Rheological properties of various colloidal disperse systems were studied in the wide view of linear and non-linear viscoelasticity. The colloidal disperse systems show a unique relaxation mechanism in relatively long-time scale region, which is due to heterogeneity of the system. The disperse systems of fibrous particles show extremely high viscosity and large elastic modulus in comparison with that of the spherical particles.
Surfaces in polymeric materials play an important role in many technological applications. Hence, systematical understanding of aggregation states and physical properties at the surfaces is of pivotal importance as the first benchmark so that highly functionalized polymeric materials based on surface peculiarity can be promisingly designed and constructed. Nevertheless, surface properties, especially rheological properties, had not been studied until early 90s because of technical difficulties. In 1993, we started to embark on this intriguing and challenging issue by mainly scanning force microscopy using monodisperse polystyrene (PS) solid films. Consequently, conclusions obtained thus far are consistently arrived that molecular motion at the PS surfaces is thermally activated in comparison with the corresponding internal bulk region. However, it is far from clear for the moment what the whole picture of such peculiar surface mobility is, although we believe that some parts of it have been successfully clarified to date. Here, experimental methods to examine surface rheological properties, which we have proposed, are mentioned at first, and then, essential points of what we have established are discussed.
Viscoelastic effects on phase separations in polymeric systems are investigated by a numerical method using a two fluid model. In the viscoelastic phase separation, the coupling of solvent diffusion and stress stored in polymeric materials strongly influences the dynamics, morphology of phase separated pattern. In our model we take into account the coupling and explain unusual phase separation phenomena observed experimentally in polymer solution systems. In our simulations, we reproduced the network pattern of polymer rich phase which is a minority phase and found that the coarsening of the network pattern is very slow. In order to clarify the origin of slowing down of coarsening dynamics of network pattern of polymer rich phase,we investigated the dynamics of an initially elongated droplet.We found that the flow field induced by the surface tension of droplet is suppressed by the stress produced by the induced flow field.
Small amplitude oscillatory squeeze flow was found to provide a convenient means of monitoring the changes in the viscoelastic properties of two types of adhesive materials as they cure, right up to their final set state. The high stiffness of the instrument, the use of band-limited pseudorandom noise as the input signal and the use of disposable disks enabling easy sample removal represent the main advantages of this technique over conventional rheometers to monitor the changes in the viscoelasticity of these materials.
This article describes the flow properties of surfactant aqueous solutions in a pipe junction with branching angle of 90 degree. The effects of concentrations and temperatures on junction loss coefficients were investigated. The surfactant used is Ethoquad O/12 (C18H35N(C2H4OH)2CH3Cl). The surfactant and equimolar amounts of NaSal (HOC6H4COONa) were dissolved in tap water. The concentrations of surfactant aqueous solution were ranged from 100 to 1000 ppm. The experiments were carried out at 15, 20, 30 and 50°C. Pressure losses due to branching and wall pressure distributions were measured. Pipe friction losses before and behind the junction were also measured. The pipe friction factors before and behind the branch differed from each other. The critical Reynolds number, at which drag reduction is lost and the friction factor agrees with the Blasius's equation, decreased with increasing concentration of surfactant and increasing temperature. Those solutions showed overshooting phenomenon that the recovery pressures of main flow became higher than the pressure at a starting point, which was not observed in tap water. Dividing loss coefficients were higher than those for Newtonian fluid below the critical Reynolds number and were identical with each other above it. The dividing loss coefficients increased with increasing concentration of the surfactant as well as with decreasing temperature.
The effects of non-neutralized carboxylic acid(-COOH) on strain hardening of EMAA-54Na and EMAA-59Zn ionomers blended with StMAA and PS were investigated. In case of EMAA-54Na/StMAA blend, unexpected strong strain hardening appeared. However, this tendency was not found to all other samples. It was considered that cause of unexpected phenomena of EMAA-54Na/StMAA blend came from strong interaction between EMAA-54Na and StMAA due to acid-cation exchange mechanism proposed by Vanhoorne et al. Further, it was considered that non-neutralized carboxylic acid(-COOH) was the new key to increase the intensity of strain hardening for EMAA-ionomers.