Solution properties and film properties of the polymer electrolyte (Nafion) were investigated by dynamic light scattering (DLS) and rheological analysis. By DLS measurement, it has been found that the Stokes diameter of Nafion molecules in a DMF solution is larger than that in a water/alcohol solution (SE5112, DuPont). This result clearly shows that the DMF is a better solvent than the solvent component of SE5112. Both SE5112 and the DMF solution behave as almost Newtonian solutions, while Nafion solution in DMF/water mixed solvent shows viscoelasticity due to the aggregation of Nafion molecules. Finally, the mechanical properties and the proton conductivities of the cast film of Nafion from SE5112 and the DMF solution were investigated. The proton conductivity is almost the same in both films, while the mechanical properties of the film made from the DMF solution are much better than those of the film from SE5112. This can be understood as a result of the weaker segregation of crystalline and amorphous regions in the former film.
Viscosity is a key property controlling the appearance of automotive coatings. However, the direct measurements of the viscosity in automotive coatings have not been achieved, since the automotive coating is a complex system consisting of a multilayer where mass transfer occurs between each thin layers. Using the laser trapping method, we have developed a rheometer to realize non-destructive viscosity measurements of the multilayers. Applying the new rheometer to automotive coatings, the viscosity has been estimated for (A) a clearcoat itself, (B) a clearcoat on a basecoat, and (C) a clearcoat on a basecoat and a surfacer. The results demonstrate an increase of viscosity in the order of (A) < (B) < (C), depending on the thickness of the lower layers. The viscosity increase suggests that the concentration of the clearcoat is likely to increase due to the diffusion of the solvent into the lower layers.
The rheological properties and the morphology of a water swellable microgel developed as a viscosity thickener for cosmetics were studied. The water swellable microgel was synthesized by a novel inversed microemulsion polymerization technique. The apparent yield stress appeared in semi-dilute regime, at around twice the overlapped concentration of the microgel and the value of the apparent yield stress increased with the concentration of the microgel. Although the deformation behavior of the microgel suspension at very small shear stress looked like elastic deformation from its flowcurve, it was revealed the suspension flowed in such case by creep measurement. It is implied that there would be a structure causing quite slow relaxation by creep and dynamic modulus measurements. The morphology of the microgel through the freeze-fracture TEM showed the microgel was swollen as a spherical shape and closely packed at a concentration at which the apparent yield stress appeared. One possible mechanism of the appearance of yield stress is the friction between the layers where the microgel particles arrange in a random closed packing state.
We have developed a non-water gel comprised of polyethylene glycol (PEG) and hydroxypropylcellulose (HPC) as a gelling agent. We investigated the gelation mechanism of the HPC/PEG system on the basis of a stress-controlled rheometer and an X-ray diffractometer. From these results, we found that two gelation mechanisms coexisted in the HPC/PEG system; the entanglement of interacting HPC polymer chains which behave like a flexible polymer and the cross-linking of the microcrystalline domains of the HPC main chains. In the lower HPC concentration range, the gelation is dominated by the cross-linking of the microcrystalline domains of the HPC main chains. In the higher HPC concentration range, on the other hand, the gelation is dominated by the entanglement of interacting HPC polymer chains.
It is necessary to provide well-designed geometries of flow channel in a slot die in order to achieve the uniform thickness of coated films for non-Newtonian fluids, especially for the fluids having nonnegligible yield stress. In this work we have studied the flow in the slot die using Bingham fluid. The present paper derives a model equation for the outflow distribution as functions of the yield stress and the geometries inside the die. Furthermore, we suggest a useful design method to predict an optimum geometry to guarantee the uniformity of outflow from die slot in Bingham fluid. The usefulness of the method is confirmed by an experiment conducted using a corresponding fluid.
We numerically demonstrate that the ratio of uniaxial to planar elongational viscosity controls the neck-in phenomena of the casting polymer films, i.e., the decrease in film width value for both viscous and viscoelastic fluids. Quasi-three-dimensional numerical simulations of an isothermal film casting process were performed using a finite element method for two viscoelastic fluids using Larson and PTT models, purely-viscous non-Newtonian fluids using Cross model and Newtonian fluids. The increase in take-up velocity relative to that in extrusion showed particular film deformations of neck-in depending upon the rheological properties in the models. The results indicate that the film width is determined by the ratio of uniaxial to planar elongational viscosity rather than the extension-thickening nature in uniaxial elongation. The computations using different fluid models show that the viscosity ratio is universal for predicting the neck-in value of the stretching polymer films not only in viscoelastic but also in pure viscous fluids.
When a viscoelastic fluid flows in a straight channel with a noncircular cross section, a secondary flow is developed. We discussed the effect of flow characteristics on the secondary flow of the viscoelastic fluid through a straight channel with a square cross section by the viscoelastic flow simulation using the finite element method. The Phan-Thien Tanner (PTT) model was employed as the constitutive equation. The second normal stress difference N2 contributes to the secondary flow motion of a viscoelastic fluid through a straight channel with a square cross section. The degree of the secondary flow expressed by the maximum streamline function |ψmax| depends on the recoverable shear for the second normal stress difference −N2/2σ , where σ is shear stress. According to the distribution of N2 on the cross section, the flow direction of the secondary flow depends on the pressure drop generated by N2. The elongational flow characteristics also contribute to the secondary flow state. On the whole, the degree of the secondary flow increases with the strain-hardening. However, the contribution of elongational flow characteristics to the secondary flow is smaller than that of −N2/2σ.