We developed new series of organogelators suitable for industrial use through linkage of the molecular design, synthesis, rheological measurements, and elucidation of the viscosity-increasing mechanism of organic compounds. New organogelators, N,N’,N’’,N’’’-1,2,4,5-tetra alkyl/alkenyl pyromellitamides, with four chemical side chains (homo-compounds) and two kinds of chemical chains (hetero-compounds) were synthesized. The solubility and rheological properties of synthesized compounds dissolved in seven kinds of organic solvents (oils) were examined by using visual observation, UV spectrophotometry, and rheological measurements. The solubility of the pyromellitamides was improved by controlling the length of the alkyl chains of the hetero-compounds. The hetero-compounds exhibited significant viscoelastic behavior in solution. To investigate the viscosity-increasing mechanism of the synthesized compounds in solution, self-assembled structures formed in solution due to hydrogen bonding among amide groups were observed using transmission electron microscopy. Differential scanning calorimetric analysis and X-ray diffraction analysis were also employed. Finally, we qualified some synthesized compounds as anti-sedimentation agents for titanium (IV) oxide slurry.
Stress relaxation after a large step strain is conducted for melts of highly entangled high density polyethylene in the uniaxial deformation by a conventional tensile tester. Prior to the stress relaxation tensile tests are made to confirm the uniformity of the elongation. The damping function for the melts in uniaxial deformation is almost identical or close to the prediction by the Doi-Edwards (DE) theory: Stronger damping than the DE prediction, which is often observed for highly entangled polymer melts in shear, is not observed in the uniaxial deformation.
We prepared aluminum borate whiskers/PEG complex powder (PEG 0.5 ∼ 5.0 wt%) by freeze-drying aqueous solutions of PEG with whiskers and studied ER properties of suspensions (contains 10 wt% powder). When the external electric field was not applied, the shear stress of complex powder (PEG 0.5 ∼ 1.5 wt%) suspensions at low shear rate was higher than that of neat whisker suspensions. The suspension of whiskers with 1.0 wt% PEG showed higher shear stress than that of neat whiskers under dc electric field. However, whiskers with 0.5 wt% PEG showed weaker ER effect than neat whiskers. When electric field is applied to neat whisker suspensions, whiskers comprise highly branched chains between electrodes. It is assumed that attached PEG alters the structure of whisker chains but this effect is weaker than that of engagement of whiskers in case of 1.0 wt% PEG. In addition, ER effect was not enhanced when whiskers and PEG powder are added in silicon oil severally. Thus, bonding whiskers with PEG by freeze-drying is effective to enhance the ER effect of whisker suspensions.
Aqueous solutions of xanthan, which is produced by Xanthomonas campestris, are used as viscosity control agents for various food materials. The viscosity is dependent on the environmental conditions affecting the xanthan macromolecule. Moreover, the viscosity frequently depends on the methods used to measure the shear rate during operation. For practical applications of xanthan solutions, the background of this phenomenon should be made clear. The solutions used in this study were prepared by dissolving xanthan in water or in an aqueous salt solution (NaCl, 1 M). The viscosity was then measured using a rotational viscometer. For the aqueous solution of xanthan, the viscosities measured at increasing shear rates showed shear thickening in the low-shear-rate region. On the other hand, no discrepancy between the behaviors was observed when xanthan was dissolved in the salt solution. This paper discusses the aforementioned viscosity behavior using a dispersion model of polymers with contact sites for the solutions.