Non-newtonian polymer solution for rheology now available. (Standard Reference Materials).A new Standard Reference Material, SRM (1) (Storage Resource Management) The management of the storage resources in an organization in order to avoid duplication of files and to determine space utilization across all servers. 2491, is available for calibration of rheometers (instruments used to measure flow behavior of fluids). SRM 2491, a polydimethylsiloxane, is a companion standard to SRM 2490 for which NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. has certified the non-Newtonian theological properties. Polymer melts and solutions often demonstrate non-Newtonian flow behavior. Such fluids commonly have a viscosity that depends on the shear rate Shear rate is a measure of the rate of shear deformation:  For the simple shear case, it is just a gradient of velocity in a flowing material. and display elastic effects like normal stresses that greatly affect their response to deformation. Accurate measurements of these material properties are critical for predicting the behavior of polymeric fluids in the complex flows they experience during processing and use. The two SRMs are intended to provide a means for comparing different methods of measuring viscoelastic Adj. 1. viscoelastic - having viscous as well as elastic properties natural philosophy, physics - the science of matter and energy and their interactions; "his favorite subject was physics" fluid behavior. For these fluids, NIST certifies the shear-rate dependence of viscosity and first normal stress difference over a range of shear rates between [10.sup.-3] [s.sup.-1] and 100 [s.sup.-1], at temperatures of 0 [degrees]C, 25 [degrees]C, and 50 [degrees]C. The linear viscoelastic response is also certified, along with the shift factors, over the same temperature range. There were several reasons for issuing a companion standard to SRM 2490. First, the zero-shear-rate viscosity of SRM 2491 at 25 [degrees]C is approximately one order of magnitude A change in quantity or volume as measured by the decimal point. For example, from tens to hundreds is one order of magnitude. Tens to thousands is two orders of magnitude; tens to millions is three orders of magnitude, etc. greater than the zero-shear-rate viscosity of SRM 2490. Secondly, the theological properties of the polydimethylsiloxane melt used for SRM 2491 exhibit less temperature dependence compared to the solution used for SRM 2490. This property could be advantageous in isolating transducer transducer, device that accepts an input of energy in one form and produces an output of energy in some other form, with a known, fixed relationship between the input and output. or actuator problems from temperature control problems in a rheometer rhe·om·e·ter n. An instrument for measuring the flow of viscous liquids, such as blood. . In addition, whereas SRM 2490 is a solution and subject to changes in properties with solvent loss, polydimethylsiloxane is stable and inert, and therefore should be free from any problems with chemical stability, evaporation, or safety. CONTACTS: Bruno Fanconi, (301) 975-6769; bruno. fanconi@nist.gov or Kathleen Flynn, (301) 975-6590; kathleen.flynn@nist.gov. |
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