Biomedical Engineering Reference
In-Depth Information
to these models, the exponent is affected by the rigidity of the fiber network.
From our experimental observation, an exponent of
1.5 holds for agarose gel
networks, which is not far from the predictions [13]. For small-molecule organogels
supported by fiber networks of branched fibers, the fiber networks are more rigid
than polymer networks. This could explain the smaller exponent of
−
−
0.49 for
GP-1/ISA gel.
On the basis of finite element analysis, it was demonstrated in our work that for
a single spherulite the elastic modulus
G
can be correlated to the microstructure
of the spherulite as log(
G
)
(
l
/
r
)
1.71
) [9]. Here,
l
is
the fiber length (branching distance
ξ
)and
r
is the radius of fiber cross-section.
This work indicates that the elastic modulus is affected not only by the fiber length,
but also by the fiber cross-section. When l/
r
is smaller than 20,
G
increases
quickly with decrease in l/
r
. When l/
r
is greater than 20,
G
tends to level off.
This implies that when fiber is short and thick, the radius of fiber cross-section
has a significant impact on the elasticity of the network. Once the fiber becomes
longer (less branched),
r
has a negligible effect on
G
. It is noteworthy that the
theoretical correlation obtained is based on a single spherulitic fiber network. In
reality, the network of a material normally consists of many spherulites rather
than a single spherulite; a decrease in the power exponent will be expected
for a material if the interactions between the neighboring spherulites are weak.
However, if strong interactions exist, the entire network will behave like a single
fiber network.
8.31 (i.e.,
G
∼
=
1.71 log (
l
/
r
)
+
2.5.3
Improving the Elasticity of a Material by Converting its Multi-Domain Network into an
Interconnecting (''Single'') Fiber Network
Converting the spherulitic fiber networks of a material into an interconnecting
fiber network can improve its elasticity if the interactions between the spherulites
are weak. For example, by converting the spherulitic fiber network of 2 wt%
GP-1/PG gel into a three-dimensionally interconnecting fiber network through
tuning the thermodynamic driving force, the elasticity of the material was more
than doubled (increased from 2.1
10
5
Nm
-2
) [12a]. With the seed-
ing approach, the elasticity of the 3 wt% GP-1/PG gel was also doubled when
the network was converted from a spherulitic pattern to an interconnecting net-
work [34]. For the 3 wt% GP-1/octanol system, after ultrasound treatment the
elasticity of the resulted material with an interconnecting fiber network was
3600 N m
-2
, which is two orders of magnitude higher than that of the paste
obtained without any treatment [41]. In brief, our results showed that confer-
ring an interconnecting fiber network to a material without a self-supporting
network or with mechanically weak (not well-integrated) fiber network is an ef-
ficient approach to enhance its elasticity. It also provides an approach to the
creation of novel supramolecular materials from otherwise useless systems such
as pastes.
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5
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