Biomedical Engineering Reference
In-Depth Information
4
Ionic Polyacrylonitrile
Chemoelectromechanical
Artificial Muscles/
Nanomuscles
4.1
INTRODUCTION
This chapter covers the fabrication, characterization, testing, and application of
chemo (pH-activated) electromechanical artificial muscles made from ionic
p
oly-
itrile, or simply PAN, material. PAN in its nonionic form can commercially
be obtained under the trade name Orlon™. It is made by polymerizing acrylonitrile
monomer:
a
crylo
n
---CH
CH---CH
CH---CH
CH---CH
CH---
2
2
2
2
|
|
|
|
(4.1)
CN
CN
CN
CN
As defined in the Merck Index, PAN is made of white fibers that stick at 235
°
C.
It becomes yellow at ironing temperatures above 160
C. It has flammability similar
to that of rayon and cotton. More importantly, it has very good resistance to mineral
acids and excellent resistance to common solvents, oils, greases, neutral salts, and
sunlight. It has fairly good resistance to weak alkalides, but is degraded by strong
alkalides. It also resists attacks by molds, mildew, and insects.
PAN material is primarily used in the textile industry to manufacture clothing
fabrics and artificial silk. Lately, these materials can be obtained in fibers made of
thousands of smaller filaments and fibrils, each less than 10
°
m in diameter. Com-
panies like Mitsubishi Rayon Co. have constantly improved their techniques in
manufacturing better fibers of PAN.
As the industry moves toward manufacturing these materials in finer and smaller
filaments, the potential for improved artificial muscle fibers also increases, as will
be explained later in this chapter. Included in this chapter is a method of encapsu-
lation and activation by electric field of PAN fiber bundle artificial muscles.
µ
4.2
PAN FABRICATION
PAN fibers are initially nonactive and require a combination of physical as well as
chemical processes to convert them into a gel-like contractile fiber material. To
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