Public Release: 

Mix masters: NIST scientists image the molecular structure of polymer blends

National Institute of Standards and Technology (NIST)


IMAGE: Typical BCARS composite image of a polyethylene blend taken at NIST showing circular polarization response. LLD polyethylene shows red in this mode, while the HD polyethylene with deuterium substituted for... view more

Credit: NIST

Using an enhanced form of "chemical microscopy" developed at the National Institute of Standards and Technology (NIST), researchers there have shown that they can peer into the structure of blended polymers, resolving details of the molecular arrangement at sub-micrometer levels.* The capability has important implications for the design of industrially important polymers like the polyethylene blends used to repair aging waterlines.

Polyethylene is one of the most widely produced and used polymers in the world. It's used in many familiar applications--milk bottles, for instance--but the NIST research is motivated by a more critical application: water pipes. Aging water infrastructure is a significant national issue. The Environmental Protection Agency has reported that in the United States there are over 240,000 water main breaks per year, leaks wasting 1.7 trillion gallons of water per year, and costs to taxpayers of $2.6 billion per year.



The problem for quantitative service-life prediction is understanding exactly why that is. Developing the necessary predictive models has been hindered by knowing just how the HDPE and LLDPE molecules blend together. They are so close chemically that X-ray or electron imaging--the usual go-to techniques for molecular structure--can't readily distinguish them.

The NIST team is using a variation of Raman spectroscopy, which can distinguish different chemical species--and measure how much of each--by analyzing the frequencies associated with the different vibrational modes of each molecule. The exact mix of these frequencies is an extremely discriminating "fingerprint" for any particular molecule without help of fluorescence labeling. Raman spectroscopy using focused laser beams has been used as a chemical microscope, able to detail the structure of complex objects by mapping the chemical composition at each point in a three-dimensional space.




The group currently is using BCARS to find the correlation between microscopic structures with characteristics of deformation and thermal fusion on polyethylene pipes. For more on Broadband CARS microscopy, see


** See, for example, the Oct. 2010 story, "Faster CARS, Less Damage: NIST Chemical Microscopy Shows Potential for Cell Diagnostics" at
