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Anne Ladegaard Skov - One of the best experts on this subject based on the ideXlab platform.

  • self healing high permittivity silicone dielectric elastomer
    ACS Macro Letters, 2016
    Co-Authors: Frederikke Bahrt Madsen, Liyun Yu, Anne Ladegaard Skov
    Abstract:

    Currently used dielectric Elastomers do not have the ability to self-heal after detrimental events such as tearing or electrical breakdown, which are critical issues in relation to product reliability and lifetime. In this paper, we present a self-healing dielectric elastomer that additionally possesses high dielectric permittivity and consists of an interpenetrating polymer network of silicone elastomer and ionic silicone species that are cross-linked through proton exchange between amines and acids. The ionically cross-linked silicone provides self-healing properties after electrical breakdown or cuts made directly to the material due to the reassembly of the ionic bonds that are broken during damage. The dielectric Elastomers presented in this paper pave the way to increased lifetimes and the ability of dielectric Elastomers to survive millions of cycles in high-voltage conditions.

  • the current state of silicone based dielectric elastomer transducers
    Macromolecular Rapid Communications, 2016
    Co-Authors: Frederikke Bah Madse, Soren Hvilsted, Anders Egede Daugaard, Anne Ladegaard Skov
    Abstract:

    ilicone Elastomers are promising materials for dielectric elastomer transducers (DETs) due to their superior properties such as high efficiency, reliability and fast response times. DETs consist of thin elastomer films sandwiched between compliant electrodes, and they constitute an interesting class of transducer due to their inherent lightweight and potentially large strains. For the field to progress towards industrial implementation, a leap in material development is required, specifically targeting longer lifetime and higher energy densities to provide more efficient transduction at lower driving voltages. In this review, the current state of silicone Elastomers for DETs is summarised and critically discussed, including commercial Elastomers, composites, polymer blends, grafted Elastomers and complex network structures. For future developments in the field it is essential that all aspects of the elastomer are taken into account, namely dielectric losses, lifetime and the very often ignored polymer network integrity and stability.

  • the influence of static pre stretching on the mechanical ageing of filled silicone rubbers for dielectric elastomer applications
    Materials today communications, 2015
    Co-Authors: Shamsul Bin Zakaria, Guggi Kofod, Anne Ladegaard Skov
    Abstract:

    Abstract Dielectric elastomer (DE) pre-stretching is a key aspect of attaining better actuation performance, as it helps prevent electromechanical instability (EMI) and usually lowers the Young’s modulus, thus leading to easier deformation. The pre-stretched DE is not only susceptible to a high risk of tearing and the formation of mechanical defects, but films with sustained and substantial strain may also experience mechanical degradation. In this study a long-term mechanical reliability study of DE is performed. Young’s moduli, dielectric breakdown strengths and dielectric permittivities of commercial silica-reinforced silicone Elastomers, with and without an additional 35% (35 phr) of titanium dioxide (TiO 2 ), were investigated after being subjected to pre-stretching for various timespans at pre-stretches to strains of 60 and 120%, respectively. The study shows that mechanical stability when pre-stretching is difficult to achieve with highly filled Elastomers. However, despite the negative outlook for metal oxide-filled silicone Elastomers, the study paves the way for reliable dielectric Elastomers by indicating that simply post-curing silicone Elastomers before use may increase reliability.

  • design of elastomer structure to facilitate incorporation of expanded graphite in silicones without compromising electromechanical integrity
    Macromolecular Materials and Engineering, 2015
    Co-Authors: Suzan Sager Hassouneh, Anders Egede Daugaard, Anne Ladegaard Skov
    Abstract:

    The development of elastomer materials with a high dielectric permittivity has attracted increased interest over the past years due to their use in, for example, dielectric Elastomers. For this particular use, both the electrically insulating properties — as well as the mechanical properties of the elastomer — have to be tightly controlled in order not to destroy favorable elastic properties by the addition of particles. This study focuses on improving the electromechanical properties of an enhanced PDMS matrix with expanded graphite (EG) as filler. The PDMS matrix is crosslinked by means of an 8-functional crosslinker, which allows for development of a suitable network matrix. The dielectric permittivity was increased by almost a factor of 4 compared to a benchmark silicone elastomer.

Zhigang Suo - One of the best experts on this subject based on the ideXlab platform.

  • chemically coupled interfacial adhesion in multimaterial printing of hydrogels and Elastomers
    ACS Applied Materials & Interfaces, 2020
    Co-Authors: Kevin Tian, Zhigang Suo, Joost J Vlassak
    Abstract:

    Functional devices that use hydrogels as ionic conductors and Elastomers as dielectrics have the advantage of being soft, stretchable, transparent, and biocompatible, making them ideal for biomedical applications. These devices are typically fabricated by manual assembly. Techniques for the manufacturing of soft materials have generally not looked at integrating multiple dissimilar materials. Silane coupling agents have recently shown promise for creating strong bonds between hydrogels and Elastomers but have yet to be used in the extrusion printing of complex devices that integrate both hydrogels and Elastomers. Here, we demonstrate the viability of silane coupling agents in a system with the rheology and functional composition necessary for three-dimensional (3D) extrusion printing of hydrogel-elastomer materials, specifically polyacrylamide (PAAm) hydrogel and poly(dimethylsiloxane) (PDMS) hydrophobic elastomer. By introducing a charge-neutral surfactant in the PDMS and adjusting silane concentrations in the PAAm, cast material samples demonstrate strong adhesion. We were also able to achieve an interfacial toughness of up to Γ = 193 ± 6.3 J/m2 for a fully extrusion printed PAAm hydrogel-on-PDMS bilayer. This result demonstrates that an integration strategy based on silane coupling agents makes it possible for extrusion printing of a wide variety of hydrogel and silicone Elastomers.

  • Fatigue-Resistant Elastomers
    Journal of The Mechanics and Physics of Solids, 2019
    Co-Authors: Hang Yang, Zhigang Suo, Jingda Tang
    Abstract:

    Abstract The resistance of a material to the growth of a crack is characterized by fracture toughness under monotonic load, and by fatigue threshold under cyclic load. The fatigue threshold of engineering Elastomers is commonly limited to ∼50 J/m2, much below their toughness (103∼105 J/m2). Here we report fatigue-resistant Elastomers with threshold beyond 500 J/m2. Such an elastomer is a composite of two Elastomers: a lattice of a hard elastomer embedded in a matrix of soft elastomer. Both the hard and soft Elastomers are elastically stretchable, with small hysteresis. At a crack front in the composite, the soft matrix shears greatly, which de-concentrates stress in the hard lattice. When the crack advances in the composite, the energy dissipated scales with the feature size of the lattice. By contrast, when a crack advances in a homogeneous elastomer, the energy dissipated scales with the mesh size of the polymer network. The fatigue-resistant Elastomers open new opportunities for applications requiring stretchable materials.

  • maximizing the energy density of dielectric elastomer generators using equi biaxial loading
    Advanced Functional Materials, 2013
    Co-Authors: Jiangshui Huang, Samuel Shia, Zhigang Suo
    Abstract:

    Dielectric elastomer generators (DEGs) for harvesting electrical energy from mechanical work have been demonstrated but the energy densities achieved are still small compared with theoretical predictions. In this study, signifi cant improvements in energy density (560 J/kg with a power density of 280 W/ kg and an effi ciency of 27%) are achieved using equi-biaxial stretching, a mechanical loading confi guration that maximizes the capacitance changes. The capacitance of dielectric Elastomers subjected to equi-biaxial stretches is demonstrated to be proportional to the fourth power of the stretch. Quantifi cation of the individual energy contributions indicates that attaining higher conversion effi ciencies is limited by viscous losses within the acrylic elastomer, suggesting that still higher conversion effi ciencies with other Elastomers should be attainable with our novel mechanical loading design.

  • Model of dissipative dielectric Elastomers
    Journal of Applied Physics, 2012
    Co-Authors: Choon Chiang Foo, Shengqiang Cai, Soo Jin Adrian Koh, Siegfried Bauer, Zhigang Suo
    Abstract:

    The dynamic performance of dielectric elastomer transducers and their capability of electromechanical energy conversion are affected by dissipative processes, such as viscoelasticity, dielectric relaxation, and current leakage. This paper describes a method to construct a model of dissipative dielectric Elastomers on the basis of nonequilibrium thermodynamics. We characterize the state of the dielectric elastomer with kinematic variables through which external loads do work, and internal variables that measure the progress of the dissipative processes. The method is illustrated with examples motivated by existing experiments of polyacrylate very-high-bond dielectric Elastomers. This model predicts the dynamic response of the dielectric elastomer and the leakage current behavior. We show that current leakage can be significant under large deformation and for long durations. Furthermore, current leakage can result in significant hysteresis for dielectric Elastomers under cyclic voltage.

  • giant voltage actuated deformation of a dielectric elastomer under dead load
    Applied Physics Letters, 2012
    Co-Authors: Jiangshui Huang, Choon Chiang Foo, Jia Zhu, Zhigang Suo
    Abstract:

    Far greater voltage-actuated deformation is achievable for a dielectric elastomer under equal-biaxial dead load than under rigid constraint usually employed. Areal strains of 488% are demonstrated. The dead load suppresses electric breakdown, enabling the elastomer to survive the snap-through electromechanical instability. The breakdown voltage is found to increase with the voltage ramp rate. A nonlinear model for viscoelastic dielectric Elastomers is developed and shown to be consistent with the experimental observations.

Muhammad Khafidh - One of the best experts on this subject based on the ideXlab platform.

  • friction and wear mechanism of short cut aramid fiber and silica reinforced Elastomers
    Wear, 2019
    Co-Authors: Muhammad Khafidh, Dirk J Schipper, Marc Arthur Masen, N Vleugels, Wilma K. Dierkes, Jacques W M Noordermeer
    Abstract:

    Abstract Important phenomena during sliding contact of elastomeric materials are friction and wear. Wear reduction of Elastomers can be achieved by minimizing the propagation of cracks in the elastomer during sliding contact. Adding fillers like silica and fibers is a way to reduce the propagation of cracks and as a result reduction of wear. In the present study, the wear processes of short-cut aramid fiber reinforced Elastomers as a function of sliding distance and their relation to friction are investigated. Two different types of systems are considered, i.e. (1) Elastomers reinforced by solely short-cut aramid fibers and (2) Elastomers reinforced by short-cut aramid fibers and silica. A pin-on-disc tribometer and a microscope are used to analyze the friction and wear mechanisms of the elastomeric composites in sliding contact with a granite counter surface. The results show that the coefficient of friction of the composites consists of different stages, these stages are influenced by the wear processes during sliding. For Elastomers which are reinforced by short-cut aramid fibers and silica, a higher energy input is needed to achieve all stages since the presence of silica in the elastomer matrix increases the resistance of matrix particle detachment. A general friction behavior of short-cut aramid fiber and silica reinforced Elastomers is proposed.

  • friction wear and noise of short cut aramid fibre reinforced Elastomers in sliding contacts
    2019
    Co-Authors: Muhammad Khafidh
    Abstract:

    Many types of elastomer based products are found in daily life, such as tyres, v-belts and wiper blades. In applications, several reinforcing materials are usually added into the Elastomers to increase their mechanical and tribological properties. The examples of these reinforcing materials are carbon black, silica and fibres. Short-cut aramid fibre is a relatively new high-performance material that can be used to reinforce Elastomers. However, the interaction between fibre and elastomer matrix is still a problem to be solved. Moreover, friction, wear and friction-induced noise of short-cut aramid fibre reinforced Elastomers is not well known. Understanding friction, wear and friction-induced noise will lead to a better design, so that the lifetime of the Elastomers can be prolonged. This research is conducted within the project FINE-FIT (Fibres IN Elastomer For Improved Tribology), which is a collaboration between the Surface Technology and Tribology (STT) group and the Elastomer Technology and Engineering (ETE) group at the University of Twente. An optimized formulation of composites to improve the interaction between the fibres and elastomer matrix was investigated by the ETE group, while the investigation of the tribological behaviour of short-cut aramid fibre reinforced Elastomers was conducted by the STT group. The short-cut aramid fibre reinforced Elastomers used in this thesis are based on the optimized formulation of the ETE group. Tribological phenomena of Elastomers during sliding friction were studied, such as the contact area, the formation of a modified surface layer and the occurrence of a wavy wear track. The size and shape of the contact area of Elastomers during sliding change in comparison with the static condition. The contact area depends on the sliding velocity and the mechanical properties of the Elastomers, such as storage modulus. During sliding contact, the composition and the mechanical properties of the elastomer surface may change. These surface alterations will lead to a change of the tribological behaviour of Elastomers. The existence of a modified surface layer is influenced by the competition between formation and wear, which depends on the contact pressure, sliding velocity and sliding distance. Another phenomenon during sliding friction is a macro surface irregularity at the wear track, called a wavy wear track. In application, the wavy wear track needs to be avoided because it will reduce the performance of the sliding system and generate vibrations and noise. The occurrence of the wavy wear track depends on the mechanical properties of the elastomer, the operating conditions (such as sliding velocity and force), the inertia mass of the counter surface frame and the circumferential length of the wear track. Friction, wear and friction-induced noise of short-cut aramid fibre reinforced Elastomers were investigated by using two types of short-cut aramid fibres, namely non-coated fibre (NF) and epoxy-coated fibre (EF). The wear mechanism during sliding contact greatly influences the frictional behaviour of the composites. For a long sliding distance, the presence of fibres on the wear track reduces the coefficient of friction and friction-induced noise drastically. The presence of fibres on the wear track causes the composites to follow Amontons’ law when the applied contact pressures are below a certain threshold value. Once the contact pressure is higher than the threshold value, Amontons’ law is no longer valid. The threshold contact pressure of composites containing EF is higher than those containing NF. Furthermore, the effect of fibre direction and fibre amount in the composites on friction and wear were studied. Elastomers reinforced with silica and short-cut aramid fibres were also studied to investigate the effect of short-cut aramid fibres. The coefficient of friction and wear of Elastomers containing EF is lower than those containing NF. During sliding contact, noise generation due to sliding friction between the composites and counter surface was investigated. Adding short-cut aramid fibres into the Elastomers reduces the friction-induced noise in comparison with the unreinforced Elastomers. The friction-induced noise was found to increase with increasing sliding velocity and contact pressure. Moreover, the friction-induced noise of the composites containing EF is lower than those containing NF. The presence of fibres on the wear track reduces the friction-induced noise. The increase of noise is caused by vibrations of the pin holder and motor noise. The noise can be reduced by two ways: (1) reduce the amplitude of friction force and (2) reduce the level of friction force.

Gabor Kovacs - One of the best experts on this subject based on the ideXlab platform.

  • Dielectric elastomer actuators used for pneumatic valve technology
    Smart Materials and Structures, 2013
    Co-Authors: Metin Giousouf, Gabor Kovacs
    Abstract:

    Dielectric elastomer actuators have been investigated for applications in the field of pneumatic automation technology. We have developed different valve designs with stacked dielectric elastomer actuators and with integrated high voltage converters. The actuators were made using VHB-4910 material and a stacker machine for automated fabrication of the cylindrical actuators. Typical characteristics of pneumatic valves such as flow rate, power consumption and dynamic behaviour are presented. For valve construction the force and stroke parameters of the dielectric elastomer actuator have been measured. Further, benefits for valve applications using dielectric Elastomers are shown as well as their potential operational area. Finally, challenges are discussed that are relevant for the use of elastomer actuators in valves for industrial applications.

  • A comparison between silicone and acrylic Elastomers as dielectric materials in electroactive polymer actuators
    Polymer International, 2010
    Co-Authors: Silvain Michel, Xuequn Q. Zhang, Michael Wissler, Christiane Löwe, Gabor Kovacs
    Abstract:

    Soft Elastomers, mostly silicones and acrylics, are interesting candidates as dielectric materials in electroactive polymer actuator technology. Generally, characteristics like large strain, high stress, high energy density, good efficiency and high response speed are required for actuator applications. However, some of these material properties may be contradictory. For this reason a comparison between Dow Corning silicone and 3M acrylic Elastomers was made based on a set of six electromechanical tests for actuator applications. The silicone elastomer shows a fast electromechanical response (3 s) with good reproducibility and the dissipated work is negligible and not frequency dependent. It also shows a stable mechanical behaviour over a wide temperature range. In contrast, the acrylic elastomer shows a slow electromechanical response with poor reproducibility. The dissipated work of the acrylic elastomer is significant: a strong frequency and temperature dependency of the dissipated work is observed for this material. The Dow Corning silicone (DC 3481) is a better material for many applications, where activation strains of less than 10% are sufficient. However, in applications where higher strains are required, it might be obligatory to use acrylic Elastomers, because only these have the potential for use with activation strains beyond 10%. The electrical activation of a circular specimen is most useful in order to evaluate a material as a dielectric in electroactive polymer actuators. Copyright © 2009 Society of Chemical Industry

Xuanhe Zhao - One of the best experts on this subject based on the ideXlab platform.

  • skin inspired hydrogel elastomer hybrids with robust interfaces and functional microstructures
    Nature Communications, 2016
    Co-Authors: Hyunwoo Yuk, German Alberto Parada, Xinyue Liu, Teng Zhang, Xuanhe Zhao
    Abstract:

    Inspired by mammalian skins, soft hybrids integrating the merits of Elastomers and hydrogels have potential applications in diverse areas including stretchable and bio-integrated electronics, microfluidics, tissue engineering, soft robotics and biomedical devices. However, existing hydrogel–elastomer hybrids have limitations such as weak interfacial bonding, low robustness and difficulties in patterning microstructures. Here, we report a simple yet versatile method to assemble hydrogels and Elastomers into hybrids with extremely robust interfaces (interfacial toughness over 1,000 Jm−2) and functional microstructures such as microfluidic channels and electrical circuits. The proposed method is generally applicable to various types of tough hydrogels and diverse commonly used Elastomers including polydimethylsiloxane Sylgard 184, polyurethane, latex, VHB and Ecoflex. We further demonstrate applications enabled by the robust and microstructured hydrogel–elastomer hybrids including anti-dehydration hydrogel–elastomer hybrids, stretchable and reactive hydrogel–elastomer microfluidics, and stretchable hydrogel circuit boards patterned on elastomer. Soft hybrids that integrate hydrogels and Elastomers can be used in applications, such as stretchable electronics and soft robotics, but usually have shortcomings. Here, Zhao and co-workers show a simple method of assembling hydrogel/elastomer hybrids with robust interfaces and functional microstructures.

  • Bioinspired surfaces with dynamic topography for active control of biofouling
    Advanced Materials, 2013
    Co-Authors: Phanindhar Shivapooja, Daniel Rittschof, Beatriz Orihuela, Gabriel P. Lopez, Qiming Wang, Xuanhe Zhao
    Abstract:

    Dynamic change of the surface area and topology of Elastomers is used as a general, environmentally friendly approach for effectively detaching micro- and macro-fouling organisms adhered on the elastomer surfaces. Deformation of elastomer surfaces under electrical or pneumatic actuation can debond various biofilms and barnacles. The bio-inspired dynamic surfaces can be fabricated over large areas through simple and practical processes. This new mechanism is complementary with existing materials and methods for biofouling control.

  • NONEQUILIBRIUM THERMODYNAMICS OF DIELECTRIC Elastomers
    International Journal of Applied Mechanics, 2011
    Co-Authors: Xuanhe Zhao, Soo Jin Adrian Koh, Zhigang Suo
    Abstract:

    This paper describes an approach to construct models of dielectric Elastomers undergoing dissipative processes, such as viscoelastic, dielectric and conductive relaxation. This approach is guided by nonequilibrium thermodynamics, characterizing the state of a dielectric elastomer with kinematic variables through which external loads do work, as well as internal variables that describe the dissipative processes. Within this approach, a method is developed to calculate the critical condition for electromechanical instability. This approach is illustrated with a specific model of a viscoelastic dielectric elastomer, which is fitted to stress-strain curves of a dielectric elastomer (VHB tape), measured at various strain rates. The model shows that a higher critical voltage can be achieved by applying a constant voltage for a shorter time, or by applying ramping voltage with a higher rate. A viscoelastic dielectric elastomer can attain a larger strain of actuation than an elastic dielectric elastomer.

  • Theory of dielectric Elastomers capable of giant deformation of actuation
    Physical Review Letters, 2010
    Co-Authors: Xuanhe Zhao, Zhigang Suo
    Abstract:

    The deformation of a dielectric induced by voltage is limited by electrical breakdown if the dielectric is stiff, and by electromechanical instability if the dielectric is compliant. The interplay of the two modes of instability is analyzed for a dielectric elastomer, which is compliant at a small stretch, but stiffens steeply. The theory is illustrated with recent experiments of interpenetrating networks, and with a model of swollen Elastomers. The theory predicts that, for an elastomer with a stress-stretch curve of a desirable form, the voltage can induce giant deformation.