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Reversible viscosity change of nanotubular colloidal aqueous suspensions responding to an electric field
Colloids and Surfaces A: Physicochem. Eng. Aspects 459 (2014) 1–3
Contents lists available at ScienceDirect
Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Reversible viscosity change of nanotubular colloidal aqueous suspensions responding to an electric field Kazuhiro Shikinaka a,∗ , Hiroshi Kimura b a b
Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei 184-8588, Japan Department of Chemistry and Biomolecular Science, Gifu University, Gifu 501-1193, Japan
h i g h l i g h t s
g r a p h i c a l
a b s t r a c t
• Imogolite
nanotube suspension shows viscosity change responding to electric field. • Shear stress increases by applying electric field, and decrease upon its removal. • Assembling of the IG nanotubes would result in the viscosity changes.
a r t i c l e
i n f o
Article history: Received 30 April 2014 Received in revised form 18 June 2014 Accepted 21 June 2014 Available online 28 June 2014 Keywords: Imogolite nanotube Electrorheological effect Non-Newtonian fluid Classical DLVO theory Electric double layer
a b s t r a c t Imogolite (IG), a perfect rigid inorganic nanotubular polyelectrolyte, shows good water dispersibility, particularly at neutral or lower pH, and affords solutions containing monofilaments and thin bundles. In this letter, we present reversible viscosity change of IG aqueous suspension responding to an electric field. The shear stress of the IG aqueous suspension (with a volume fraction 0.001) reaches 0.14 Pa under an 8.0 V/mm electric field and 19 s−1 shear rate. Application of an electric field would disturb the electric double layer of the IGs that affords their assembling in thick bundles and increases the viscosity of the suspension. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Reversible changes in rheological properties upon applying and removing an electric field to materials are defined as the electrorheological (ER) effect [1,2]. Due to the reversible response to the electric field, the ER effect has been of interest not in only academic investigations but also in industrial applications [3]. Previously, it has been reported that suspensions of particles with various shape (e.g., nano-fibrous polyaniline [4] and
∗ Corresponding author. Tel.: +81 42 388 7406; fax: +81 42 381 8175. E-mail address: [email protected] (K. Shikinaka). http://dx.doi.org/10.1016/j.colsurfa.2014.06.035 0927-7757/© 2014 Elsevier B.V. All rights reserved.
titanium-silicon coated carbon nanotube [5]) show the ER effect under the electric field of several kV/mm. Recently, one of the authors reported an aqueous suspension of hectorite particles in the deionized state that showed a change in viscosity upon the application of a direct current (DC) electric field on the order of a few V/mm [6]. It is possible to consider that the electrical double layer is easily deformed by applying an electric field, and that this deformation would weaken the repulsive forces among the particles and result in the formation of a three-dimensional network structure. Imogolite (IG), with the formula (HO)3 Al2 O3 SiOH [7–12], is a single-walled aluminosilicate-type clay nanotube having external and internal diameters of ∼2 and 1 nm, respectively. The IG
2
K. Shikinaka, H. Kimura / Colloids and Surfaces A: Physicochem. Eng. Aspects 459 (2014) 1–3
nanotube lengths range from several tens of nanometers to several m. Since IG is a perfectly rigid polyelectrolyte [13,14], it has been used as a constituent of inorganic–organic nanocomposites [15–17]. The outer and inner surfaces of IG are covered with aluminol and silanol groups, respectively, on which (de)protonation equilibrium processes such as Al(OH)2 + H+ Al(OH)O+ H2 (outer surface) and Si OH Si O− + H+ (inner surface) are known to occur. Therefore, the dispersibility of IG in water is highly dependent on the pH and ionic strength; that is, when dissolved in a neutral-to-acidic aqueous medium having relatively low ionic strength, IG yields solutions containing monofilaments and thin bundles [18]. Previously, one of the authors reported that synthesized, appropriate purified IGs were sonicated in pure water to obtain slightly opaque solutions with concentrations of 6.4 wt% (i.e., 0.16 mol/L with respect to the aluminol groups) [19,20]. The good dispersibility of IG in aqueous media and its (de)protonation equilibria encouraged us to estimate the ER effect of IG aqueous suspension as shown in hectorite aqueous suspension [6]. In this letter, we first disclose a reversible viscosity change of an IG aqueous suspension responding to the electric field (i.e., the ER effect). Then, a structural assessment of the suspended IGs after the application of an electric field was performed by means of transmission electron microscopy (TEM). 2. Materials and methods 2.1. Chemicals Deionized water, purified using a Milli-Q® Advantage A10® system (MilliporeTM , Eschborn, Germany), was used. Other reagent-grade chemicals for the synthesis of IG were purchased from Tokyo Kasei Chemicals or Wako Pure Chemical Industries, and used as received. 2.2. IG synthesis [19,20] Aqueous solutions of AlCl3 ·6H2 O (9.96 g in 369 mL) and Na4 SiO4 (6.90 g in 362 mL) were mixed to prepare a solution that was 12.5 mol/L in Al and 2.5 mol/L in Si. The pH of the mixture was adjusted as quickly as possible to 6.0 by adding 1.0 mol/L NaOH aq. (ca. 26 mL), while avoiding areas of localized high pH with appropriate agitation. The resulting solution was stirred for 1 h. The white precipitate was collected by centrifugation and redispersed in water (400 mL) with stirring. After adding additional water (2.4 L), the solution was acidified by the addition of 1.0 mol/L HCl (7–8 mL) to pH 4.5. The solution was then continuously stirred at 100 ◦ C for 4 d. After cooling to room temperature, finely powdered NaCl (16.4 g) was added to the solution with rapid agitation. The resulting gel was collected by centrifugation (5000 rpm, 30 min) and then washed portion-wise with water (500 mL) on a 100 nm Millipore filter with suction. The wet products (Caution!: Do not allow to dry.) were then freeze-dried. The yield was typically 42% which is based on an amount of AlCl3 ·6H2 O and Na4 SiO4 .
Fig. 1. The shear stress dependency as a function of shear rate under different DC electric fields for the IG suspension: open circles, 0 V/mm; crosses, 2.0 V/mm; triangles, 4.0 V/mm; squares, 6.0 V/mm; and closed circles, 8.0 V/mm.
capable of applying the electric field. The outer cup and inner cylinder were made of stainless steel. The outer cup and inner cylinder functioned as electrodes to apply a homogeneous DC electric field to the sample suspensions. The gap between the inner cylinder and the outer cup was 1.5 mm. The shear rate, , was controlled by the rotation speed of the outer cup. The electric field strength, E, was 2.0–8.0 V/mm. The measurement was performed at 25 ◦ C. 2.4. TEM observation The TEM observation was performed using a JEM-2100 (JEOL, Tokyo, Japan) at a 200 kV acceleration voltage. Sample solution (5 L) was dropped on carbon-coated grids (Oken Shouji Co., Tokyo), after their surfaces were made hydrophilic by a glow discharge under reduced pressure. After 3 min, the sample on the grid was blotted with filter paper, and then the grid was dried in an atmosphere of ethanol vapor according to the sample preparation method described previously [22]. The digital TEM data were obtained using a slow-scan charge-coupled device (CCD) camera (Gatan USC1000, Gatan Inc.) and converted into images with a frame size of 1024 × 1024 pixels. A cold finger and a cold trap cooled with liquid nitrogen were used to prevent sample contamination by the electron beams.
2.3. Viscoelastic measurements of IG aqueous suspension under an electric field An IG suspension (0.27 wt%, volume fraction ϕ = 0.001) in pure water which was sonicated for 4 h at 100 W (FU-21H, SD-Ultra Ltd., Korea) while the sonicator bath was maintained at room temperature by the occasional addition of ice. Using this procedure, transparent suspensions of IG were obtained. The structural stability of the IGs in pure water under an electric field (∼10 V) has been confirmed previously [21]. The viscoelastic behavior of the IG suspension under an electric field was measured with a modified coaxial-type rheometer (Rheosol-G2000W-GF, UBM Co., Ltd.)
Fig. 2. The change in the shear stress for an IG suspension without a DC electric field (t = 0–200 and 6500–9500 s) or with application of an 8.0 V/mm DC electric field (t = 200–6500 s) under 19 s−1 of shear rate. The broken line indicates the value of the water.
K. Shikinaka, H. Kimura / Colloids and Surfaces A: Physicochem. Eng. Aspects 459 (2014) 1–3
3
Fig. 3. TEM images of IGs in the suspension (a) before (t = 0 s in Fig. 2) or (b) after applying an 8 V/mm DC electric field (t = 6500 s in Fig. 2). (c) TEM image of IGs in the suspension after aging without DC electric field via applying an 8 V/mm DC electric field (t > 9500 s in Fig. 2).
Fig. 4. Schematic illustration of the reversible assembly/disassembly of the IGs due to the reducing/recovering of their electric double layer (EDL) responding to applying/removing the electric field.
3. Results and discussion The average length and diameter of the IGs in the prepared suspensions is 69 nm and 2.1 nm [19,20] with an aspect ratio of ∼32.9, respectively. A 0.27 wt% (ϕ = 0.001) IG suspension has low viscosity (i.e., it behaves as a typical Newtonian fluid). However, by applying an electric field to the suspension, the shear stress increases and the IG suspension behavior becomes non-Newtonian under a DC electric field greater than 6.0 V/mm (Fig. 1). Below a DC electric field of 8.0 V/mm and a 19 s−1 shear speed, the gradually increases and reaches 0.14 Pa (Fig. 2). Then, the removal of the DC electric field and continuous shear causes the decline of . The fact that the shear stress was recoverable by removing the electric field means that this system, under the electric field, exists in a secondary minimum of the potential energy curve, in light of classical DLVO theory. After application of the electric field, the IG suspension exhibits a gold color, i.e., the transmittance of the suspension at 450 nm (T450 ) changes from 100% to 82%. In TEM images of the dried suspension after applying the electric field, the IGs had assembled in thick bundles (Fig. 3(b)). The continuous shear after removal of the electric field diminishes the gold color in the suspension (T450 = 90%) that equals the disassembly of the thick bundles of IGs as shown in TEM image (Fig. 3(c)). These results indicate that the assembly/disassembly of the IGs causes reversible increases/decreases in the value, i.e., the ER effect of the IG suspension. Reducing/recovering in the electric double layer (EDL) of the IG surface by applying/removing an electric field would bring about the assembly/disassembly of the IG nanotubes (Fig. 4). This type of IG assembly also occurred under high pH conditions due to the decreasing electric field intensity of the IG surface [23]. In conclusion, the IG aqueous suspension shows reversible viscosity change responding to the electric field. This phenomenon is
typical ER effect: the shear stresses increase upon application of an electric field, and decrease upon its removal. The assembly of the IGs into thick bundles after applying the electric field would result in the shear stress increases, as indicated by viscosity changes, in the suspension. The ER effect of IG suspension is quite unique because it emerges in an aqueous system under the electric field of a few V/mm (typical nanotubular suspensions need the electric field of several kV/mm for emergence of ER effect [4,5]). Acknowledgements The authors acknowledge the supports of Ms. Tomomi Yokoi (Tokyo University of Agriculture and Technology) for her assistance with preparation of the IG suspension. This work was partly supported by the JSPS KAKENHI Grant Numbers 26870179 and 25550055. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]
T.C. Halsey, Science 258 (1992) 761–766. T. Hao, Adv. Mater. 13 (2001) 1847–1857. H. Block, J.P. Kelly, J. Phys. D: Appl. Phys. 21 (1988) 1661–1677. J. Yin, X. Zhao, X. Xia, L. Xiang, Y. Qiao, Polymer 49 (2008) 4413–4419. S.Y. Oh, T.J. Kang, Soft Matter 10 (2014) 3726–3737. H. Kimura, T. Sugiyama, S. Takahashi, A. Tsuchida, Rheol. Acta 52 (2013) 139–144. P.D.G. Cradwick, V.C. Farmer, J.D. Russell, C.R. Masson, K. Wada, N. Yoshinaga, Nat. Phys. Sci. 240 (1972) 187–189. S. Mukherjee, V.M. Bartlow, S. Nair, Chem. Mater. 17 (2005) 4900–4909. C. Levard, A. Masion, J. Rose, E. Doelsch, D. Borschneck, C. Dominici, F. Ziarelli, J.-Y. Bottero, J. Am. Chem. Soc. 131 (2009) 17080–17081. V.C. Farmer, M.J. Adams, A.R. Fraser, F. Palmieri, Clay Miner. 18 (1983) 459–472. L.A. Bursill, J.L. Peng, L.N. Bourgeois, Philos. Magn. A 80 (2000) 105–117. V.C. Farmer, A.R. Fraser, J.M. Tait, J. Chem. Soc., Chem. Commun. 13 (1977) 462–463. N. Donkai, H. Inagaki, K. Kajiwara, H. Urakawa, M. Schmidt, Makromol. Chem. 186 (1985) 2623–2638. J.B. Harsh, S.J. Traina, J. Boyle, Y. Yang, Clays Clay Miner. 40 (6) (1992) 700–706. K. Yamamoto, H. Otsuka, S. Wada, D. Sohn, A. Takahara, Soft Matter 1 (2005) 372–377. H. Yang, Y. Chen, Z. Su, Chem. Mater. 19 (2007) 3087–3089. A. Kuc, T. Heine, Adv. Mater. 21 (43) (2009) 4353–4356. J. Karube, Clays Clay Miner. 46 (5) (1998) 583–585. K. Shikinaka, Y. Koizumi, K. Kaneda, Y. Osada, H. Masunaga, K. Shigehara, Polymer 54 (2013) 2489–2492. K. Shikinaka, K. Kaneda, S. Mori, T. Maki, H. Masunaga, Y. Osada, K. Shigehara, Small 10 (9) (2014) 1813–1820. J. Park, J. Lee, S. Chang, T. Park, B. Han, J.W. Han, W. Yi, Bull. Korean Chem. Soc. 29 (2008) 1048–1050. H. Yang, Z. Su, Chin. Sci. Bull. 52 (16) (2007) 2301–2303. Y.L. Ma, J. Karube, Soil Sci. Plant. Nutr. 59 (2013) 125–129.
Contents lists available at ScienceDirect
Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Reversible viscosity change of nanotubular colloidal aqueous suspensions responding to an electric field Kazuhiro Shikinaka a,∗ , Hiroshi Kimura b a b
Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei 184-8588, Japan Department of Chemistry and Biomolecular Science, Gifu University, Gifu 501-1193, Japan
h i g h l i g h t s
g r a p h i c a l
a b s t r a c t
• Imogolite
nanotube suspension shows viscosity change responding to electric field. • Shear stress increases by applying electric field, and decrease upon its removal. • Assembling of the IG nanotubes would result in the viscosity changes.
a r t i c l e
i n f o
Article history: Received 30 April 2014 Received in revised form 18 June 2014 Accepted 21 June 2014 Available online 28 June 2014 Keywords: Imogolite nanotube Electrorheological effect Non-Newtonian fluid Classical DLVO theory Electric double layer
a b s t r a c t Imogolite (IG), a perfect rigid inorganic nanotubular polyelectrolyte, shows good water dispersibility, particularly at neutral or lower pH, and affords solutions containing monofilaments and thin bundles. In this letter, we present reversible viscosity change of IG aqueous suspension responding to an electric field. The shear stress of the IG aqueous suspension (with a volume fraction 0.001) reaches 0.14 Pa under an 8.0 V/mm electric field and 19 s−1 shear rate. Application of an electric field would disturb the electric double layer of the IGs that affords their assembling in thick bundles and increases the viscosity of the suspension. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Reversible changes in rheological properties upon applying and removing an electric field to materials are defined as the electrorheological (ER) effect [1,2]. Due to the reversible response to the electric field, the ER effect has been of interest not in only academic investigations but also in industrial applications [3]. Previously, it has been reported that suspensions of particles with various shape (e.g., nano-fibrous polyaniline [4] and
∗ Corresponding author. Tel.: +81 42 388 7406; fax: +81 42 381 8175. E-mail address: [email protected] (K. Shikinaka). http://dx.doi.org/10.1016/j.colsurfa.2014.06.035 0927-7757/© 2014 Elsevier B.V. All rights reserved.
titanium-silicon coated carbon nanotube [5]) show the ER effect under the electric field of several kV/mm. Recently, one of the authors reported an aqueous suspension of hectorite particles in the deionized state that showed a change in viscosity upon the application of a direct current (DC) electric field on the order of a few V/mm [6]. It is possible to consider that the electrical double layer is easily deformed by applying an electric field, and that this deformation would weaken the repulsive forces among the particles and result in the formation of a three-dimensional network structure. Imogolite (IG), with the formula (HO)3 Al2 O3 SiOH [7–12], is a single-walled aluminosilicate-type clay nanotube having external and internal diameters of ∼2 and 1 nm, respectively. The IG
2
K. Shikinaka, H. Kimura / Colloids and Surfaces A: Physicochem. Eng. Aspects 459 (2014) 1–3
nanotube lengths range from several tens of nanometers to several m. Since IG is a perfectly rigid polyelectrolyte [13,14], it has been used as a constituent of inorganic–organic nanocomposites [15–17]. The outer and inner surfaces of IG are covered with aluminol and silanol groups, respectively, on which (de)protonation equilibrium processes such as Al(OH)2 + H+ Al(OH)O+ H2 (outer surface) and Si OH Si O− + H+ (inner surface) are known to occur. Therefore, the dispersibility of IG in water is highly dependent on the pH and ionic strength; that is, when dissolved in a neutral-to-acidic aqueous medium having relatively low ionic strength, IG yields solutions containing monofilaments and thin bundles [18]. Previously, one of the authors reported that synthesized, appropriate purified IGs were sonicated in pure water to obtain slightly opaque solutions with concentrations of 6.4 wt% (i.e., 0.16 mol/L with respect to the aluminol groups) [19,20]. The good dispersibility of IG in aqueous media and its (de)protonation equilibria encouraged us to estimate the ER effect of IG aqueous suspension as shown in hectorite aqueous suspension [6]. In this letter, we first disclose a reversible viscosity change of an IG aqueous suspension responding to the electric field (i.e., the ER effect). Then, a structural assessment of the suspended IGs after the application of an electric field was performed by means of transmission electron microscopy (TEM). 2. Materials and methods 2.1. Chemicals Deionized water, purified using a Milli-Q® Advantage A10® system (MilliporeTM , Eschborn, Germany), was used. Other reagent-grade chemicals for the synthesis of IG were purchased from Tokyo Kasei Chemicals or Wako Pure Chemical Industries, and used as received. 2.2. IG synthesis [19,20] Aqueous solutions of AlCl3 ·6H2 O (9.96 g in 369 mL) and Na4 SiO4 (6.90 g in 362 mL) were mixed to prepare a solution that was 12.5 mol/L in Al and 2.5 mol/L in Si. The pH of the mixture was adjusted as quickly as possible to 6.0 by adding 1.0 mol/L NaOH aq. (ca. 26 mL), while avoiding areas of localized high pH with appropriate agitation. The resulting solution was stirred for 1 h. The white precipitate was collected by centrifugation and redispersed in water (400 mL) with stirring. After adding additional water (2.4 L), the solution was acidified by the addition of 1.0 mol/L HCl (7–8 mL) to pH 4.5. The solution was then continuously stirred at 100 ◦ C for 4 d. After cooling to room temperature, finely powdered NaCl (16.4 g) was added to the solution with rapid agitation. The resulting gel was collected by centrifugation (5000 rpm, 30 min) and then washed portion-wise with water (500 mL) on a 100 nm Millipore filter with suction. The wet products (Caution!: Do not allow to dry.) were then freeze-dried. The yield was typically 42% which is based on an amount of AlCl3 ·6H2 O and Na4 SiO4 .
Fig. 1. The shear stress dependency as a function of shear rate under different DC electric fields for the IG suspension: open circles, 0 V/mm; crosses, 2.0 V/mm; triangles, 4.0 V/mm; squares, 6.0 V/mm; and closed circles, 8.0 V/mm.
capable of applying the electric field. The outer cup and inner cylinder were made of stainless steel. The outer cup and inner cylinder functioned as electrodes to apply a homogeneous DC electric field to the sample suspensions. The gap between the inner cylinder and the outer cup was 1.5 mm. The shear rate, , was controlled by the rotation speed of the outer cup. The electric field strength, E, was 2.0–8.0 V/mm. The measurement was performed at 25 ◦ C. 2.4. TEM observation The TEM observation was performed using a JEM-2100 (JEOL, Tokyo, Japan) at a 200 kV acceleration voltage. Sample solution (5 L) was dropped on carbon-coated grids (Oken Shouji Co., Tokyo), after their surfaces were made hydrophilic by a glow discharge under reduced pressure. After 3 min, the sample on the grid was blotted with filter paper, and then the grid was dried in an atmosphere of ethanol vapor according to the sample preparation method described previously [22]. The digital TEM data were obtained using a slow-scan charge-coupled device (CCD) camera (Gatan USC1000, Gatan Inc.) and converted into images with a frame size of 1024 × 1024 pixels. A cold finger and a cold trap cooled with liquid nitrogen were used to prevent sample contamination by the electron beams.
2.3. Viscoelastic measurements of IG aqueous suspension under an electric field An IG suspension (0.27 wt%, volume fraction ϕ = 0.001) in pure water which was sonicated for 4 h at 100 W (FU-21H, SD-Ultra Ltd., Korea) while the sonicator bath was maintained at room temperature by the occasional addition of ice. Using this procedure, transparent suspensions of IG were obtained. The structural stability of the IGs in pure water under an electric field (∼10 V) has been confirmed previously [21]. The viscoelastic behavior of the IG suspension under an electric field was measured with a modified coaxial-type rheometer (Rheosol-G2000W-GF, UBM Co., Ltd.)
Fig. 2. The change in the shear stress for an IG suspension without a DC electric field (t = 0–200 and 6500–9500 s) or with application of an 8.0 V/mm DC electric field (t = 200–6500 s) under 19 s−1 of shear rate. The broken line indicates the value of the water.
K. Shikinaka, H. Kimura / Colloids and Surfaces A: Physicochem. Eng. Aspects 459 (2014) 1–3
3
Fig. 3. TEM images of IGs in the suspension (a) before (t = 0 s in Fig. 2) or (b) after applying an 8 V/mm DC electric field (t = 6500 s in Fig. 2). (c) TEM image of IGs in the suspension after aging without DC electric field via applying an 8 V/mm DC electric field (t > 9500 s in Fig. 2).
Fig. 4. Schematic illustration of the reversible assembly/disassembly of the IGs due to the reducing/recovering of their electric double layer (EDL) responding to applying/removing the electric field.
3. Results and discussion The average length and diameter of the IGs in the prepared suspensions is 69 nm and 2.1 nm [19,20] with an aspect ratio of ∼32.9, respectively. A 0.27 wt% (ϕ = 0.001) IG suspension has low viscosity (i.e., it behaves as a typical Newtonian fluid). However, by applying an electric field to the suspension, the shear stress increases and the IG suspension behavior becomes non-Newtonian under a DC electric field greater than 6.0 V/mm (Fig. 1). Below a DC electric field of 8.0 V/mm and a 19 s−1 shear speed, the gradually increases and reaches 0.14 Pa (Fig. 2). Then, the removal of the DC electric field and continuous shear causes the decline of . The fact that the shear stress was recoverable by removing the electric field means that this system, under the electric field, exists in a secondary minimum of the potential energy curve, in light of classical DLVO theory. After application of the electric field, the IG suspension exhibits a gold color, i.e., the transmittance of the suspension at 450 nm (T450 ) changes from 100% to 82%. In TEM images of the dried suspension after applying the electric field, the IGs had assembled in thick bundles (Fig. 3(b)). The continuous shear after removal of the electric field diminishes the gold color in the suspension (T450 = 90%) that equals the disassembly of the thick bundles of IGs as shown in TEM image (Fig. 3(c)). These results indicate that the assembly/disassembly of the IGs causes reversible increases/decreases in the value, i.e., the ER effect of the IG suspension. Reducing/recovering in the electric double layer (EDL) of the IG surface by applying/removing an electric field would bring about the assembly/disassembly of the IG nanotubes (Fig. 4). This type of IG assembly also occurred under high pH conditions due to the decreasing electric field intensity of the IG surface [23]. In conclusion, the IG aqueous suspension shows reversible viscosity change responding to the electric field. This phenomenon is
typical ER effect: the shear stresses increase upon application of an electric field, and decrease upon its removal. The assembly of the IGs into thick bundles after applying the electric field would result in the shear stress increases, as indicated by viscosity changes, in the suspension. The ER effect of IG suspension is quite unique because it emerges in an aqueous system under the electric field of a few V/mm (typical nanotubular suspensions need the electric field of several kV/mm for emergence of ER effect [4,5]). Acknowledgements The authors acknowledge the supports of Ms. Tomomi Yokoi (Tokyo University of Agriculture and Technology) for her assistance with preparation of the IG suspension. This work was partly supported by the JSPS KAKENHI Grant Numbers 26870179 and 25550055. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]
T.C. Halsey, Science 258 (1992) 761–766. T. Hao, Adv. Mater. 13 (2001) 1847–1857. H. Block, J.P. Kelly, J. Phys. D: Appl. Phys. 21 (1988) 1661–1677. J. Yin, X. Zhao, X. Xia, L. Xiang, Y. Qiao, Polymer 49 (2008) 4413–4419. S.Y. Oh, T.J. Kang, Soft Matter 10 (2014) 3726–3737. H. Kimura, T. Sugiyama, S. Takahashi, A. Tsuchida, Rheol. Acta 52 (2013) 139–144. P.D.G. Cradwick, V.C. Farmer, J.D. Russell, C.R. Masson, K. Wada, N. Yoshinaga, Nat. Phys. Sci. 240 (1972) 187–189. S. Mukherjee, V.M. Bartlow, S. Nair, Chem. Mater. 17 (2005) 4900–4909. C. Levard, A. Masion, J. Rose, E. Doelsch, D. Borschneck, C. Dominici, F. Ziarelli, J.-Y. Bottero, J. Am. Chem. Soc. 131 (2009) 17080–17081. V.C. Farmer, M.J. Adams, A.R. Fraser, F. Palmieri, Clay Miner. 18 (1983) 459–472. L.A. Bursill, J.L. Peng, L.N. Bourgeois, Philos. Magn. A 80 (2000) 105–117. V.C. Farmer, A.R. Fraser, J.M. Tait, J. Chem. Soc., Chem. Commun. 13 (1977) 462–463. N. Donkai, H. Inagaki, K. Kajiwara, H. Urakawa, M. Schmidt, Makromol. Chem. 186 (1985) 2623–2638. J.B. Harsh, S.J. Traina, J. Boyle, Y. Yang, Clays Clay Miner. 40 (6) (1992) 700–706. K. Yamamoto, H. Otsuka, S. Wada, D. Sohn, A. Takahara, Soft Matter 1 (2005) 372–377. H. Yang, Y. Chen, Z. Su, Chem. Mater. 19 (2007) 3087–3089. A. Kuc, T. Heine, Adv. Mater. 21 (43) (2009) 4353–4356. J. Karube, Clays Clay Miner. 46 (5) (1998) 583–585. K. Shikinaka, Y. Koizumi, K. Kaneda, Y. Osada, H. Masunaga, K. Shigehara, Polymer 54 (2013) 2489–2492. K. Shikinaka, K. Kaneda, S. Mori, T. Maki, H. Masunaga, Y. Osada, K. Shigehara, Small 10 (9) (2014) 1813–1820. J. Park, J. Lee, S. Chang, T. Park, B. Han, J.W. Han, W. Yi, Bull. Korean Chem. Soc. 29 (2008) 1048–1050. H. Yang, Z. Su, Chin. Sci. Bull. 52 (16) (2007) 2301–2303. Y.L. Ma, J. Karube, Soil Sci. Plant. Nutr. 59 (2013) 125–129.