Critical Value Γc Research Articles

Structure development under transient shear flow in semidilute polystyrene solution

AbstractThe shear‐induced concentration fluctuations or phase separation of a semidilute solution comprised of polystyrene (PS) as a solute and dioctylphthalate (DOP) as a solvent (PS/DOP) was investigated by using real‐time and in‐situ shear‐small‐angle light scattering and shear‐phase‐contrast optical microscopy. When a transient shear flow with a fixed shear rate γ greater than a critical value γC was imposed on the solution, a unique anisotropic scattering pattern was observed some time after onset of shear. This pattern was found to be identical to the “butterfly pattern” previously reported for the same solutions under steady shear flow with γC. When the shear flow was ceased before the scattered intensity reached a steady state, the scattered intensity rapidly increased toward a maximum intensity, and then decreased toward the intensity of the quiescent solution with time. From the phase‐contrast microscopy, this immediate increment of the scattered intensity after the shear cessation was found to arise from the increment in amplitude of the concentration fluctuations along flow direction. The characteristic length scale of the fluctuations was about 2.5 μm in this experiment, almost independent of the shear rate imposed on the solution.

粉流体の対流運動の数値モデル

Numerical modeling of convection of powder was done. Convection of powder occurs when a strong vertical vibration is applied. When the control parameter, the acceleration amplitude Γ, exceeds some critical value Γc, convection and heaping start. In our simulation, the powder is modelled with a discrete elementary method but without rotation and with isotropic linear elastic interaction. The convection is reproduced, and Γc turns out to be about the gravity acceleration g, which agrees with the experiment, an other remarkable phenomena, surface fluidization, is also reproduced, and the critical value Γc again agrees with the experiment. It is suggestde that this convection is caused by the instability of the powder induced by the elastic interaction.

Phase transitions of dense systems of charged ‘‘dust’’ grains in plasmas

The behavior of ‘‘dust’’ grains (particulates) in microelectronics process plasmas has been studied using N-body simulations. Grains are assumed to be negatively charged and interact through a screened Coulomb potential Φ(r). The dimensionless parameters κ=a/λ and Γ=Φ(a)/kBT characterize the thermodynamics of the particulate system, where λ is the ion Debye length, a=(3/4πnD)1/3 is the mean intergrain distance, and nD and T are the dust density and temperature. The simulations exhibit a transition between ‘‘fluid’’ and ‘‘solid’’ phases at a critical value Γc that depends on κ and weakly on the system history (i.e., whether it ‘‘melts’’ from an ordered state or ‘‘freezes’’ from a random one).

The exact phase diagram of the quantumXY spin glass model in a transverse field

The infinite rangeXY spin glass model in a transverse field is investigated by means of the Trotter-Suzuki approach. The exact phase diagram is obtained showing that a spin glass transition takes place for non-zero values of the transverse field γ up to a critical value γc=1.44α0.01. The present numerically exact calculations are in good agreement with our previous approximate results and they clear remaining discrepancies from previous work.

Numerical modeling of convective motion in granular materials

Numerical modeling of convection of powder was performed. Convection of powder occurs when a strong vertical vibration is applied. When the control parameter, the acceleration amplitude r, exceeds some critical value Γc, convection and heaping start. In our simulation, the powder is modeled with a discrete elementary method but without rotation and with isotropic linear visco-elastic interaction. The convection is reproduced and Γc turns out to be about the gravity acceleration g, which agrees with experimental findings. Another remarkable phenomena, surface fluidization, is also reproduced and the critical value Γc'again agrees with experimental findings. It is suggested that this convection is caused by the instability of powder induced by the elastic interaction.

Incorporation of Functional Groups onto the Surface of Polyethylene

WE report here a new method for modifying polyethylene surfaces by incorporating various functional groups onto the surface. The critical surface tension value (γc) of polyethylene treated with an electron deficient moiety (EDM) such as a carbene or nitrene can be changed to a desired value by selecting the proper electron deficient moiety. The γC of untreated polyethylene is 31 dynes/cm, but on exposure to carbethoxycarbene the value is increased to 39 dynes/cm and when exposed to difluorocarbene the value approaches 21 dynes/cm.