Flexoelectricity in soft elastomers and the molecular mechanisms underpinning the design and emergence of giant flexoelectricity

Abstract

Soft robotics requires materials that are capable of large deformation and amenable to actuation with external stimuli such as electric fields. Energy harvesting, biomedical devices, flexible electronics and sensors are some other applications enabled by electro-active soft materials. The phenomenon of flexoelectricity is an enticing alternative that refers to the development of electric polarization in dielectrics when subjected to strain gradients. In particular, flexoelectricity offers a direct linear coupling between a highly desirable deformation mode (flexure) and electric stimulus. Unfortunately, barring some exceptions, the flexoelectric effect is quite weak and rather substantial bending curvatures are required for an appreciable electro-mechanical response. Most experiments in the literature appear to confirm modest flexoelectricity in polymers although perplexingly, a singular work has measured a "giant" effect in elastomers under some specific conditions. Due to the lack of an understanding of the microscopic underpinnings of flexoelectricity in elastomers and a commensurate theory, it is not currently possible to either explain the contradictory experimental results on elastomers or pursue avenues for possible design of large flexoelectricity. In this work, we present a statistical-mechanics theory for the emergent flexoelectricity of elastomers consisting of polar monomers. The theory is shown to be valid in broad generality and leads to key insights regarding both giant flexoelectricity and material design. In particular, the theory shows that, in standard elastomer networks, combining stretching and bending is a mechanism for obtaining giant flexoelectricity, which also explains the aforementioned, surprising experimental discovery.

arXiv commentA copy of the SI can be found in the Ancillary files

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Cited by in corpus (13)

• Statistical mechanics of a dielectric polymer chain in the force ensemble
• Polymer networks which locally rotate to accommodate stresses, torques, and deformation
• Statistical field theory for nonlinear elasticity of polymer networks with excluded volume interactions
• Thermal fluctuations (eventually) unfold nanoscale origami
• Statistical Field Theory of Polarizable Polymer Chains with Nonlocal Dipolar Interactions
• Active matter as the underpinning agency for extraordinary sensitivity of biological membranes to electric fields
• Exploiting Instabilities to Enable Large Shape Transformations in Dielectric Elastomers
• Nonuniqueness in Defining the Polarization: Nonlocal Surface Charges and the Electrostatic, Energetic, and Transport Perspectives
• Soft Electromechanical Elastomers Impervious to Instability
• Propagation of elastic waves in a flexomagnetic solid
• Nonlocal Electrostatics and Boundary Charges in Continuum Limits of Two-Dimensional Materials
• Two-Scale Analysis of the Electrostatics of Dielectric Crystals: Emergence of Polarization Density and Boundary Charges
• Generalization of Stoney's equation for flexoelectric thin films on elastic substrates