Proposal of a generic constitutive model for deformation-dependent dielectric constant of dielectric elastomers

Kumar, Abhimanyu; Patra, Karali

doi:10.1016/j.jestch.2021.04.001

Cited by 13 publications

(18 citation statements)

References 37 publications

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“…The exact mechanism that causes the change is not established, but there is clear evidence that under tensile strain, many elastomers show a reduction in permittivity. Kumar and Patra (2021) showed a reduction in dielectric permittivity from 5.67 to 2.89 when VHB was subjected to a 5× biaxial stretch . Cohen et al (2017) demonstrated a reduction in the dielectric permittivity of LDPE, HDPE, PTFE, and VHB 4910 under stretches of 2–4× .…”

Section: Liquid Metal Composite Pressure Sensingmentioning

confidence: 99%

Multimodal Deformation of Liquid Metal Multimaterial Composites as Stretchable, Dielectric Materials for Capacitive Pressure Sensing

Bury

Koh

2022

ACS Appl. Mater. Interfaces

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Traditional electronic devices are composed of rigid materials and components that tend to be unsuitable for soft robotic and stretchable electronic applications, such as wearable or continuous pressure sensing. However, deformable materials have the potential to improve upon traditional devices through enhanced sensitivity and responsiveness, better conformability and biocompatibility at the human–machine interface, and greater durability. This work presents deformable composite materials composed of the gallium–indium–tin alloy galinstan (GaInSn) that combines the conductivity of a metal and the intrinsic deformability of a liquid. Dispersing galinstan in an elastomer allows for the formation of deformable dielectric materials that have tunable mechanical and electrical behavior, for example, modulus and relative permittivity. Galinstan composites have been shown previously to have a minimal modulus impact on the elastomer but concurrently achieve impressive dielectric performance. However, galinstan dispersions can be costly and face challenges of mechanical and electrical reliability. Thereby, this work investigates multimaterial composites composed of galinstan and a rigid filler, either iron or barium titanate, with respect to morphology, mechanical behavior, dielectric behavior, and pressure sensing performance for the purpose of achieving a balance between a low modulus and superior electrical performance. By combining galinstan and rigid fillers, it was found that the mechanical and electrical properties, such as modulus, permittivity, loss behavior, sensitivity, and linearity of the multimaterial composites can be improved by tuning filler formulation. This suggests that these dielectric materials can be used for sensing applications that can be precisely calibrated to specific material properties and the needs of the user. These deformable multimaterial composites, found to be stretchable and highly responsive in sensing applications, will expand the current mechanical abilities of deformable dielectric materials to improve soft robotic and stretchable electronic devices.

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Section: Liquid Metal Composite Pressure Sensingmentioning

confidence: 99%

Multimodal Deformation of Liquid Metal Multimaterial Composites as Stretchable, Dielectric Materials for Capacitive Pressure Sensing

Bury

Koh

2022

ACS Appl. Mater. Interfaces

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“…The series was expanded at stretches close to unity. The equation approximates the permittivity at large deformations with two parameters Cohen et al [20,21,49] and Grasinger and Dayal [22] The models connect the polymer dipole movement to the permittivity through a statistical mechanics approach Li et al [67] The model proposed is based on a statistical mechanics view of the molecular polarization and dipole orientation constrained by the mechanical deformation which was modeled with a Gent model Empirical Sheng et al [56] The model is an empirical approach to predict the biaxial stretch and temperature influence on the dielectric permittivity Gei et al [51] An investigation of the instabilities in soft dielectrics with an electric free energy term based on the invariants of the electric displacement Kumar and Patra [25] An empirical model for a general deformation state. The model utilizes two parameters for measuring the undeformed permittivity and the sensitivity to deformation Schlögl and Leyendecker [57] The model utilizes a lumped approach to separate the changes in the dielectric permittivity based on both the electrical load and the mechanical load Ogden and Dorfmann [18] An invariant modeling approach for nonlinear electroelasticity where ε 0 is the undeformed permittivity, κ is the ratio electrostrictive coefficient to the undeformed permittivity of the incompressible material, λ i is the stretch in the i-direction of the membrane (see Fig.…”

Section: Deformation-dependent Permittivity Modelsmentioning

confidence: 99%

“…In order to alleviate some of the modeling challenges, researchers and developers assume simplified models such as constant electrical properties. Unfortunately, these assumptions can become critical in certain applications requiring a large range of deformations [25,26] or high accuracy requirements.…”

Section: Introductionmentioning

confidence: 99%

“…It has been shown that, in fact, the electrical permittivity can exhibit a highly nonlinear dependency on stretch [25,[42][43][44][45][46][47][48][49][50]. Furthermore, under certain conditions, deformation-dependent permittivity can reveal material instabilities and/or potential dielectric breakdowns [42,[51][52][53].…”

Section: Introductionmentioning

confidence: 99%

“…Based on the pioneering work by Kuhn and Grün [54], some authors have proposed deformation-dependent permittivity models [20,[42][43][44][45][46]55]. Others have attempted to accomplish this by empirical means [18,25,56,57]. The implementation of such models has been limited, however, to uniaxially or biaxially loaded planar DE actuators (DEAs), and hence their utilization on more complex (or realistic) configurations is lacking.…”

Section: Introductionmentioning

confidence: 99%

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Effects of electrostriction on the bifurcated electro-mechanical performance of conical dielectric elastomer actuators and sensors

Farmer

Medina

2022

Robotica

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Dielectric elastomers (DEs) find applications in many areas, particularly in the field of soft robotics. When modeling and simulating DE-based actuators and sensors, a substantial portion of the literature assumes the selected DE material to behave in some perfectly hyperelastic manner, and the vast majority have assumed invariant permittivity. However, studies on simple planar DEs have revealed instabilities and hastened breakdowns when a variable permittivity is allowed. This is partly due to the intertwined electromechanical properties of DEs rooted on their labyrinthine polymeric microstructures. This work focuses on studying the effects of a varying (with stretch) permittivity on the out-of-plane deformation of a circular DE, using a model derived from principles of strain-induced polymer birefringence. In addition, we utilize the Edward–Vilgis model, which attempts to account for effects related to crosslinking, and length extension, slippage, and entanglement of polymer chains. Our approach reveals the presence of “stagnation” regions in the electromechanical behavior of the DE actuator material. These stagnation regions are characterized by both electrical and mechanical critical electrostrictive coefficient ratios. Mechanically, certain values of the electrostrictive coefficient ratio predict cases where deformation does not occur in response to a change in voltage. Electrically, certain cases are predicted where changes in capacitance cannot be measured in response to changes in deformation. Thus, some combined conditions of loading and material properties could limit the effectiveness of DE membranes in either actuation or sensing. Therefore, our results reveal mechanisms that could be useful to designers of actuators and sensors and unveil an opportunity for exploring new theoretical materials with potential novel applications. Furthermore, since there are known analogous formulations between electrical and optical properties, criticality principles studied in this article could be extended to optomechanical coupling.

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Impact of cryogenic treatment on mechanical and electro active actuation properties of soft polymers

Mallick

Patra

2023

J of Applied Polymer Sci

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The goal of this study is to investigate the change in stretchability property of soft polymers before and after cryogenic treatment. To achieve this, the influences of cryogenic treatment on the rate dependent tensile properties, hysteresis behavior, and stress‐relaxation of soft polymers are extensively analyzed. Results indicated that the effects of cryogenic treatment for both VHB and Ecoflex samples on mechanical responses were more prominent at low strain rate. It was also observed that VHB polymer could exhibit more strain rate sensitivity than Ecoflex sample after cryogenic treatment. For stress relaxation test, both cryo‐treated polymer samples were found to yield less overall stress and takes longer time to reach equilibrium stress in comparison to untreated polymer. Extensive experimental findings showed that the amount of energy dissipated while cooling below glass transition temperature (Tg), causes stress softening with lowering of viscoelastic property. On the other hand, there is a good enhancement of the electro‐active actuation strain for the cryo‐treated VHB 4910 and Ecoflex specimens. The results of this work could be used as a helpful guide for applying cryogenic treatment to improve electro‐mechanical properties of soft polymers, as the theory underlying this treatment has not been well explored

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Proposal of a generic constitutive model for deformation-dependent dielectric constant of dielectric elastomers

Cited by 13 publications

References 37 publications

Multimodal Deformation of Liquid Metal Multimaterial Composites as Stretchable, Dielectric Materials for Capacitive Pressure Sensing

Multimodal Deformation of Liquid Metal Multimaterial Composites as Stretchable, Dielectric Materials for Capacitive Pressure Sensing

Effects of electrostriction on the bifurcated electro-mechanical performance of conical dielectric elastomer actuators and sensors

Impact of cryogenic treatment on mechanical and electro active actuation properties of soft polymers

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