Electroactive polymer materials

Wirsen A (1987) Electroactive polymer materials, Technomic, Basel... 

Non-ionic polymer gel, swollen with dielectric solvent, can be extremely deformed as is the case for non-ionic polymer plasticised with non-ionic plasticiser. Instead of the charge-injected solvent drag as a mechanism of the gel actuation, the principle is based on local asymmetrical charge distribution at the surface of the gel18. The mechanism can also be applied to non-ionic elastomers in which the motion of the polymer chain is relatively free. In spite of their many difficulties for practical actuators, polyelectrolyte gels and related materials are the most interesting electroactive polymer materials. 

Wirsen, A. Electroactive Polymer Materials. Technomic Publishing Co., Inc., Lancaster, 1990. 

The ability to lock in strain is very important for applications wherein the device must hold its actuated state for an extended period of time. Conventional dielectric materials consume energy when actuated due to current leakage through the film, and can succumb to premature breakdown when held at high strain for an extended period of time. By locking in the actuated shape, BSEPs can hold their actuated shape without draining power and can maintain that shape indefinitely without failure. This combination of properties places BSEP materials at the forefront in terms of electroactive polymer materials for artificial muscle applications. 

Active research scientists are very busy people, and the editor has been fortunate to have been able to persuade a number of the leading contributors to the development and understanding of electroactive polymer materials to contribute to this project. I thank them for their labors and for the first-rate contributions produced. 

In Chapter 9, Bartlett and Cooper discuss the applications of electroactive polymers in bioelectrochemistry and bioelectronics. This is a very exciting and rapidly developing field, and it is proper that the volume includes this topic. Electroactive polymer materials will feature strongly in future developments in this area. Again Bartlett and Cooper have made major contributions in this field. 

Conclusively, there still remains a lot of research to be done in the field of the electroactive polymer materials. However, as we have a solid understanding of the fundamentals, the research will be focused more on the practical applications. Here we have only demonstrated a few. Given the favorable biocompability of the materials, there is a great potential for a broad spectrum of biomimetic applications in the future. 

FIGURE 1.68. A flowchart outlining the mode of examining electroactive polymer materials using complex impedance spectroscopy. 

An important feature of the electroactive polymer materials is the presence of two different kinds of mobile charge carriers, electronic and ionic. These polymers constitute mixed conductors. As in the case of ionic transfer phenomena in electrolyte solutions, there are generally two reasons for coupling between fluxes of different charge species. First creation in the concentration gradient of a charged species must be compensated by a redistribution of other components to retain the local electroneutrality of the system. Another factor is an electric field inside the polymer phase whose distribution is adjusted to the fluxes of charged species in a self-consistent way. 

Besides the possibility of inserting fluorescent substituents in only one monomer unit, such as pyrrole or thiophene, it is noteworthy that suitable fluorescent groups have been appended in dimeric or trimeric monomer systems. Using this approach, Cihaner and Algi have initiated a programme aimed at the design and synthesis of photo- and electroactive polymer materials based on 2,5-di(2-thienyl)pyrroles (SNS). This system consist of thiophene and pyrrole rings interconnected by their a-positions and exhibit intense blue emission upon irradiation. They have reported the synthesis and characterisation of a series of novel fluorescent and electrochromic polymers based on N-substituted... 

Polymer gel is an electroactive polymer material. There are various types of electroactive polymeric materials. As mentioned in the above section, polyelectrolyte is one of them and is most commonly investigated as an electroactive gel. We will come back to discuss this material in more detail in the next section. 

In the case of electric field application, the gels usually bend, because the field application induces asymmetric charge distribution and hence the asymmetric strain in the gel. Asymmetric charge distribution can easily be induced in polyelectrolyte gels, and this is why polyelectrolyte gel has mainly been investigated as on electroactive polymer material (see Fig. 2.11). 

Carlsson D, Jager E, Krogh M, Skoglund M (2007) Systems, device and object comprising electroactive polymer material, methods and uses relating to operation and provision thereof Patent W02009038501... 

Kawamura J, Hattori K, Mizusaki J. In Hashmi SA, Chandra A, Khare N, Chandra A, editors. Electroactive polymer materials and devices. Allied Publishers 2007. p. 144. 

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