Viscoelasticity and Morphology of Soft Polycarbonate as a Substitute for Poly(vinyl chloride) (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Rheology)

The soft polycarbonate resins, SPC, were newly developed as a substitute for soft poly(vinyl chloride). The soft polycarbonates are multiblock copolymers composed of bisphenol A polycarbonate, PC, and polydimethylsiloxane, PDMS. SPC resins are clear, transparent, and tough. Viscoelasticity and morphology of the resins were investigated to control physical properties of the resin. Electron microscope and small angle X-ray scattering experiments revealed that the SPC formed microdomain structures. Rheological measurements were used to discuss continuity of PC-rich phase domain, which determined the modulus around the room temperature

Molecular Rheology of Glassy Polymers (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Rheology)

Molecular origin of the viscoelasticity around the glass transition zone is investigated by means of dynamic birefringence and dynamic viscoelasticity measurements. The present study show that the viscoelasticity around the glass transition zone has two molecular origins: One is the orientation relaxation of main chain axis and the other one is the rotational motion of structure units about the main chain axis

Nonlinear Rheology and Flow-Induced Structure in a Concentrated Spherical Silica Suspension (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Rheology)

In hard-sphere suspensions of solid particles, the stress has the Brownian (thermodynamic) and hydrodynamic components σB and σH, the former reflecting the anisotropy of the particle distribution while the latter being determined by the hydrodynamic interaction between the particles. These two components exhibit nonlinearities under steady shear flow with different mechanisms. The nonlinearity of σB results from the particle distribution insensitive to the shear rate, while σH becomes nonlinear due to flowinduced clustering of the particles. These structural origins of the nonlinearities were confirmed from flow-SANS experiments

Rheo-Dielectric Behavior of Oligostyrene and Polyisoprene (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Rheology)

Flow effects were examined for dielectric behavior of oligostyrene (OS; M = 950) and cis-polyisoprene (PI; M = 8200). OS-1 has monomeric dipoles perpendicular to its backbone and the terminal dielectric relaxation results from the segmental motion, while for PI-8 having parallel dipoles this relaxation reflects the global chain motion. The dielectric loss e” and viscosity h were measured for OS and PI at T well above respective Tg under steady shear flow at rates g << 1/t1, with t1 being the linear viscoelastic terminal relaxation time. The e” and h of PI were independent of g, as usually expected under such slow flow. In contrast, OS exhibited acceleration of the dielectric relaxation and the shear-thinning of h at g << 1/t1. This thinning was related to flow-induced changes in some sort of dynamic structure, probably a cooperative domain structure, and the dielectric change detected acceleration of the segmental motion due to this structural change

Nonlinear Viscoelasticity of Amorphous Polymers in the Vicinity of the Glass Transition Temperature (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Rheology)

Nonlinear viscoelasticity of atactic polystyrene around the glass transition was studied by means of constant rate elongation. The strain-induced birefringence and the stress were simultaneously measured and then the stress was separated into two components (Rubbery and Glassy components) by using the modified stress-optical rule. Behavior of the R component, having the molecular origin of chain orientation, was essentially linearly viscoelastic. On the other hand, the G component, originated by rotational orientation of chain units, showed remarkable thinning phenomena, which is commonly observed for glassy materials. Thus, the separation of stress for polymeric material simplifies phenomenological interpretation of nonlinear viscoelasticity of polymers near the glass transition zone