Intercalated graphite as a smart material for high-stress, high-strain, low-electric-field electromechanical switching

This paper describes a new smart material system using intercalated graphite as the material and using exfoliation as the phase transition that gives rise to the electromechanical switching action. In this action, a stress of up to 3 MPa (400 psi) or a strain of up to 4500% results reversibly from an applied electric field of only 7 V cm^-1. This high-stress, high-strain, low-electric-field type of electromechanical switching is in sharp contrast to the electromechanical switching provided by piezoelectric materials. The exfoliation is a phase transition involving the vaporization of the intercalate between the graphite layers to form bubbles. For bromine as the intercalate, the bubbles remain mostly closed and exfoliation is reversible. The resulting stress or strain is along the c axis of the graphite, so highly oriented pyrolytic graphite and graphite flakes are both possible for achieving electromechanical switching. Applications of this new smart material include electrically activated thermal contacts, electrical contacts and micromanipulations. 1992 IOP Publishing Ltd.