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J. Phys. Chem. B 2008, 112, 12618–12624
Effect of Initial Substrate Concentration of the Belousov-Zhabotinsky Reaction on Self-Oscillation for Microgel System Daisuke Suzuki† and Ryo Yoshida*,†,‡ Department of Materials Engineering, Graduate School of Engineering, The UniVersity of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan, and PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama, Japan ReceiVed: April 30, 2008; ReVised Manuscript ReceiVed: August 3, 2008
Self-oscillation for the microgel particles (∼200 nm in diameter) was studied by changing initial substrate concentrations (i.e., malonic acid, sodium bromate, and nitric acid) of the Belousov-Zhabotinsky (BZ) reaction that is used for chemical energy for the self-oscillation. The cross-linked microgels are composed of N-isopropylacrylamide and ruthenium tris(2,2′-bipyridine), Ru(bpy)3, which is a catalyst for the BZ reaction. Comparing with the homogeneous, stirred solution of the bulk solution for the BZ reaction, swelling/deswelling oscillation of the microgels showed longer induction period, different dependence of initial substrate concentrations on oscillation period, and different oscillation rhythm. The change in oscillation for the microgels can be understood by considering the microgel network effect. Introduction reaction1
The Belousov-Zhabotinsky (BZ) has been a research subject of nonlinear dynamics including chemical, physical and biological interest. The BZ reaction shows temporal or spatio-temporal structures such as redox oscillation of the catalyst, and traveling waves.1-5 The overall process of the BZ reaction is the oxidation of an organic substrate such as citric or malonic acid by an oxidizing agent (bromate) in the presence of metal catalyst under acidic conditions. Metal ions or a metal complex with high redox potential, such as cerium ion, ferroin, or ruthenium tris(2,2′-bipyridine), Ru(bpy)3, are widely used as catalysts. Over the past decade, our group has investigated the “selfoscillating” gel,6-10 which shows a periodical swelling/deswelling oscillation with the redox oscillation of the BZ reaction induced inside the gel. The hydrogels are composed of crosslinked N-isopropylacrylamide (NIPAm) and Ru(bpy)3, a catalyst for the BZ reaction. Poly-NIPAm, denoted pNIPAm, is a representative thermosensitive polymer exhibiting a lower critical solution temperature (LCST) around 32 °C,11,12 and LCST is altered by copolymerization of the charged species including Ru(bpy)3. So, the hydrogel swells in the oxidized RuIII state, and deswells in the reduced RuII state, respectively, at constant temperature. Using the self-oscillating gel, so far, our group has developed “self-walking” actuators13 with millimeter size, which may be useful as artificial muscles. Recently, we have synthesized monodispersed, self-oscillating microgel particles (less than 1 µm in diameter) by surfactantfree aqueous precipitation polymerization.14,15 Compared to macrogels, microgels additionally have the properties of colloidal dispersions16-19 (e.g., microgel particles are used as microreactors,20 emulsifiers,21 and photonic crystals22). Thus, the self-oscillating microgels may be useful not only as artificial * Author to whom correspondence should be addressed. E-mail: ryo@ cross.t.u-tokyo.ac.jp. † Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo. ‡ PRESTO, Japan Science and Technology Agency.
oscillators, but also as rheological modifiers, light modulating liquid, and so on. Moreover, we have found that the selfoscillating microgels showed not only swelling/deswelling oscillation, but also flocculating/dispersing oscillation at around the volume phase transition temperature (VPTT) of the microgels, which is because interparticle interaction among the microgels is periodically changed by both redox oscillation of the Ru(bpy)3 catalyst and volume oscillation of the microgels.14,15 This new technology that changes interparticle interactions periodically and autonomously would be useful for regulating microgel assembly. For this purpose, understanding of the microgel oscillation should be important. It has been suggested from our previous study that the microgel oscillation is controlled by cross-linking network structures (i.e., the BZ reaction of cross-linked microgels show longer duration of refractory state and shorter duration of resting state than that of the bulk solution.).15 In this study, in order to clarify the effect of the gel network structure on the microgel oscillation, and to understand the microgel oscillation more deeply, we carried out the BZ reaction using the Ru(bpy)3immobilized microgels by changing initial substrate concentrations (i.e., malonic acid, sodium bromate, and nitric acid). The oscillation profiles of the optical transmittance were measured at an isosbestic point (570 nm) of the RuII and the RuIII states for the microgel systems to neglect absorbance changes of the Ru(bpy)3 catalyst, while the oscillation profiles for the stirred, bulk solution of the BZ reaction were detected at 460 nm, which is the wavelength of maximum absorbance for the RuII state. By comparing induction period, oscillation period, and oscillation waveforms between the microgel systems and the bulk solution system, effect of the Ru(bpy)3 immobilization into microgels on the oscillation reaction was discussed. Experimental Details Materials. Unless stated otherwise, all reagents were purchased from Wako Pure Chemical Industries, Ltd. N-Isopropylacrylamide (NIPAm, Sigma-Aldrich) was recrystallized from hexanes and dried in vacuo prior to use. The cross-linker N,N′methylenebisacrylamide (BIS, Kanto Chemical Co., Inc.), the
10.1021/jp8037973 CCC: $40.75 2008 American Chemical Society Published on Web 09/12/2008
Effect of Initial Substrate Concentration
J. Phys. Chem. B, Vol. 112, No. 40, 2008 12619
Figure 1. Chemical structure of the microgel.
TABLE 1: Microgel Sizes Under the RuII and the RuIII States Ru(bpy)3 amount, mol % samplea
Fed
Introducedb
NRu1(1) NRu1(10)
1 1
0.56 0.50
RuII state
RuIII state
D, nmc PDIc
D, nmc
PDIc
227 167
0.042 0.026
210 156
0.026 0.008
a In the sample code, N and Ru stand for NIPAm and Ru(bpy)3, respectively, while the number following each letter represents the mole percentage of Ru(bpy)3 fed in polymerization. After the number, the mole percentage of BIS fed in polymerization is shown in bracket. b Introduced Ru(bpy)3 amount into the microgels were calculated using absorption of Ru(bpy)3. c D denotes hydrodynamic diameters of microgels and PDI is polydispersity index.
Figure 2. Typical self-oscillating profiles of optical transmittance for NRu1(1) microgels. The microgels (100 µM of Ru(bpy)3) were dispersed in aqueous solutions containing MA(62.5 mM), NaBrO3 (84 mM), and HNO3 (0.3 M) at 25 °C.
initiator azobis-amidinopropane dihydrochloride (V-50) were all used as received. Ruthenium(II) (4-vinyl-4′-methyl-2,2′bipyridine)bis(2,2′-bipyridine)bis(hexafluorophosphate) [Ru(bpy)3 monomer] was synthesized according to the previous work.8,23 Malonic acid (MA), sodium bromate (NaBrO3, Kanto Chemical Co., Inc.), nitric acid (HNO3, Kanto Chemical Co., Inc.) and sodium chloride (NaCl) were all used as received. Water for all reactions, solution preparation, and polymer purification was first distilled then ion-exchanged. Preparation of Poly(NIPAm-co-Ru(bpy)3) Microgels. The Ru(bpy)3 copolymerized pNIPAm microgels were prepared via surfactant-free aqueous radical precipitation polymerization as previously reported.14,15 The chemical structure of the microgel is shown in Figure 1. A mixture of NIPAm, Ru(bpy)3, BIS, and water (95 mL) was poured into a 200-mL three-neck, roundbottom flask equipped with a stirrer, a condenser, and a nitrogen gas inlet. The initial total monomer concentration was held constant at 150 mM, and the comonomer ratio, (99 - X:1:X) (NIPAm:Ru(bpy)3:BIS), was varied according to the desired
Figure 3. Effect of initial substrate concentrations on induction period for the bulk solution system (black diamond) and the microgel systems of NRu1(1) (blue open triangle) and NRu1(10) (red open square). One substrate concentration was varied at constant concentrations of the others. Ru(bpy)3 concentration in all system is fixed at 100 µM.
cross-linker concentration. Under a stream of nitrogen to purge oxygen and with constant stirring at 200 rpm, the solution was heated in an oil bath to 70 °C. After stabilizing the solution for 1 h, the V-50 initiator (0.054 g) dissolved in 5 mL water was added to the flask to start the polymerization, which then continued for 6 h. After polymerization, the dispersion was cooled to room temperature. The obtained microgels were purified by centrifugation/redispersion with water four times using a relative centrifugal force (RCF) of 52 490g, and by daily changes of water by means of dialysis for a week. Microgel sizes were determined by dynamic light scattering (DLS, Malvern, Zetasizer3000HSA). Diluted microgels were analyzed in a quartz cuvette. The samples were allowed to equilibrate at the desired temperature for 10 min before data collection. Scattered light was collected at 90°. The amount of introduced Ru(bpy)3 into the microgels was calculated on the basis of UV-vis measurements (Shimadzu UV-2500PC). Absorbance at 460 nm, which is a wavelength
12620 J. Phys. Chem. B, Vol. 112, No. 40, 2008
Suzuki and Yoshida detect the redox change of Ru(bpy)3 for the homogeneous (stirred) bulk solution system.14,15 Results and Discussion
Figure 4. Effect of initial substrate concentrations on oscillation period for the bulk solution system (black diamond) and the microgel systems of NRu1(1) (blue open triangle) and NRu1(10) (red open square). One substrate concentration was varied at constant concentrations of the others. Ru(bpy)3 concentration in all system is fixed at 100 µM.
of the maximum absorbance for [Ru(bpy)3]2+, of the microgels dispersed in pure water was determined to calculate the introduced Ru(bpy)3 monomer into the microgels. Measurements of Microgel Oscillation Profiles. The volume oscillations of the microgels were detected by changes in optical transmittance, which is collected on a Shimadzu UV-2500PC spectrophotometer. The microgels (100 µM of Ru(bpy)3) were dispersed in the aqueous solution containing MA, NaBrO3, and HNO3. Under constant temperature (25 °C) and stirring conditions, the time course of transmission was monitored. The Ru(bpy)3 complex has different absorption spectra in the reduced RuII state and the oxidized RuIII state as an inherent property. The solution exhibited the absorption maximum at ∼460 nm in the reduced state and at ∼420 nm in the oxidized state, and has isosbestic point at 570 nm. In this study, the 570-nm wavelength was selected to detect the swelling/deswelling signals of microgels while the 460 nm wavelength was used to
The self-oscillating microgel was prepared by surfactant-free aqueous precipitation polymerization using NIPAm, Ru(bpy)3 monomer, and BIS cross-linker as described in our previous paper.14,15 Table 1 shows the information on the microgels used in this study. Figure 2 shows the oscillation profiles of optical transmittance for the microgel dispersion. Here the oscillation is observed after an induction period, which is a typical phenomenon of the BZ reaction. In the present study, our aim is to clarify the characteristics of the self-oscillation for the catalyst-immobilized microgel system, in other word, the effect of Ru(bpy)3 catalyst immobilization into the cross-linked microgels on the BZ reaction. Characteristics of the BZ reaction in the microgel system would resemble that of enzyme reaction in the microgel. The effects of enzyme immobilization on the kinetic behavior of enzymes can be classified as follows:24 (i) partitioning effects; (ii) microenvironmental effects; (iii) diffusional or mass-transfer effects. These effects change the rate of immobilized enzyme reaction by causing differences between the bulk and gel network in the concentrations of substrates, products, and other effectors. Thus, we thought a kinetic study of the reactions in the bulk and the immobilized system as a function of initial substrate concentrations would be a classic and reliable approach for better understanding the self-oscillation of microgel. In the present case in which oscillating redox changes take place, one should encounter a principal difficulty about how to estimate the oxidizing and reducing rates. To overcome this problem, we examined the oscillation period, induction period, and oscillation waveform both in the bulk and the microgel systems as a function of each initial substrate concentration. Effect of Initial Substrate Concentrations on Induction Period. Figure 3 shows the effect of initial substrate concentrations on induction period. Herein, one substrate was changed under fixed concentrations of the other substrates. From these results, it is clear that there are some differences in induction period of the BZ reactions between the bulk solution and the microgel systems. In the case of initial HNO3 concentration, [HNO3]0, dependence as shown in Figure 2a, induction period became longer with increasing [HNO3]0 in all samples. Then, induction period for the microgel systems became longer than that for the bulk solution, and it became longer as cross-linked density of microgels increased. In addition, the concentration dependence became stronger in the microgel systems than in the bulk solution. The most accepted hypothesis to explain the induction period of the BZ reaction is that crucial concentration of the organic brominated species, mainly bromomalonic acid (BrMA), must be reached before oscillation begins.4,25 So, the longer induction period for the microgel systems can be understood by the effect of Ru(bpy)3 immobilization into microgels, i.e., Ru(bpy)3 immobilization into microgel network resulted in the lowered rate of BrMA production reactions mainly due to difficulties in the diffusion or mass transfer of the substrates into microgels. Increase in induction periods with increasing [HNO3]0 should be also a result of the lowered rate of BrMA production although we can not explain the particular reaction in detail due to complexity of the BZ reaction. In the case of initial NaBrO3 concentration, [NaBrO3]0, dependence as shown in Figure 2b, induction period for the microgel systems showed different tendency against [NaBrO3]0
Effect of Initial Substrate Concentration
J. Phys. Chem. B, Vol. 112, No. 40, 2008 12621
Figure 5. Typical oscillation waveforms in bulk solution (a-c), and NRu1(1) microgels (d-f) containing different initial concentrations of HNO3 ()[HNO3]0). [HNO3]0 was varied at constant concentrations of NaBrO3 (84 mM), MA (62.5 mM), and Ru(bpy)3 (100 µM).
from that for the bulk solution (i.e., induction period became longer with increasing [NaBrO3]0 for the microgel systems while it was almost constant for the bulk solution). It is known that critical BrMA concentration for beginning oscillation depends on [NaBrO3]0 (i.e., an increase in critical BrMA concentration as [NaBrO3]0 increases.)4,26 although it does not agree with mechanistic explanation based on FKN models. This previous experimental results well correspond to our results for the microgel systems, but do not correspond to that for the bulk solution. The difference between for the microgel systems and for the bulk solution may be due to other factors related to induction period such as metal catalyst and MA concentrations. In fact, the tendency that the longer induction period with increasing [NaBrO3]0 became stronger with decreasing metal catalyst concentration for cerium ion system.26 In our system here, effective concentration of Ru(bpy)3 for the microgel systems should be lower than that for the bulk solution due to the cross-linking networks effects.24 Thus, the different tendency of induction period with increasing [NaBrO3]0 between for the microgel systems and for the bulk solution might be mainly due to differences in the apparent Ru(bpy)3 concentrations. In the case of initial MA concentration, [MA]0, dependence as shown in Figure 2c, induction period became shorter with increasing [MA]0 in all samples. Induction period for the microgel systems became longer than that for the bulk solution at any [MA]0, and it became longer as cross-linked density of microgels increased, particularly at low [MA]0 (84 mM), while there are large differences in the oscillation period at high [MA]0 between the bulk solution and the microgel systems. As a result, NaBrO3 was found to be the most effective substrate to control oscillation period for the microgel system (e.g., 50-300 s for the NRu1(1) microgel system). In order to clarify the dependence of initial substrate concentrations on the oscillation period, we compared the representative waveforms observed in the bulk solution and NRu1(1) microgel system. Before comparing these waveforms, we will provide the outline of the FKN mechanism.2-4 According to this scheme, the overall BZ reaction may be divided into the following three main processes: consumption of bromide ion (process A), autocatalytic reaction of bromous acid with oxidation of the catalyst (process B), and organic reaction with reduction of the catalyst (process C).
BrO3- + 2Br- + 3H+ f 3HOBr (A) + BrO3 + HBrO2 + 2Mred + 3H f 2HBrO2 + 2Mox + H2O (B) -
2Mox + MA + BrMA f fBr + 2Mred + other products (C) Following the FKN mechanism, we divided the waveforms into processes A, B, and C as shown in Figures 5-7. Here we define
each process as follows: region where transmittance is constant (process A), region where transmittance increases (process B), and region where transmittance decreases (process C). Tables 2–4 summarizes the oscillation periods Posc, durations of processes A-C, and A/Posc, B/Posc and C/Posc values for the bulk solution and the microgel systems. Herein, B/Posc values were neglected for discussion because changes in the values were too small. For the bulk solution, A/Posc values dramatically decreased as [HNO3]0 increased, while C/Posc values dramatically increased as [HNO3]0 increased (see Figure 5 and Table 2). This is reasonable because process A includes H+; thus, the rate of process A reaction became faster as [HNO3]0 increased. For NRu1(1) microgel system, the same tendency appears as the bulk solution, but degree of change became smaller. This difference between the bulk solution and the microgel system is due to the cross-linking network effect on the oscillation, i.e., the lowered rate of process C reaction due to less accessibility of substrates to Ru(bpy)3 catalyst, and the shorten duration of process A for the microgel systems.15 As a result, we found that the shorten oscillation period with increasing [HNO3]0 both in the bulk solution and the microgel systems are mainly due to shorten duration of process A, and degree of change was due to the cross-linking network effect in the microgel system. Note that clearly different waveform was observed at 0.5 M (Figure 5f). This is due to self-flocculating/ self-dispersing oscillation of microgels,14 indicating that the
Effect of Initial Substrate Concentration
J. Phys. Chem. B, Vol. 112, No. 40, 2008 12623
Figure 7. Typical oscillation waveforms in bulk solution (a-c), and NRu1(1) microgels (d-f) containing different initial concentrations of MA ()MA]0). [MA]0 was varied at constant concentrations of HNO3 (0.3 M), NaBrO3 (84 mM), and Ru(bpy)3 (100 µM).
TABLE 2: A/Posc, B/Posc, and C/Posc Values as a Function of [HNO3]0 for the Bulk Solution System and the NRu1(1) Microgel System sample bulk solution bulk solution bulk solution NRu1(1) NRu1(1) NRu1(1)
[HNO3]0, M Posc, s A, s B, s C, s A/Posc B/Posc C/Posc 0.2 0.4 0.5 0.2 0.4 0.5
187 91 86 118 95 83
132 9 46 34 7 50 23 8 55 32 17 69 13 11 71 N.A. 13 N.A.
0.71 0.37 0.27 0.27 0.14 0.16
0.05 0.08 0.09 0.14 0.12
0.25 0.55 0.64 0.58 0.75
TABLE 3: A/Posc, B/Posc, and C/Posc Values as a Function of [NaBrO3]0 for the Bulk Solution System and the NRu1(1) Microgel System sample bulk solution bulk solution bulk solution NRu1(1) NRu1(1) NRu1(1)
[NaBrO3]0, mM Posc, s A, s B, s C, s A/Posc B/Posc C/Posc 42 168 200 42 168 200
282 84 72 185 65 58
199 32 28 56 7 N.A.
21 18 13 23 8 8
62 34 31 106 50 N.A.
0.71 0.38 0.39 0.30 0.11 0.14
0.07 0.21 0.18 0.12 0.12
0.22 0.40 0.43 0.57 0.77
phase transition temperature should be changed, thus degree of swelling were changed slightly by changing [HNO3]0 in the microgel systems. As can be seen from Figure 6 and Table 3, A/Posc values dramatically decreased as [NaBrO3]0 increased, while C/Posc values increased as [NaBrO3]0 increased in the bulk solution.
TABLE 4: A/Posc, B/Posc, and C/Posc Values as a Function of [MA]0 for the Bulk Solution System and the NRu1(1) Microgel System sample bulk solution bulk solution bulk solution NRu1(1) NRu1(1) NRu1(1)
[MA]0, mM Posc, s A, s B, s C, s A/Posc B/Posc C/Posc 20 125 200 20 125 200
175 93 84 149 84 56
104 37 37 26 20 11
8 8 6 15 18 13
63 48 41 108 46 36
0.59 0.40 0.44 0.17 0.24 0.20
0.05 0.09 0.07 0.10 0.21 0.23
0.36 0.52 0.49 0.72 0.55 0.64
This is reasonable because process A includes BrO3-, thus the rate of process A became faster with increasing [NaBrO3]0. For NRu1(1) microgel system, the same tendency appears as the bulk solution. But, difference was seen in degree of change; it became smaller in process A, but larger in process C. This can be also explained by the cross-linking network effect on the oscillation as mentioned above for the dependence of [HNO3]0. In addition, we also found self-flocculating/self-dispersing oscillation of microgels14 at 200 mM, which is also due to change of the phase transition temperature of the microgel (Figure 6f). Different from the dependences of [HNO3]0 and [NaBrO3]0, C/Posc value increased with increasing [MA]0 for the bulk solution, while the oscillation period decreases (see Figure 7 and Table 4). According to the FKN mechanism, MA should affect process C, thus the rate of process C should be faster with increasing [MA]0. Indeed, durations of process C became
12624 J. Phys. Chem. B, Vol. 112, No. 40, 2008 short, which is the same as the [NaBrO3]0 dependence. But deference is seen in process A; degree of shorten duration of process A is smaller in [MA]0 dependent than in [NaBrO3]0 dependent with increasing the concentrations. For NRu1(1) microgel system, the same tendency appears as the bulk solution; durations of processes A, C decrease. But, because of the crosslinking network structure effect, durations of processes A and C are preaffected in the microgel systems. Thus, degree of shorten duration of process C with increasing [MA]0 for the microgel system might become larger than for the bulk solution. As a result, the cross-linking network effect led to strong dependence of [MA]0 in the microgel system. Conclusion For the submicrometer-sized Ru(bpy)3 copolymerized pNIPAm microgels dispersing in solvent, the swelling/deswelling selfoscillation was studied by changing initial substrate concentrations of the BZ reaction which is used for chemical energy of the self-oscillation. By comparing with the bulk solution of the BZ reaction in terms of induction period, oscillation period, and oscillation waveforms, effect of catalyst immobilization into the microgel network structures became clear. The obtained results are summarized as follows: (i) Induction period for the microgel systems became longer than for the bulk solution at any initial substrate concentrations. In addition, induction period became longer with increasing cross-linked density of microgels at any initial substrate concentrations. These results are due to the cross-linking network effect on Ru(bpy)3 catalyst, i.e., the rate of BrMA production became smaller by immobilizing the Ru(bpy)3 catalyst into microgels due to less accessibility of substrates to Ru(bpy)3, following to longer induction period. (ii) Oscillation period for the microgel systems depends on the initial substrate concentrations. Each substrate affects particular oscillation processes divided by the FKN mechanism. In contrast to [MA]0 dependence, dependences of [HNO3]0 and [NaBrO3]0 for the microgel systems became weaker than that for the bulk solution. The difference among each substrate can be understood by considering the cross-linking network effect, that it, the longer duration of process C and shorter duration of process A. As a result, NaBrO3 was found to be the most effective substrate to control oscillation period for the microgel system (e.g., 50-300 s for the NRu1(1) microgel system). Acknowledgment. D.S. is grateful to the research fellowships of the Japan Society for the Promotion of Science for Young Scientists.
Suzuki and Yoshida References and Notes (1) Zaikin, A. N.; Zhabotin, A. M. Nature 1970, 225, 535–537. (2) Field, R. J.; Ko¨ro¨s, E.; Noyes, R. M J. Am. Chem. Soc. 1972, 1 94, 8649–8664. (3) Field, R. J.; Noyes, R. M. J. Chem. Phys. 1974, 60, 1877–1884. (4) Field, R. J.; Burger, M. Oscillations and TraVeling WaVes in Chemical Systems; John Wiley & Sons: New York, 1985. (5) Epstein, I. R.; Pojman, J. A. An Introduction to Nonlinear Chemical Dynamics: Oscillation, WaVes, Patterns, and Chaos; Oxford University Press: New York, 1998. (6) Yoshida, R.; Takahashi, T.; Yamaguchi, T.; Ichijo, H. J. Am. Chem. Soc. 1996, 118, 5134–5135. (7) Yoshida, R.; Tanaka, M.; Onodera, S.; Yamaguchi, T.; Kokufuta, E. J. Phys. Chem. A 2000, 104, 7549–7555. (8) Yoshida, R.; Onodera, S.; Yamaguchi, T.; Kokufuta, E. J. Phys. Chem. A 1999, 103, 8573–8578. (9) Yoshida, R.; Kokufuta, E.; Yamaguchi, T. CHAOS 1999, 9, 260– 266. (10) Yoshida, R.; Takei, K.; Yamaguchi, T. Macromolecules 2003, 36, 1759–1761. (11) Heskins, M.; Guillet, J. E. J. Macromol. Sci., Chem. 1968, A2, 1441–1455. (12) Schild, H. G. Prog. Polym. Sci. 1992, 17, 163–249. (13) Maeda, S.; Hara, Y.; Sakai, T.; Yoshida, R.; Hashimoto, S. AdV. Mater. 2007, 19, 3480–3484. (14) Suzuki, D.; Sakai, T.; Yoshida, R. Angew. Chem., Int. Ed. 2008, 47, 917–920. (15) Suzuki, D.; Yoshida, R. Macromolecules 2008, 41, 5830–5838. (16) Pelton, R. AdV. Colloid Interface Sci. 2000, 85, 1–33. (17) Nayak, S.; Lyon, L. A. Angew. Chem., Int. Ed. 2005, 44, 7686– 7708. (18) Saunders, B. R.; Vincent, B. AdV. Colloid Interface Sci. 1999, 80, 1–25. (19) Kawaguchi, H. Prog. Polym. Sci. 2000, 25, 1171–1210. (20) (a) Suzuki, D.; Kawaguchi, H. Langmuir 2005, 21, 8175–8179. (b) Suzuki, D.; Kawaguchi, H. Langmuir 2005, 21, 12016–12024. (c) Suzuki, D.; Kawaguchi, H. Langmuir 2006, 22, 3818–3822. (d) Suzuki, D.; Kawaguchi, H. Colloid Polym. Sci. 2006, 284, 1443–1451. (21) (a) Fujii, S.; Read, E. S.; Binks, B. P.; Armes, S. P. AdV. Mater. 2005, 17, 1014–1018. (b) Suzuki, D.; Tsuji, S.; Kawaguchi, H. J. Am. Chem. Soc. 2007, 129, 8088–8089. (22) (a) Weissman, J. M.; Sunkara, H. B.; Tse, A. S.; Asher, S. A. Science 1996, 274, 959–960. (b) Suzuki, D.; McGrath, J. G.; Kawaguchi, H.; Lyon, L. A. J. Phys. Chem. C 2007, 111, 5667–5672. (c) Lyon, L. A.; Debord, J. D.; Debord, S. B.; Jones, C. D.; McGrath, J. G.; Serpe, M. J. J. Phys. Chem. B 2004, 108, 19099–19108. (23) Ghosh, P. K.; Spiro, T. G. J. Am. Chem. Soc. 1980, 102, 5543– 5549. (24) Kokufuta, E. Prog. Polym. Sci. 1992, 17, 647–697. (25) Sirimungkala, A.; Forsterling, H. D.; Dlask, V.; Field, R. J. J. Phys. Chem. A 1999, 103, 1038–1043. ´ greda, J. A.; Barraga´n, D. J. Braz. Chem. (26) Cadena, A.; Pe´rez, N.; A Soc. 2005, 16, 214–219. (27) Smoes, M.-L J. Phys. Chem. 1979, 71, 4669–4679.
JP8037973
