In this illustration, the pin-like forms represent polymer chains, with the color indicating average angle off the vertical plane and the size of the pinhead representing the distribution of orientations around that average. The image in the background shows the raw data, which was produced by BCARS. Image: Y.J. Lee/NIST.In some materials, the molecules line up in a regular, repeating pattern. In others, they all point in random directions. But in many of the advanced polymer materials used in medicine, computer chip manufacturing and other industries, the molecules arrange themselves in complex patterns that dictate the material’s properties.
Scientists have always lacked good ways to measure molecular orientation in three dimensions at a microscopic scale, leaving them in the dark about why some materials behave the way they do. Now, however, researchers at the US National Institute of Standards and Technology (NIST) have come up with a method that can measure the 3D orientation of the molecular building blocks of polymers, observing details as small as 400nm in size.
The new measurements were made using a souped-up version of a technique called broadband coherent anti-Stokes Raman scattering (BCARS). As the researchers report in a paper in the Journal of the American Chemical Society, these measurements show polymer chains twisting and undulating in complex and unexpected ways.
BCARS works by shining laser beams at a material, causing its molecules to vibrate and emit their own light in response. This technique, developed about a decade ago at NIST, is mainly used to identify what a material is made of. To use it for measuring molecular orientation, NIST research chemist Young Jong Lee added a system for controlling the polarization of the laser light and new mathematical methods for interpreting the BCARS signal.
Specifically, the souped-up technique can measure the average orientation of the polymer chains within 400nm-regions, along with the distribution of orientations around that average. These measurements will allow scientists to identify the molecular orientation patterns that produce the mechanical, optical and electrical properties they seek.
“Understanding that structure/function relationship can really speed up the discovery process,” Lee said.
This will help researchers to optimize the materials used in medical devices such as arterial stents and artificial knees. The orientation of the molecules on the surface of those devices helps determine how well they bond with muscle, bone and other bodily tissues.
It can also help with additive manufacturing, in which products are fabricated by printing them layer-by-layer – a technique that is transforming the electronics, automotive, aerospace and other industries. Additive manufacturing often uses polymers, and researchers are constantly seeking new ones with better strength, flexibility, heat resistance and other properties.
The new measurement technique might also be used to optimize the polymer-based ultrathin films used in semiconductor manufacturing. As the components within computer chips get smaller and smaller – as Moore’s law predicts they will – the molecular orientations in those films become increasingly important.
This story is adapted from material from NIST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.