Dr. Steen Skaarup Profile

Dr. Steen Skaarup

Associate Professor at Danmarks Tekniske Univ

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Publications (4)

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Proceedings Article | 28 July 2003 Paper

Polypyrrole actuators for tremor suppression

Steen Skaarup, Naja Mogensen, Lasse Bay, Keld West

Proceedings Volume 5051, (2003) https://doi.org/10.1117/12.484406

KEYWORDS: Actuators, Polymers, Molecules, Ions, Sensing systems, Crystals, Sodium, Polymeric actuators, Electroactive polymers, Electrodes

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Neurological tremor affecting limbs can be divided into at least 6 different types with frequencies ranging from 2 to about 20 Hz. In order to alleviate the symptoms by suppressing the tremor, sensing and actuation systems able to perform at these frequencies are needed. Electroactive polymers exemplify "soft actuator" technology that may be especially suitable for use in conjunction with human limbs. The electrochemical and mechanical properties of polypyrrole dodecyl benzene sulphonate actuator films have been studied with this application in mind. The results show that the time constants for the change of length and for the stiffness change are significantly different; the stiffness change being about 10 times faster. Both force measurements and Electrochemical Quartz Crystal Microbalance measurements indicate that the actuation process is complex and involves at least two different processes. The EQCM results make it possible to formulate a hypothesis for the two different time constants: Sodium ions enter the polymer correlated with a fast mass change that probably involves a few (~4) strongly bound water molecules as well. On further reduction, about 10 additional water molecules enter the polymer in a slower process driven by osmotic pressure. Earlier work has tended to focus on achieving the maximum length change, therefore taking the time needed to include all processes. However, since the slower process described above is associated with the lowest strength of the actuator, concentrating on the faster stiffness change results in only a small reduction in the work done by the actuator. This may make actuation at higher frequencies feasible.

Proceedings Article | 16 July 2001 Paper

Properties of polypyrrole doped with alkylbenzene sulfonates

Lasse Bay, Steen Skaarup, Keld West, Tanja Mazur, Ole Joergensen, Helle Rasmussen

Proceedings Volume 4329, (2001) https://doi.org/10.1117/12.432632

KEYWORDS: Polymers, Ions, Doping, Polymer thin films, Polymeric actuators, Sodium, Actuators, Carbon, Chemical species, Polymerization

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Conducting polymers such as polypyrrole (PPy) doped with large anionic detergents have high stability in aqueous systems. PPy can be reversibly oxidised and reduced electrochemically. The redox change of PPy is accompanied by a change in volume of the polymer. This is partly ascribed to take-up of ions and solvent molecules. This volume change can be used as a polymer actuator (artificial muscle) working in a narrow voltage range (less than 1 V). The properties of the PPy polymer are largely determined by the dopant ions and also by the deposition conditions and the substrate. A free-standing 10 micrometers thick film is prepared electrochemically at a constant current from an aqueous solution of pyrrole and sodium alkylbenzene sulfonate. The mechanical properties of the film (tensile strength and Young's modulus) and the reversible linear elongation between the oxidised and reduced states are measured. Alkylbenzene sulfonates with alkyl chain lengths between 1 and 22 carbon atoms are used as dopant anion. The films made with the different anions have highly different properties and are here compared to outline the influence of the size of the anion. A maximum in linear elongation is found for p-(n-octyl)benzene sulfonate and in conductivity for p-(n-butyl)benzene sulfonate.

Proceedings Article | 16 July 2001 Paper

Potential profile in a conducting polymer strip

Lasse Bay, Keld West, Nicolaos Vlachopoulos, Steen Skaarup

Proceedings Volume 4329, (2001) https://doi.org/10.1117/12.432690

KEYWORDS: Polymers, Oxygen, Actuators, Polymeric actuators, Artificial muscles, Diffusion, Gold, Nitrogen, Chemistry, Interfaces

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Many conjugated polymers show an appreciable difference in volume between their oxidized and reduced forms. This property can be utilized in soft electrochemically driven actuators, "artificial muscles". Several geometries have been proposed for the conversion of the volume expansion into useful mechanical work. In a particularly simple geometry, the length change of polymer strips is exploited. The polymer strips are connected to the driving circuit at the end of the strip that is attached to the support of the device. The other end of the strip is connected to the load. The advantage of this set-up is simplicity and that the maximum force generated in the polymer can be transferred directly to the load. There is, however, an inherent problem in this design that will be examined in this paper. If the potential of the reduced state is below that for oxygen reduction, only a finite length of the free-standing film will be fully reduced. This is due to the reduction of oxygen at the surface of the polymer competing with the reduction of the polymer. For a long strip, the potential will therefore approach the reduction potential of oxygen. This will lower the efficiency of the artificial muscles and complicate measurements on free-standing films. A model of the potential profile in a free-standing strip is derived. It is found that the active length (the length with a given potential change) of the polymer will scale as &sqrt;dσ/i_d. (d is the thickness, σ the conductivity of the film, and id the diffusion limited current density for oxygen reduction). The active length is typically of the order of millimeters. The model is compared with measurements on a strip of polypyrrole doped with dodecylbenzene sulfonate.

Proceedings Article | 28 May 1999 Paper

Performance of polymer-based actuators: the three-layer model

Mohammed Benslimane, Peter Gravesen, Keld West, Steen Skaarup, Peter Sommer-Larsen

Proceedings Volume 3669, (1999) https://doi.org/10.1117/12.349667

KEYWORDS: Actuators, Polymers, Polymeric actuators, Performance modeling, Polymer thin films, Thin films, Metals, Composites, Artificial muscles, Device simulation

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Conducting polymers show volume changes during electrochemical doping. Their high strength make them potential candidates for being used as artificial muscles. We consider actuators based on three-layer structures consisting of a passive polymer substrate sheet, a thin metal film electrode and a thin film of conducting polymer. In this paper we describe our Three- layer model to study the performance of an actuator based on the transduction of bending to linear movements. We show calculated results for an undulator and C-block characterized, respectively, by a flat and semi-circular shape in the relaxed state. Knowing the mechanical parameters of the considered materials, we evaluate the efficiency of the composite structure in terms of the performed stroke and work. The model shows that the undulator contracts in a nonlinear way with respect to the relative expansion of the materials, whereas the C-block is approximately linear. Contractions as large as 80% and 45% are obtained with the undulator and C-block, respectively. Although the C-block performs better than the undulator in terms of linearity, the undulator is easier to design and manufacture due to its flat shape in the relaxed state.

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