title: Electrets in soft materials: nonlinearity, size effects, and giant electromechanical coupling.
abstract: Development of soft electromechanical materials is critical for several tantalizing applications such as soft robots and stretchable electronics, among others. Soft nonpiezoelectric materials can be coaxed to behave like piezoelectrics by merely embedding charges and dipoles in their interior and assuring some elastic heterogeneity. Such so-called electret materials have been experimentally shown to exhibit very large electromechanical coupling. In this work, we derive rigorous nonlinear expressions that relate effective electromechanical coupling to the creation of electret materials. In contrast to the existing models, we are able to both qualitatively and quantitatively capture the known experimental results on the nonlinear response of electret materials. Furthermore, we show that the presence of another form of electromechanical coupling, flexoelectricity, leads to size effects that dramatically alter the electromechanical response at submicron feature sizes. One of our key conclusions is that nonlinear deformation (prevalent in soft materials) significantly enhances the flexoelectric response and hence the aforementioned size effects.
authors.affiliation: Materials Program and Department of Mechanical Engineering, University of Houston, Houston, Texas 77204, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Deng
authors.affiliation: Department of Mathematics and Department of Mechanical Aerospace Engineering, Rutgers University, Piscataway, New Jersey 08854, USA.
authors.forename: Liping
authors.initials: L
authors.lastname: Liu
authors.affiliation: Department of Physics, Materials Program, and Department of Mechanical Engineering, University of Houston, Houston, Texas 77204, USA.
authors.forename: Pradeep
authors.initials: P
authors.lastname: Sharma
mesh_terms: D017097:Electric Impedance; D004560:Electricity; D006244:Hardness; D017711:Nonlinear Dynamics