Design and Processing of Electret Structures
A team of experts in materials synthesis, processing, and computation at Harvard and Princeton Universities has been selected for research funding under the Department of Defense Multidisciplinary University Research Initiative (MURI) program. The goals of this new MURI are to understand the nature and mechanisms of formation of electrets and to design and fabricate new electret materials and structures. Profs. George M. Whitesides (Harvard) and Ilhan A. Aksay (Princeton) will head the project, working with Zhigang Suo and Mara Prentiss of Harvard University and Dudley A. Saville and Roberto Car of Princeton.
The conventional definition of an “electret” has come to mean almost any material that shows a permanent, fixed electrostatic surface charge or an oriented permanent dipole. Although electrets are often characterized as solid (dielectric) materials, a less restrictive view encompasses both solid and liquid systems. Rigid particles or macroscopic surfaces that retain permanent charge or oriented dipoles are rightly termed "solid electrets." "Liquid electrets," on the other hand, are formed by inserting charge in the form of electrons, ions, nanometer size micelles, or charged colloidal particles into a liquid or onto a liquid-gas or liquid-solid interface; charge relaxation is slow. The body (or bodies) can then be manipulated with external electrostatic fields. With some liquid electrets (e.g., a polymer above its glass transition temperature), unique interface morphologies can be “frozen in” by cooling. Charge diffusion, and dissipation of patterned charge by diffusion of charge or by diffusion of molecules bearing charge will be faster than in polymers, but there are many potential uses for systems in which liquids could be given a permanent, net charge.
The proposed work seeks to understand the nature of the charge and the mechanisms and limits of these materials, building upon new information to develop new electret materials. The team has existing programs in the use of solid and liquid electrets and is thus in possession of the requisite experimental background and facilities. A significant part of the effort will be laboratory-scale demonstrations of prototype devices, aiming to transfer research to useful technology and as a demonstration of new phenomena. The focus will be on microxerography, information storage, optical waveguides, and actuation and power generation.
A copy of the DoD Press Release of 12 March 2004 is available here.
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