When solvent permeates a gel membrane the gel shows swelling, and when a gel is put into a centrifugal field the gel shows shrinking. These are examples of the stress (deformation) induced swelling, or the stress-diffusion coupling, of polymer gels. This article describes various types of the coupling and related issues. Among them an approach to the volume phase transition of polymer gels under tension based on the classical thermodynamics gives a new method to estimate the transition enthalpy of the transition.
In this study, the fast numerical computation method by using simplified momentum equations, which exactly clarified the flow state inside a slot die, was developed, in order to obtain higher coating quality. The computation results elucidated the dependence of the uniformity of coating thickness on non-Newtonian characteristics. In addition, it was found that the computational procedure enables us to seek the optimum internal figures of a slot die immediately. The method was extended to a variety of rheological models, such as Power-Law, Ellis and Hershel-Bulkley model. As a result, the computation technique industrially contributed to the development of precise coating productions, such as optical elements, semiconductor and LCD display components.
This paper briefly summarizes two representative examples of investigation of fundamental polymer dynamics with dielectric and viscoelastic methods: 1) Entangled dynamics of flexible polymers: For type-A polymers having the electrical dipoles parallel along the chain backbone, the entanglement dynamics is differently reflected in the dielectric and viscoelastic relaxation functions. A simple relationship between these functions was deduced for the case of full dynamic tube dilation (full-DTD). This full-DTD relationship was found to hold experimentally for monodisperse linear chains, but not for branched (star and Cayley-tree) chains and linear/linear blends. A refined relationship, referred to as partial-DTD, was developed by taking into account the time necessary for constraint release equilibration. This partial-DTD relationship was found to valid for the linear, branched, and blend systems. 2) Effect of carbon dioxide (CO2) on polymer dynamics: Pressurized CO2 dissolves into polymers to exhibit a plasticizing effect. Dielectric tests revealed that the local dynamics of polymer chains was accelerated by pressurized CO2 without changing relaxation mode distribution. This unusual plasticizing effect of pressurized CO2 for the local dynamics was attributed to extraordinary fast diffusion of CO2 compared to the segmental motion of the polymer chain. The concentration fluctuation of the polymers, being responsible for the relaxation mode broadening usually observed for plasticized polymer systems, is smeared by the fast CO2 molecules in the time scale of segmental motion. In contrast, pressurized CO2 behaves just as an ordinary solvent for the slow, global dynamics of polymer chains.
Silica sols are produced with sodium silicate and sulfuric acid by their neutralization. We have previously reported that both the onset time of the gelling and the sol-gel transition are strongly affected by the preparation conditions of acid silica sols. In this study, we evaluated the effect of the temperature and pH on the rheological properties of silica gels by both the dynamic viscoelastic measurement and the creep test in order to probe the structure of gels during aging. The results indicate that the heating plays a role in the fast-forwarding of the gelling time. In contrast, increasing in pH affect not only the gelling time but also the elastic modulus of the four-component model adopted for the silica gel. The mechanism of the particle bonding might be related to pH, and the predicted bonding images are presented.
A formulation for simulating the kinematics of a droplet of polymer solution in solvent is proposed. In this formulation both polymer solution and solvent are characterized by Newtonian viscous fluids, the viscosity of polymer solution is much higher than that of solvent. Furthermore the effects of both osmotic pressure and friction force between polymers and solvent are considered. The deformation of a droplet is described by the convection equation of the volume fraction of polymer solution. Numerical simulations for a swelling and de-swelling problem of a polymer droplet in solvent are performed. The numerical results indicate that both the osmotic pressure and the friction force significantly affect the behavior of polymer droplet.