Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.

Can extensional viscosity be measured with opposed-nozzle devices?

Abstract: Opposed-nozzle devices are widely used to try to measure the extensional viscosity of low-viscosity liquids. A thorough literature survey shows that there are still several unanswered questions on the relationship between the quantity measured in opposed-nozzle devices and the “true” extensional viscosity of the liquids. In addition to extensional stresses, opposed nozzle measurements are influenced by dynamic pressure, shear on the nozzles, and liquid inertia. Therefore the ratio of the apparent extensional viscosity that is measured to the shear viscosity that is independently measured is greater than three even for Newtonian liquids. The effect of inertia on the extensional measurements is analyzed by computer-aided solution of the Navier-Stokes system, and by experiments on low-viscosity Newtonian liquids (1 mPa s

Study of rheological property of nylon‐1212 with Haake Rheometer

Abstract: Rheological properties of nylon-1212 have been studied by means of Haake Rheometer. The effect of shear rate and temperature on the apparent vicosity of nylon-1212 was discussed. A correlation of non-Newtonian index with the temperature was obtained. The results showed that the apparent viscosity decreases with the increase of the temperature. With increasing shear rate, shear thinning of nylon-1212 was observed clearly. From the relation of the temperature dependence of the polymer, we obtained the viscous flow activation energy. We conclude that the apparent viscosity is sensitive to temperature at lower shear stress because of higher viscous flow activation energy, and the temperature affect on the apparent viscosity becomes weaker at higher shear stress because of lower viscous flow activation energy. We have investigated the creep and elastic recovery of nylon-1212. A creep test was carried out to define the linear viscoelastic range as 1.0 and 5.0 Pa for 195 and 190°C nylon-1212 melts, respectively. A time-dependent response was found for the creep and recovery phases at a lower applied shear stress. However, at higher shear stress, the creep and recovery phases were time-independent.

Steady shear rheometry of dissipative particle dynamics models of polymer fluids in reverse Poiseuille flow.

Abstract: Polymer fluids are modeled with dissipative particle dynamics (DPD) as undiluted bead-spring chains and their solutions. The models are assessed by investigating their steady shear-rate properties. Non-Newtonian viscosity and normal stress coefficients, for shear rates from the lower to the upper Newtonian regimes, are calculated from both plane Couette and plane Poiseuille flows. The latter is realized as reverse Poiseuille flow (RPF) generated from two Poiseuille flows driven by uniform body forces in opposite directions along two-halves of a computational domain. Periodic boundary conditions ensure the RPF wall velocity to be zero without density fluctuations. In overlapping shear-rate regimes the RPF properties are confirmed to be in good agreement with those calculated from plane Couette flow with Lees–Edwards periodic boundary conditions (LECs), the standard virtual rheometer for steady shear-rate properties. The concentration and the temperature dependence of the properties of the model fluids are shown to satisfy the principles of concentration and temperature superposition commonly employed in the empirical correlation of real polymer-fluid properties. The thermodynamic validity of the equation of state is found to be a crucial factor for the achievement of time-temperature superposition. With these models, RPF is demonstrated to be an accurate and convenient virtual rheometer for the acquisition of steady shear-rate rheological properties. It complements, confirms, and extends the results obtained with the standard LEC configuration, and it can be used with the output from other particle-based methods, including molecular dynamics, Brownian dynamics, smooth particle hydrodynamics, and the lattice Boltzmann method.