NEW TECHNIQUE FOR BLENDING POLYMERS YIELDS NOVEL STRUCTURES.

Two polymers may be incompatible with each other, yet, when forced together during processing, can produce a material that combines the best features of each. Most engineering plastics are polymer blends. Blending technologies are already in wide use for large parts such as car bumpers, but new applications are emerging for parts that are similar in size to the dispersed polymer droplets.

Using visualization technology to study the polymer blending process, MIST scientists have discovered the formation of novel polymer structures that can occur in such microscale applications. NIST measurements show that, when two incompatible polymer liquids are mechanically blended together, one may deform into very long strings that are extremely stable. This remarkable transformation occurs under special conditions-- when the size of a typical polymer droplet is comparable to the size of the part being made, such as ultrathin films and other micron-scale components. When the processing meets these conditions, the droplets spontaneously reorganize into "superstrings."

Potential microscale applications of super-string components could include conductive plastic wires, ultrathin composite materials and tissue engineering.

A NIST scientist has published a paper on these findings, "String formation in sheared polymer blends: Coalescence, breakup, and finite size effects," in the Feb. 5, 2001, issue of Physical Review Letters.