Magnetoelectromechanical Coupling Mechanisms in Soft Materials

Soft materials are everywhere around and inside us. Because of their abundance, low cost and ease of fabrication along with interesting physical properties, they have numerous promising applications such as artificial muscles, sensors and actuators, smart materials and energy harvesters to name a few. Soft materials deform easily under the presence of external stimuli due to their low mechanical stiffness. This response makes them ideal candidates for the design of multifunctional smart materials. Recently, it was shown that soft materials can produce apparent piezoelectric and magnetoelectric behavior even in the absence of those intrinsic properties provided certain conditions apply. In this dissertation, we will highlight some characteristics and implications of magneto-electro-elastic coupling behavior in specific soft materials structures: The emergence of apparent magnetoelectric behavior in soft materials and its stability: We explore the interplay between elastic strain, electric voltage and magnetic field and its effect on the maximum stretch and voltage that the material can sustain. We present physical insights to support the design of wireless energy harvesters that can be remotely activated with an external magnetic field. Engineering concurrent magnetoelectricity and piezoelectricity in soft materials using electret structure: We prove that by embedding charges in an elastically heterogeneous soft dielectric structure, it is possible to obtain simultaneous piezoelectricity and magnetoelectricity even in the absence of these intrinsic properties. We show that the coupling coefficients in this case are large and compare to some of the well-known ceramic composites. Enhanced electromagnetomechanical response in solid and liquid inclusions: We design a composite made of a dielectric elastomer as the matrix and a spherical inclusion made of iron or ferrofluid while accounting for capillary effects. The beauty of this composite resides on its ability to respond to external electric and magnetic stimuli. We investigate the effect of surface energy at the inclusion/matrix interface on the effective response of this composite. Microscopic mechanisms underpinning flexoelectricity in soft materials: We prove that the existence of frozen dipoles and their thermal fluctuations contribute to the flexoelectric response of the dielectric material. We also predict a temperature dependence of the coupling coefficient.Mechanical Engineering, Department o