Magazine article Science News

Droplets String Themselves Together

Magazine article Science News

Droplets String Themselves Together

Article excerpt

When designing products such as car bumpers, engineers often call for polymers that mix as poorly as vinegar and oil. Materials scientists can circumvent this problem by blending the ingredients so that one polymer forms droplets that disperse in the other.

New research has revealed that in very small spaces, these blends can yield unexpectedly well-organized microstructures that might prove useful for making such novel items as all-plastic electrical wires. In the Feb. 5 PHYSICAL REVIEW LETTERS, Kalman B. Migler of the National Institute of Standards and Technology in Gaithersburg, Md., reports his observations of polymer droplets lining up to form microscopic strings.

"There's a growing industry of making smaller-and-smaller-scale parts," says Migler. But in the case of polymer blending, researchers haven't understood the physics and chemistry that unfold on these small scales, he says.

While examining flows of polymer droplets in blends, Migler made a surprising observation. After placing a polymer blend between two clear, quartz disks, he rotated the top disk to generate twisting, shearing forces. Peering through a micro-scope as he slowed the disk's rotation, Milger could see polymer drops of one of the ingredients spontaneously assuming unexpected arrangements within the surrounding polymer. First, the drops grew until just one layer of them could fit in the space between the disks, and then they lined up like pearls in a necklace. Next, the individual drops coalesced into a long string. …

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