Nonlinear fluid standard reference material: Progress report

NIST is in the process of developing a new Standard Reference Material (SRM 2490 Nonlinear Fluid for Rheological Measurements) that replaces the previous SRM 1490 Nonlinear Fluid Standard. The purpose of the material and its development is two-fold: first, to help equipment manufacturers and researchers in different laboratories to better understand the inherent lab-to-lab variability in their measurements and consequently help reduce these; and second, to provide a standard fluid that is useful to researchers and analytical laboratories alike as a research material and as a secondary standard because it is homogeneous and has well known material properties. The material property ranges of interest will be decided through consultation with the Rheology community; this process is already underway and has led to a preliminary selection of a solution of polyisobutylene dissolved in 2,2,4,4,6,8,8-heptamethylnonane. NIST is performing the initial measurements on this material and is organizing a round robin to ensure that the chosen material properties are acceptable to those participating in the round robin and to bring a consensus concerning the lab-to-lab variability in the measurements. Based on these results, the fluid will be certified for the shear rate dependence of viscosity and first normal stress difference over a temperature range of approximately 50 °C. The linear viscoelastic responses will also be certified along with the temperature dependence of the shift factors and the zero-shear-rate viscosity. Here we present progress up to the current time.