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Friday November 14, 2008
3 PM
PHO 901

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"Ionic Electrets and Contact Electrification"
George M Whitesides

This talk will describe mechanistic investigations and applications of space-charge electrets fabricated by contact electrification, the mechanisms of which remain a subject of active controversy at the atomic/molecular level. The polarity of charging during contact electrification of ionic electrets (materials with surface-bound ionic functional groups and oppositely charged, mobile counterions) is consistent with an ion-transfer mechanism for contact electrification. Dielectric breakdown of the surrounding gas limits the maximal density of charge that the electrets can sustain. Oppositely-charged electrets can self-assemble in two and three dimensions, and are useful for studying simplified physical models of complicated processes such as crystallization and the folding of beads on a string. Surfaces fabricated from combinations of oppositely charged ionic electrets can resist contact electrification and prevent electrical discharges. These examples demonstrate that a more developed understanding of electrets in general, and of the mechanisms of contact electrification in particular, can lead to new applications for space-charge electrets.

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