Biomedical Engineering Reference
In-Depth Information
16.2 ELECTROACTIVE POLYMERS
The term “electroactive polymers” identifi es a broad family of synthetic polymers sharing, as a
common and fundamental feature, a capability of changing dimensions and/or shapes when a suit-
able electrical input is applied. Accordingly, they are studied as soft materials with intrinsic actua-
tion properties. They are particularly attractive for their ability to show sizable active strains and/or
stresses, large compliance, low density, low power consumption, ease of processing, and low costs.
Due to such properties, EAP are currently considered the most promising class of materials for
pseudomuscular actuators: their potential to implement a functional biomimesis of natural muscles
is studied in the perspective development of future “artifi cial muscles” [1,2].
EAP can be classifi ed according to a division into two main classes: ionic EAP and electronic
EAP [1,2]. The fi rst group comprehends materials whose actuation principles are based on diffu-
sions of ions and solvents (as better clarifi ed in the following paragraphs), while electronic EAP are
activated (according to different mechanisms) by the direct application of an electric fi eld. Both these
groups can be further divided, depending on the specifi c actuation mechanism and the related types
of materials. In particular, ionic EAP comprehend polymer gels, ionic polymer-metal composites
(IPMC), conducting polymers and carbon nanotubes (which are conventionally classifi ed as EA P, even
though they are just nonpolymeric macromolecular materials). Electronic EAP include piezoelectric
polymers, electrostrictive polymers, dielectric elastomers, and fl exoelectric polymers. Table 16.1 sum-
marizes this classifi cation and reports, for each group, the most studied examples of polymers.
Although these materials have been known since many decades, they have found limited uses so
far despite their potentialities. This should be mainly attributed to their scarce development toward
mature technological levels. However, promising recent results in materials science, materials
processing, and confi guration design for such polymers are encouraging the concentration of efforts
for a concrete exploitation of their performance, as briefl y reported in the following discussion.
TABLE 16.1
Classifi cation and Examples of EAP
EAP Class
EAP Subcategories
Examples of Materials
Ionic EAP
Polymer gels
Poly(acrylic acid) (PAAc)
Poly(vinyl alcohol) (PVA)
Modifi ed Poly(acrylonitrile) (PAN)
Ionic polymer-metal
composites (IPMC)
Nafi on/Pt
Conducting polymers
Poly(pyrrole) (PPy)
Poly(aniline) (PANi)
Carbon nanotubes
Single-walled nanotubes
Multiwalled nanotubes
Electronic EAP
Piezoelectric polymers
Poly(vinylidene fl uoride) (PVDF)
Electrostrictive polymers
PVDF-based copolymers, for example,
Poly(vinylidene fl uoride-trifl uoroethylene)
(P(VDF-TrFE)),
Poly(vinylidene fl uoride-hexafl uoropropylene)
(P(VDF-HFP))
Dielectric elastomers
Silicone elastomers
Acrylic elastomers
Polyurethane elastomers
Flexoelectric polymers
Liquid crystal elastomers
