Symposium H
Electroactive Polymers and Shape Memory Polymers: Advances in Materials and Devices


Session H-1 - Advances in EAP Materials

H-1:IL01  The Evolution of Strong, Fast, Powerful, Durable, and Cheap Polymer Artificial Muscles from Carbon Nanotube Muscles
R.H. BAUGHMAN, A.G. MACDIARMID, NanoTech Institute, the University of Texas at Dallas, Dallas, TX, USA

Three successive generations of twist-spun artificial muscles are described that provide both torsional and tensile actuation. Our first generation of twist-spun muscles, which are electrochemically powered by volume changes induced by double-layer charge injection, provide torsional rotation speeds of 590 rpm, and torsional strokes of 250° per millimeter of actuator length, which is 1000 times that for earlier artificial muscles. Our second generation muscles, which require no electrolyte and are based on guest-infiltrated carbon nanotube yarns, can torsionally actuate at 11,500 rpm and deliver 85 times higher power density during contraction than natural muscles. Our third generation muscles, which are thermally, electrothermally, or chemically powered polymer fibers, can rotate at 100,000 rpm, contract by up to 49%, generate 5 times the gravimetric power of a car engine, lift 100 times heavier loads than the same length and weight human muscle, or actuate at 7.5 cycles/s for millions of cycles. These polymer muscles can be cheaply made from fishing line or sewing thread. This work resulted from collaboration between The University of Texas at Dallas, The University of Wollongong, Hanyang University, The University of British Columbia, and Namık Kemal University.

H-1:IL02  Electromechanical Properties of CNT-ionic Gel Actuators
KINJI ASAKA, T. SUGINO, K. KIYOHARA, National Institute of Advanced Industrial Sciece and Technology (AIST), Ikeda, Osaka, Japan

Recently, there is significant growing interest in research field of electroactive polymer (EAP) actuators, since they have many advantages as compared to conventional actuators, such as large actuation strains, large compliance, low mass density, easy processing, etc.They are expected to be applied to many human friendly applications such as bionic implant, limb prosthetics, tactile display, biomedical applications, etc. The EAP actuators can be divided into two main types: ionic, which are activated by electrically transport of ions and/or solvent, and electronic, which are activated by electric field. We have developed an ionic-type electromechanical actuator based on carbon-nanotube (CNT) -dispersed ionic-gel electrodes sandwiching an ioic-gel electrolyte layer (bucky-gel actuator). The bucky-gel actuator has several advantages for the applications, such as low drive voltage, large displacement, possible and easy to miniaturize or to fabricate into thin film, can be activated in air, relatively high blocking force, etc. In the presentaion, recent developments of the various materials and electromechanical properties of the bucky-gel actuator, and its application will be described.

H-1:L04  Stronger VHB Dielectric Elastomer Actuator
GIH-KEONG LAU, THANH-GIANG LA, School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 

Early advance of dielectric elastomer actuators was achieved by extensive material selection and testing. In 2000, Pelrine et al. reported a breakthrough in the voltage-induced strain greater than 100% by using highly pre-stretched silicone and acrylic elastomers. This advance is attributed to enhanced dielectric breakdown strength of up to 412MV/m by means of membrane pre-stretching. Pre-stretching stiffens the soft dielectric elastomer and thus suppresses electromechanical instability from prematurely failing DEAs. Yet, the subsequent decade of material development does not yield electrically stronger elastomer, which by itself can sustain a higher field to produce muscle-like high-stress (>1MPa). This work reviews novel methods to make acrylic DEAs stronger so that they can perform better as artificial muscles. These novel methods, such oil immersion, and dielectric oil encapsulation, and even dielectric gel encapsulation, help suppress electro-thermal breakdown of acrylic DEAs. In these ways, the soft acrylic elastomer can be made electrically stronger to drive soft robots.

H-1:L05  Piezoelectric Polymer Foams: Structure and Property Adjustment for Air-borne Ultrasonic Transducer
M. SBORIKAS1, J. EALO2, M. WEGENER1, 1Department of Sensors and Actuators, Fraunhofer IAP, Potsdam, Germany; 2School of Mechanical Engineering, University of Valle, Ciudad Universitaria Meléndez, Cali, Colombia

Ferroelectrets are presenting one of the recent developments in the field of piezoelectric transducer materials. After charging, ferroelectrets exhibit huge electrical dipoles based on trapped charges which are embedded in a soft cellular polymer matrix. Thus, ferroelectrets show strong piezoelectric activity with thickness-extension resonance frequencies in the high kilo Hertz range and thus well below the resonance frequency of thickness vibrations of other piezoelectric materials. Here, we present the optimization of the foam structure, the adaptation of the charging process as well as the transducer integration in order to develop transducer films with low resonance frequencies and low acoustic impedance. The suitability of the developed materials for air-borne ultrasonic purposes is proved with demonstrated high piezoelectric activities and low resonance frequencies of down to about 120 kHz. These ferroelectrets show low acoustic impedances between 0.024 and 0.027 MRayls. Acoustic measurements revealed a relative bandwidth of 35 % at -6 dB at a resonance frequency of around 150 kHz. The vibratory pattern of the transducer films were determined below, at and above the resonance frequencies. At frequencies below the resonance, the transducer acts like an ideal piston.

H-1:L06  Polymeric Electrochemical Motors Sense Physical and Chemical Working Conditions: Artificial Proprioception
T.F. OTERO1, Y.A. ISMAIL2, L. VALERO1,3, J.G. MARTINEZ1, 1Laboratory for Electrochemistry, Intelligent Materials and Devices, Univ. Politécnica de Cartagena, Cartagena, Spain; 2Dept.of Basic Sciences, College of Applied Science, A’Sharqiyah University, Ibra, Oman; 3Electronic Engineering School, Universidad Autónoma del Estado de México, Toluca, México

Designers and engineers have been dreaming for decades with motors sensing, by themselves,their working and surrounding conditions, as biological muscles do leading to proprioception. The evolution of the working potential, the consumed electrical energy, or the involved charge of electrochemical artificial muscles based on electroactive materials driven by constant currents senses, while working, any variation of the mechanical, thermal, electrical or chemical conditions affecting the work. They are linear Faradaic polymeric motors: currents control the muscle movement, rate and charges control the muscle displacements. One physically uniform artificial muscle includes one chemically based polymeric motor and several sensors working simultaneously under the same driving reaction. Actuating (current and charge) and sensing (potential and energy) magnitudes are present, simultaneously, within the same two connecting wires and can be read by the computer.Experimental results support the theoretical predictions.The ensemble computer-generator-muscle-theoretical equation constitutes and describes artificial mechanical, thermal and chemical proprioception of the system.We predict using these materials proprioceptive tools and zoomorphic or anthropomorphic soft robots can be envisaged.

H-1:L08  Impact of Structural Modifications on Electrically Induced Properties of Relaxor Polymer Systems
V. BOBNAR, G. CASAR, S. GLINSEK, J. KORUZA, B. MALIC, J. Stefan Institute, Ljubljana, Slovenia; X. Li, Q.M. Zhang, Department of Electrical Engineering and Materials Research Institute, The Pennsylvania State University, University Park, PA, USA

Electroactive polymers based on poly(vinylidene fluoride-trifluoroethylene) are of great interest for a wide range of applications as they exhibit fast response speeds, high electric energy density, giant electrostriction and large electrocaloric effect. We present the impact of structural modifications on dielectric, electromechanical and electrocaloric properties of P(VDF-TrFE)-based ferroelectric and relaxor (here the long-range ordering of chains is broken by introduction of additional monomers that contain large chlorine atoms) polymers. Substantially different properties were detected after adopting various processing procedures and modifications, such as (i) uniaxial stretching, (ii) low-dose irradiation of ferroelectric polymer with high-energy electrons and (iii) blending a relaxor polymer with the ferroelectric one. In particular, we show that (i) stretching increases polarization and thus strongly enhances the electrostrictive response, (ii) irradiation results in the coexistence of ferroelectric and relaxor states, which enhances the electrocaloric response and that (iii) blending results in the similar coexistence, only without undesirable side effects of irradiation, which suggests blends as a model system for tailoring various properties of electroactive polymers.

H-1:L09  High Dielectric Permittivity Elastomers for Artificial Muscles
D.M. OPRIS, S. DÜNKI, E. PERJU, F. NÜESCH, Swiss Federal Laboratories for Materials Science and Technology Empa, Duebendorf, Switzerland

Elastomers that respond to an electric field are of great interest for many fields of applications. Dielectric elastomer actuators (DEAs) are stretchable capacitors made of a thin elastic film coated with two compliant electrodes which expend their area when charged. Due to their simple working principle and muscle-like actuation, DEA could find a large variety of applications in engines, optical devices, sensors, energy harvesters, artificial muscles to name a few. However, the high voltages required to induce the mechanical motion hider their use in some applications. Here, new dielectric elastomers with increased permittivity, excellent mechanical properties and increased electromechanical sensitivity are presented. They show a maximum lateral actuation strain of 20.5% at 10.8 MV/m and ability to self-repair after a breakdown. Due to the low actuation voltage and the large actuation strain, applications of this material in commercial products might become reality.

Session H-2 - Analysis and Mechanical Mechanisms

H-2:IL02  Asymmetric Bilayer Artificial Muscles Based on Polypyrrole
MASAKI FUCHIWAKI, Kyushu Institute of Technology, Iizuka, Fukuoka, Japan; J.G. MARTINEZ, T.F. OTERO, Universidad Politecnica de Cartagena, Spain

Conducting polymer (CP) artificial muscles constitute the base for the development of promising polymeric motors for the development of zoomorphic and anthropomorphic soft robots. Both, the constitutive materials and the devices mimic natural muscles. Some asymmetric bilayers constituted by two different conducting polymers, CP1/CP2, thus both reactive, have been described. Here, looking for cooperative and synergic mechanical effects we present the coulodynamic characterization of the PPy-ClO4(Lithium perchlorate)/PPy-DBS (dodecyl benzyl sulphonate) asymmetric bilayer. The parallel coulodynamic characterization of the PPy-ClO4/tape and PPy-DBS/tape bilayer muscles can corroborate the two reactions driven ions and water exchanges, so actuation, in each layer. Bilayer muscles translate small ionic exchanges into large bending movements. Asymmetric bilayers are constituted by two layers of the same conducting polymer (polypyrrole, PPy) one layer electrogenerated in presence of dodecylbenzenesulfonic acid (HDBS). The PPy second layer was electrogenerated on the PPy-DBS film, now in the presence of the Lithium perchlorate pyrrole and solvent. The conducting polymer asymmetric bilayer muscles based on Polypyrrole produce cooperative and synergic electrochemo-mechanical actuation.

H-2:IL03  New Resonance Mode in Dielectric Elastomer Actuators
JIANWEN ZHAO, YONG GE, SHU WANG, BO HUANG, Harbin Institute of Technology, Weihai, China

Dielectric elastomer (DE) actuator is working by deformation of DE film, to some device actuated by DE, such as dielectric elastomer minimum energy structure (DEMES), the shape of DE film during deformation is so complicated; therefore, some new vibration modes maybe occur in these actuators. Taking DEMESs as examples, a special resonance mode was found. The vibration with the largest amplitude does not occur while the voltage frequency is equal to natural response frequency of the DEMES; rather, it occurs while the former is near to two times of the latter and the vibrational frequency of DEMES is half of the voltage frequency. Four types of DEMES actuated by acrylic and silicone were fabricated to validate the special resonance principle; the type with two layers of DE film on both side of the frame has more regular vibration curves, and all the DEMES prototypes demonstrate the special resonance mode. This phenomenon was analyzed by a comparison of the timing sequences between voltage and DEMES vibration.

H-2:L04  Theoretical Model of the Stress-composition Interaction for Electrochemical Actuators Based on Single-walled Carbon Nanotubes and Ionic Liquids
H. RANDRIAMAHAZAKA, Université Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR 7086 CNRS, Paris Cedex, France; KINJI ASAKA, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan

We develop theoretical model based on a general thermodynamic theory of the stress-composition interaction. This theory implies the existence of a coupling between the elastic properties of the host material and the structure and/or the dynamics associated with the guest species. The model takes into account the electrochemical stress due to the intercalation (de-intercalation) process which generates the strain and bending of the electrochemical actuators. We investigate the electromechanical properties of bucky-gel electrochemical actuators incorporating various amounts of single-walled carbon nanotubes and an ionic liquid electrolyte, 1-butyl-3-methylimidazolium tetrafluoroborate. The electromechanical responses are investigated by means of electrochemical impedance spectroscopy and bending displacement measurements. This approach allows us to analyze the relationship between the strains and the real part of the complex capacitance by introducing the strain-capacitance coefficient. This coefficient is related to the electrochemical stress and the amount of the ionic adsorption (desorption) at the double-layer. The theoretical model allows us to rationalize the electromechanical properties of the bucky-gel actuators.

H-2:L05  Thermodynamics and Stability of Dielectric Elastomer
LIWU LIU¹, YANJU¹, JINSONG LENG2, ¹Department of Astronautical Science and Mechanics, Harbin Institute of Technology (HIT), Harbin, China; 2Centre for Composite Materials, Science Park of Harbin Institute of Technology (HIT), Harbin, China

Dielectric elastomer is a kind of typical soft active material. It can deform obviously when subjected to an external voltage. When a dielectric elastomer with randomly oriented dipoles is subject to an electric field, the dipoles will rotate to and align with the electric field. The polarization of the dielectric elastomer may be saturated when the voltage is high enough. When subjected to a mechanical force, the end-to-end distance of each polymer chain, which has a finite contour length, will approach the finite value, reaching a limiting stretch. On approaching the limiting stretch, the elastomer stiffens steeply. Here, we develop a thermodynamic constitutive model of dielectric elastomers undergoing polarization saturation and strain-stiffening, and then investigate the stability (electromechanical stability, snap-through stability) and voltage induced deformation of dielectric elastomers. Analytical solution has been obtained and it reveals the marked influence of the extension limit and polarization saturation limit on its instability. The developed thermodynamic constitutive model and simulation results would be helpful in future to the research of dielectric elastomer based high-performance transducers.

H-2:L06  Detection and Quantification of Structural Processes in Conducting Polymers Exchanging Cations
L. VALERO1,2, J.G. MARTINEZ2, T.F. OTERO2, M. FUCHIWAKI3, Y.A. ISMAIL4, 1Electronic department, Engineering school, Universidad Autónoma del Estado de México, Toluca, México; 2Centre for Electrochemistry and Intelligent Materials (CEMI), Universidad Politécnica de Cartagena, Aulario II, Cartagena, Murcia, Spain; 3Kyushu Institute of Technology, Department of Mechanical Information Science and Technology, Iizuka (Fukuoka), Japan; 4Dept.of Basic Sciences, College of Applied Science, A’Sharqiyah University, Ibra, Oman

Technology is trying to produce materials mimicking biological composition, reactions and functions. The simplest bio mimicking materials are reactive gels composed of conducting polymers. Interactions of polymeric chains with the electric currents have got electro-chemo-mechanical materials with properties like sensors/ actuators [1]. Films of conducting polymers can change their properties along with their composition during electrochemical reactions in a reversible way [2, 3]. Nowadays chemical kinetic model doesn’t include any reaction induced structural change. In blend films of CP with large organic acids (DBS), only cations are exchanged during reactions (swelling by reduction and shrinking by oxidation in this way we describe how electrochemical responses from dense reactive and biomimetic gels of conducting polymers include and quantify different structural changes induced by the reaction. Coulovoltammetric responses present abrupt changes of the charge/potential slope, indicating the abrupt variation of the concomitant oxidation or reduction reaction rates and the initial and final potential for each of the structural reaction rate control process, the structural process is described and explained by the Electrochemical Stimulated Conformational Relaxation (ESCR) Model.

Session H-3 - Device Development and Integration Technologies

H-3:IL01  Stretchable Conducting Polymer Electrodes for Soft Actuators
HIDENORI OKUZAKI, University of Yamanashi, Kofu, Japan 

We have developed stretchable and highly conductive films by casting a water dispersion of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) containing polyglycerin (PG). The electrical conductivity significantly increased by adding PG, where the value of the PEDOT/PSS/PG film attained as high as 411 S/cm. Upon adding 60 wt% PG, Young’s modulus and tensile strength significantly decreased to 0.2 GPa and 21 MPa. It is noted that the elongation at break of the PEDOT/PSS/PG film attained as high as 26%, which is more than four times larger than the PEDOT/PSS film (6%). Furthermore, we fabricated soft actuators consisting of ionic liquid/polyurethane elastomer (IL/PU) composite gel with PEDOT/PSS/PG electrodes spray-deposited on both sides of the IL/PU gel, and their electromechanical-active polymer (EAP) actuating behavior was demonstrated. Upon application of 2 V, the IL/PU/PEDOT/PSS/PG actuator showed quick bending toward anode, the mechanism of which was associated with the polarization caused by electrophoretic diffusion of IL in the PU matrix based on the electric-double-layer capacitor. It was found that the actuator still worked at frequencies higher than 100 Hz.

H-3:IL02  Solid State Electrochemical Microactuator on Soft Substrates
C. PLESSE, A. MAZIZ, G.T.M. NGUYEN, F. VIDAL, LPPI, University of Cergy-Pontoise, Cergy, France; M. BENFETRIT, C. SOYER, E. CATTAN, IEMN, CNRS, Villeneuve D'Ascq, France

Electrochemical micromuscles converting electrical energy into micromechanical response are presented. These electroactive materials are based on the volume variations induced by the redox process of an electroactive polymer, the poly(3,4-ethylenedioxythiophene) (PEDOT). These microactuators are synthesized in a trilayer configuration, with two PEDOT electrodes sandwiching a membrane containing the ions necessary to the redox process, and patterned into microbeam actuators as thin as 6 µm with existing technologies, such as standard photolithography and dry etching. Electromechanical characterizations of the micromuscles are presented and compared to existing model. Thanks to downscaling large displacements under low voltage stimulation (+/- 4V) are reported at a frequency as high as 930 Hz corresponding to the fundamental eigenfrequency of the microbeam. These electrochemical micromuscles are then presenting unprecedented combination of softness, low driving voltage, large displacement and fast response speed which are the keys for further development of new MEMS. Finally, new considerations on process, contact positioning and direct integration on soft substrates will be discussed.

H-3:IL03  Skin-inspired Multimodal Sensors for Soft Robots
I. GRAZ, Soft Matter Physics, Johannes Kepler University, Linz, Austria

Initially constructed to “work” for mankind, robots are now envisioned to closely interact with humans, especially owing to our ever aging society. To ensure save contact between humans and robots, true to Asimov’s “A robot may not harm a human being”, they must be able to perceive their environment. A route to allow robots to feel is offered by stretchable electronic skins (e-skins). They not only emulate the human skin’s abilities to sense touch, pressure and motion, but also its mechanical compliance. E-skins can be stretched and conformably coat 3D objects while maintaining their electrical functionalities throughout the deformations. We present such multimodal e-skins that measure temperature and pressure. Additionally they allow monitoring motion of robotic limbs by tracking strain in analogy to human proprioception. The concept of e-skin is further extended to visual and haptic feedback inspired by the octopus: Spherical deformation of a rubber membrane accompanied by a color change becomes feasible with soft actuators driven by a phase transition. Such actuators represent a novel route to completely soft robots. Together with conformable e-skins they enable autonomous, self-sensing systems that interact with humans true to their mission to “work” for mankind.

H-3:IL04  IPMC Actuators Fabricated Using MEMS Technology
SHIGEKI TSUCHITANI1, K. KIKUCHI1, I. SHIMIZU2, T. TANIGUCHI2, H. MIKI1, 1Department of Systems Engineering, Wakayama University, 2Graduate School of Systems Engineering, Wakayama University, Wakayama, Japan

IPMC is a polymer actuator with large bending movement at low driving voltages. It has potential applications as actuators for biomimetic robots. Microminiaturization of IPMC enlarges the application to medical and biological fields. MEMS technology is a powerful tool for microminiaturizing IPMC. Fabrication of IPMC on Si substrate and micromachining of IPMC are basic technologies for microminiaturizing IPMC. Adhesion of IPMC with the substrate is essential to fabricate IPMC on the substrate. Swelling of IPMC with water makes IPMC peel from the substrate due to the interfacial stress. To enlarge adhesion force of IPMC with Si substrate, we have fabricated IPMCs by coating Nafion dispersion on porous Si surfaces that were formed by anodic oxidation. The fabricated IPMCs didn't peel from the Si substrate in the operation in water. Photolithography is a key technology in MEMS fabrication. However, the use of photo resists and developers also swells IPMC and lowers machining accuracy. We have developed a machining technology of microminiaturized IPMC by using reactive ion etching of Nafion film through metal mask and a selective electroless plating using plasma irradiation. An array of IPMCs with a width of 100 µm was fabricated and their operations in water were confirmed.

H-3:IL05  Interpenetrating Polymer Networks for Novel Actuators
C. PLESSE, G.T.M. NGUYEN, F. VIDAL, LPPI / Université de Cergy Pontoise, Neuville sur Oise, France

Electronic conducting interpenetrating polymer networks (conducting IPN) is proposed as an alternative to multilayer architectures for the design of novel actuators. The synthesis of conducting IPN devices is based on high molecular weight NBR, PEO derivative and PEDOT. The specific procedure allows an inhomogeneous distribution of PEDOT across the sample thickness, i.e. the concentration decreases from the outside towards the center, leading to a very poor connectivity of PEDOT inside the bulk of the SPE. After swelling with an ionic liquid and applying an alternative low voltage between the two sides of the film, this device can work as an actuator. Furthermore when submitted to a mechanical bending, open circuit voltage (Voc) variation is measured. Values and sign of the Voc changes are directly related to the direction and to the amplitude of the mechanical stimulation. The electroactive-IPN has also the ability to behave like an electronic skin. The e-skin is sensitive to various stimuli such as pressure, temperature and responds by a change in the voltage. Thus all these results allow us to consider Electroactive-IPNs as a unique material with multiple functionalities as artificial muscles, strain, pressure and temperature sensors.

H-3:IL06  Miniaturized Dielectric Elastomer Actuators (DEA): Towards Intelligent Soft Machines
H. SHEA, EPFL, Neuchatel, Switzerland

Dielectric Elastomer Actuators (DEAs), often referred to as artificial muscles, are stretchable soft transducers consisting of an elastomer membrane sandwiched between two compliant electrodes. DEAs can be used as actuators with strains of over 200%, but also for energy harvesting, as sensors, switches and as lightweight structural elements. These attributes make them particularly well suited for intelligent deformable machines. Our research centers on µm- to cm-scale miniaturized DEAs. We present the microfabrication, design and operation of DEA devices based on soft silicone elastomers and printed carbon-based inks. A wide range of applications are shown including: compliant grippers capable of holding 50x their own weight for soft robotics, foldable DEA elevons enabling full flight control of remotely operated model airplanes, extremely fast (200 µs) tunable lenses, low-voltage DEAs operating below 100V, and arrays of mm-scale devices to apply periodic mechanical strain to biological cells. Our research goal is fully flexible smart machines that are reliable, self-powered, incorporating high strain, high energy-density silicone elastomers actuators, with integrated sensing and flexible printed control circuitry.

H-3:IL07  Humanoids and the Role of Electroactive Materials/Mechanisms in Advancing their Capability
Y. BAR-COHEN, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Humanoids are increasingly becoming capable biologically inspired robots that are appearing and behaving lifelike. Making humanlike robots is the ultimate challenge to biomimetics and, while for many years they were considered a science fiction, such robots are becoming an engineering reality. Advances in producing such robots are allowing them to perform impressive functions and tasks. In 2012, in an effort to promote significant advances in developing such robots, DARPA posed a Robotic Challenge to produce such robots that operate in disaster scenarios that would make society more resilient. The challenge was focused on the requirements that have been needed after the Fukushima accident in Japan, hoping to advance the field of disaster robotics. This disaster posed significant challenges to emergency responders since radiation prevented people from going into the station and venting the explosive gas. Another significant development in this field is the fact that major US corporations have entered into the race to produce commercial humanlike robots. As a result, one can expect significant and rapid advances in this field. Developing such robots is critically dependent of the use of highly efficient, compact, lightweight actuators and electroactive materials are offering.

H-3:L08  Comparison of Annealing Treatments on Contact Resistance between Au Contacts and IGZO Semiconductor on TFTs on Shape Memory Polymer
G. GUTIERREZ-HEREDIA, O. RODRIGUEZ, J. ESPINOZA, R. REIT, W. VOIT, University of Texas at Dallas, Richardson, TX, USA

In recent years, indium-gallium-zinc-oxide (IGZO) have emerged as a semiconductor candidate for the fabrication of flexible applications. Among other characteristics such as high mobility, performance stability is a crucial parameter for the success on complex circuits. In this work, a comparison of different annealing treatments on the electrical behavior of thin film transistors (TFTs) based on IGZO semiconductor is presented, using shape memory polymer (SMP) as substrate. Full photolithographic processes were used for the IGZO TFTs fabrication on glass substrate with 50 μm of SMP. An electrical characterization of untreated IGZO results on a saturation mobility (µsat) at VGS=6 V of 1.1x10-2 cm2/V-s. After annealing treatments (at 250 °C) the TFTs electrical performance results on µsat improvements up to 30 cm2/V-s. Similarly, it was found a significant reduction of the contact resistance which improves the physical interface metal-semiconductor due to the annealing processes, decreasing it from values around 1 MΩ to 20 kΩ. Finally, the contributions of resistive effects are compared between the channel and contact resistances in terms of IGZO TFTs electrical parameters such as threshold voltage, On/Off current ratio and subthreshold swing.

Session H-4 - Applications of EAPs

H-4:IL01  Organic Bionics Enabled by 3D Printing
G.G. WALLACE, ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong, Wollongong, NSW, Australia

The advent of organic conductors such as inherently conducting polymers, carbon nanotubes and graphene has greatly increased the inventory of electromaterials available to the modern bionics engineer.  These materials can be manipulated to facilitate electrode-cellular interactions and to enhance the efficacy of bionic communication with living cells. We have demonstrated the ability to promote electronic communication, most recently using the extraordinary properties of carbon nanotube structures and graphene to provide platforms capable of muscle cell and nerve cell communication respectively.  In parallel with such fundamental material studies – many in this field have been acutely aware of the need for alternative methods of fabrication if devices containing them are to be realised.  Here we will focus on 3D printing and the ability to spatially distribute multiple components. For bionic devices printing of the structural and electronic conducting components is essential. Structural elements may comprise naturally occurring materials such as chitosan. Conducting elements may comprise inherently conducting polymers or nanostructured carbons. The ultimate bioactive centre within a bionic structure is perhaps living cells and rapid progress is being made in that area.

H-4:IL02  Elastomer Transducers
S.A. CHIBA, Chiba Science Institute, Tokyo, Japan; M. WAKI, Wits Inc., Tochigi, Japan; Y. TANAKA, N. TSURUMI, K. OKAMOTO, K. NAGASE, ROHM Co., Ltd., Kyoto, Japan; M. HOMMA, H. YOKOTA, K. ODAGIRI, H. SATO, T. SAIKI, J. KANEKO, ADEKA Corp., Tokyo, Japan

Electroactive polymer transducers have many features that are desirable for various devices. An especially attractive type of electroactive polymer is dielectric elastomer. Our recent progress that a DE actuator having only 0.1g of DE lifted the weight of 1.5kg using carbon system electrodes. We also developed the ribbon form DE actuators having a sensor function can be used to measure force, or pressure as well as motion at the same time. This actuator can assist human and robot motions. At the same time, it can work as motion feedback sensor. We hope that it may be useful for smart rehabilitation equipments for hands, legs, and fingers. DE has also been shown to operate in reverse as a generator. Experiments have been performed portable DE generators/ wearable generators powered by human motion, ocean wave power harvesters mounted on buoys, solar heat generator, and water turbines. While the power output levels of such demonstration devices is small, the performance of these devices has supported the potential benefits of DE. We are developing elastomers having larger dielectric constant using barium titanium oxide to produce a “super artificial muscle for energy harvesting devices, actuators & sensors” in near future.

H-4:L04  A Viscoelastic Soft Dielectric Elastomer Generator Operating in an Electrical Circuit
R. DENZER, Division of Solid Mechanics, Lund University, Lund, Sweden; E. BORTOT, Department of Civil, Environmental and Mechanical Engineering, University of Trento, Trento, Italy; M. GEI, School of Engineering, Cardiff University, Cardiff, Wales, UK; A. MENZEL, TU Dortmund University, Dortmund, Germany and Division of Solid Mechanics, Lund University, Lund, Sweden

We propose a framework for reliable simulations of soft energy harvesters. A simple electrical circuit is realised by connecting the capacitor, stretched periodically by a source of mechanical work, in parallel with a battery through a diode and with an electrical load consuming the energy produced. As these devices undergo a high number of electro-mechanical loading cycles at large deformation, the time-dependent response of the material must be taken into account as it strongly affects the generator outcome. To this end, the viscoelastic behaviour of the polymer and the possible change of permittivity with strains are analysed carefully by means of a proposed coupled electro-viscoelastic constitutive model, calibrated on experimental data available in the literature for an incompressible polyacrylate elastomer (3M VHB4910). Numerical results showing the importance of time-dependent behaviour on the evaluation of performance of DEGs for different loading conditions, namely equi-biaxial and uniaxial, are reported in the final section, see [1].
[1] Bortot, E, Denzer, R, Menzel, A, Gei, M. Analysis of viscoelastic soft dielectric elastomer generators operating in an electrical circuit, International Journal of Solids and Structures, (2015), doi: 10.1016/j.ijsolstr.2015.06.004

Session H-5 - Advances in SMPs

H-5:IL01  Rewritable Shape Memory Polymers – Materials with Latent Ability to Change Permanent Shapes by Photoirradiation
C.N. BOWMAN, Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO, USA

With a wide array of formulations, chemistries and mechanisms to choose from, the science of making a stimuli responsive material has been studied and documented extensively over the past decade. Shape memory polymers (SMPs) with network properties such as high and tunable glass transition temperatures, multiple shape memory transitions, shape memory composites and two-way transition materials are recent examples of new directions that have been undertaken within the broad field of ‘smart’ materials. Among these new directions, particularly appealing seems to be the ability to resize the material in-situ or repeatedly re-write shapes once it has been cast. Such shape manipulations would be very desirable from the standpoint of SMPs applications, especially those requiring the excellent mechanical properties of thermosets. The concept of photoinduced addition-fragmentation chain transfer (AFCT) enables Covalent Adaptable Networks (CANs) in which the presence of photochemically active moieties can be used to induce network rearrangement in a controlled manner. Adopting this concept, it is demonstrated that by incorporating the photochemically active monomers, crosslinked polymer networks can then be induced to repeatedly undergo covalent bond rearrangement, and hence bulk material rearrangement.

H-5:L02  Fractional Calculus Approach to Viscoelastic Behavior of Amorphous Shape Memory Polymers
CHANGQING FANG, HUIYU SUN, State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, China; JIANPING GU, Department of Materials Engineering, Nanjing Institute of Technology, Nanjing, China

The viscoelastic response of thermally activated shape memory polymers (SMPs) is investigated utilizing constitutive models based on fractional calculus. Fractional calculus-based viscoelastic equations are fitted to experimental data existing in literature compared with traditional viscoelastic models. The fit results show that fractional models can give an adequate description of static and dynamic response of thermally activated SMPs. There is a significant improvement in the description of relaxation modulus by the fractional differential equation with less number of parameters compared with the Prony series and a Kohlrausch-Williams-Watts (KWW) stretched exponential.

H-5:L03  Light-matter Concepts in Azobenzene-based Photoresponsive Polymers
W. OATES, J. BIN, Florida State University, Tallahassee, FL, USA

Complex interactions between photoisomerization of azobenzene and different polymer networks have limited our understanding of light induce deformation as a function of the light's wavelength and polarization. A unified modeling framework is presented to advance the understanding of complex deformation states controlled by linear or circularly polarized light or optical vortex beams. Prior research that uses higher order field gradients to model surface relief grating deformation is found to be unnecessary. The proposed model which couples time-dependent Maxwell equations with nonlinear mechanics and internal electronic structure evolution is found to compare well with a broad range of photomechanical data including both surface relief gratings and deformation of free standing films. A critical conclusion is that the molecular structure of the azobenzene monomers dramatically influence the photostrictive behavior leading to a sign change in the photostrictive constants. The results of these developments have now been extended to include upconversion to enhance material performance and efficiency. These new developments will be summarized and compared with conventional azobenzene polymer performance.

H-5:L06  Stereolithography 3D Printing of Shape Memory Polymers
M. LAYANI, M. ZAREK, D. COHN, S. MAGDASSI CASALI, Center for Applied Chemistry, Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel

In recent years shape memory polymers have been a very promising material for various fields of applications, yet the challenges in processing them into complex three-dimensional shapes have limited their use. Digital Light Processing (DLP) is one of the most promising 3D printing technology, due to its simplicity and versatility of printable monomers. Typically, DLP printers utilize low molecular weight compounds as the resin precursors. By modifying a commercial low cost DLP 3D printer we could generate 3D structures composed of shape memory polymers, using a methacrylated polycaprolactone (PCL) with a high molecular weight. This stereolithography technique enabled fabrication of a variety of structures exhibiting shape memory behavior including electrical heat sensors and kinetic jewelry. In addition, it was found that by varying the degree of methacrylation of the polycaprolactone prepolymer, the mechanical properties of the printed shape memory objects can be tailored.
M. Zarek, M. Layani, I. Cooperstein, E. Sachayani, D. Cohn, S. Magdassi. 3D Printing of Shape Memory Polymers for Flexible Electronic Devices. Advanced Materials. DOI: 10.1002/adma.201503132.

H-5:L08  Characterization for Carbon Fiber Reinforced Epoxy based Shape Memory Polymer Composite
FENGFENG LI1, JIANGUO CHEN1, LIWU LIU1, YANJU LIU1, JINSONG LENG2, 1Department of Astronautical Science and Mechanics, Harbin Institute of Technology (HIT); 2Centre for Composite Materials and Structures, Science Park of Harbin Institute of Technology (HIT), Harbin, P.R. China

Shape memory polymer and its composite are new smart materials which can produce large recovery deformation under certain external stimuli. Shape memory polymer composites have advantages of low density, large recoverable deformation, high strength, and large recovery force. Analyzing and studying mechanics theory of the composite can make it more rational in the application. The objective of this paper is to detail experimental investigations of the carbon fiber reinforced epoxy based shape memory polymer composite. Included in this paper are the preparation of the specimens and the details of the test. The epoxy based shape memory polymer mechanical properties are first carried out by dynamic mechanical analysis test, isothermal uniaxial tensile test. For investigating the influences of carbon fiber weight fraction on mechanical and shape memory properties of the composites at different temperatures, isothermal uniaxial tensile test, three-point bending test, constrained displacement recovery test and free recovery test are performed. The results of the tests help to determine the basic material parameters which can be applied to evaluate the potential use of SMPC applications in deployable structures.

H-5:IL09  From Programming Smart Materials to Growing Dynamic Shapes
S.K. SMOUKOV, Active and Intelligent Materials Lab, University of Cambridge, Cambridge, UK

Bottom-up processes are more sustainable as they are material-efficient, and often scalable due to the lack of expensive equipment, such as in lithography, necessary to impose outside system constraints. Yet easily controlling or obtaining a variety of shapes by such methods is a challenge. By controlling reactions in confined geometries, we generate spontaneous symmetry breaking to solve this problem. We explore nature-inspired processes but create non-biological morphogenesis at the molecular level in artificial systems.
We demonstrate simplified chemical syntheses of dynamic shapes, and novel shape-memory composites. We show the development of a general combinatorial strategy for incorporating multiple functions in a single material, with the goal that materials would themselves be the next generation of autonomous micro-robots. We synthesize Janus and other asymmetric particles by coupling chemical reactions to non-linear mechanical stresses in materials. We describe the first bottom-up phase change mechanism transforming liquid droplets into multiple geometric shapes, including octahedra, hexagons, rhomboids, triangles and fibers. This scalable process has implications for further fundamental discoveries and for potential applied explorations in manufacturing and nanoscience.

Session H-6 - Applications of SMPs and their Composites

H-6:IL01  Novel Behavior in Smart Polymeric Materials: Stress Memory and its Potential Applications
JINLIAN HU, H. NARAYANA, Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Materials, structures and systems, responsive to an external stimulus are smart and adaptive to our human demands. Among smart materials, polymers with shape memory effect are at the forefront of research leading to comprehensive publications and wide applications. In this paper, we extend the concept of shape memory polymers to stress memory ones, which have been discovered recently. Like shape memory, stress memory represents a phenomenon where the stress in a polymer can be programmed, stored and retrieved reversibly with an external stimulus such as temperature and magnetic field. Stress memory may be mistaken as the recovery stress which was studied quite broadly. Our further investigation also reveals that stress memory is quite different from recovery stress containing multi-components including elastic and viscoelastic forces in addition to possible memory stress. Stress memory could be used into applications such as sensors, pressure garments, massage devices, electronic skins and artificial muscles. The current revelation of stress memory potentials is emanated from an authentic application of memory fibres, films, and foams in the smart compression devices for the management of chronic and therapeutic disorders.

H-6:L02  Form-filling ADP/Chitosan/Ceramic (ACC) Sponge for Potential Use in Bone Defects
K. JAHAN, M. MEKHAIL, M. TABRIZIAN, McGill University, Montreal, Quebec, Canada

Bone defects are bone injuries that will not repair without medical intervention. Currently, the gold standard treatment is an autologous bone graft. However, this intervention is challenging due to donor scarcity and donor site morbidity that follows the procedure. Tissue engineering has shown potential as an alternative intervention; it is based on the use of scaffolds which mimic the structure of the tissue that requires repair and simultaneously supports, reinforces and organizes the regenerating tissue. An injectable purine/chitosan sponge with rapid gelation time has been developed showing to be a biocompatible, biodegradable, and potentially osteoconductive scaffold. Based on these results, the current project focuses on the characterization of a form-filling adenosine diphosphate/chitosan/ceramic sponge to be used as a bone repair scaffold. The physico-chemical characterization was done through SEM, microCT, XPS and FTIR. In vitro tests were also done (live/dead, proliferation, differentiation, mineralization). The results show potential as a delivery system for encapsulating nanoparticles and/or cells. Ultimately, this sponge may be a clinical alternative by decreasing the complications associated with graft donor sites while delivering agents to the site of injury.

H-6:IL05  Elastomers with High Elastic Energy Storage Capacity and Shape-actuating Ability
M. ANTHAMATTEN, YUAN MENG, JISU JIANG, JEY-CHANG YANG, University of Rochester, Rochester, NY, USA

Controlling network architecture and chain connectivity is critical to understanding elastic energy storage and improving performance of shape-memory polymers. Acrylate-terminated poly(caprolactones) (PCLs) are engineered to store large amounts of strain energy upon crystallization. The highly efficient thiol-acrylate coupling reaction ensures that the molecular weight between crosslinks is uniform, resulting in tougher, elastic materials with a high degree of crystallinity and outstanding shape-memory properties with high levels of elastic energy storage. The trigger temperature can also be tuned to be near the human body temperature. In a related effort, a two-stage curing process is describe that enables novel shape actuators that undergo fully reversible, elastic elongation in programmed direction, upon cooling. Unlike the two-way shape memory effect, actuation occurs without applied stress, and it is significant—exceeding 15% strain—placing this material in a class of only a few other known materials. Actuation is triggered as configurationally biased poly(caprolactone) chains undergo strain-induced crystallization.
Poster Presentations

H:P01  Towards a New Class of Green Hibryd Ionic Polymer-polymer Metal Composites
G. DI PASQUALE1, S. GRAZIANI2, A. POLLICINO1, R. PUGLISI1, V. DE LUCA2, 1Dipartimento Ingegneria Industriale (DII), Università di Catania, Catania, Italy; 2Dipartimento Ingegneria Elettrica Elettronica e Informatica (DIEEI), Università di Catania, Catania, Italy 

Ionic Polymer–Polymer Composites (IP2Cs) are totally organic Electroactive Polymers. The electrodes are, in fact, obtained by using a conducting polymer (PEDOT/PSS). In last decades, there is large interest on the study of conducting polymers with incorporated metallic nanoparticles. The authors have investigated the possibility to load IP2Cs by using platinum nanoparticles. Unfortunately, typical routes to produce metallic platinum involve the use of reducing agents, such as hydrazine, which are a toxic or explosive chemicals. Recently, there is a great interest in synthesizing metal nanoparticles using green chemistry principles. Relevant for the green production of nanoparticles are reagents such as vitamins, sugars, plant extracts and biodegradable polymers. The authors are working on the synthesis of hybrid IP2Cs, by loading the PEDOT/PSS layer with platinum nanoparticles, while using green chemistry. The possibility to use a green reagent as the L-ascorbic acid (AA, vitamin C) is addressed. In the final paper, the production technique developed for the realization of this class of hybrid green EAPs will be described. Also, results of the investigation of their electromechanical transduction capabilities will be reported.

H:P03  Conducting Electroactive Polyaniline Thin Films applied as Conductometric pH Sensor
H.J.N.P.D. MELLO, M. MULATO, Department of Physics, Faculty of Philosophy, Sciences and Letters at Ribeirão Preto, University of São Paulo (USP), Ribeirão Preto, SP, Brazil

The conducting (electroactive conjugated) polymer polyaniline (PANI) presents important properties for the development of conductometric pH chemical sensors. PANI´s conductivity depends on the formation of charge carriers (localized electronic states) upon doping of their conjugated backbone. The proton doping of PANI occurs by acid treatment of the imine nitrogen groups, forming cation radicals that are responsible for the electronic conduction. The maximum conductivity occurs when the number of these radicals in the polymer chains is maximized. It depends on PANI´s structural oxidative state, which is related to the fabrication process. We demonstrate that the parameters of the galvanostatic electrodeposition process control the response of a conductometric pH sensor due to distinct oxidative states of PANI thin films´ structure. This method requires the application of a constant current density for a specific period of time. The variation of passivated charge (150 up to 600 mC/cm²), obtained with two current densities of 0.5 and 1.0 mA/cm², were correlated to the variations in the sensor´s response. Surface morphology was investigated using scanning electron microscopy and thickness using profilometry. Visible optical reflectance analysis was used to study films’ properties.

H:P07  Efficient Linear Approach for the Closed-loop Control of a Ionic Polymer Bending Actuator
B. TONDU, A. SIMAITE, P. SOUERES, C. BERGAUD, Electrical Engineering Department, INSA, University of Toulouse and LAAS/CNRS, Toulouse, France

Artificial muscles are highly non-linear actuators whose closed-loop positioning is a true challenge. Artificial muscles are also stable systems in open-loop. We analyze how this last property can be particularly useful for deriving a simple linear control for the closed-loop positioning of a typical bending ionic polymer whose contraction can be identified as a first order linear system. The proposed approach is applied to a PEDOT:PSS/PVDF/ionic liquid actuator in the form of a 15mmx2mmx140um strip recently designed at the laboratory [1]: we show the relevance of a single PI-controller whose gains are directly derived from the open-loop identification in the form of constants or functions of identified parameters. Experimental results were obtained using a laser-beam and the LabView software. We report, in particular, the tracking of sinus-waves whose strip tip amplitude is in a +/- 2mm range, frequency between 0.05 and 0.2 hz, and for which the tracking error belongs to the range [-0.08 mm,+0.08mm].
[1] A. Simaite, B.Tondu, P.Soueres and C.Bergaud, 'Hybrid PVDF/PVDF-graft-PEGMA Membranes for Improved Interface Strength and Lifetime of PEDOT:PSS/PVDF/Ionic Liquid Actuators', ACS Applied Materials & Interfaces, 2015, 7 (36), pp. 19966-19977.

H:P10  Two-way Shape Memory Behaviour of Electrospun Non-woven Mats prepared from Sol-gel Crosslinked Poly(e-caprolactone)
S. PANDINI1, S. AGNELLI1, A. MERLETTINI2, C. GUALANDI2, M.L. FOCARETE2, M. TOSELLI3, K. PADERNI4, M. MESSORI4, 1Dipartimento di Ingegneria Meccanica e Industriale, Università degli Studi di Brescia, Brescia, Italy; 2Dipartimento di Chimica "G. Ciamician”, Università degli Studi di Bologna, Bologna, Italy; 3Dipartimento di Chimica Industriale "Toso Montanari", Università degli Studi di Bologna, Bologna, Italy; 4Dipartimento di Ingegneria "Enzo Ferrari", Università degli Studi di Modena e Reggio Emilia, Modena, Italy

The development of shape memory materials, obtained through electrospinning of polymer fibers, allows to prepare miniaturized systems with controlled micro-structures, whose macroscopic shape and microstructural arrangements may be significantly transformed through an external stimulus. Further, when non-woven fabrics are made of semicrystalline networks, beside enhancing their recovery ability, it may also be possible to provide them a two-way shape memory behavior, i.e. the ability to reversibly change between two different shapes within heating-cooling cycles. Non-woven fibrous mats were prepared by combining electrospinning process and sol-gel reaction, starting from a poly(ε-caprolactone) solution of partially crosslinked α,ω- triethoxysilane-terminated poly(ε-caprolactone). The mats, made of continuous, randomly oriented 2 μm-thick fibers, were obtained with two different crosslinking densities. The effect of the crosslinking extent was correlated to the mechanical and two-way shape memory properties of the materials. Thermo-mechanical cycles, consisting in the application of a fixed stress and heating/cooling cycles  from above melting to below the crystallization temperature, allowed to quantify the two-way response. The mats are capable of reversible elongation/contraction cycles, with overall strain variations of 35%, under the application of few hundreds of kPa; a lower stress was required to obtain a same strain variation in case of the less crosslinked system. An ex-situ SEM analysis, allowed to describe the microstructural evolution accompanying the two-way effect, showing that fibers reversibly change between randomly oriented configurations and highly oriented ones.

H:P11  Deformation and Recovery Properties of Shape Memory Polymer Composites Tube
TIANZHEN LIU, LIWU LIU, YANJU LIU, JINSONG LENG, Department of Astronautical Science and Mechanics, Harbin Institute of Technology (HIT), Harbin, P.R. China

As a typical smart material, shape memory polymers (SMPs) and their composites have the capability of variable stiffness in response to external stimuli, such as heat, electricity, magnetism and solvents. In our work, a new kind of shape memory polymer composites (SMPC) tube is developed, which possesses considerable flexibility under high temperature and rigidity under low temperature. In this paper, the elastic modulus and glass transition temperature of an epoxy-based SMPC material reinforced with carbon fiber are obtained under different temperature by tensile tests and dynamic mechanical analysis (DMA). Then, the SMPC tube is fabricated by filament winding technology. Resistor heater is applied to heat the device and actuate the shape recovery process. Finally, compression tests and recovery process are performed under different temperature, during which the depth and recovery time are recorded. In addition, the packaging efficiency of tube is investigated through a series of stowage and redeployment tests. Due to the flexible and expandable properties, the SMPC tube has great potential in future aerospace field, such as satellite and space station.

H:HP13  Shape-memory Polymers: 3D Constitutive Modeling and Simulation of Biomedical Devices
G. SCALET, E. BOATTI, F. AURICCHIO, DICAr, University of Pavia, Pavia, Italy

Shape-memory polymers (SMPs) belong to the class of smart materials which are able to store a temporary shape and to recover the original shape upon an external stimulus. Among the others, the most common SMPs are those in which the shape-recovery is thermally-induced. Thanks to their fascinating properties, SMPs are promising materials for many applications in, e.g., the biomedical, aerospace, and packaging field.
The present work aims to introduce a three-dimensional finite-strain macroscopic model for thermo-responsive SMPs to be used for the simulation of complex devices. Model equations are formulated within a thermodynamically consistent mathematical framework. The proposed model addresses new material features to increase its applicability over a broad variety of polymer types and conditions. Several numerical simulations, including the application to SMP biomedical devices, are reported. The model is shown to be able to reproduce both heating-stretching-cooling and cold drawing shape-fixing procedures and the non-ideal behavior of real SMPs. Comparison with experimental data taken from the literature is also provided to validate the model.

Cimtec 2016

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