Rheometer

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

Determination of elongational viscosity of polymer melts by RME and Rheotens experiments

Abstract: Several linear (LLDPE, HDPE, PS) and long-chain-branched (LDPE, PP) polymer melts were investigated by an elongational rheometer (RME Rheometrics) and by Rheotens (Gottfert). The Molecular Stress Function (MSF) theory is briefly reviewed and used to extrapolate the steady-state elongational viscosity. To evaluate Rheotens experiments, a new process model is introduced which assumes that the elongational viscosity in the Rheotens test is a function of the draw ratio only. The apparent elongational viscosities extracted from Rheotens curves are found to lie in between the steady-state elongational viscosity and three times the shear viscosity.

The development of the bending beam rheometer; basics and critical evaluation of the rheometer

Abstract: The bending beam rheometer is proposed by the Strategic Highway Research Program (SHRP) for direct measurements of the rheological properties of asphalts at the lowest pavement temperatures. The purpose of this paper is to present the basic concepts upon which the rheometer was developed, to describe the testing procedure and the important procedural factors that affect test results, and to discuss the methodology of data interpretation. Typical results from the research program using a large number of asphalts to evaluate the rheometer are presented to illustrate the differences in behavior of asphalts from different sources and of different grades. The paper highlights the features of the testing system and the specimen preparation procedure. The results of the rheometer evaluation indicate that the rheometer is a repeatable test that can be used effectively to characterize the visco-elastic nature of asphalts at the lowest pavement temperatures. The paper includes discussion of the rationale behind selecting the specification parameters and the specification criteria to enhance binder contribution to resistance to thermal cracking.

Characteristics of Thixotropic Behavior

Abstract: The shear stress‐shear rate behavior of a thixotropic hectorite clay‐water suspension was studied in a Couette viscometer under a wide variety of rest and shear rate histories. Shear stress decay and build‐up transients resulting from step changes in shear rate were measured. The transient stress data were used to construct equilibrium and constant structure flow curves. The constant structure curves could be described by the Power Law model with a constant exponent but varying coefficient. Normalized stress transients could be described by an exponential time series similar to those used in stress relaxation studies on viscoelastic polymers. This method was applicable to literature data and to data obtained for other fluids in our laboratory. The transient behavior of thixotropic fluids is heavily influenced by past history of deformation. Structural rebuilding during rest seemed to begin with the formation of a weak gel structure. Structural rebuilding was also observed under shear rate. In experiments ...

Distinguishing between linear and branched wormlike micelle solutions using extensional rheology measurements

Abstract: A filament stretching extensional rheometer and capillary breakup extensional rheometer is used to measure the effect of branching on the extensional rheology of a series of wormlike micelle solutions. The experiments are performed using a series of linear and branched wormlike micelle solutions consisting of sodium oleate (NaOA) and octyl trimethyl ammonium bromide (C8TAB). The ratio of NaOA to C8TAB is fixed at 70∕30 while the total surfactant concentration is varied. The shear rheology of wormlike micelle solutions is found to demonstrate a maximum in shear viscosity at 4wt% followed by a sharp decrease in viscosity with increasing surfactant concentration. It has been shown through cryo-transmission electron microscopy imaging that the maximum in the shear viscosity for these fluids corresponds to the transition from linear entangled to branched micelles. The extensional rheology measurements for all of the wormlike micelle solutions below 4wt% demonstrated some degree of strain hardening of the exten...