Download Enhancement of MCF Rubber Utilizing Electric and Magnetic Fields

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Article
Enhancement of MCF Rubber Utilizing Electric and
Magnetic Fields, and Clarification of
Electrolytic Polymerization
Kunio Shimada
Faculty of Symbiotic Systems Sciences, Fukushima University, 1 Kanayagawa, Fukushima 960-1296, Japan;
[email protected]; Tel.: +81-24-548-5214
Academic Editors: Vamsy P. Chodavarapu and Andreas Hütten
Received: 10 February 2017; Accepted: 31 March 2017; Published: 4 April 2017
Abstract: Many sensors require mechanical durability to resist immense or impulsive pressure and
large elasticity, so that they can be installed in or assimilated into the outer layer of artificial skin on
robots. Given these demanding requirements, we adopted natural rubber (NR-latex) and developed
a new method (NM) for curing NR-latex by the application of a magnetic field under electrolytic
polymerization. The aim of the present work is to clarify the new manufacturing process for NR-latex
embedded with magnetic compound fluid (MCF) as a conductive filler, and the contribution of the
optimization of the new process for sensor. We first clarify the effect of the magnetic field on the
enhancement of the NR-latex MCF rubber created by the alignment of magnetic clusters of MCF. Next,
SEM, XRD, Raman spectroscopy, and XPS are used for morphological and microscopic observation of
the electrolytically polymerized MCF rubber, and a chemical approach measuring pH and ORP of the
MCF rubber liquid was used to investigate the process of electrolytic polymerization with a physical
mode. We elucidate why the MCF rubber produced by the NM is enhanced with high sensitivity
and long-term stability. This process of producing MCF rubber by the NM is closely related to the
development of a highly sensitive sensor.
Keywords: sensor; electrolytic polymerization; magnetic field; magnetic cluster; natural
rubber; magnetic compound fluid (MCF); magnetic fluid; isoprene; filler; electrical resistivity;
oxidation-reduction reaction
1. Introduction
Sensors are currently used in many fields to detect force, temperature, pressure, etc. However, in
robotics, sensors must have the mechanical durability to withstand immense or impulsive pressure,
as well as large elasticity or extensibility. Certain sensors should be suitable for installation as an
outer layer on robots, or for assimilation into an artificial skin. These characteristics are not, of
course, limited to the sensors in robotics; sensors with mechanical durability are also required in
other engineering fields. Regarding the concept of a skin sensor, there has been only a few general
investigations [1]. The paradigm is that the sensor should be based on the effective control or
management of human-machine systems. One new natural-contact biosensor has been designed
as an interface between humans and machines for nonintrusive and real-time sensing. Although this
sensor utilizes microelectromechanical systems (MEMS) or nanoelectromechanical systems (NEMS) to
enable miniature sensors, flexibility remains a fundamental problem.
Therefore, as described above, there is a need for a suitable rubber material with the durability to
withstand impulsive, immense or repeated force while maintaining large elasticity and extensibility [2].
Researchers have examined many materials in the search for a sensor made of rubber: silicon oil
rubber [3–8], chloroprene [9], styrene-butadiene [10], acrylonitrile butadiene [11], nitrile butadiene
Sensors 2017, 17, 767; doi:10.3390/s17040767
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rubber [12], and natural rubber (NR-latex) [13–16]. Shimada proposed a new sensor made of silicon-oil
rubber that uses magnetic compound fluid (MCF) as filler (called MCF rubber) [17]. MCF was devised
in 2001 as a colloidal fluid containing Fe3 O4 sphere particles on the order of 10 nm, coated by oleic
acid and other metal particles such as Ni, Fe, and Cu, on the order of 1 µm. These particles are
dispersed in a solvent such as water, kerosene, or silicone oil to compound a magnetic fluid (MF),
which is an ordinary intelligent fluid responsive to the magnetic field with Fe3 O4 particles. When a
magnetic field is applied, the Fe3 O4 particles play a bonding role among the metal particles, causing
numerous metal and Fe3 O4 particles to aggregate [18]. Due to these magnetic clusters, MCF is useful
for many engineering applications [19]. The mechanism of electric conductivity of silicon-oil type
MCF rubber is explained mainly by the percolation theory [20] and tunnel theory [21]. Percolation
threshold is significant factor in the former. Therefore, in the case of a small mass concentration of MCF
rubber, it is possible that electric conductivity is demonstrated by this theory. On the other hand, for a
large aggregation of particles with large aspect ratio, the latter theory can better explain the electric
conductivity of MCF rubber. Electrons jump between metal particles such as Fe3 O4 and Ni through
the barrier of non-conductive materials such as silicon-oil rubber and oleic acid coated around Fe3 O4 .
Silicon-oil type MCF rubber has a large electrical resistivity, however, which does not fulfill the
needs of a skin sensor. In order to obtain sensitivity at a shearing motion, such as touching a body
and scrubbing, a skin sensor requires high sensitivity, as shown by a previous investigation. When
two electrodes are set between skin rubber and supplied with voltage, the electric current flowing
inside the rubber can be measured. The electrical conductivity changed by the force applied on the
skin rubber is related to the degree of sensitivity.
In order to achieve the requirement of high sensitivity, we can enhance the sensitivity of MCF
rubber using NR-latex. NR-latex type MCF rubber is made by solidification under a constant
temperature (the drying method (DM)) and the application of a magnetic field. The DM has also
been used to produce ordinary, commercial, pressure-sensitive electrically conductive rubber (PSECR).
The application of the magnetic field causes the Fe3 O4 and metal particles to aggregate, and magnetic
clusters are created in NR-latex type as well as silicon-oil type MCF rubber. In general, water involved
in NR-latex plays an important role in electric conductivity, which is based on ionic conduction.
Therefore, owing to the filler and the water role, electric conductivity is superior to that of PSECR.
Furthermore, as shown in a previous investigation, NR-latex type MCF rubber has been evaluated the
following technical cases as a physical value: surface roughness of a hard plate surface with coarse
or smooth roughness in the range of Ra = 0.19–20.86 µm, which is related to finishing in precision
machinery industry; softness of a soft surface of texture of clothes, paper, gel, etc.; geometric shape
of concave and convex surface less than 5.7 mm in height, which is related to the evaluation of a
biological surface such as a fish, insect, etc.
NR-latex type MCF rubber made by the DM, however, has a problem in that deterioration occurs
in a short period of about a week. In addition, it has electrical resistivity on the order of 1 Ω·m [22],
which does not provide high enough sensitivity to fulfill the requirements for a skin sensor. Shimada
has proposed a new method (NM), which involves solidifying rubber using both magnetic and electric
fields. The rubber liquid is poured between electrodes, and a magnetic field is applied. NR-latex
without MCF is created as a thin film, and its thickness does not increase even with an extended
application of the electric field. With NR-latex MCF rubber, however, since the magnetic field is
applied along the same direction as the electric field line, the thickness increases substantially due to
the magnetic clusters. When the electric field or magnetic field is used alone, the electrical property
is less sensitive than with both, and the mechanical property is less extensible. These characteristics
have been shown in the case of a narrow electrode gap of 1 mm in previous studies [22]. It was also
clarified that NR-latex MCF rubber made with NM maintains a smaller electrical resistivity on the
order of 10−2 − 10−3 Ω·m from its creation to a period of more than a year. The NM is a noteworthy
and effective production method for avoiding deterioration due to aging.
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However, how enhancement of MCF rubber thickness is affected by various strengths of the
electric and magnetic fields has not yet been clarified. While the effect of the magnetic field on
electrolytic polymerization is significant, parameters including the magnetic field distribution and
magnitude have not yet been elucidated. In particular, the phenomenon of how MCF rubber is
enhanced by both fields at a large electrode gap remains unknown. Investigating the enhancement
of MCF rubber at a large electrode gap is related to clarifying the configuration of the enhancement.
Therefore, in the present paper, we first investigate the effect of the magnetic field on the metamorphosis
of MCF rubber by electrolytic polymerization.
On the other hand, magnetic clusters in the filler play a very significant role in the solidification
of MCF rubber with the NM. Controlling the applied magnetic field allows the magnetic clusters to
grow freely in the filler. In terms of whether the filler is magnetic or conductive, there have been
many studies on the use of polymers such as polymethyl methacrylate (PMMA). Carbon nanotubes
is another well-known filler [23]. The properties of a sensor can be controlled by the alignment of
the carbon nanotube with a magnetic field. The idea and concept of embedding fillers of carbon
nanotubes in a polymer is similar to that of the MCF rubber. Only the material of the solvent and
substrate is different. There has been research that looked at carbon nanotube in NR-latex [24–28].
Most of these studies, however, did not consider the alignment of the filler with the aid of a magnetic
field. As for NR-latex with magnetic particles other than carbon nanotube, there have also been some
studies [29–33]. A few dealt with the alignment of the filler with the help of a magnetic field. However,
investigation of filler alignment with the help of a magnetic field under electrolytic polymerization
such as the NM has not been clarified. Therefore, the present paper contributes to the optimization of
a new manufacturing process for an NR-latex embedded with MCF as a conductive filler by adding
electric and magnetic fields.
From mentioned above, the mechanisms behind the enhancement, long-term stability and
high sensitivity of electric conductivity have not been elucidated, nor the process of electrolytic
polymerization of NR-latex type MCF rubber been clarified. In our previous study [22], we could
only guess at the physical model. Clarification of this is related to the development of high-sensitivity
sensors, or skin sensors if you will. Therefore, the second aim of the present study is to investigate
the physical model, and the processes of enhancement of electrolytically polymerized MCF rubber
by morphological and microscopic examination, including observations by SEM, XRD, Raman
spectroscopy and XPS, as well as by chemical analysis including measurement of pH and ORP
of the MCF rubber liquid.
2. Effect of Magnetic Field on Metamorphosis of MCF Rubber
It is clear from the results of previous studies [22] that the thickness of MCF rubber solidified
by electric and magnetic fields depends on the magnetic field. However, the effect of magnetic field
distribution and magnitude on the enhancement of solidified MCF rubber is not clear. In our previous
study [22], we applied permanent magnets to the inside of plates to form the outer surface of each
plate. The liquid in the MCF rubber consisted of 12-g Ni powder, with particles on the order of µm and
pimples on the surface (No. 123, Yamaishi Co., Ltd., Noda, Japan), 3-g water-based MF with 50 wt %
Fe3 O4 (M-300, Sigma Hi-Chemical Co., Ltd., Tsutsujigasaki, Japan), 16-g NR-latex (Rejitex Co., Ltd.,
Atsugi, Japan), and 31-g water, poured into a container as shown in Figure 1. The mass concentration
of MCF rubber liquid was 21.7 wt % of Ni and Fe3 O4 particles. Electrodes were immersed in the liquid.
Permanent rectangular magnets, 10 mm × 15 mm in size, and 5-mm thick, were applied from outside
the container. An electric field held constant at 6 V voltage and 2.7 A electric current was supplied
between the plates for 30 min. The plates were held apart at a constant thickness with a spacer to
create an electrodes gap of 19 mm, and a 40 mm × 40 mm square made of stainless steel. In the case of
NR-latex only, and the application of an electric field without a magnetic field, the NR-latex created an
anode plate as a thin film, as shown in Figure 2a. In contrast, compounding MCF into the NR-latex with
an electric but not magnetic field increased the thickness of the MCF rubber to 2 mm at the electrode
Sensors 2017, 17, 767
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surface, double the NR-latex alone, as shown in Figure 2b. The enhancement of the MCF solidified
rubber at the lower side was due to the sedimentation of the MCF at the bottom of the container.
This enhancement did not depend on the magnetic field, as it was not applied. This phenomenon is
investigated later in the subsequent figure from these figures.
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Figure 1.
Schematic
used to
investigate the
effect of
magnetic field
Figure
Schematic diagram
diagram of
of experimental
experimental apparatus
apparatus
Figure 1.
1. Schematic
diagram
of
experimental
apparatus used
used to
to investigate
investigate the
the effect
effect of
of magnetic
magnetic field
field
distribution and
and magnitude
magnitude on
on the
the solidification
solidification of
of MCF
MCF rubber
rubber liquid
liquid by
by the
the NM.
NM.
distribution
distribution and magnitude on the solidification of MCF rubber liquid by the NM.
(a)
(a)
(b)
(b)
(c)
(c)
(d)
(d)
Figure 2. Photographs of electrolytically polymerized rubber: (a) NR-latex without application of a
Figure 2.
2. Photographs
of
polymerized
rubber: (a)
without
application
ofofa
Figure
Photographs
of electrolytically
electrolytically
polymerized
(a)NR-latex
NR-latex
without
application
permanent
magnet; (b) MCF
rubber without
application rubber:
of a permanent
magnet;
(c) MCF
rubber with
permanent
magnet;
(b)
MCF
rubber
without
application
of
a
permanent
magnet;
(c)
MCF
rubber
with
aapplication
permanentofmagnet;
(b) MCF
rubber
application
a permanent
(c) MCF
rubber
a permanent
magnet;
(d)without
image from
viewingoftransversely
tomagnet;
the electrode
of (c).
NRapplication
of
a
permanent
magnet;
(d)
image
from
viewing
transversely
to
the
electrode
of
(c).
with
of a permanent
magnet;
(d) image
from viewing
transversely
to the polymerization
electrode ofNR(c).
latex application
or MCF rubber
solidified and
attached
to an anode
electrode
after electrolytic
latex or MCF
rubber
solidified
and attached
to anananode
electrolytic polymerization
NR-latex
MCF
rubber
solidified
attached
anodeelectrode
electrodeafter
after
under theorconditions
in which
the and
electrodes
aretoimmersed
transversely
inelectrolytic
a containerpolymerization
(see Figure 1).
under the
the conditions
conditions in
in which
which the
the electrodes
electrodes are
are immersed
immersedtransversely
transverselyin
inaacontainer
container(see
(seeFigure
Figure1).
1).
under
Meanwhile, by compounding MCF into the NR-latex and applying both an electric and magnetic
Meanwhile, by compounding MCF into the NR-latex and applying both an electric and magnetic
field Meanwhile,
(Magnet 2 in
1), the thickness
of the
the NR-latex
MCF rubber
grew significantly
along and
the magnetic
byTable
compounding
MCF into
and applying
both an electric
field (Magnet 2 in Table 1), the thickness of the MCF rubber grew significantly along the magnetic
line, as 2shown
in 1),
Figure
2c. NR-latex
MCFgrew
generally
forms along
as a thin
film, and
its
field (Magnet
in Table
the thickness
of thewithout
MCF rubber
significantly
the magnetic
field
field line, as shown in Figure 2c. NR-latex without MCF generally forms as a thin film, and its
thickness
doesinnot
increase
even with
a longer
of theas electric
field.
Therefore,
the
line,
as shown
Figure
2c. NR-latex
without
MCFapplication
generally forms
a thin film,
and
its thickness
thickness does not increase even with a longer application of the electric field. Therefore, the
application of the magnetic field is necessary to create MCF magnetic clusters. Since the magnetic
application of the magnetic field is necessary to create MCF magnetic clusters. Since the magnetic
field is applied along the same direction as the electric field line, as may be seen in the figure, the
field is applied along the same direction as the electric field line, as may be seen in the figure, the
thickness of the MCF rubber grows substantially. The NM is related to so-called electric
thickness of the MCF rubber grows substantially. The NM is related to so-called electric
polymerization. The curing of NR-latex is promoted by the alignment of magnetic clusters in the filler
polymerization. The curing of NR-latex is promoted by the alignment of magnetic clusters in the filler
due to the application of a magnetic field under electrolytic polymerization.
Sensors 2017, 17, 767
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does not increase even with a longer application of the electric field. Therefore, the application of
the magnetic field is necessary to create MCF magnetic clusters. Since the magnetic field is applied
along the same direction as the electric field line, as may be seen in the figure, the thickness of the
MCF rubber grows substantially. The NM is related to so-called electric polymerization. The curing of
NR-latex is promoted by the alignment of magnetic clusters in the filler due to the application of a
magnetic field under electrolytic polymerization.
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Table 1. Magnetic field strength of Magnets 1–4.
Table 1. Magnetic
strength
Magnets
1–4. 3
Magnet 1field
Magnetof
Magnet
Table 1. Magnetic
field strength
of2 Magnets
1–4.
Location
Magnet 1 34.5
Magnet 248.3
Magnet
at b or c in Figure 1 (mT)
80.1 3
Location
Magnet 1
Magnet 2
Magnet 3
at b or c inat
Figure
1 (mT)1 (mT) 34.5
48.3 28.1
80.1
a in Figure
22.0
43.4
at b or c in Figure 1 (mT)
34.5
48.3
80.1
at a in Figure 1 (mT)
22.0
28.1
43.4
at a in Figure 1 (mT)
22.0
28.1
43.4
Location
Magnet 4
107Magnet 4
Magnet 4
55.3 107
107
55.3
55.3
Magnet 2 used to create the NR-latex shown in Figure 2c had a magnetic field strength of 188 mT,
Magnet 2 used to create the NR-latex shown in Figure 2c had a magnetic field strength of
2 used
to create
theone
NR-latex
shown 107.5
in Figure
had
a magnetic
strength
of
based Magnet
on previous
studies
[22]; the
at the surface
mT in2cthe
case
of a singlefield
magnet.
The size
188 mT, based on previous studies [22]; the one at the surface 107.5 mT in the case of a single magnet.
based on
previous
[22];2c
thecorresponded
one at the surface
in the case
magnet.
of188
themT,
solidified
MCF
rubberstudies
in Figure
d = 8107.5
mm mT
(diameter),
e =of13a single
mm (diameter),
The size of the solidified MCF rubber in Figure 2c corresponded d = 8 mm (diameter), e = 13 mm
The
solidified
MCF rubber
in Figure
2c corresponded
d = field,
8 mmMCF
(diameter),
= 13 mm
f=
1.5size
mm,ofgthe
= 13
mm in Figure
3. Before
application
of the electric
rubbere liquid
was
(diameter), f = 1.5 mm, g = 13 mm in Figure 3. Before application of the electric field, MCF rubber
(diameter),
f
=
1.5
mm,
g
=
13
mm
in
Figure
3.
Before
application
of
the
electric
field,
MCF
rubber
attracted to the electrodes attached to Magnet 2 on the outside of the container, as shown in Figure 4.
liquid was attracted to the electrodes attached to Magnet 2 on the outside of the container, as shown
liquid
attracted
tothe
the magnetic
electrodesfield
attached
to Magnet
on the
outside
of the container,
as shown
Ifin
both
awas
magnet
with
strength
1302 mT
in used
previous
studiesstudies
[22]
with
Figure
4. If both
a magnet
with the magnetic
field of
strength
of used
130 mT
in previous
[22] a
in
Figure
4.
If
both
a
magnet
with
the
magnetic
field
strength
of
130
mT
used
in
previous
studies
[22]
single
magnetmagnet
of 84.7ofmT
(Magnet
1) were
used,
the same
solidified
MCF
rubber
would
with asurface
single surface
84.7
mT (Magnet
1) were
used,
the same
solidified
MCF
rubber
wouldbe
with
a
single
surface
magnet
of
84.7
mT
(Magnet
1)
were
used,
the
same
solidified
MCF
rubber
would
created.
However,
if magnetic
field
strengths
ofof312
3),or
or490
490mT
mTwere
were
be created.
However,
if magnetic
field
strengths
312mT
mTand
and177.7
177.7 mT
mT (Magnet
(Magnet 3),
be created.
However,
if amagnetic
field
strengths
of mT
312 (Magnet
mT and 177.7
mT (Magnet
3),rubber
or 490 would
mT were
used,
[22]
together
with
surface
magnet
of
191.3
4),
solidified
MCF
not
used, [22] together with a surface magnet of 191.3 mT (Magnet 4), solidified MCF rubber would not
used,
[22]
together
with
a
surface
magnet
of
191.3
mT
(Magnet
4),
solidified
MCF
rubber
would
not
form.
1–4 are
are listed
listedin
inTable
Table1.1.We
Wefound
foundthat
thatMCF
MCFrubber
rubber
form.The
Themagnetic
magnetic field
field strength
strength of
of Magnets
Magnets 1–4
form. not
Thesolidify
magnetic
field too
strength
of
Magnets
1–4field
are listed
in Table
1.
We found
thatmagnetic
MCF rubber
would
when
large
of
a
magnetic
strength
was
applied.
When
field
would not solidify when too large of a magnetic field strength was applied. When magnetic field
would not
solidify
when
too50large
of
a magnetic
field strength
wasHowever,
applied. this
When
magnetic
fieldof
strength
was
less
than
about
mT,
MCF
rubber
liquid
solidified.
was
in
the
case
strength was less than about 50 mT, MCF rubber liquid solidified. However, this was in the case of
strength was less than about 50 mT, MCF rubber liquid solidified. However, this was in the case of
21.7
MCF rubber
rubberliquid
liquidwas
wasconsidered
consideredtotodepend
dependonon
21.7wt
wt%%particles.
particles.As
Asaaresult,
result, the
the solidification
solidification of MCF
21.7 wt % particles. As a result, the solidification of MCF rubber liquid was considered to depend on
magnetic
field
strength.
magnetic field strength.
magnetic field strength.
Figure3. 3.
Schematic
diagram
of MCF
rubber
solidified
using
The for
position
for
Figure
Schematic
diagram
of MCF
rubber
liquidliquid
solidified
using the
NM.the
TheNM.
position
measuring
Figure 3.
Schematic
diagram
of MCF
rubber
liquid
solidified
using
the
NM.
The position
for
measuring
magnetic
field
distributions
shown
in
Figure
5
is
also
delineated.
magnetic
field
distributions
shown
in
Figure
5
is
also
delineated.
measuring magnetic field distributions shown in Figure 5 is also delineated.
Figure 4. Photograph of MCF rubber liquid attracted to the electrodes before the application of electric
Figure 4. Photograph of MCF rubber liquid attracted to the electrodes before the application of electric
Figure
field. 4. Photograph of MCF rubber liquid attracted to the electrodes before the application of
field. field.
electric
In the case of Magnet 2, the magnetic field distribution at position <a> and <b> in Figure 3 was
In the case of Magnet 2, the magnetic field distribution at position <a> and <b> in Figure 3 was
measured; the results are shown in Figure 5. The yellow bands in Figure 5 correspond to the positions
measured; the results are shown in Figure 5. The yellow bands in Figure 5 correspond to the positions
at which the solidified MCF rubber increased as in Figure 2c. These results suggest that the MCF
at which the solidified MCF rubber increased as in Figure 2c. These results suggest that the MCF
rubber grows at the position between the maximum magnetic field strength and the maximum
rubber grows at the position between the maximum magnetic field strength and the maximum
magnetic field gradient. It is considered that this is due to the aggregation of the Ni and Fe3O4
magnetic field gradient. It is considered that this is due to the aggregation of the Ni and Fe3O4
Sensors 2017, 17, 767
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In the case of Magnet 2, the magnetic field distribution at position <a> and <b> in Figure 3 was
measured; the results are shown in Figure 5. The yellow bands in Figure 5 correspond to the positions
at which the solidified MCF rubber increased as in Figure 2c. These results suggest that the MCF rubber
grows at the position between the maximum magnetic field strength and the maximum magnetic
field gradient. It is considered that this is due to the aggregation of the Ni and Fe3 O4 particles by the
force of the magnetic field strength and field gradient. The permanent magnet used had a circular
maximum magnetic field and field gradient. Therefore, the solidified MCF rubber was cylindrical in
shape (Figure
3).17, 767
Sensors 2017,
6 of 18
(a)
(b)
Figure 5. Magnetic field distribution of Magnet 2 corresponding to the location labeled <a> and <b>
Figurein
5.Figure
Magnetic
field distribution of Magnet 2 (a,b) corresponding to the location labeled <a> and
3.
<b> in Figure 3.
On the other hand, the enhancement of the solidified MCF rubber can be perceived at the lower
side
of
the solidified
MCF
rubber shownofinthe
Figure
2c, as well
as rubber
in the case
application
of lower
On the other
hand, the
enhancement
solidified
MCF
canwithout
be perceived
at the
magnetic field shown in Figure 2b, due to the sedimentation of the particles in the MCF rubber.
side of the solidified MCF rubber shown in Figure 2c, as well as in the case without application
Therefore, large mass concentration is another factor that enhances the solidification of MCF rubber.
of magnetic
field6a
shown
Figure
2b,solidified
due to the
sedimentation
of was
the attracted
particlesoninthe
theanode
MCFofrubber.
Figure
shows in
MCF
rubber
by the
NM; this rubber
Therefore,
large
concentration
another
factor
enhances
the solidification
of MCF of
rubber.
Magnet
2 inmass
an MCF
rubber liquidiswith
50 wt %
largerthat
mass
concentrations
of particles, consisting
Figure
shows3-g
MCF
rubber and
solidified
by theInNM;
this particles
rubber was
onliquid
the anode
of
12-g Ni6apowder,
MF (M-300)
12-g NR-latex.
contrast,
in theattracted
MCF rubber
in
2 were
wt %.liquid
The solidified
Figure
6 was larger than
that in Figure
2c,
MagnetFigure
2 in an
MCF21.7
rubber
with 50 MCF
wt %rubber
largerinmass
concentrations
of particles,
consisting
of
reaching
from
anode
to
cathode
with
g
=
19
mm.
Thus,
the
higher
the
mass
concentration,
the
larger
12-g Ni powder, 3-g MF (M-300) and 12-g NR-latex. In contrast, particles in the MCF rubber liquid
the solidified MCF rubber.
in Figure 2 were 21.7 wt %. The solidified MCF rubber in Figure 6 was larger than that in Figure 2c,
reaching from anode to cathode with g = 19 mm. Thus, the higher the mass concentration, the larger
the solidified MCF rubber.
Sensors 2017, 17, 767
7 of 18
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7 of 18
7 of 18
(a)
(a)
(b)
(b)
(c)
(c)
Figure 6. Photographs of solidified MCF rubber with large mass concentration: (a,b) attracted on the
Figure
of
Figure 6.
6. Photographs
Photographs
of solidified
solidified MCF
MCF rubber
rubber with
with large
largemass
massconcentration:
concentration: (a,b)
(a,b) attracted
attracted on
on the
the
anode;
(c)
between the electrodes.
anode; (c) between the electrodes.
anode; (c) between the electrodes.
The solidified MCF rubber in Figure 6a,b, which shows the rubber between the electrodes, has
The
ininFigure
6a,b,
which
shows
thethe
rubber
between
theis
electrodes,
has the
The solidified
solidified
MCFrubber
rubber
Figure
which
shows
rubber
between
the
electrodes,
has
the same
wire-likeMCF
shape
as that
shown
in6a,b,
Figure
2c.
Where
the
magnetic
field
applied,
needlesame
wire-like
shape
as that
in Meanwhile,
Figure
2c. Where
theoutside
magnetic
is field
applied,
needle-shaped
the same
wire-like
shape
asshown
that
shown
in Figure
Where
the magnetic
isfield,
applied,
shaped
magnetic
clusters
are
created.
in2c.areas
of field
the magnetic
suchneedleas the
magnetic
clusters
are
created.
Meanwhile,
in
areas
outside
of
the
magnetic
field,
such
as
the
lower
shaped
magnetic
clusters
are
created.
Meanwhile,
in
areas
outside
of
the
magnetic
field,
such
asside
the
lower side of the solidified MCF rubber shown in Figure 1b, no needle-shaped magnetic
clusters
of
the
solidified
MCF
rubber
shown
in
Figure
1b,
no
needle-shaped
magnetic
clusters
form,
and
the
lowerand
sidethe
of particles
the solidified
MCFinto
rubber
shown
inNote
Figure
1b,if no
clusters
form,
aggregate
a dense
state.
that
the needle-shaped
electrode gap ismagnetic
small, like
the 1particles
aggregate
into
a
dense
state.
Note
that
if
the
electrode
gap
is
small,
like
the
1-mm
gap
used
in
form,
and
the
particles
aggregate
into
a
dense
state.
Note
that
if
the
electrode
gap
is
small,
like
1mm gap used in previous studies [22], the solidified MCF rubber reaches from anode to cathodethe
and
previous
studies
[22],
the
solidified
MCF
rubber
reaches
from
anode
to
cathode
and
becomes
a
solid,
mm
gap
used
in
previous
studies
[22],
the
solidified
MCF
rubber
reaches
from
anode
to
cathode
and
becomes a solid, 1-mm thick plate. In that case, the needle-like magnetic clusters are confined between
1-mm
thick
plate.
In as
that
case,
theour
needle-like
are confined
the electrode
becomes
a solid,
1-mm
thick
plate.
In
that
case, magnetic
the needle-like
magnetic
clustersbetween
are confined
between
the
electrode
plates,
shown
in
previous
study
[22].clusters
plates,
as
shown
in
our
previous
study
[22].
the electrode
plates,
as
shown
in
our
previous
study
[22].
When the MCF rubber liquid does not include MF, the phenomena of the electrolytically
When
MCF
liquid
not
MF,
of
electrolytically
When the
the
MCF rubber
rubber
liquid does
does
not include
include
MF,
the phenomena
phenomena
of the
theliquid
electrolytically
polymerized
configuration
is different,
as shown
in Figure
7, the
where
the MCF rubber
consisted
polymerized
configuration
is
different,
as
shown
in
Figure
7,
where
the
MCF
rubber
liquid
consisted
polymerized
configuration
is
different,
as
shown
in
Figure
7,
where
the
MCF
rubber
liquid
consisted
of 12-g Ni powder, 16-g NR-latex and 34-g water. Magnet 2 was used here. The black area is
Ni and
of
12-g
Ni
powder,
16-g
NR-latex
and
34-g
water.
Magnet
2
was
used
here.
The
black
area
is
of
12-g
Ni
powder,
16-g
NR-latex
and
34-g
water.
Magnet
2
was
used
here.
The
black
area
is Ni
Ni and
and
the white or pale yellow is NR-latex. Even if the Ni particles were aggregated by the application
of
the
white
or
pale
yellow
is
NR-latex.
Even
if
the
Ni
particles
were
aggregated
by
the
application
of
the
white
or
pale
yellow
is
NR-latex.
Even
if
the
Ni
particles
were
aggregated
by
the
application
of
the magnetic field, the solidified MCF rubber would not grow. This suggests that MF is the important
the
field,
rubber
not
grow.
the magnetic
magnetic
field, the
the solidified
solidified
MCF
rubber would
would
notrubber.
grow.This
Thissuggests
suggeststhat
thatMF
MF is
is the
the important
important
factor
in the enhancement
of theMCF
solidification
of MCF
factor
factor in
in the
the enhancement
enhancement of
of the
thesolidification
solidificationof
ofMCF
MCFrubber.
rubber.
Figure 7. Photograph of solidified MCF rubber without MF.
Figure
Figure 7.
7. Photograph
Photograph of
of solidified
solidified MCF
MCF rubber
rubber without
without MF.
MF.
Thus, we have demonstrated that MCF rubber liquid with 21.7 wt % can be solidified at less than
wemagnetic
have demonstrated
demonstrated
thatand
MCF
rubberliquid
liquid
with
21.7wt
wt%
% can
canthe
be solidified
solidified
atmagnetic
less than
than
Thus,
we
have
that
MCF
rubber
21.7
be
at
less
aboutThus,
50-mT
field strength
enhanced
at thewith
position
between
maximum
about
50-mT
magnetic
field
strength
and
enhanced
at
the
position
between
the
maximum
magnetic
about
50-mT magnetic
field strength
and
enhanced
at the
between
the maximum
field strength
and maximum
magnetic
field
gradient.
Theposition
rubber grows
substantially
withmagnetic
a higher
field strength
strength
and maximum
maximum
magnetic
fieldrubber
gradient.
TheThe
rubber
grows
substantially
with ais
a higher
higher
field
and
magnetic
field
gradient.
The
rubber
grows
substantially
with
mass
concentration
of particles
in the MCF
liquid.
MF in
the MCF
rubber liquid
a very
mass
concentration
of
particles
in
the
MCF
rubber
liquid.
The
MF
in
the
MCF
rubber
liquid
is
a very
important factor in the enhancement of solidified MCF rubber with a wire-like shape.
important factor in the enhancement of solidified MCF rubber with a wire-like shape.
Sensors 2017, 17, 767
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mass concentration of particles in the MCF rubber liquid. The MF in the MCF rubber liquid is a very
important factor in the enhancement of solidified MCF rubber with a wire-like shape.
3. Mechanisms and Process of Electrolytically Polymerized MCF Rubber
In this section, we first describe the electrolytic polymerization model of MCF rubber, because
all the following investigations are based on this model. Figure 8 shows the physical model of the
solidification
of MCF rubber by electrolytic polymerization proposed in our previous study
[22]. Using
Sensors 2017, 17, 767
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this model can help to clarify the mechanisms behind the MCF rubber enhancement, long-term stability
3. Mechanisms
andthe
Process
of Electrolytically
Polymerizedfield,
MCF Rubber
and high sensitivity.
With
application
of the magnetic
the magnetic clusters align along the
In this section,
first describe
theaelectrolytic
polymerization
MCFelectrodes,
rubber, because
lines of the magnetic
field,we
which
runs in
transverse
direction model
to theoftwo
as indicated
the following investigations are based on this model. Figure 8 shows the physical model of the
by E in the all
figure.
The C=C are arrayed in the same direction as the magnetic clusters. As a result,
solidification of MCF rubber by electrolytic polymerization proposed in our previous study [22].
solidification
of this
themodel
MCFcan
rubber
guessed
to expand
in the
direction
of the applied
magnetic field.
Using
help tois
clarify
the mechanisms
behind
the MCF
rubber enhancement,
long-term
When a magnetic
is not
applied,
the
bonds
undergo
solidification,
and
the direction
stability field
and high
sensitivity.
With
theC=C
application
of simply
the magnetic
field, the
magnetic clusters
align
along the lines is
of random.
the magneticAs
field,
which runs
a transverseof
direction
to the two electrodes,
as
of the polymerization
a result,
theinthickness
the solidified
MCF rubber
and the
indicated by E in the figure. The C=C are arrayed in the same direction as the magnetic clusters. As a
solidification effect are very small. At the cathode, the surface of the MCF rubber becomes rugged,
result, solidification of the MCF rubber is guessed to expand in the direction of the applied magnetic
as shown infield.
[22],
duea to
the tipfield
of the
magnetic
clusters.
Cationic
polymerization
When
magnetic
is notgrowing
applied, the
C=C bonds
simply undergo
solidification,
and the occurs at
direction
of
the
polymerization
is
random.
As
a
result,
the
thickness
of
the
solidified
MCF
rubber
and
the anode, and anionic polymerization at the cathode (A and F in Figure 8). With the application
of
the
solidification
effect
are
very
small.
At
the
cathode,
the
surface
of
the
MCF
rubber
becomes
rugged,
electricity, each polyisoprene of a particle in the NR-latex is guessed to be mutually polymerized to
as shown in [22], due to the tip of the growing magnetic clusters. Cationic polymerization occurs at
bind between
the ends
of C=C
bonds in aatcoordinated
way,
many
C=C
be of
formed in a
the anode,
and anionic
polymerization
the cathode (A and
F inand
Figure
8). With
the bonds
application
long chain, electricity,
as indicated
by B in Figure
8. At the
time,
the C=C
bonds
arepolymerized
vulcanized
each polyisoprene
of a particle
in thesame
NR-latex
is guessed
to be
mutually
to by radical
bind between
the ends
C=C
in a 8.
coordinated
way, and many
C=C bonds
be formed
in aC=C
long bonds are
polymerization,
as shown
byofG
inbonds
Figure
If the NR-latex
includes
sulfur
S, the
chain, as indicated by B in Figure 8. At the same time, the C=C bonds are vulcanized by radical
vulcanized by radical polymerization, as shown by C in Figure 8. In addition, from the results of
polymerization, as shown by G in Figure 8. If the NR-latex includes sulfur S, the C=C bonds are
the last Section
2, where
we polymerization,
showed that as
enhancement
of the8. solidified
needle-shaped
MCF rubber
vulcanized
by radical
shown by C in Figure
In addition, from
the results of the
where
we rubber
showed that
enhancement
the solidified
MCF rubber occurred
depends onlast
theSection
MF in2, the
MCF
liquid,
it can beofguessed
thatneedle-shaped
radical polymerization
depends
on the MF in
the MCF
rubber liquid,
can beacid
guessed
that radical
as a result of
the carboxyl
group
COOH
of theitoleic
coating
Fe3 polymerization
O4 , bondingoccurred
C=C, and Fe3 O4 ,
as a result of the carboxyl group COOH of the oleic acid coating Fe3O4, bonding C=C, and Fe3O4, as
as shown by
D
in
Figure
8.
shown by D in Figure 8.
Figure 8. Physical model of electrolytic polymerization of the MCF rubber by the NM [22]. Note that
Figure 8. Physical
model of electrolytic polymerization of the MCF rubber by the NM [22]. Note that G
G in the figure was added in the present study.
in the figure was added in the present study.
As shown in our previous study [22], the magnetic clusters that align along the magnetic field
form needle-like structures. Figure 9a is an SEM image of part of a magnified magnetic cluster
As shown
in our previous study [22], the magnetic clusters that align along the magnetic field
involved in the electrolytically polymerized solid MCF rubber of the image shown in our previous
form needle-like
structures.
is an
SEM image
of a(M-300)
magnified
magnetic
study [22].
The MCFFigure
rubber 9a
liquid
consisted
of 12-g of
Ni,part
3-g MF
and 12-g
NR-latex.cluster
MCF involved
in the electrolytically polymerized solid MCF rubber of the image shown in our previous study [22].
The MCF rubber liquid consisted of 12-g Ni, 3-g MF (M-300) and 12-g NR-latex. MCF rubber was
Sensors 2017, 17, 767
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Sensors 2017, 17, 767
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rubber was electrolytically polymerized by a 30-min application of 6 V and 2.7 A, a 1-mm space
between electrodes, and Magnet 2. The molecules of the NR-latex coiled around the magnetic clusters.
Sensors 2017, 17, 767
9 of 18
electrolytically
polymerized
by aby30-min
6 V and
2.7 A, a9a.
1-mm
between
electrodes,
Figure 9b shows
the mapping
X-ray application
diffraction of
(XRD)
of Figure
The space
electrolytic
polymerized
and
Magnet
2.
The
molecules
of
the
NR-latex
coiled
around
the
magnetic
clusters.
Figure
9b
shows the
rubber
was electrolytically
polymerized
by a 30-min
application of 6NR-latex,
V and 2.7 A,
1-mm
space
MCF rubber
presents
a complicated
configuration
of intertwined
Fea3O
4 and
Ni, indicating
between
and(XRD)
Magnet
2.not
The
molecules
of theelectrolytic
NR-latex coiled
around the magnetic
mapping
X-rayelectrodes,
diffraction
Figure
The
polymerized
MCF clusters.
rubber presents a
that theseby
ingredients
of NR-latex
doof
exist9a.
independently.
9b shows theof
mapping
by X-rayNR-latex,
diffraction (XRD)
Figure
9a.indicating
The electrolytic
complicatedFigure
configuration
intertwined
Fe3 O4ofand
Ni,
thatpolymerized
these ingredients of
MCF rubber presents a complicated configuration of intertwined NR-latex, Fe3O4 and Ni, indicating
NR-latex dothat
not
exist independently.
these ingredients of NR-latex do not exist independently.
(a)
(a)
(b)
(b)
Figure 9. (a) SEM photograph (5000× magnification of 5000) of microspores of magnetic clusters
Figure 9. (a)inside
SEMsolidified
photograph
(5000(b)
× XRD
magnification
of 5000) of microspores of magnetic clusters inside
MCF rubber;
mapping of (a).
Figure 9. (a) SEM
photograph
(5000×
magnification
of 5000) of microspores of magnetic clusters
solidified MCF rubber; (b) XRD mapping of (a).
inside solidified
MCF rubber; (b) XRD mapping of (a).
Figure 10a,b present SEM and XRD images of the anode side surface, corresponding to A in
Figure 8, and Figure 10c,d are those of the cathode side, corresponding to F in Figure 8. The MCF
Figure
10a,b
present
and
XRD
images
the
anode
surface,
corresponding
to
is thatSEM
shown
in Figure
10bof
shows
on theside
anode-side
surface,
the quantity
Figurerubber
10a,bsample
present
SEM
and
XRD9. Figure
images
of
thethat
anode
side
surface,
corresponding
to A
A in
in
of
Ni
and
Fe
310c,d
O
4 particles
involved
in
the
NR-latex
is
larger
than
that
of
C.
In
contrast,
Figure
10d
Figure
8,
and
Figure
are
those
of
the
cathode
side,
corresponding
to
F
in
Figure
8.
The
MCF
Figure 8, and Figure 10c,d are those of the cathode side, corresponding to F in Figure 8. The MCF
shows
that onshown
the cathode-side
surface,
the quantity
of C is larger
thanthe
thatanode-side
of Ni and Fe3O
4 particles.
rubber
is
Figure
10b shows
shows
that on
on
surface,
the quantity
quantity
rubber sample
sample
is that
that shown in
in Figure
Figure 9.
9. Figure
10b
that
the anode-side
surface,
the
The electrolytic polymerization of NR-latex is thus thought to be different at the anode and cathode
of
Ni
and
Fe
O
particles
involved
in
the
NR-latex
is
larger
than
that
of
C.
In
contrast,
Figure
33Oof
of Ni and Fe
44 particles
involved
NR-latex
is larger than that of C. In contrast, Figure 10d
10d
sides
the MCF rubber.
This is in
thethe
typical
distinction.
shows
that
on
the
cathode-side
surface,
the
quantity
of
particles.
shows that on the cathode-side surface, the quantity of C
C is
is larger
larger than
than that
that of
of Ni
Ni and
and Fe
Fe33O
O44 particles.
The
The electrolytic
electrolytic polymerization
polymerization of
of NR-latex
NR-latex is
is thus
thus thought
thought to
to be
be different
different at
at the
the anode
anode and
and cathode
cathode
sides
of
the
MCF
rubber.
This
is
the
typical
distinction.
sides of the MCF rubber. This is the typical distinction.
(a)
(b)
(a)
(b)
(c)
(d)
Figure 10. Photographs of (a) anode-side and (c) cathode-side surfaces of solidified MCF rubber by
SEM (2000× magnification); (b) XRD mapping on (a); (d) XRD mapping on (c).
(c)
(d)
Figure 10. Photographs of (a) anode-side and (c) cathode-side surfaces of solidified MCF rubber by
Figure 10. Photographs of (a) anode-side and (c) cathode-side surfaces of solidified MCF rubber by
SEM (2000× magnification); (b) XRD mapping on (a); (d) XRD mapping on (c).
SEM (2000× magnification); (b) XRD mapping on (a); (d) XRD mapping on (c).
Sensors 2017, 17, 767
10 of 18
SensorsWe
2017,next
17, 767investigate
10 of 18
the MCF rubber by chemical analysis. Regarding the electrolytic
polymerization of NR-latex, there have been only a few invaluable reports [34,35]. In contrast, there
Sensors 2017, 17, 767
10 of 18
haveWe
been
investigations
of NR-latex
as analysis.
a composite
without
chemical polymerization
nextseveral
investigate
the MCF rubber
by chemical
Regarding
the electrolytic
polymerization
[13–16].
The
former
[34,35]
useful
their
description
of contrast,
theRegarding
results
of the
FT-IR
spectra,
etc.
We there
next have
investigate
the
rubberofby
chemical
analysis.
electrolytic
of NR-latex,
beenare
only
aMCF
fewbecause
invaluable
reports
[34,35].
In
there
have
been
several
However,
the structure
of as
thea electrolytic
polymerization
ofpolymerization
NR-latex
has not
been
clarified.
To[34,35]
select
polymerization
of NR-latex,
there have been
onlychemical
a few invaluable
reports
[34,35].
InThe
contrast,
there
investigations
of NR-latex
composite
without
[13–16].
former
have beenanalytical
several investigations
of
NR-latex
as atocomposite
without
chemical
polymerization
the
optimum
instrument,
it
is
important
consider
that
MCF
rubber
involves
magnetic
are useful because of their description of the results of FT-IR spectra, etc. However, the structure of
[13–16].
The former
are useful
because of theirby
description
of the results
ofelectric
FT-IR spectra,
etc.thus
material,
0.1-mm
thick,[34,35]
and created
instantaneously
application
of anthe
field.analytical
We
the electrolytic
polymerization
of NR-latex
has not beenthe
clarified.
To select
optimum
However,
the
structure
of
the
electrolytic
polymerization
of
NR-latex
has
not
been
clarified.
To
select
selected
Raman
spectroscopy
and XPSthat
(X-ray
spectroscopy)
as effective
measures
for
instrument,
it is important
to consider
MCFphotoelectron
rubber involves
magnetic material,
0.1-mm
thick, and
the
optimum analytical instrument, it is important to consider that MCF rubber involves magnetic
MCF
rubber.
created
instantaneously
byand
thecreated
application
of an electric
field.
We thus of
selected
Raman
material,
0.1-mm thick,
instantaneously
by the
application
an electric
field.spectroscopy
We thus
Raman
spectroscopy
spectra
were
taken
from
the
anode-side
surface
of
the
MCF rubber
and selected
XPS (X-ray
photoelectron
asphotoelectron
effective measures
for MCF
Raman
spectroscopyspectroscopy)
and XPS (X-ray
spectroscopy)
asrubber.
effective measures for
electrolytically
polymerizedspectra
under were
the conditions
described
in the last
Section
MCFrubber
used
Raman
spectroscopy
taken from
the anode-side
surface
of 2;
thethe
MCF
MCF
rubber.
consisted
of
12-g
Ni,
3-g
MF
(M-300)
and
12-g
NR-latex,
and
Magnet
2.
Figure
11
compares
MCF
electrolytically
under the
described
in the surface
last Section
the MCF
Raman polymerized
spectroscopy spectra
wereconditions
taken from
the anode-side
of the2;MCF
rubberused
rubber
liquid
before
the
application
of
electric
and
magnetic
fields
with
that
of
MCF
rubber
of
the
electrolytically
polymerized
under the
described
the last2.Section
thecompares
MCF used
consisted
of 12-g Ni,
3-g MF (M-300)
andconditions
12-g NR-latex,
andinMagnet
Figure2;11
MCF
anode-side
surface
solidified
by
the
DM
with
a
magnetic
field.
It
is
well
known
that
NR-latex
contains
consisted
12-g Ni,
MF (M-300)
12-gand
NR-latex,
and fields
Magnetwith
2. Figure
11MCF
compares
MCF
rubber
liquidofbefore
the3-g
application
of and
electric
magnetic
that of
rubber
of the
molecules
polyisoprene,
asbyshown
in
Figure
12.
characteristic
peaks
at 1663
and 1710
rubber of
liquid
before
the application
ofwith
electric
andThe
magnetic
with
thatare
of that
MCF
rubber
ofcontains
thecm−1
anode-side
surface
solidified
the DM
a magnetic
field. fields
It is well
known
NR-latex
−1
(C=C
stretching
for carbon
ofaisoprene);
2852,
and
2960
2 stretching
anode-side
surface
solidified
by the bonds
DM
with
magnetic
field.
It is2915
wellpeaks
known
that
NR-latex
molecules
of polyisoprene,
asdouble
shown
in Figure
12.
The characteristic
are
atcm
1663(CH
andcontains
1710 cm−1
−1 (C-H
molecules
of
polyisoprene,
as
shown
in
Figure
12.
The
characteristic
peaks
are
at
1663
and
1710
cm−1 at
vibration
of
C-CH
2CH3 of isoprene);
3036
cm
stretching
vibration
of
isoprene);
in
addition,
−
1
(C=C stretching for carbon double bonds of isoprene); 2852, 2915 and 2960 cm (CH2 stretching
−1 (CH
−1
−2
(C=C
stretching
for
carbon
double
bonds
of
isoprene);
2852,
2915
and
2960
cm
2
stretching
1000 cm of
(C-C
of joint
between each isoprene).
−1 Comparison of the peak at 3036 cm of C-H, which
vibration
C-CH
2 CH3 of isoprene); 3036 cm −1 (C-H stretching vibration of isoprene); in addition, at
−1 of C=C
vibration
of C-CHto2CH
3 of
isoprene); polymerization,
3036 cm (C-H stretching
vibration
isoprene);
in
at of
does
not
contribute
the
electrolytic
with the
at of
1663
andcm
1710
cm
−
1
−2 addition,
1000 cm (C-C
of joint between each isoprene). Comparison
ofpeaks
the peak
at 3036
of C-H,
which
−1 (C-C of joint between each isoprene). Comparison of the peak at 3036 cm−2 of C-H, which
1000
cm
electrolytically
polymerized
MCF rubber,
and at 1000with
cm−1the
of peaks
C-C are
and cm
presented
in
−1 of C=C
doesdoes
not not
contribute
to to
the
electrolytic
polymerization,
at estimated
1663
and
1710
−1 of C=C
contribute
the
electrolytic
polymerization,
with
the
peaks
at
1663
and
1710
cm
of
Table
2. Results indicate the typical
that
thecm
quantity
of C=C
and C-C bonds
increase by
−1
of electrolytically
MCFcharacteristic
rubber,and
andatat
1000
C-C
estimated
presented
electrolytically polymerized
polymerized MCF
rubber,
1000
cm−1 of of
C-C
areare
estimated
andand
presented
in in
electrolytic
polymerization.
Table 2. Results indicate the typical characteristic that the quantity of C=C and C-C bonds increase by
Table 2. Results indicate the typical characteristic that the quantity of C=C and C-C bonds increase by
electrolytic
polymerization.
electrolytic
polymerization.
Figure
11. Raman
spectroscopy
spectraof
ofthe
the electrolytically
electrolytically polymerized
MCF
rubber
of anode-side
Figure
11. Raman
spectroscopy
spectra
polymerized
MCF
rubber
of anode-side
surface indicated as “Polymerized solid”: MCF rubber liquid before the application of electric and
MCF rubber
rubber liquid
liquid before the application of electric and
surface indicated as “Polymerized solid”: MCF
magnetic fields as “Liquid”; MCF rubber of anode-side surface solidified by the DM with a magnetic
magnetic fields as “Liquid”; MCF rubber of anode-side surface solidified by the DM with a magnetic
field as “Dried solid”.
field as “Dried solid”.
Figure 12. Scheme of polyisoprene structure of NR-latex.
Figure 12. Scheme of polyisoprene structure of NR-latex.
Figure 12. Scheme of polyisoprene structure of NR-latex.
Sensors 2017, 17, 767
11 of 18
Table 2. Comparison of spectra from Figure 11.
Location
Sensors 2017, 17, 767
at 1663 and 1710 cm−1 of C=C
Electrolytically polymerized MCF rubber
55.88
MCF rubber liquid before Table 2. Comparison of spectra from Figure 11.
13.18
electrolytic polymerization
Location
at 1663 and 1710 cm−1 of C=C
MCF rubber solidified by
Drying
13.73
Electrolytically
polymerized
MCF rubber
55.88
Method with
magnetic
field
MCF rubber liquid before electrolytic polymerization
MCF rubber solidified by Drying Method with magnetic field
13.18
13.73
at 1000 cm−1 of C-C
11 of 18
12.94
3.21
at 1000 cm−1 of C-C
3.36
12.94
3.21
3.36
The electrolytically polymerized MCF rubber of the anode-side surface in Figure 11 was analyzed
The 13
electrolytically
theelectrolytically
anode-side surface
in Figure under
11 wasthe
by XPS. Figure
presents thepolymerized
results. TheMCF
MCFrubber
rubberofwas
polymerized
analyzed by XPS. Figure 13 presents the results. The MCF rubber was electrolytically polymerized
same experimental conditions as in Figure 11. Figure 13 shows a comparison with rubber solidified by
under the same experimental conditions as in Figure 11. Figure 13 shows a comparison with rubber
the DM.
solidified by the DM.
(a)
(b)
Figure 13. XPS spectra of MCF rubber of anode-side surface: (a) electrolytically polymerized MCF
Figure 13. XPS spectra of MCF rubber of anode-side surface: (a) electrolytically polymerized MCF
rubber; (b) MCF rubber solidified by the DM with a magnetic field.
rubber; (b) MCF rubber solidified by the DM with a magnetic field.
Comparing polarization of the spectra of C to those of C=C (green line in Figure 13) and C-C
(blue and yellow
lines), the
of C-C
blue
in of
Figure
is increased
that13)
in Figure
Comparing
polarization
of quantity
the spectra
of C
to line
those
C=C13b
(green
line infrom
Figure
and C-C
13a.yellow
Therefore,
thethe
quantity
of C-C
bonds
increases
electrolytic
Figures
(blue and
lines),
quantity
of C-C
blue
line in by
Figure
13b is polymerization.
increased from From
that in
Figure1113a.
Sensors 2017, 17, 767
12 of 18
Therefore, the quantity of C-C bonds increases by electrolytic polymerization. From Figures 11 and 13,
Sensors 2017, 17, 767
12 of 18
it can be deduced that by electrolytic polymerization of the MCF rubber, some polymerization occurs.
The
quantity
ofby
C=C
and C-Cpolymerization
bonds is related
to the
electro-chemical
reaction, which
and
13,changes
it can bein
deduced
that
electrolytic
of the
MCF
rubber, some polymerization
− ] and [H+ ] by
in turn
is
based
on
the
oxidation-reduction
reaction.
This
can
be
evaluated
by
[OH
occurs.
measuring
values
redox of
potential
and pH.
Thethe
changes
in of
quantity
C=C and(ORP)
C-C bonds
is related to the electro-chemical reaction, which
+] by
is well
known
surface particles
have
negative
charge in
condition.
inItturn
is based
onthat
the NR-latex
oxidation-reduction
reaction.
Thisa can
be evaluated
by their
[OH-]initial
and [H
+
measuring
theinvalues
of redox
potential
(ORP) and
When
the water
NR-latex
reacts
as in Equation
(1),pH.
hydrogen ions H attract some anionic NR-latex
It
is
well
known
that
NR-latex
surface
particles
have
charge inmay
theirbe
initial
condition.
particles, neutralized particles are aggregated, and a parta negative
of the NR-latex
solidified,
which
+ attract some anionic NR-latex
When
the
water
in
NR-latex
reacts
as
in
Equation
(1),
hydrogen
ions
H
does not mean vulcanization. This phenomenon is equivalent to solidification by drying in the air (i.e.,
neutralized particles are aggregated, and a part of the NR-latex may be solidified, which
the particles,
DM):
does not mean vulcanization. This phenomenon
H2 O → His+ equivalent
+ OH− to solidification by drying in the air (1)
(i.e., the DM):
Therefore, the quantity of [OH− ] is greater than that of [H+ ]. As a result, NR-latex is alkaline.
(1)[H+ ],
2O → By
H+electrolytic
+ OH−
This is before the application of the electricHfield.
polymerization, the [OH− ] and
or the ratio
of oxidation and reduction, is altered. Thus, by electric-chemical measurement of ORP
Therefore, the quantity of [OH−] is greater than that of [H+]. As a result, NR-latex is alkaline. This
andispH,
we
canapplication
determineofthe
of the
polymerizationthe
of[OH
the−MCF
rubber
based
+], or the
before the
the reaction
electric field.
By electrolytic
electrolytic polymerization,
] and [H
on the
physical
model
shown
in
Figure
8.
We
therefore
investigated
the
ORP
and
pH
of
the
MCF
ratio of oxidation and reduction, is altered. Thus, by electric-chemical measurement of ORP and pH,
rubber
under
the application
of electric
magnetic
fields. The liquid
in MCF
the MCF
rubber
consisted
we can
determine
the reaction
of theand
electrolytic
polymerization
of the
rubber
based
on the of
12 g-Ni
powder,
3-gshown
MF (W-40)
and 8.
24-g
was pouredthe
into
a container,
shown
Figure 1.
physical
model
in Figure
WeNR-latex;
therefore itinvestigated
ORP
and pH ofasthe
MCFin
rubber
Theunder
mass the
concentration
of electric
the MCF
liquid
was
33.8
wt %
andrubber
Fe3 O4consisted
particles.ofORP
application of
andrubber
magnetic
fields.
The
liquid
inof
theNi
MCF
12 g-and
powder,
3-gsettled
MF (W-40)
and 24-g
NR-latex; itimmersed
was poured
container,
asliquid.
shown in
Figure21.was
pH Ni
meters
were
between
the electrodes
ininto
the aMCF
rubber
Magnet
The mass
of the MCF
rubber
liquid
was
33.8
wt constant
% of Ni and
4 particles.
ORPsupplied
and
applied
fromconcentration
outside the container.
The
electric
field
was
held
at 6FeV,3Oand
2.7 A was
pH
meters
were
settled
between
the
electrodes
immersed
in
the
MCF
rubber
liquid.
Magnet
2
was
between the plates. The plates were held apart at a constant thickness using a spacer with a 19-mm
applied gap,
fromcreating
outside the
container.
The
electric
field
held constant
at 6 V,14
and
2.7 A was
supplied
electrodes
a 40
mm × 40
mm
square
ofwas
stainless
steel. Figure
shows
the results.
between
the
plates.
The
plates
were
held
apart
at
a
constant
thickness
using
a
spacer
with
First, we consider the NR-latex liquid. As mentioned, in its initial condition, the pH aof19-mm
NR-latex
electrodes gap, creating a 40 mm × 40 mm square of stainless steel. Figure 14 shows the results.
liquid is alkaline as shown in Figure 14b. This state is the same as that of the MCF rubber liquid (see
First, we consider the NR-latex liquid. As mentioned, in its initial condition, the pH of NR-latex
Figure 14d). At the anode, by the application of the electric field, OH− from Equation (1) changes by
liquid is alkaline as shown in Figure 14b. This state is the same as that of the MCF rubber liquid (see
radial reaction with indicating by as follows:
−
Figure 14d). At the anode, by the application of the electric field, OH from Equation (1) changes by
radial reaction with indicating by as follows:
−
·
−
OH → OH + OH
・
OH− → OH
+ e−
(2)
(2)
However,
thethe
Equation
(2)(2)
reaction
of of
does
notnot
occur
at at
thethe
initial
condition,
However,
Equation
reaction
does
occur
initial
condition,leaving
leavingthe
theNR-latex
NRliquid
alkaline.
latex liquid alkaline.
(a)
Figure 14. Cont.
Sensors 2017, 17, 767
13 of 18
Sensors 2017, 17, 767
13 of 18
(b)
(c)
(d)
Figure 14. Changes in ORP, pH, temperature, electric current and voltage over time during
Figure
14. Changes
in ORP, pH,
electric
current
andMCF
voltage
over
timeinduring
electrolytic
polymerization
by temperature,
the NM: NR-latex
liquid
in (a,b);
rubber
liquid
(c,d). electrolytic
polymerization by the NM: NR-latex liquid in (a,b); MCF rubber liquid in (c,d).
At the initial condition, the quantity of reductant [red] is larger than that of oxidizer [ox].
Therefore,
the condition,
ORP of thethe
NR-latex
is negative,
in the
initial
ORP in[ox].
Figure
14a.
At the initial
quantityliquid
of reductant
[red]asis shown
larger than
that
of oxidizer
Therefore,
the ORP of the NR-latex liquid is negative, as shown in the initial ORP in Figure 14a. Equation (2)
Sensors 2017, 17, 767
Sensors 2017, 17, 767
Sensors 2017, 17, 767
14 of 18
14 of 18
14 of 18
Equation
(2)application
occurs
the
of electric
the
[OH−]
decreases,
becoming
+ ].
Sensors
2017,
17,the
767
14
ofsmaller
18
occurs
with
theapplication
electricoffield,
andelectric
[OH
−]field,
decreases,
becoming
smaller
thansmaller
[OH
Equation
(2)
occurs
withwith
theof
application
the
field,
and and
[OH−]
decreases,
becoming
+]. Therefore, ORP changes from negative to positive, as shown by A in Figure 14a (hereafter,
than
[OH
+ Therefore,
Therefore,
from
negative
to positive,
byasAshown
in Figure
14a
than
[OH
ORP
changes
from
negativeas
to shown
positive,
by A
in(hereafter,
Figure 14aReaction
(hereafter,
Sensors
2017,].ORP
17, 767changes
14 ofA).
18
Equation
(2)
occurs
with
the
application
of as
theshown
electricby
field,
and
[OH−]
decreases,
becoming
smaller
Reaction
A).
The
pH
becomes
acidic,
A
in
Figure
14b.
In
other
words,
the
oxidation
The pH becomes
as shown
by Aasinshown
Figure by
14b.AIn
words,
oxidation
process
occurs
at
Reaction
A). The acidic,
pH becomes
acidic,
inother
Figure
14b. the
In other
words,
the oxidation
thanprocess
[OH+]. Therefore,
ORP
changes
from
negative to
as shown
occurs
at anode
the
anode
by application
the
application
ofpositive,
the electric
field. by A in Figure 14a (hereafter,
the
anode
by
the
application
of
the
electric
field.
process
occurs
at
the
by
the
of
the
electric
field.
Equation (2) occurs with the application of the electric field, and
[OH−] decreases,
becoming smaller +
+, and
−] becomes
Reaction Next,
A). The
pH becomes
acidic,
as shown
by A in to
Figure
14b. [OH
In
other
words, higher
the oxidation
anionic
NR-latex
particles
are
attracted
−]] becomes
Next,
anionic
NR-latex
particles
arenegative
attracted
to H
and
[OH−
higher
thanthan
[H++].[H
]. ].
NR-latex
particles
H++ , H
higher
[H
thanNext,
[OH+].anionic
Therefore,
ORP changes
from
to positive,
as shown
bybecomes
A in Figure
14a than
(hereafter,
process
occurs
at
the
anode
by
the
application
of
the
electric
field.
Therefore,
the
pH
of NR-latex
the
NR-latex
liquid
changes
to alkaline,
as shown
by
in Figure
14b
(hereafter,
Therefore,
theThe
pHpH
of the
the
NR-latex
liquid
changes
toalkaline,
alkaline,
asshown
shown
by
inBFigure
Figure
14b
(hereafter,
Therefore,
the
pH
of
liquid
to
as
by
BB
in
14b
Reaction
A).
becomes
acidic,
aschanges
shown by
A in Figure
14b. −In
other
words,
the(hereafter,
oxidation
+].
Next, anionic
NR-latex
particles
are than
attracted
to
H+,then
and changes
[OH ] becomes
higher
than [H
Reaction
B);
the
[red]
becomes
larger
[ox].
ORP
to
negative,
as
shown
by
Reactionoccurs
B); the
the
[red]
becomes
larger
than [ox].
[ox].
ORP
then changes
changes to
to negative,
negative, as
as shown
shown by
by BB
inB in
Reaction
B);
becomes
larger
than
ORP
then
in
process
at[red]
the anode
by the
application
of the
electric
field.
Therefore,
the
pH of the NR-latex liquid changes to alkaline,
as
shown
by
B
in
Figure
14b
(hereafter,
Figure
14a.
Figure
14a. anionic NR-latex particles are attracted to H+, and [OH−] becomes higher than [H+].
Figure
14a.
Next,
Reaction Next,
B); the
becomes
larger
than liquid.
[ox]. ORP
then itchanges
toNR-latex,
negative,the
as pH
shown
by B results
in
we[red]
consider
the
MCF
rubber
Because
involves
and
ORP
Next, we
we consider
consider
the
MCF
rubber
liquid.
Because
involves
NR-latex,
theFigure
pH and
and
ORP
results
Next,
MCF
rubber
Because
itit involves
NR-latex,
the
pH
ORP
results
Therefore,
the
pH of thethe
NR-latex
liquidliquid.
changes
to alkaline,
as shown
by B in
14b
(hereafter,
Figure
14a.
described
can
be
compared
to
those
of
MCF
rubber
liquid,
as
shown
in
Figure
14c,d.
These
are
the
describedB);
canthe
be[red]
compared
to those
those
ofthan
MCF[ox].
rubber
liquid,
as
shownto
innegative,
14c,d.
Theseby
areBthe
the
described
can
be
compared
to
of
MCF
rubber
liquid,
shown
in
Figure 14c,d.
These
are
Reaction
becomes
larger
ORP
then as
changes
as shown
in
Next,
we
consider
the
MCF
rubber
liquid.
Because
it
involves
NR-latex,
the
pH
and
ORP
results
reactions
atanode.
the
anode.
Meanwhile,
at the
cathode,
undergoes
a radial
reaction
reactions
at
Meanwhile,
at at
thethe
cathode,
the oleic
acidoleic
undergoes
a radial
as follows:
reactions
at the
the
anode.
Meanwhile,
cathode,
the the
oleic
acidacid
undergoes
a reaction
radial
reaction
as as
Figure
14a.
described
can be compared to those of MCF rubber liquid, as shown in Figure 14c,d. These are the
follows:
follows:
Next, we consider the MCF rubber liquid. Because it involves NR-latex, the pH and ORP results
reactions at the anode. Meanwhile, at the cathode, the oleic acid undergoes a radial reaction as
described can be compared to those of MCF rubber liquid, as shown in Figure 14c,d. These are the
follows:
(3)
reactions at the anode. Meanwhile, at the cathode, the oleic acid undergoes a radial reaction(3)
as(3)
follows:
(3)MF is
The
possibility
of this
reaction
has already
been
presented
[36,37].
Figure
7 indicated
that
The
possibility
of
this
reaction
has
already
been
presented
[36,37].
Figure
77 indicated
that
MF
is
The
possibility
of
this
reaction
has
already
been
presented
[36,37].
Figure
indicated
that
MF
is on
an
important
factor
in
the
enhancement
of
the
solidification
of
MCF
rubber.
Therefore,
we
focus
(3)
an
important
factor
in
the
enhancement
of
the
solidification
of
MCF
rubber.
Therefore,
we
focus
on
an important
in
of the solidification
of MCF
rubber.
Therefore,
we focus
on the
Therole
possibility
of the
this
reaction
haspolymerization.
already
been presented
[36,37].
Figure
7 indicated
that MF
is
the
offactor
oleic
acid
inenhancement
electrolytic
the
role
of oleic
acid
in electrolytic
polymerization.
role
of
oleic
acid
in
electrolytic
polymerization.
an important
factor in(3)the
enhancement
of thethan
solidification
of MCF
rubber.
Therefore,
we focus
on
In
Equation
[red]
becomes
larger
[ox],
the
ORP
of
MCF
rubber
liquid
becomes
negative,
In
(3)
than [ox],
the
ORP of
rubber
liquid
becomes
negative,
The
possibility
of
thisbecomes
reactionlarger
has+already
been
presented
[36,37].
Figure
7 indicated
that
MF is
In Equation
Equation
(3) [red]
[red]
becomes
larger
[ox],
the
ofMCF
MCF
rubber
liquid
becomes
negative,
−] becomes
the role
of
oleic
acid
in
electrolytic
polymerization.
and
[OH
higher
than
]. than
Therefore,
theORP
pHthe
of
the NR-latex
liquid
becomes
alkaline.
At
−−
+].[H
and
[OH
]
becomes
higher
than
[H
Therefore,
the
pH
of
NR-latex
liquid
becomes
alkaline.
At
+
an
important
factor
in
the
enhancement
of
the
solidification
of
MCF
rubber.
Therefore,
we
focus
on
andthis
[OH
] becomes
higher
than
[H ]. simultaneously
Therefore,
theORP
pH
of
the
NR-latex
liquid
becomes
alkaline.
In
Equation
(3) [red]
becomes
larger
than [ox], the
of MCF
rubber
liquid
becomes
negative,
time,
Reactions
A
and
B
occur
at
the
cathode.
Since
the
data
of
Figure
14
are
this
time,ofReactions
B occur
simultaneously
at the
cathode.
SinceSince
the data
of Figure
14 are
the
role
oleic
acid A
in and
electrolytic
polymerization.
At this
Reactions
A and
B[H
occur
simultaneously
at the
the
cathode.
the
data
of
Figure
14
−] becomes
+]. Therefore,
and
[OHtime,
higher
than
the
pH
of
NR-latex
liquid
becomes
alkaline.
At
between
the
electrodes,
they
are
measured
as
a
mix
of
the
reactions
at
the
anode
and
cathode.
between
the
electrodes,
they
are
measured
as
a
mix
of
the
reactions
at
the
anode
and
cathode.
In
Equation
(3)
[red]
becomes
larger
than
[ox],
the
ORP
of
MCF
rubber
liquid
becomes
negative,
are Therefore
between
the
electrodes,
arein
measured
asofaORP
ofcathode.
the
the
anode
and
cathode.
this
time,− Reactions
A summarized
and Bthey
occur
simultaneously
atmix
theand
Sinceinat
the
data
of Figure
14 are
they
are
the results
pHreactions
shown
Figure
14c,d,
respectively.
+]. Therefore,
Therefore
are
summarized
results
of ORP
ORP
andof
pH
shown
in Figure
Figure
14c,d,
respectively.
and
[OH ]they
becomes
higher thanin
[Hthe
the pH
theshown
NR-latex
liquid14c,d,
becomes
alkaline. At
Therefore
they
are
summarized
in
the
results
of
and
pH
in
respectively.
between From
the electrodes,
they
arewe
measured
as a mix
of the reactions
at thepolymerization.
anode and cathode.
the
above
results,
can
construct
the
process
of
electrolytic
As shown
From
the
above
results,
we
canconstruct
constructthe
theprocess
process
of
electrolytic
polymerization.
As
shown
this time,
Reactions
A
and Bwe
occur
simultaneously
at the
cathode.
Since
the data of Figure
14 are
From
the
above
results,
can
of
electrolytic
polymerization.
As
shown
in
Therefore
they
are
summarized
in
the
results
of
ORP
and
pH
shown
in
Figure
14c,d,
respectively.
in previous
the previous
Section
2, enhancement
of solidified
the solidified
MCF
rubber
with
needleor wire-like
shapes
in
the
Section
2,
enhancement
of
the
MCF
rubber
with
needleor
wire-like
shapes
between
the
electrodes,
they
are
measured
as
a
mix
of
the
reactions
at
the
anode
and
cathode.
the by
previous
2,
enhancement
of the
solidified
MCF
with needleor wire-like
shapes
by the
From
theSection
above
results,
we can
construct
process
of
electrolytic
polymerization.
As
shown
electrolytic
polymerization
is due
to effect
the the
effect
of
therubber
magnetic
It particularly
depends
on
by
electrolytic
polymerization
is
due
to
the
ofthe
the
magnetic
field.field.
particularly
depends
on
the
Therefore
they
are summarized
in
the
results
ofof
ORP
and
pH shown
inItItFigure
14c,d, depends
respectively.
electrolytic
polymerization
is
due
to
the
effect
magnetic
field.
particularly
on
the
in the
previous
Section
enhancement
of the
solidified
MCF
rubber
or wire-like
shapes
MF
involved
in MCF
the2,MCF
rubber
liquid.
The
oleic
acid
coating
Fe3with
O4 ofneedleMF
is thought
to play
a role
in
MF
involved
the
rubber
The
oleic
acid
coating
3O4 of MF polymerization.
is
thought
to
play
role
in
From thein
above
results,
weliquid.
can construct
the
process
of Fe
electrolytic
Asaashown
MFelectrolytic
involved
in
the
MCF
rubber
liquid.
The
oleic
acid
coating
Fe
O
of
MF
is
thought
to
play
role
in
3
4
by
polymerization
is
due
to
the
effect
of
the
magnetic
field.
It
particularly
depends
on
the
the solidification.
In addition,
as previously
shown,
C-C
bonds
increase,
and
changes
in and
pH and
ORP
the
solidification.
In
addition,
as
previously
shown,
C-C
bonds
increase,
and
changes
in pH
ORP
in
previous Section
2, enhancement
of the
solidified
MCF
rubber
with
needleor wire-like
shapes
thethe
solidification.
InMCF
addition,
asthe
previously
shown,
C-C
bonds
and
changes
pH
and
ORP
MF
involved
in
the
rubber
liquid.
The field,
oleic
acid
coating
Feincrease,
3O4 of MF
is thought
toinplay
a role
in
occur
by
the
application
of
electric
confirming
electrolytic
polymerization
of
MCF
rubber.
occur
by
application
of
confirming
electrolytic
polymerization
MCF
rubber.
by
electrolytic
polymerization
iselectric
due to field,
the
effect
of the magnetic
field.
It particularlyof
depends
on the
occur
by the
the
application
of the
the
field,
confirming
electrolytic
polymerization
ofpH
MCF
rubber.
the
solidification.
In addition,
as electric
previously
shown,
C-Celectrolytic
bonds
increase,
and changesprocess
in
and
ORP as
Based
on
these
results,
we
hypothesize
that
the
polymerization
proceeds
Based
on
these
results,
we
hypothesize
that
the
electrolytic
polymerization
process
proceeds
as
MF
involved
in
the
MCF
rubber
liquid.
The
oleic
acid
coating
Fe
3
O
4
of
MF
is
thought
to
play
a
role
in
Based
on
these
results,
we
hypothesize
that
the
electrolytic
polymerization
process
proceeds
as
follows.
occur
by the First,
application
the electric
field,ofconfirming
electrolytic
polymerization
of MCFtorubber.
follows.
at anode,
the of
anode,
the anion
the NR-latex
particle
(Figure
12)thought
is thought
change
as
follows.
First,
at
the
the
anion
of
the
NR-latex
particle
(Figure
12)
is
to
change
as
the
solidification.
In
addition,
as
previously
shown,
C-C
bonds
increase,
and
changes
in
pH
and
ORP
First,
at
anode,
the anion
of the NR-latex
(Figure 12)polymerization
is thought to change
as proceeds
follows: as
Based
onthe
these
results,
we hypothesize
thatparticle
the electrolytic
process
follows:
follows:
occur by the application of the electric field, confirming electrolytic polymerization of MCF rubber.
follows. First, at the anode, the anion of the NR-latex particle (Figure 12) is thought to change as
Based on these results, we hypothesize that the electrolytic polymerization process proceeds as
follows:
follows. First, at the anode, the anion of the NR-latex particle (Figure 12) is thought to change(4)
as(4)
(4)
follows:
(4)
From
Equation
(4) derive
we derive
Equation
From
Equation
(4) we
Equation
(5). (5).
From Equation (4) we derive Equation (5).
From Equation (4) we derive Equation (5).
(4)
(5) (5)
From Equation (4) we derive Equation (5).
(5)(5) on
possibility
of reaction
the reaction
of Equation
(5) has
already
presented
The The
possibility
of the
of Equation
(5)
has
already
beenbeen
presented
[36].[36].
The The
firstfirst
termterm
on
・
the right
in Equation
is rewritten
Brsimplicity,
for simplicity,
the polyisoprene
shown
in(5)
Figure
the right
sideside
in Equation
(5) is(5)
rewritten
as ・as
Br for
and and
the polyisoprene
shown
in Figure
The
possibility
of
the
reaction
of
Equation
(5)
has
already
been
presented
[36].
The
first
term
on
to is
RH
is rewritten
as follows
12 to12RH
rewritten
as follows
to R.to R. ・
Theside
possibility
of the(5)
reaction
of Equation
alreadyand
been
presented
[36]. shown
The first
on
the right
in Equation
is rewritten
as Br (5)
for has
simplicity,
the
polyisoprene
interm
Figure
The
possibility
of
the
reaction
of
Equation
(5)
has
already
been
presented
[36].
The
first
term
on
·
thetoright
side
in Equation
(5) is rewritten
as Br
for simplicity, and the polyisoprene shown in Figure 12
12
RH is
rewritten
as follows
to R.
the
right
side in Equation
(5) is
as ・Br for simplicity, and the polyisoprene shown in Figure
(6) (6)
to RH
is rewritten
as follows
torewritten
R.
12 to RH is rewritten as follows to R.
(6)
From
the right
in Equation
(5)derive
we derive
Equation
(7)presented
as presented
a previous
study
From
the right
sideside
in Equation
(5) we
Equation
(7) as
in a in
previous
study
[37].[37].
・
(6)
(6)
+ RH
→RBr
→ RBr
+ H・
・
・
+Br
RH
→ Br
H R→H RBr
(7) (7)
From the right side in EquationBr(5)
we derive
Equation
(7) +asHpresented in a previous study [37].
Br(5)
+ RH
→ Br REquation
H → RBr
H presented in a previous study [37].
(7)
From the right side in Equation
we derive
(7)+as
・
・
・
Br + RH → Br R H → RBr + H・
(7)
Sensors 2017, 17, 767
15 of 18
From the right side in Equation (5) we derive Equation (7) as presented in a previous study [37].
Sensors 2017, 17, 767
·
.
Br + RH → Br R H → RBr + H·
Sensors 2017, 17, 767
15 of(7)
18
15 of 18
RBr is created by radical
asas
shown
in
RBr
radical polymerization,
polymerization,as
asshown
shownbelow
belowininEquation
Equation(8).
(8).Therefore,
Therefore,
shown
Figures
1111
and
13,13,
C-C
bonds
increase
and
MCF
rubber
liquid
is vulcanized
as as
shown
byby
B and
GG
in
in
Figures
and
C-C
bonds
increase
and
MCF
rubber
liquid
is
vulcanized
shown
B
and
RBr is created by radical polymerization, as shown below in Equation (8). Therefore, as shown
Figure
8. 8.
in
Figure
in Figures 11 and 13, C-C bonds increase and MCF rubber liquid is vulcanized as shown by B and G
in Figure 8.
(8)
(8)
(8)
Here,
Here, the
the following
following reaction
reaction may
may occur,
occur,
Here, the following reaction・
may occur,・
OH·
H· ++ OH
・
→
→
・
H22O
H
(9)
(9)
(9)
+ side
OH in Equation
→
H(3)
2O and ・Br react as follows,
H right
Next, at the cathode, the radicals of the
Next, at the cathode, the radicals of the right side in Equation (3) and · Br react as follows,
Next, at the cathode, the radicals of the right side in Equation (3) and ・Br react as follows,
(10)
(10)(10)
Therefore the NR-latex and oleic acid are vulcanized as shown by D in Figure 8. We have already
demonstrated
that the
polymerization
of NR-latexasisshown
different
theFigure
anode8.and
cathode
Therefore
theelectrolytic
NR-latex and
oleic acid are vulcanized
by at
D in
We have
already
sidesdemonstrated
of the MCF rubber
surface
(Figure
10).
Therefore,
electrolytic
polymerization
of
the
MCF
rubber
that the electrolytic
polymerization
ofasNR-latex
is different
at 8.
theWe
anode
cathode
Therefore the NR-latex
and oleic acid
are vulcanized
shown by
D in Figure
haveand
already
is different
theMCF
anode and cathode
sides, as10).
shown
in Equations
(8) and
(10).
sides ofatthe
surface
(Figure
Therefore,
electrolytic
polymerization
the cathode
MCF rubber
demonstrated
that therubber
electrolytic
polymerization
of NR-latex
is different
at the anodeofand
The vulcanization
phenomenon
of MCF
rubber
liquidinisEquations
similar to (8)
that
of (10).
conductive polymers
the anode
and(Figure
cathode
sides,
as shown
and
sidesisofdifferent
the MCFatrubber
surface
10).
Therefore,
electrolytic polymerization
of the MCF rubber
such as polyacetylene.
Equations (2) and (5)
describe
howliquid
an electron
occurs
andof
moves
through
πThe
vulcanization
rubber
is (8)
similar
to that
conductive
polymers
is different
at the
anode and phenomenon
cathode sides,ofasMCF
shown
in Equations
and (10).
conjugation
as
π-electron,
like
the
carrier
of
dopant
in
the
C=C
bond.
As
shown
by
B
and
G
in
Figure
such
as polyacetylene.
Equationsof
(2)MCF
and rubber
(5) describe
an electron
and moves
through πThe vulcanization
phenomenon
liquidhow
is similar
to thatoccurs
of conductive
polymers
8, bonds
of C=C and
C-C are connected
like a of
network.
Therefore,
electric
conductivity
isand
enhanced
conjugation
as
π-electron,
like
the
carrier
dopant
in
the
C=C
bond.
As
shown
by
B
G
in Figure
such as polyacetylene. Equations (2) and (5) describe how an electron occurs and moves through
−3 Ω·m, as shown in our previous study [22]. As a
and electrical
resistivity
reaches
on
the
order
of
10
8, bonds ofasC=C
and C-Clike
are connected
a network.
Therefore,
electric
enhanced
π-conjugation
π-electron,
the carrierlike
of dopant
in the
C=C bond.
Asconductivity
shown by Bisand
G
reference,
polyphenylene-based
conductive
plastic
doped
withas
ASF
5 is on the order of 10−2 Ω·m. On
−3 Ω·m,
and
electrical
resistivity
reaches
on
the
order
of
10
shown
in
our
previous
study
[22].
in Figure 8, bonds of C=C and C-C are connected like a network. Therefore, electric conductivityAs a
−7
the other
hand,polyphenylene-based
ordinary metals such as silver and
copper
are on
order
of 10
By
the
−the
3 Ω
reference,
doped
with
ASF
the Ω·m.
order
of previous
10−2NM,
Ω·m. On
is enhanced
and electrical resistivityconductive
reaches onplastic
the order
of 10
·m,5 is
as on
shown
in our
we obtained
a
soft
and
highly
conductive
material
with
high
sensitivity
that
could
be
applicable
to NM,
−7
the
other
ordinary
metals such as silver
and copper
are on
the order
of 10
Ω·m.
By
the
study
[22].
As hand,
a reference,
polyphenylene-based
conductive
plastic
doped
with ASF
is
on
the
order
5
sensors.
In
addition,
because
the
bonds
of
C=C
and
C-C
produced
by
the
electrolytic
polymerization
−2 obtained
softother
and highly
material
with
high sensitivity
that
could
be applicable
of 10we
Ω·m. Ona the
hand, conductive
ordinary metals
such
as silver
and copper
are
on the
order of to
have
large
bonding
force,
it
makes
the
MCF
rubber
long-term
stability
of
electric
conductivity.
−
7
addition,
theabonds
of C=C
and
C-C produced
by the
electrolytic
polymerization
10 sensors.
Ω·m. ByInthe
NM, webecause
obtained
soft and
highly
conductive
material
with
high sensitivity
that
have
large
bonding
force,
it
makes
the
MCF
rubber
long-term
stability
of
electric
conductivity.
could be applicable to sensors. In addition, because the bonds of C=C and C-C produced by the
4. Conclusions
electrolytic polymerization have large bonding force, it makes the MCF rubber long-term stability of
4. Conclusions
Our
aim was to develop a new manufacturing process for NR-latex as a soft rubber embedded
electric
conductivity.
with MCFOur
as magnetic
using the
NM.
The effect of the
magnetic
field on as
theametamorphosis
of
aim was filler
to develop
a new
manufacturing
process
for NR-latex
soft rubber embedded
4.
Conclusions
MCFwith
rubber
byaselectrolytic
polymerization
and
the
process
electrolytic
were of
MCF
magnetic filler
using the NM.
The
effect
of theofmagnetic
fieldpolymerization
on the metamorphosis
clarified.
Our aim
was by
to develop
a new
manufacturingand
process
for NR-latex
as a soft rubber
embeddedwere
MCF
rubber
electrolytic
polymerization
the process
of electrolytic
polymerization
first
rubber
canThe
be enhanced
bymagnetic
electrolytic
polymerization.
The MF in
withWe
MCF
as clarified
magnetichow
fillerMCF
using
the NM.
effect of the
field
on the metamorphosis
of
clarified.
MCF
rubber
liquid
is
a
very
important
factor
in
the
enhancement
of
wire-shaped
solidified
MCF
MCF rubber
electrolytic
andcan
thebe
process
of electrolytic
polymerization
were clarified.
Weby
first
clarified polymerization
how MCF rubber
enhanced
by electrolytic
polymerization.
The MF in
rubber.
magnetic
field
distribution
is also
significant.
field
gradient
andThe
strength
WeThe
first
clarified
how
rubber
can
be enhanced
electrolytic
polymerization.
MF
inmust
MCFMCF
MCF
rubber
liquid
isMCF
a very
important
factor
in by
theMagnetic
enhancement
of wire-shaped
solidified
be
considered
in
order
to
obtain
large
solidified
MCF
rubber.
Specifically,
MCF
rubber
liquid
with
rubber
liquidThe
is a magnetic
very important
factor in theisenhancement
of wire-shaped
solidified
MCF
rubber.
Themust
rubber.
field distribution
also significant.
Magnetic field
gradient
and
strength
21.7
wt
%field
can distribution
be solidified
less
than
about
50-mT MCF
magnetic
fieldSpecifically,
strength,
and
enhanced
at the with
magnetic
also
significant.
Magnetic
field gradient
and
strength
must
be considered
be considered
in orderisat
to
obtain
large
solidified
rubber.
MCF
rubber
liquid
position
the
fieldabout
strength
andmagnetic
maximum
magnetic
field
gradient.
This
in order
to
large
solidifiedmagnetic
MCF
Specifically,
MCF
rubber
liquid
with
21.7
wt
% can
be
21.7between
wtobtain
% can
bemaximum
solidified
at
lessrubber.
than
50-mT
field
strength,
and
enhanced
at the
enhanced
MCF
rubber
depends
on
the
aggregation
of
magnetic
clusters
aligned
along
the
magnetic
position between the maximum magnetic field strength and maximum magnetic field gradient. This
field enhanced
line, likeMCF
needles.
clarified
thataggregation
this enhancement
of clusters
MCF rubber
electrolytic
rubberWe
depends
on the
of magnetic
alignedby
along
the magnetic
polymerization
based
on radical
shown
in Equation
The production
NRfield line, islike
needles.
Wepolymerization,
clarified that as
this
enhancement
of(3).
MCF
rubber by of
electrolytic
latex polymerization
MCF rubber by is
the
NM
could
be
related
to
production
of
a
highly
sensitive
sensor.
based on radical polymerization, as shown in Equation (3). The production of NRSEM
and rubber
XRD images
revealed
electrolytically
polymerized
rubber
presents a
latex MCF
by the NM
couldthat
be related
to production
of a highlyMCF
sensitive
sensor.
complicated
configuration
of intertwined
NR-latex,
Fe3O4 and Ni. They
also clarified
electrolytic
SEM
and XRD images
revealed
that electrolytically
polymerized
MCFthat
rubber
presents a
Sensors 2017, 17, 767
16 of 18
solidified at less than about 50-mT magnetic field strength, and enhanced at the position between the
maximum magnetic field strength and maximum magnetic field gradient. This enhanced MCF rubber
depends on the aggregation of magnetic clusters aligned along the magnetic field line, like needles.
We clarified that this enhancement of MCF rubber by electrolytic polymerization is based on radical
polymerization, as shown in Equation (3). The production of NR-latex MCF rubber by the NM could
be related to production of a highly sensitive sensor.
SEM and XRD images revealed that electrolytically polymerized MCF rubber presents a
complicated configuration of intertwined NR-latex, Fe3 O4 and Ni. They also clarified that electrolytic
polymerization of NR-latex is different at the anode and cathode sides of the MCF rubber surface.
Therefore, electrolytic polymerization of MCF rubber is also different at the anode and cathode sides,
as shown in Equations (8) and (10). Raman spectroscopy and XPS showed that the quantity of C=C
and C-C bonds increases by electrolytic polymerization.
Meanwhile, the chemical approach revealed that the pH and ORP of MCF rubber liquid is altered
by electrolytic polymerization. Based on these results, we were able to propose a hypothetical process
for electrolytic polymerization of MCF rubber, as shown in the physical model. We clarified why
NR-latex MCF rubber produced by the NM has high sensitivity and long-term conductive stability.
Therefore, we showed that the NM may be useful in the development of a high-sensitivity sensor.
Because the new production of NM uses small quantity of voltage, electric current and magnetic field
strength in the application of electric and magnetic fields, it brings about such an easy implementation
that the sensing fields would develop.
Acknowledgments: This work was supported in part by JSPS KAKENHI Grant Number JP 15K05886, and we are
very grateful for this support.
Author Contributions: For this research article, Kunio Shimada conceived, designed the experiments, performed
the experiments, analyzed the data and wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
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