Biomedical Engineering Reference
In-Depth Information
Contact electrode
+
IPMC
-
Pt particles
Pt
Off
IPMC
+
IPMC
-
ON
FIGURE 6.10
Bending of an ionic gel strip due to an imposed electric field gradient.
The proposed theoretical development considers the spatial distributions of cat-
ions and anions within the gel network before and after the application of an electric
field. The model will then derive exact expressions relating the deformation charac-
teristics of the gel as a function of electric field strength or voltage gradient; gel
dimensions and physical parameters, such as diffusivities of cations
D
GM
and anion
D
GP
; elastic modulus
E
; temperature
T
; charge concentration of cations
C
GM
and
anions
C
GP
; resistance
R
g
; and capacitance
C
g
of the gel.
In the following sections, a model is presented for the deformation of a hydrated
and swollen ionic gel strip chemically plated by a conductive medium and placed
in a transverse electric field gradient.
Suppose a long, thin, straight strip of an ionic gel of length
l
g
, width
w
g
, and
thickness
t
g
is bent into a curve strip by the presence of a transverse electric field across
its thickness
t
g
. Figure 6.10 clearly depicts the schematics of large bending deformation
of a strip of IPMNC and the basic actuation configuration under an electric field.
This load can easily be applied by redistribution of fixed and mobile charges in
an ionic gel due to the presence of an electric field. It is further assumed that, initially,
the gel is in a natural bending-stress-free state equilibrated with a pH = 7.
For a discussion on the effect of pH on swelling of gels or the relationship
between the strain in a gel and the pH of its environment, see Shahinpoor (1993c),
Tanaka et al. (1982), and Umemoto et al. (1991). Now, referring to figure 6.11, note
that the strain
ε
(defined as the ratio of the actual incremental deformation (
δ
l
) to
the initial length (
l
0
) is given by:
εε κηλ
=+
=−
1,
(6.19)
c
E
where
ε
c
is the strain along the neutral central line (line going through the centers of
areas of all cross-sections)
