Standard Non-Newtonian fluid for rheological measurements. (Standard Reference Materials).

A new Standard Reference Material (SRM), SRM 2490, is available for calibration of rheometers, instruments used to measure the flow behavior of fluids. Complex fluids, such as suspensions or polymer melts and solutions, often do not follow the simple Newtonian ideal in their flow behavior. Such fluids are found in numerous applications in everyday life (injection molding, paints and coatings, food products, etc.), and the ability to measure accurately and characterize their behavior is very important to optimizing their processing conditions. Since there are a number of commonly used methods to measure the flow behavior of polymers, the new Standard Reference Material will provide a means for comparing the performance of different instruments, as well as a tool for research into better methods of measuring the rheological properties of polymeric fluids. The new standard fluid is certified by NIST for the shear-rate dependence of viscosity and first normal force difference at shear rates from 0.001 [s.sup.-1] to 100 [s.sup.-1] over a temperature range from 0-[degrees]C to 50[degrees]C. The linear viscoelastic storage modulus and loss modulus are also certified at frequencies from 0.04 rad/s to 100 rad/s over the same temperature range.

The new fluid supersedes the previous Standard Reference Material 1490 Non-linear Fluid Standard, which was composed of a high-molecular-mass polyisobutylene dissolved in normal hexadecane. The new standard fluid SRM 2490 consists of a similar high-molecular-mass polyisobutylene dissolved in 2,6,10, 14-tetramethylpentadecane (common name pristane). Pristane is a branched alkane of a slightly higher molecular mass than the normal hexadecane; the branching prevents crystallization or vitrification down to -60[degrees]C, while the higher molecular mass reduces the rate of evaporation of pristane as compared to normal hexadecane.

CONTACT: Carl Schultheisz, [phone]; carl. [e-mail].