (DTD) is also correctly included. A new interpretation of DTD in the framework of the slip-link model is proposed.
We have been focusing on an action peculiar to lips, and the new rheological approach to improve moisture feel for lipsticks was developed. It was revealed that the normal force difference in the high shear rate region was connected with moisture feel for lipsticks. It is widely known that the use of polymeric materials is effective to increase the normal force. However the control of spinnability has been a problem for ordinary polymers like polyether. A cellulose derivative with low spinnability has been developed. Spinnability and viscoelasticity were evaluated for a polyether (POE) and a long-alkyl acylated cellulose derivative (RCE). Since dynamic moduli of both samples could not be expressed with a single Maxwell mode, one of these samples is shifted by the correspondence of their tan d. The storage modulus, G′, of RCE with low spinnability is greater than that of POE with high spinnability. For the non-linear rheology, we found that the correspondence between the first normal stress coefficient, Ψ1, and G′/ω2 is different between two samples. POE with high spinnability has no correspondence of this relationship. We developed new liquid rouge with RCE with low spinnability. This liquid rouge came to have high moisture performance totally.
Micro fluid mechanics, which deal with relative small-sized flow field, is very attractive and interesting study for many applications. We investigated flow properties of several types of complex fluids passing through small apertures and capillaries. Pressure drops were measured with constant flow rates due to observe flow properties of water, polymer solutions, surfactant solutions, and their fine bubble mixtures. For flows through small-sized apertures with ranges from 5 μm to 1.0 mm, agreement between the experimental results of water and the numerical predictions of the Navier-Stokes equation was obtained in more than 100 μm. However, the resultant pressure drops for less than 100 μm did not agree with the predicted ones. The results for glycerol and silicone oils suggested the same tendency. Furthermore, the possibility of elastic properties of water flows in high strain rates was explained because of discussing the anomalous phenomena. For spherical micelle surfactant solutions, the pressure drops were dependent of the electric charges (cationic, non-ionic, and anionic). For rod-like micelle surfactant solutions, the experimental values were increased at any Reynolds number which was approximately 102 order. For capillary flows of 133 μm and 430 μm, pseudo-laminarization of rod-like micelle surfactant solutions was observed, which maintained the laminar flows in the transition regions. Moreover, relationship between the phenomena and their non-Newtonian viscosities was discussed. For fine bubble (FB) mixtures, the pressure drops were measured with constant flow rates by using relative small-sized orifices. Agreement polymer solutions and their FB mixtures was not obtained. Additionally, elastic properties were measured by using jet thrust method due to discuss the relationship between the flow properties and their elastic properties.
Soft materials including polymers, micelles, gels and liquid crystals possess hierarchical structure with various length scales ranging from nanometer to micrometer. Thus, to give a better understanding of dynamics, it is necessary to examine the structure and physical properties at various length scales, and clarify the correlation between them. Recently, measurements of local rheological properties in soft materials have become possible with the advent of various techniques, called microrheology. In these techniques, rheological information can be accessed on the basis of the movement of probe particles dispersed in a sample to be measured. We have made an effort for time- and spatial-resolved rheological measurements for soft materials, by using optical tweezers and particle tracking that fall under active and passive methods in microrheology, respectively. Such studies can provide information on a concentration fluctuation and a spatial heterogeneity in the systems. Notably, a worm-like micelle solution, a supramolecular hydrogel and lyotropic liquid crystals were spatially heterogeneous on the comparable or at a smaller length scale less than the characteristic length of network and interfacial structures, and on the time scale shorter than the relaxation time.
The present investigation is to analyze the three dimensional stagnation flow of an Oldroyd-B fluid over an off-centered rotating disk. The governing non-linear model and the boundary conditions coupled with it are reduced into ordinary differential equations by means of suitable similarity transformation. To estimate the solution analytically in the form of the infinite series homotopy analysis method is employed. The region of convergence for the solution achieved is also determined and displayed. The influence of various parameters on the velocities of the fluid on radial, azimuthal and induced directions of the flow is presented graphically and discussed.
We investigated the spinning process of a polymeric material by using a multiscale simulation method which connects the macroscopic and microscopic states through the stress and strain-rate tensor fields, by using Lagrangian particles (filled with polymer chains) along the spinning line. We introduce a large number of Lagrangian fluid particles into the fluid, each containing Np-Hookean-dumbbells to mimic the polymer chains (Np = 104), which is equivalent to the upper convected Maxwell fluid in the limit that Np → ∞. Depending on the Reynolds number Re, we studied the dynamical behaviors of fibers for the (a) Re → 0 and (b) finite Re cases, for different draw ratios Dr, ranging from 10 to 30, and two typical Deborah numbers De = 10-3 and De = 10-2. In the limit Re → 0 (a), as the Deborah number De increases, the elastic effect makes the system stable. At finite Re (b), we found that inertial effects play an important role in determining the dynamical behavior of the spinning process, and for Dr = 10-2 the system is quite stable, at least up to a draw ratio of Dr = 30. We also found that the fiber velocity and cross section area are determined solely by the draw ratio. By comparing the velocity and cross section area profiles with the end-point distribution for the dumbbell connective vectors, for dumbbells located in Lagrangian particles along typical places along the spinning line, we show that our multiscale simulation method successfully bridges the microscopic state of the system with its simultaneous macroscopic flow behavior. It is also confirmed that the present schemes gives good agreements with the results obtained by the Maxwell constitutive equation.
In mixing highly viscous materials, like polymers, foods, and rubbers, the geometric structure of the mixing device is a determining factor for the quality of the mixing process. In pitched-tip kneading disks (ptKD), a novel type of mixing element, based on conventional kneading disks (KD), the tip angle is modified to change the channel geometry as well as the drag ability of KD. We discuss the effects of the tip angle in ptKD on mixing characteristics based on numerical simulation of the flow in the melt-mixing zone under different feed rates and a screw rotation speed. It turns out that the passage of fluid through the high-stress regions increases in ptKD compared to conventional KD regardless of the directions and sizes of the tip angle, while the fluctuation in residence time stays at the same level as the conventional KD. Furthermore, pitched tips of backward direction increase the mean applied stress on the fluid elements during its residence in the melt-mixing zone, suggesting the enhancement of dispersive mixing quality in ptKD. These understandings of the role of the tip angle on KD can give a basic guide in selecting and designing suitable angle parameters of ptKD for different mixing purposes.
This study examines the simplest relevant molecular model of a polymeric liquid in large-amplitude oscillatory shear (LAOS) flow: the suspension of rigid dumbbells in a Newtonian solvent. For such suspensions, the viscoelastic response of the polymeric liquid depends exclusively on the dynamics of dumbbell orientation. We have previously derived explicit analytical expressions for the shear rate amplitude and frequency dependences of the first and third harmonics of the alternating shear stress response in LAOS. Higher harmonics sculpt the shear stress, distorting it from its sinusoidal shape. In this work, we derive the polymer contribution to the shear stress response up to and including the next higher, fifth harmonic. For this, we use the fourth order term in the expansion of the orientation distribution to calculate the shear stress response. Our analysis employs the general method of Bird and Armstrong [J Chem Phys, 56, 3680 (1972)]. Our expression is the only one to have been derived from a molecular theory for a fifth harmonic. Our paper thus provides the first glimpse of the molecular origins of a shear stress harmonic higher than the third.