Biomedical Engineering Reference
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induced strain can operate at frequencies higher than 100 kHz, resulting in a very high elastic power
density compared with other EAP materials.
The irradiation of P(VDF-TrFE) into a relaxor ferroelectric with high electrostriction also
introduces many undesirable defects to the copolymer including the formation of crosslinkings,
radicals, and chain scission (Mabboux and Gleason, 2002; Bharti et al., 2000). By a proper
molecular design which enhances the degree of molecular level conformational changes in the
polymer, terpolymers are produced that can exhibit a higher electromechanical response than the
high energy electron irradiated copolymer (Zhang et al., 2004).
Ferroelectric EAP polymer actuators can be operated in air, vacuum, and water. To reduce the,
level of voltage that is needed to activate the ferroelectric EAP, Zhang et al. (2004) used an all-
organic composite with organic particulates that have a high dielectric constant (
K
>
10,000).
These researchers used a blend of the particulates in a polymer matrix to increase the dielectric
constant from single digits to the range from 300 to 1,000 (at 1 Hz). This approach led to an EAP
that requires significantly lower voltage as predicted by the author (Section 14.2.2 in Bar-Cohen,
2001). For example, a strain of about 2% is generated by a field of 13 V/mm for a CuPc-PVDF-
based terpolymer composite having an elastic modulus of 0.75 GPa. A photographic view of this
EAP in passive and activated states is shown in Figure 10.3. One of the challenges to using this
material in practical applications is the large dielectric losses involved.
10.3.1.3
Electrostrictive Graft Elastomers
In 1998, a graft-elastomer EAP was developed at NASA Langley Research Center (Su et al., 1999).
This EAP material exhibits a large electric-field-induced strain due to electrostriction (Zhang
Figure 10.3 A photographic view of ferroelectric EAP in passive (left) and activated (right) states. The material
was constructed in a bimorph configuration to turn the contraction to bending.
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