Polymer Superstrings

Many advanced polymers are composed of blends of two or more components that do not mix--like oil and water--but are forced into intimate contact. In this way, scientists can construct materials that combine the best features of each polymer. For example, polystyrene is very brittle on its own, but when rubbery particles are incorporated, it can withstand large impacts.

Blending two polymers ordinarily produces a mayonnaise-like mixture or emulsion in which one polymer is distributed or dispersed in a matrix of the other. (In case you were wondering, mayonnaise contains egg-coated oil droplets dispersed in vinegar.) Polymer blending technologies are well developed for the case where the final part (such as a car bumper) is much larger than the size of the dispersed polymer droplet (one micron is a typical size). However, much less is known in the case where the size of the drops becomes comparable to the part.

Now, in a new experiment, a NIST researcher (Kalman Migler, 301-975 4876, kalman.migler@nist.gov) has shown that the droplets massively reorganize themselves under such conditions. In a four-stage process, tens of thousands of the droplets join together to form extremely large strings--up to 10 centimeters in length. This is in marked contrast to the micron-scale droplets typical of polymer blends. Once the strings are formed, they are extremely stable and it's hard to break them. Possible applications are polymer wires in which the string component is a conducting polymer and the matrix is an insulator with good mechanical properties. (Physical Review Letters, 5 Feb. 2001; figure at Physics News Graphics; text at Physics News Select.