Rheometer

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

Nuclear magnetic resonance visualization of anomalous flow in cone-and-plate rheometry

Abstract: We demonstrate the use of nuclear magnetic resonance (NMR) microscopy to image the velocity distribution for fluids sheared within the gaps (4° and 7°) of cone-and-plate rheometers. These measurements employ a specially constructed rheogoniometer, which fits within the NMR probe system. While the uniform shear rate assumption is verified in the case of simple Newtonian and non-Newtonian fluids, a range of anomalous behavior (apparent slip, shear banding, and fracture) is observed in other systems, including wormlike surfactants, semidilute solutions of 18 MDa polyacrylamide, and dispersed silica in silicone grease.

Relation between steady shear flow and dynamic rheology

Abstract: The relationships between steady shear flow and dynamic rheology are investigated at relatively high shear rates and frequencies A useful empirical relationship in this region predicts that the magnitude of the complex dynamic viscosity |η*| should be compared with the shear viscosityη at equal values of frequency and shear rate (Cox-Merz-rule) Polystyrenes (PS) and Polyacrylamides (PAAm) have been investigated over a wide range of concentration and molecular weight Only in case of PAAm/H2O solutions we have found that the results do not coincide with Cox-Merz-rule As far as we know this is the first time that deviations from Cox-Merz-rule were observed in a homogeneous system A molecular interpretation is given

Morphological and Rheological Properties of Polyamide 6/Poly(propylene)/Organoclay Nanocomposites

Abstract: Summary: Polyamide 6 (PA6)/Poly(propylene) (PP)/organoclay (octadecylamine intercalated montmorillonite) systems with and without compatibilizer (maleated poly(propylene) and ethylene/propylene-based rubber (PPgMA and EPRgMA, respectively)) were produced by extrusion melt blending and the clay dispersion was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The rheological behaviour of the nanocomposites was determined by various methods, viz melt flow index (MFI), capillary and plate/plate rheological measurements. Attempts were made to trace the rheological parameters that reliably reflect the observed changes in the clay dispersion. It was found that some parameters in the viscoelastic range derived from frequency sweep measurements using a plate/plate rheometer are a suitable indicator for changes in the clay dispersion. High initial viscosity with a strong reduction as a function of frequency was attributed to improved clay exfoliation. The latter was also reflected by a high initial shear storage modulus (G′) along with its small change with the frequency. Variation of the storage modulus (G′) as a function of frequency for the PA6/PP nanocomposites. Note: this figure also indicates how the slopes at low and high shear rates were determined.

Nonlinear shear and extensional rheology of long-chain randomly branched polybutadiene

Abstract: We present nonlinear shear and uniaxial extensional measurements on a series of polybutadienes with varying amounts of long-chain, random branching. Startup of steady shear experiments is used to evaluate the damping function of the melts. The damping function is found to show a trend toward decreased dependency on strain with increasing branching content. Interior chains, which are believed to be responsible for changing the damping function, are calculated to comprise less than 3 wt % of the melt. Extensional measurements are used to investigate the role of branching in strain hardening. We show that samples with increased branch contents do show larger deviations of the transient Trouton ratio from the linear viscoelastic limit of three. However, we also show that the extensional data can be fit using parameters determined solely by the shear measurements. Furthermore, we show that the changes in the damping function seen in shear have little impact on extensional behavior. The extensional behavior of the melt is found to be most affected by changes in the relaxation spectra which can result from both branching and increases in the high end of the molecular weight distribution. This statement runs contrary to the often expressed view that strain hardening behavior in extension is exclusively produced by branching.