Supporting Information
Control of Viscoelasticity Using Redox Reaction
Koji Tsuchiya†, Yoichi Orihara†, Yukishige Kondo‡,§, Norio Yoshino‡,§,
Hideki Sakai*,†,§, and Masahiko Abe†,§
† Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda,
Chiba 278-8510, Japan
‡ Faculty of Engineering, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo
162-8601, Japan
§ Institute of Colloid and Interface Science, Tokyo University of Science, 1-3 Kagurazaka,
Shinjuku, Tokyo 162-8601, Japan
Preparation of Aqueous FTMA/NaSal Mixtures
FTMA and NaSal were purchased from Dojin Co. and Wako Pure Chemical Industries, Ltd.,
respectively.
All preparations were performed in an N2 atmosphere using distilled water for
injection (Otsuka Pharmaceutical Co., Ltd.) as the solvent after being pretreated by bubbling N2 for
30 min.
An aqueous stock solution of FTMA at a fixed concentration of 50mM (about 2.3 wt%)
and aqueous stock solutions of NaSal at different concentrations were prepared.
Aqueous
solutions of mixed FTMA and NaSal were then prepared by gently vortex-mixing both stock
solutions at given molar ratios for 5 sec.
The samples thus prepared were equilibrated in a
thermostatic bath at 25ºC.
Freeze-Fracture TEM Method
A small amount of the sample solution was rapidly frozen by plunging into liquid propane
cooled with liquid nitrogen in a cryo-preparation system (LEICA EM CPC, LEICA Microsystems).
The frozen sample was transferred into a freeze-replica preparing apparatus (FR-7000A, Hitachi
S1
Science Systems, Ltd.) and fractured with a glass knife at -120°C.
A replica film was prepared by
evaporating platinum-carbon at 45° and then carbon at 90° onto the fractured sample face.
The
replica film thus obtained was washed several times with acetone and distilled water after being
taken out of the apparatus, transferred onto a 300-mesh copper grid, and observed with a
transmission electron microscope (JEM-1200EX, JEOL).
UV-vis Spectra Before and After Electrolytic Oxidation
Figure
S1
shows
UV-vis
spectra
for
aqueous
(CNaSal/CFTMA=0.4) before and after electrolytic oxidation.
FTMA(50mM)/NaSal
mixture
A peak assigned to the ferricinium
cation1,2 appeared at 628 nm and a peak assigned to ferrocenyl group1,2 at 440nm diminished
considerably in the UV-vis spectrum of the electrolyzed mixture.
This means that FTMA
Absorbance
molecules in the sample were oxidized by the electrolysis.
Wavelength / nm
Figure S1. UV-vis spectra for aqueous FTMA (50mM)/NaSal mixture (CNaSal/CFTMA=0.4) before and
after electrolytic oxidation.
S2
Rheological Behavior after electrolytic oxidation
We examined the viscoelastic behavior of the oxidized mixture with a double-concentric
cylinder type rheometer. The shear stress was proportional to the shear rate and no hysteresis was
observed between the flow curves obtained by increasing and then decreasing shear rate (Figure S2a).
The oxidized sample is therefore a Newtonian fluid with no elasticity and its viscosity has a value of
2.5×10-3 Pa⋅s (Figure S2b), which is about “1/6000” of the zero shear viscosity of the reduced
Shear stress / Pa
Viscosity η / Pa ⋅ s
sample.
Shear rate / s-1
(a)
Shear rate / s-1
(b)
Figure S2. (a) Flow and (b) viscosity curves for aqueous FTMA (50mM)/NaSal mixture
(CNaSal/CFTMA=0.4) after electrolytic oxidation.
S3
Reversible Control of Rheological Behavior
The sample solution described in our manuscript contains no added electrolyte except NaSal
to prevent the change in aggregation state.
In this solution condition, the electrochemical
reduction of the oxidized solution resulted in not enough recovery of viscosity of the solution
because the resulting formation of thick electric double layer on the electrode makes the diffusion
velocity slow.
In our recent experiments, however, we succeeded in reversible control of rheological
behavior using the FTMA/NaSal solution containing the added NaBr electrolyte (0.1 M).
In the
absence of additional electrolyte (NaBr), a reduced solution at the molar ratio CNaSal/CFTMA of 0.4
exhibited the highest viscoelasticity, while the addition of NaBr to the mixture produced two-phase
separation of the solution in this composition (Figure S3).
Then, an aqueous FTMA/NaSal
solution at the molar ratio of 0.2 containing 0.1M NaBr was used.
(a)
(b)
(c)
Figure S3. Photograph showing the appearance of aqueous FTMA(50mM)/NaSal mixtures containing
0.1M NaBr at the molar ratios of CNaSal/CFTMA=(a) 0, (b) 0.2, and (c) 0.4, respectively.
S4
The reduced solution with NaBr was a non-Newtonian fluid and the zero shear viscosity η0
for the mixture was about 0.65 Pa·s (Figure S4).
G’’
|η*|
|η*| / Pa⋅s
G’ or G’’ / Pa
G’
ω / rad ⋅ s-1
Figure S4. Storage modulus G’, loss modulus G’’, and the real part of the complex viscosity | η* | as a
function of angular frequency ω for aqueous FTMA (reduced form)/NaSal mixture with 0.1M NaBr
(CNaSal/CFTMA=0.2)
This viscoelastic solution was then oxidized by potentiostatic electrolysis at +0.5V vs. SCE.
The oxidized sample was a Newtonian fluid and its viscosity had a value of 1.2×10-3 Pa·s, which is
about 1/540 of the zero shear viscosity of the reduced sample (Figure S5).
S5
Viscosity / Pa ⋅ s
Shear stress / Pa
Shear rate / s-1
Shear rate / s-1
(a)
(b)
Figure S5. (a) Flow and (b) viscosity curves for aqueous FTMA/NaSal mixture (CNaSal/CFTMA=0.2) with
0.1M NaBr after electrolytic oxidation.
The following electrolytic reduction (0 V vs. SCE) of the oxidized solution causes the
recovery of rheological behavior and the viscosity was 0.38 Pa·s s (Figure S6).
This fact supports
our consideration that viscoelasticity change is caused by the redox reaction of FTMA but not by its
degradation.
Figure S7 shows the (zero shear) viscosities of aqueous FTMA(50mM)/NaSal
mixture (CNaSal/CFTMA=0.2) containing 0.1M NaSal measured during the repeated cycle between
oxidation and reduction states.
Incomplete recovery in viscoelasticity by the electrolytic
reduction seems to be caused by the slow diffusion of ferricinium cation to the electrode surface
because of the enhanced viscoelasticity as a result of the formation of the entangled worm-like
micelles.
S6
G’’
|η*|
|η*| / Pa⋅s
G’ or G’’ / Pa
G’
ω / rad ⋅ s-1
Figure S6.
Storage modulus G’, loss modulus G’’, and the real part of the complex viscosity | η* | as a
(Zero shear) viscosity / Pa ⋅ s
function of angular frequency ω after electrolytic reduction of the oxidized solution.
Oxidation Reduction
Figure S7. The (zero shear) viscosities of aqueous FTMA(50mM)/NaSal mixture (CNaSal/CFTMA=0.2)
containing 0.1M NaSal measured during the repeated cycle between oxidation and reduction states.
S7
Reference
1. Saji, T.; Hoshino, K.; Ishii, Y.; Goto, M. J. Am. Chem. Soc. 1991, 113, 450.
2. Saji, T.; Hoshino, K.; Aoyagui, S. J. Chem. Soc., Chem. Commun. 1985, 865.
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