Elastomer Membrane Research Articles

Realizing pure shear mode of dielectric elastomers by tuning biaxial prestress of a deformation controller

In this article, we propose a method to realize the pure shear deformation mode of dielectric elastomer (DE) membranes by tuning two in-plane prestresses. With utilization of carbon grease electrodes, VHB 4905 membranes are prestretched and attached into a retractable device, forming a pure-shear deformation controller. Experimental results demonstrate that, accurate pure shear deformation mode of DEs can be realized by tuning the mechanical loads in the two directions of the deformation controller. Furthermore, large deformation in the direction of free state can be achieved without electromechanical instabilities. The designed deformation controller accurately realizes the specific pure shear deformation mode of DEs and can be utilized to help design the practical soft actuators.

Monitoring Flexions and Torsions of the Trunk via Gyroscope-Calibrated Capacitive Elastomeric Wearable Sensors.

Reliable, easy-to-use, and cost-effective wearable sensors are desirable for continuous measurements of flexions and torsions of the trunk, in order to assess risks and prevent injuries related to body movements in various contexts. Piezo-capacitive stretch sensors, made of dielectric elastomer membranes coated with compliant electrodes, have recently been described as a wearable, lightweight and low-cost technology to monitor body kinematics. An increase of their capacitance upon stretching can be used to sense angular movements. Here, we report on a wearable wireless system that, using two sensing stripes arranged on shoulder straps, can detect flexions and torsions of the trunk, following a simple and fast calibration with a conventional tri-axial gyroscope on board. The piezo-capacitive sensors avoid the errors that would be introduced by continuous sensing with a gyroscope, due to its typical drift. Relative to stereophotogrammetry (non-wearable standard system for motion capture), pure flexions and pure torsions could be detected by the piezo-capacitive sensors with a root mean square error of ~8° and ~12°, respectively, whilst for flexion and torsion components in compound movements, the error was ~13° and ~15°, respectively.

Highly conductive and elastic nanomembrane for skin electronics.

Skin electronics require stretchable conductors that satisfy metallike conductivity, high stretchability, ultrathin thickness, and facile patternability, but achieving these characteristics simultaneously is challenging. We present a float assembly method to fabricate a nanomembrane that meets all these requirements. The method enables a compact assembly of nanomaterials at the water-oil interface and their partial embedment in an ultrathin elastomer membrane, which can distribute the applied strain in the elastomer membrane and thus lead to a high elasticity even with the high loading of the nanomaterials. Furthermore, the structure allows cold welding and bilayer stacking, resulting in high conductivity. These properties are preserved even after high-resolution patterning by using photolithography. A multifunctional epidermal sensor array can be fabricated with the patterned nanomembranes.

Thin, sensitive skin electronics

Applied Physics The properties of the human sense of touch, including high sensitivity to differences in temperature, pressure, or surface roughness, are challenging to replicate in robotics because skin materials must be highly conductive, stretchable, and thin. Jung et al. developed a process to assemble nanomaterials as a monolayer that is partially embedded in an ultra-thin elastomer. The process works by depositing a mixed solvent containing nanostructured silver and/or gold, along with elastomer, onto deionized water. This results in a layer of nanoparticles residing at the interface coating with elastomer, which is further densified by the addition of surfactant. The process is scalable, and the resulting elastomer membranes can be transferred to other substrates. Science , abh4357, this issue p. [1022][1] [1]: /lookup/doi/10.1126/science.abh4357

Contact mechanics of inflated circular membrane under large deformation: Analytical solutions

Pressurization of thin elastomeric membranes has been exploited as a key actuation mechanism in soft robotics, leading to soft pneumatic actuators that can deform reversibly upon inflation and deflation. The contact mechanics of an inflated membrane with another object underlies several important functionalities of soft pneumatic actuators such as gripping, haptic feedback and locomotion. Motivated by the technological relevance, we study the contact between an inflated circular membrane consisting of incompressible neo-Hookean solid and a substrate that is: i) flat and rigid, ii) spherically curved and rigid, iii) flat and elastic, or iv) spherically curved and elastic. By assuming that the contact interface is adhesionless and frictionless and that the membrane is subjected to very large stretch ratios, we obtained approximate analytical solutions for the membrane’s deformation profile as well as the relationship between the applied force, displacement and contact radius. These solutions agree well with results of numerical simulations. In particular, when the substrate is elastic, we obtained a dimensionless parameter γ that captures the transition between two limiting cases, i.e., either the substrate or the inflated membrane is effectively rigid relative to the other component and thus experiences negligible deformation upon contact. The analytical solutions provided in this work can offer insights towards designing soft pneumatic actuators with desired contact compliance.

A detailed solution framework for the out‐of‐plane displacement of circular dielectric elastomer actuators

AbstractThe out‐of‐plane displacement (OPD) of a circular dielectric elastomer actuator (DEA) membrane has been explored in recent years for a variety of important applications. Circular DEAs consist of an elastomer membrane that is prestretched to a rigid frame and coated with compliant electrodes. Such a simple configuration has found many interesting applications such as in pumps, pulse tracking, hopping search and rescue robots, dielectric elastomer generators for renewable energy harvesting, linear actuators, and many others. Here, we present an easy‐to‐implement solution framework of the OPD for circular DEAs via a detailed numerical solution using the shooting method (SM) on a system of differential algebraic equations (DAE). The material model incorporated follows the robust Gent hyperelastic representation, and a comparison (of the OPD of a single‐cone DEA) against a neo‐Hookean based solution is included. The SM‐based numerical solution to the resulting boundary value DAE problem is applied to a practical range of values based on the reported literature. Analysis of the results and comparison against other studies are provided. The current work provides a go‐to framework for implementation in further research and development that can be useful to a broader audience including nonexperts in the field of soft robotics.

Deterministic assembly of chromosome ensembles in a programmable membrane trap array

Selective spatial isolation and manipulation of single chromosomes and the controlled formation of defined chromosome ensembles in a droplet-based microfluidic system is presented. The multifunctional microfluidic technology employs elastomer valves and membrane displacement traps to support deterministic manipulation of individual droplets. Picoliter droplets are formed in the 2D array of microscale traps by self-discretization of a nanoliter sample plug, with membranes positioned over each trap allowing controllable metering or full release of selected droplets. By combining discretization, optical interrogation, and selective droplet release for sequential delivery to a downstream merging zone, the system enables efficient manipulation of multiple chromosomes into a defined ensemble with single macromolecule resolution. Key design and operational parameters are explored, and co-compartmentalization of three chromosome pairs is demonstrated as a first step toward formation of precisely defined chromosome ensembles for applications in genetic engineering and synthetic biology.

Investigation And Simulation Of Dielectric Elastomer Actuators Used In Artificial Muscle Applications

Dielectric Elastomer Actuator (DEA) consists of a thin dielectric elastomer membrane sandwiched between two electrode layers. When low current high voltage is applied to the two conductive layers, opposite loads occur on the surface which tends to pull one another. This voltage application causes thinning in width and expansion in surface area. DEAs are the favourite subject of research due to their low cost advantages, fast response, high energy density, wide deformation and softness. Due to the rigidity of the electric motors and the metal components of the robot, soft-acting robots using DEA are preferred to perform complex tasks instead of conventional robots. Robots with DEA have higher flexibility and better adaptability. Therefore, soft robots are popular topics in robotics research. DEAs are the best candidate materials for next-generation soft robot actuators and artificial muscles. In this study, simulation of robotic system has been realized by using DEAs calculation methods. Simulation results were compared with the data obtained from the application. This study will be the source of future studies on the subject. In the simulation, Matlab 2016 student and Labview Home and Students programs were used.

Elastomeric Cardiowrap Scaffolds Functionalized with Mesenchymal Stem Cells-Derived Exosomes Induce a Positive Modulation in the Inflammatory and Wound Healing Response of Mesenchymal Stem Cell and Macrophage.

A challenge in contractile restoration of myocardial scars is one of the principal aims in cardiovascular surgery. Recently, a new potent biological tool used within healing processes is represented by exosomes derived from mesenchymal stem cells (MSCs). These cells are the well-known extracellular nanovesicles released from cells to facilitate cell function and communication. In this work, a combination of elastomeric membranes and exosomes was obtained and tested as a bioimplant. Mesenchymal stem cells (MSCs) and macrophages were seeded into the scaffold (polycaprolactone) and filled with exosomes derived from MSCs. Cells were tested for proliferation with an MTT test, and for wound healing properties and macrophage polarization by gene expression. Moreover, morphological analyses of their ability to colonize the scaffolds surfaces have been further evaluated. Results confirm that exosomes were easily entrapped onto the surface of the elastomeric scaffolds, increasing the wound healing properties and collagen type I and vitronectin of the MSC, and improving the M2 phenotype of the macrophages, mainly thanks to the increase in miRNA124 and decrease in miRNA 125. We can conclude that the enrichment of elastomeric scaffolds functionalized with exosomes is as an effective strategy to improve myocardial regeneration.

Adaptive Self-Sealing Suction-Based Soft Robotic Gripper.

While suction cups prevail as common gripping tools for a wide range of real‐world parts and surfaces, they often fail to seal the contact interface when engaging with irregular shapes and textured surfaces. In this work, the authors propose a suction‐based soft robotic gripper where suction is created inside a self‐sealing, highly conformable and thin flat elastic membrane contacting a given part surface. Such soft gripper can self‐adapt the size of its effective suction area with respect to the applied load. The elastomeric membrane covering edge of the soft gripper can develop an air‐tight self‐sealing with parts even smaller than the gripper diameter. Such gripper shows 4 times higher adhesion than the one without the membrane on various textured surfaces. The two major advantages, underactuated self‐adaptability and enhanced suction performance, allow the membrane‐based suction mechanism to grip various three‐dimensional (3D) geometries and delicate parts, such as egg, lime, apple, and even hydrogels without noticeable damage, which can have not been gripped with the previous adhesive microstructures‐based and active suction‐based soft grippers. The structural and material simplicity of the proposed soft gripper design can have a broad use in diverse fields, such as digital manufacturing, robotic manipulation, transfer printing, and medical gripping.

Fully Polymeric Domes as High-Stroke Biasing System for Soft Dielectric Elastomer Actuators.

The availability of compliant actuators is essential for the development of soft robotic systems. Dielectric elastomers (DEs) represent a class of smart actuators which has gained a significant popularity in soft robotics, due to their unique mix of large deformation (>100%), lightweight, fast response, and low cost. A DE consists of a thin elastomer membrane coated with flexible electrodes on both sides. When a high voltage is applied to the electrodes, the membrane undergoes a controllable mechanical deformation. In order to produce a significant actuation stroke, a DE membrane must be coupled with a mechanical biasing system. Commonly used spring-like bias elements, however, are generally made of rigid materials such as steel, and thus they do not meet the compliance requirements of soft robotic applications. To overcome this issue, in this paper we propose a novel type of compliant mechanism as biasing elements for DE actuators, namely a three-dimensional polymeric dome. When properly designed, such types of mechanisms exhibit a region of negative stiffness in their force-displacement behavior. This feature, in combination with the intrinsic softness of the polymeric material, ensures large actuation strokes as well as compliance compatibility with soft robots. After presenting the novel biasing concept, the overall soft actuator design, manufacturing, and assembly are discussed. Finally, experimental characterization is conducted, and the suitability for soft robotic applications is assessed.

Modeling and parametric study on DE-based vibro-impact energy harvesters for performance improvement

This paper develops a dynamic electromechanical coupling model to investigate the energy harvesting (EH) performance of the vibro-impact (VI) energy harvester comprising a cylindrical capsule, an internal free moving ball, and two dielectric elastomer (DE) membranes at both ends of the capsule. The developed model can describe the electromechanical properties of the collision between the ball and the membrane, which is verified by the existing experimental data. On this basis, the effect of system parameters, such as the mass and the radium of the ball, the internal radium and the length of the capsule, and the pre-stretch ratio of DEs, on the average power density of the energy harvester is also studied under diverse external stimuli including the inclined angle and the excitation frequency. The results show that at the small excitation frequency, the EH performance of the energy harvester can be improved by increasing the pre-stretch ratio of membranes and the mass of the ball and decreasing the radium of the ball and the internal radium of the capsule. The conclusions can help provide a guide for the optimal design of the energy harvester in the practical application so as to improve the EH performance.

In Situ Electric-Induced Switchable Transparency and Wettability on Laser-Ablated Bioinspired Paraffin-Impregnated Slippery Surfaces.

Switchable wetting and optical properties on a surface is synergistically realized by mechanical or temperature stimulus. Unfortunately, in situ controllable wettability together with programmable transparency on 2D/3D surfaces is rarely explored. Herein, Joule‐heat‐responsive paraffin‐impregnated slippery surface (JR‐PISS) is reported by the incorporation of lubricant paraffin, superhydrophobic micropillar‐arrayed elastomeric membrane, and embedded transparent silver nanowire thin‐film heater. Owing to its good flexibility, in situ controllable locomotion for diverse liquids on planar/curved JR‐PISS is unfolded by alternately applying/discharging low electric‐trigger of 6 V. Simultaneously, optical visibility can be reversibly converted between opaque and transparent modes. The switching principle is that in the presence of Joule‐heat, solid paraffin would be melt and swell within 20 s to enable a slippery surface for decreasing light scattering and frictional force derived from contact angle hysteresis (F CAH). Once Joule‐heat is discharged, undulating rough surface would reconfigure by cold‐shrinkage of paraffin within 8 s to render light blockage and high F CAH. Upon its portable merit, in situ thermal management, programmable visibility, as well as steering functionalized droplets by electric‐activated JR‐PISSs are successfully deployed. Compared with previous Nepenthes‐inspired slippery surfaces, the current JR‐PISS is more competent for in situ harnessing optical and wetting properties on‐demand.

Non steady-state intersonic cracks in elastomer membranes under large static strain

Dynamic crack propagation in elastomer membranes is investigated; the focus is laid on cracks reaching the speed of shear waves in the material. The specific experimental setup developed to measure crack speed is presented in details. The protocol consists in (1) stretching an elastomer membrane under planar tension loading conditions, then (2) initiating a small crack on one side of the membrane. The crack speed is measured all along the crack path in both reference and actual configurations, including both acceleration and deceleration phases, i.e. non steady-state crack propagation phases. The influence of the prescribed stretch ratio on crack speed is analysed in the light of both these new experiments and the few previously published studies. Conclusions previously drawn for steady-state crack growth are extended to non steady-state conditions: stretch perpendicular to the crack path governs crack speed in intersonic crack propagation regime, and the role of the stretch in crack direction is minor.

A thermal actuated switchable dry adhesive with high reversibility for transfer printing

Transfer printing based on switchable adhesive that heterogeneously integrates materials is essential to develop novel electronic systems, such as flexible electronics and micro LED displays. Here, we report a robust design of a thermal actuated switchable dry adhesive, which features a stiff sphere embedded in a thermally responsive shape memory polymer (SMP) substrate and encapsulated by an elastomeric membrane. This construct bypasses the unfavorable micro- and nano-fabrication processes and yields an adhesion switchability of over 1000 by combining the peel-rate dependent effect of the elastomeric membrane and the thermal actuation of the sub-surface embedded stiff sphere. Experimental and numerical studies reveal the underlying thermal actuated mechanism and provide insights into the design and operation of the switchable adhesive. Demonstrations of this concept in stamps for transfer printing of fragile objects, such as silicon wafers, silicon chips, and inorganic micro-LED chips, onto challenging non-adhesive surfaces illustrate its potential in heterogeneous material integration applications, such as flexible electronics manufacturing and deterministic assembly.

Geometric optimization of dielectric elastomer electrodes for dynamic applications

Dielectric elastomers are soft actuators, made of an elastomer membrane sandwiched by compliant electrodes. Because of their high energy density and quick response, they are well suited for dynamic applications such as loudspeakers. Thanks to progress in the manufacturing process of dielectric elastomer actuators, the electrode shape can be patterned to very diverse shapes. In this study, we focus on the relation between the electrode shape and the dynamical and acoustical behavior of a dielectric elastomer loudspeaker. By using a finite element model of the loudspeaker, an optimization algorithm is set up to compute optimal electrode shapes according to chosen objectives, such as maximizing or minimizing the contribution of an eigenmode to the radiated sound. The optimal designs are then tested experimentally, and the efficiency of the optimization procedure is assessed. It is shown that the frequency response of dielectric elastomer loudspeakers can be tuned by optimizing the shape of the electrodes, and simulations suggest that the directivity can also be controlled. Finally, perspectives of the proposed optimization method are briefly discussed.

The driven flow vacuum infusion process: An overview and analytical design

This article describes a novel variant of the vacuum infusion process based on a multifunctional elastomeric reusable vacuum bag. The main innovation of this process is an elastomeric membrane having resin flow channels that can be controlled during the infusion process: they can be activated for the impregnation stage to enhance resin flow and removed during the curing stage to provide a smooth surface finish to the part. In addition, the size of the resin flow channels can be modified during the infusion providing control on the impregnation rate. This article describes the driven flow vacuum infusion (DFVI) process and presents analytical calculations regarding the effect of the geometrical design of the membrane and the processing variables on the porosity, permeability, and volume of resin transported by the flow medium. Preliminary results of unidirectional resin infusion tests comparing the DFVI process to traditional vacuum infusion and SCRIMP are also presented.

Spontaneous photo-buckling of a liquid crystal elastomer membrane

In this paper, the surface instability of a constrained square liquid crystal elastomer (LCE) membrane under UV light is investigated. Firstly, the governing equations for the LCE membrane with an arbitrary pre-designed uniaxial director (common orientation vector) pattern are established. By adopting the finite difference method, for a fixed incident light intensity, the transformation of the surface buckling morphology with respect to length-thickness ratio and light decay distance of the LCE membrane is discussed in detail. The buckling condition is given and instability patterns are clarified. This work enhances the understanding and provides the guidance in design of the LCE based light driven membrane elements.

Numerical Investigation of T-Shaped Microfluidic Oscillator with Viscoelastic Fluid.

Oscillatory flow has many applications in micro-scaled devices. The methods of realizing microfluidic oscillators reported so far are typically based on the impinging-jet and Coanda effect, which usually require the flow Reynolds number to be at least at the order of unity. Another approach is to introduce elastomeric membrane into the microfluidic units; however, the manufacturing process is relatively complex, and the membrane will become soft after long-time operation, which leads to deviation from the design condition. From the perspective of the core requirement of a microfluidic circuit, i.e., nonlinearity, the oscillatory microfluidic flow can be realized via the nonlinear characteristics of viscoelastic fluid flow. In this paper, the flow characteristics of viscoelastic fluid (Boger-type) in a T-shaped channel and its modified structures are studied by two-dimensional direct numerical simulation (DNS). The main results obtained from the DNS study are as follows: (1) Both Weissenberg (Wi) number and viscosity ratio need to be within a certain range to achieve a periodic oscillating performance; (2) With the presence of the dynamic evolution of the pair of vortices in the upstream near the intersection, the oscillation intensity increases as the elasticity-dominated area in the junction enlarges; (3) Considering the simplicity of the T-type channel as a potential oscillator, the improved structure should have a groove carved toward the entrance near the upper wall. The maximum oscillation intensity measured by the standard deviation of flow rate at outlet is increased by 129% compared with that of the original standard T-shaped channel under the same condition. To sum up, with Wi number and viscosity ratio within a certain range, the regular periodic oscillation characteristics of Oldroyd-B type viscoelastic fluid flow in standard T-shaped and its modified channels can be obtained. This structure can serve as a passive microfluidic oscillator with great potential value at an extremely low Reynolds number, which has the advantages of simplicity, no moving parts and fan-out of two.

Stretchable, Transparent, Permeation Barrier Layer for Flexible Optics

AbstractFlexible, compliant permeation barrier layers are critically needed in the optics/optoelectronics industry to protect deformable, polymer‐based optical elements, such as those found in variable focus lenses. To address these needs, a transparent and deformable polymeric permeation barrier coating consisting of poly(1H,1H,6H,6H‐perfluorohexyl diacrylate) (pPFHDA) is prepared by initiated chemical vapor deposition. pPFHDA is a highly crosslinked fluoropolymer, which is deposited onto temperature‐sensitive elastomeric membranes at ambient temperature with high uniformity and conformality. This is believed to be the first demonstration of vapor deposition of the PFHDA monomer. Coatings with thicknesses nominally ranging from 200 to 750 nm are prepared and shown to be impermeable to high‐index optical fluid (polyphenyl thioether) over 2 months at 70 °C, which translates to more than 4 year lifespan at room temperature, even after being subjected to 0.26% biaxial strain. Moreover, due to its amorphous nature, the pPFHDA is transparent from wavelengths of 300–1690 nm and also thermally stable to temperatures of 300 °C. These properties should make pPFHDA coating a particularly compelling candidate for flexible optical/optoelectronic devices requiring transparent and compliant barrier layers.