Sources of Static

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Science  15 May 2009:
Vol. 324, Issue 5929, pp. 857-859
DOI: 10.1126/science.324_857d

Contact electrification can be a nuisance (as in a static electricity shock) but can also be harnessed in applications such as photocopying. Many issues about this process are still unresolved—for example, in materials such as polymers, are the charges being transferred during rubbing electrons, or ions? Liu and Bard examined fresh samples of the thermoplastic poly(methylmethacrylate), or PMMA, which develops a positive charge if rubbed against Teflon. They found that the pristine PMMA tubing samples could undergo a number of reactions that are most readily explained as electron rather than ion transfers: plating out silver, copper, and palladium metal from ions in solution, for example, and reducing ferricyanide. Powdered samples increased the pH of aqueous solutions and generated hydrogen. The authors estimate that PMMA has a surface density of 5 × 1013 “cryptoelectrons,” which could be recharged by contact with sodium amalgam, and further argue that the electrons occupy surface states created by damaged bonds, as opposed to states created by impurities.

J. Am. Chem. Soc. 131, 6397 (2009).

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