Electro-active Interpenetrating Polymer Networks actuators and strain sensors: Fabrication, position control and sensing properties

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Abstract

Electro-active interpenetrated polymer networks (IPN) actuators were fabricated by oxidative polymerization of 3,4-ethylenedioxythiophene within a flexible Solid Polymer Electrolytes (SPEs) combining poly(ethylene oxide) (PEO) and Nitrile Butadiene Rubber (NBR). The electronic conductivity and the morphology of the interpenetrated poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes within the SPE were characterized. The free strain as well as the blocking force was investigated as a function of the PEDOT and ionic liquid contents. Furthermore the strain control was demonstrated by using a Pulse Width Modulation technique. These materials act also as displacement sensors. It has been shown that applying strain generates a proportional change in voltage.

Introduction

Electronic conducting polymers (ECP) have interested numerous research groups all over the world since they represent a promising active material to elaborate biomimetic actuators and sensors, i.e. realizing motions and sensing, similar to those of living systems [1]. Actuators are based on ECP dimensional changes generated by the ion expulsion/inclusion motions during oxido-reduction reactions whereas strain sensor properties originate from electric potential changes during external mechanical stress [1], [2], [3]. ECP based actuators and sensors working in air are usually built in a configuration where the internal layer is a Solid Polymer Electrolyte (SPE) containing ions sandwiched between two ECP layers (ECP//SPE//ECP) [4], [5], [6].

Interpenetrating Polymer Networks (IPNs) represent an interesting class of material for SPE applications since they can improve physical properties such as mechanical strength and elasticity without impairing the ionic conductivity capacity [7]. Previously we have demonstrated that the synthesis of flexible Solid Polymer Electrolytes (SPEs) combining poly(ethylene oxide) (PEO) and Nitrile Butadiene Rubber (NBR) in IPN architecture can be very promising for the elaboration and the integration of ECP actuators [8]. Conducting Interpenetrating Polymer Networks (C-IPNs) actuators have been prepared from oxidative polymerization of the 3,4-ethylenedioxylthiophene (EDOT) monomer within the PEO/NBR IPN matrix. A pseudo-trilayer configuration has been obtained with PEO/NBR IPN sandwiched between two interpenetrated PEDOT electrodes. This type of actuator can operate in open air if the SPE provides the source of ions required for actuation. Therefore, before operation, the materials are immersed in an ionic liquid for a given length of time. After the swelling step the NBR/PEO based SPE can play the role of ion reservoir during actuation in open air.

The primary contribution of this study is to report on the influence of the EDOT polymerization experimental conditions on the C-IPN actuators performances. Then, in order to get rid of the back relaxation during actuation, displacements are controlled using the Pulse Width Modulation signal (PWM) technique. Finally, we report for the first time on the mechanical sensor abilities of this specific class of materials, i.e. C-IPN materials.

Section snippets

Materials

Anhydrous iron III chloride (Acros), 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)-imide (EMITFSI) (from Solvionic), were used without further purification. 3,4-Ethylenedioxythiophene (EDOT) (Bayer) was distilled under reduced pressure prior to use.

C-IPN synthesis

The PEO/NBR IPN films were synthesized according to the procedure described elsewhere [8]. PEO/NBR IPN films were soaked into pure EDOT up to 155 wt% and their surface was wiped off with filter paper afterward. The swollen films were then

Conducting IPN synthesis and characterization

C-IPN actuator is a pseudo-trilayer actuator in which a SPE is sandwiched between two interpenetrated PEDOT electrodes. In a previous study PEO/NBR/PEDOT IPN was prepared as our first attempt to design robust conducting IPN actuators [8]. In this present study, the influence on the actuation properties of PEDOT content as well as the electrode morphology is examined. A series of actuators was therefore prepared by dipping EDOT swollen PEO/NBR IPNs (155 wt% EDOT) into a FeCl3/water solution for

Conclusions

In this study the influence of PEDOT content on C-IPN actuation properties has been investigated. The PEDOT content in the C-IPN was adjusted in order to get the best actuation performances, while keeping the two PEDOT electrodes well separated. C-IPN actuator with a PEDOT content of 22 wt%, and swollen with EMITFSI up to saturation (134%), showed a strain of 2.4% and a blocking force of 30 mN. For real application, the actuator position needs to be fully controlled and feedback is essential in

Acknowledgements

This work was financially supported by Brain Vision Systems (BVS) and ANRT CIFRE number of contract 1201/2008. This research was partly supported by the European Scientic Network for Artificial Muscles (ESNAM) COST Action (MP1003)

Nicolas Festin received his PhD degree (2012) in Polymer chemistry from Cergy-Pontoise University. He then joined Prof. Fichet's group in LPPI laboratory Cergy-Pontoise University as a Post-doctoral. His research interests include synthesis and application of Interpenetrated Polymer Network (IPN) and electronic conducting polymer for electrochemical devices such as fuel cell energy, electrochromic devices and actuators.

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    Nicolas Festin received his PhD degree (2012) in Polymer chemistry from Cergy-Pontoise University. He then joined Prof. Fichet's group in LPPI laboratory Cergy-Pontoise University as a Post-doctoral. His research interests include synthesis and application of Interpenetrated Polymer Network (IPN) and electronic conducting polymer for electrochemical devices such as fuel cell energy, electrochromic devices and actuators.

    Cedric Plesse received his PhD (2004) degree in Polymer Chemistry from Cergy-Pontoise University. His research focused on conducting polymer based Interpenetrating Polymer Networks (IPN) to develop electrochemical actuators. He joined Prof. Mario Leclerc’ s group in Laval University (Quebec, Canada) as a postdoctoral fellow (2004–2006) working on the development of conducting polymers based DNA sensors. He joined LPPI at the University of Cergy-Pontoise as an assistant professor in 2006. His research currently deals with pi-conjugated molecular glasses for hybrid photovoltaic devices and conducting IPN based actuators, from material synthesis to electrochemomechanical characterizations on a macro and micro scale.

    Patrick Pirim is engineer in electronic since 1977 from ENSEA (France). After 2 years of hardware development in a SME and 5 years in MATRA as project manager in remote sensing system, he started his own SME in 1986 with idea to use histogram computation and bio-inspired process done in electronic component. A first patent, 1987, explains the spatio-temporal histogram computation. This new process was upgraded up today with the generic visual perception processor conception using tree modalities (global, dynamic, and structural) described in many patents and publish in 2013 at Living machines 2013.

    Claude Chevrot received his PhD degree (1975) on analytical chemistry of organometallic compounds from Paris University. Since 1980, he worked on the synthesis, the characterization and the opto-electronic properties of electronic conducting polymers for various applications (OLEDs, photovoltaic cells, supercapacitors). Appointed as full professor at the University Paris nord (1990) and then at the university of Cergy Pontoise, he developed since 2000 electrically stimulable Interpenetrating Polymer Networks for actuator and electrochromic devices in the visible and near infrared ranges. He is currently Emeritus Professor at Cergy-Pontoise University.

    Frederic Vidal received his PhD (1995) degree on Polymer Chemistry from Lyon University. He then joined Prof. German's group in Eindhoven Technology University as a postdoctoral fellow (1995–1996). His interest focused on the emulsion polymerization. He joined Cergy-Pontoise University as an associate professor in 1997 in the laboratory of Profs. D. Teyssié and C. Chevrot ad he was appointed as a full Professor in 2008. His research currently includes development of Interpenetrating Polymer Networks (IPNs), conducting polymer and conducting IPN based electrochemical devices such as electrochromic devices or actuators.

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