Article pubs.acs.org/JPCB
Influence of Belousov−Zhabotinsky Substrate Concentrations on Autonomous Oscillation of Polymer Chains with Fe(bpy)3 Catalyst Yusuke Hara,*,† Hiroyuki Mayama,‡ and Kenji Fujimoto§ †
Nanosystem Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), Central 5-2, 1-1-1 Higashi, Tsukuba 305-8565, Japan ‡ Department of Chemistry, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa 078-8510, Japan § Fuji Molecular Planning Co., Ltd., Techno-Core 4F-A, Yokohama-Kanazawa High Tech Center, 1-1-1, Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan ABSTRACT: We studied the effect of initial substrate concentrations in the Belousov−Zhabotinsky (BZ) reaction on the optical transmittance self-oscillation behavior of a polymer chain consisting of N-isopropylacrylamide (NIPAAm) and a Fe catalyst ([Fe(bpy)3]). The driving force of this transmittance self-oscillation was the solubility difference between the reduced and oxidized states of the [Fe(bpy)3] moiety in the polymer chain. The amplitude of the soluble−insoluble selfoscillation of poly(NIPAAm-co-[Fe(bpy)3]) was significantly smaller than that of poly(NIPAAm-co-[Ru(bpy)3]). Theoretical simulation results attributed this behavior to the small difference in the solvent qualities, C*, of the reduced and oxidized states. Furthermore, we clarified that poly(NIPAAm-co-[Fe(bpy)3]) required a narrower concentration range of HNO3 to exhibit selfoscillation than poly(NIPAAm-co-[Ru(bpy)3]), since transmittance self-oscillation occurred only for [HNO3] = 0.3 M. The period of self-oscillation of poly(NIPAAm-co-[Fe(bpy)3]) in solution was controlled mainly by NaBrO3 concentration and was hardly influenced by the initial concentration of malonic acid.
■
INTRODUCTION Various kinds of stimuli-responsive polymer systems, which change their conformation on the basis of changing pH, temperature, and electric field, have been studied extensively for applications in actuators, biosensors, molecular robots, etc.1−9 In particular, there have been several studies on the thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) gel used for medical devices and microactuators.10−15 However, to drive intelligent polymer systems, devices that allow control of external stimuli are necessary. In contrast, living organisms move autonomously without any device to input external stimuli. If we can construct autonomous systems like living organisms using custom designs, unique spontaneous polymer systems can be developed. Recently, self-oscillating polymers and gels have been developed for use in soft actuators and soft robots.16−22 For such applications, either the Belousov−Zhabotinsky (BZ) reaction or the Landolt pH-oscillator have been utilized as a chemical energy source for the autonomous polymer systems.19−21 In this study, we adopted the BZ reaction because it does not need the external pump system, an essential component of the pH oscillation reaction used to ensure flow of the substrate solution. In the BZ reaction, self-oscillating redox reactions of the metal catalyst occur; also, target or spiral patterns are observed in an unstirred condition, while a periodic change in the color of the entire solution occurs in the stirred condition.23−33 The overall BZ reaction involves the oxidation of malonic acid (MA), an organic acid, by sodium bromate (NaBrO3), used as an oxidant, in an aqueous solution containing nitric acid (HNO3) and the Fe © 2014 American Chemical Society
catalyst moiety covalently bonded to the polymer chain. We observe periodic color changes originating from cyclic changes in oxidation number. As the catalyst oxidation number changes in the BZ reaction, the solubility of the catalyst moiety changes cyclically at the same time. With the spontaneous cyclic solubility change of the metal catalyst moiety, the solubility of the polymer chain containing it changes. Simultaneously, since transmittance is affected by solubility, the transmittance of the polymer solution changes cyclically. In a polymer system driven by the BZ reaction, the linear polymer chain exhibits a soluble−insoluble self-oscillation, while a BZ-driven gel system with cross-linkage structure causes swelling−deswelling self-oscillation. Many previous studies investigated self-oscillating polymer systems containing a Ru catalyst moiety for applications in many fields, especially in actuators and chemical robots.34−37 However, the driving environment for self-oscillations must overcome many problems for practical applications to be realized. One major problem was that the polymer system undergoes the autonomous oscillation in a strong acidic environment, since the BZ reaction requires a strong acid. In a previous study, Hara et al. succeeded in providing the molecular design of a self-oscillating system under strong-acid-free conditions by not adding a strong acid directly to the polymer solution.38−43 The other major problem arose from the self-oscillating polymer system being too Received: January 23, 2014 Revised: May 22, 2014 Published: May 22, 2014 6931
dx.doi.org/10.1021/jp500824e | J. Phys. Chem. B 2014, 118, 6931−6936
The Journal of Physical Chemistry B
■
expensive for application in many fields owing to the use of Ru, an expensive rare metal, as part of the catalyst moiety required for the reaction. Therefore, we have faced the challenge of constructing a self-oscillating polymer system with a cheap metal catalyst moiety in order to expand its application in various fields. To confront the issue, we first synthesized the self-oscillating polymer chain with an Fe catalyst moiety and evaluated the effect of temperature on its optical self-oscillation.44 In this study, we investigated the influence of the initial concentration of the substrates for the BZ reaction on the optical self-oscillation of the polymer chain covalently bonded to the Fe catalyst moiety. The self-oscillating polymer consisted of poly(N-isopropylacrylamide) (poly-NIPAAm) covalently bonded to 4-vinyl-4′-methyl-2,2′-bipyridinebis(2,2′-bipyridine)bis(hexafluorophosphate) iron ([Fe(bpy)3]), the catalyst for the BZ reaction. We confirmed that the concentration range of nitric acid (HNO3, one of the three BZ substrates) that facilitates optical self-oscillation in poly(NIPAAm-co-[Fe(bpy)3]) was significantly narrower than that required for poly(NIPAAm-co[Ru(bpy)3]). We also confirmed that the amplitude of selfoscillation in poly(NIPAAm-co-[Fe(bpy)3]) was hardly affected by the concentrations of the other two BZ substrates (malonic acid (MA) and sodium bromate (NaBrO3)). In addition, we used a theoretical model to evaluate the self-oscillation mechanism and behavior of the polymer chain.
Article
RESULTS AND DISCUSSION
Figure 2 shows the soluble−insoluble self-oscillations of the poly(NIPAAm-co-[Fe(bpy)3]) solution for different concentrations of sodium bromate ([NaBrO3] = 0.1, 0.2, 0.3, 0.4, and 0.5 M) at 12 °C against fixed concentrations of malonic acid ([MA] = 0.1 M) and nitric acid ([HNO3] = 0.3 M). In a previous investigation, the lower critical solution temperature (LCST) of the poly(NIPAAm-co-[Fe(bpy)3]) solution was determined to be 29.5 °C in the reduced state and 31.0 °C in the oxidized state.44 In general, the LCST of the polymer solution depends on its solubility. The solubility difference between the reduced and oxidized states is attriuted to be the driving force of the self-oscillation of poly(NIPAAm-co-[Fe(bpy)3]).38−42 The difference in the LCST of poly(NIPAAm-co-[Fe(bpy)3]) was significantly smaller than the corresponding difference of poly(NIPAAm-co-[Ru(bpy)3]). This is attributed to the smaller amplitude of the soluble−insoluble self-oscillation in poly(NIPAAm-co-[Fe(bpy)3]) when compared to the amplitude of the self-oscillating polymer chain with the [Ru(bpy)3] moiety. The poly(NIPAAm-co-[Ru(bpy)3]) solution had a LCST of 36 °C in the oxidized state and 31.5 °C in the reduced state;45 this larger difference in the two LCST values was attributed to the larger amplitude of the self-oscillation compared to the poly(NIPAAm-co-Fe(bpy)3).44 Furthermore, the width of the waveform decreased with increasing NaBrO3 concentration, since the BZ reaction rate increased (see Figure 2).45,46 This trend was similar to that associated with the self-oscillating behavior of poly(NIPAAm-co-[Ru(bpy)3]).45 In Figure 3, the amplitudes of the soluble−insoluble selfoscillation of poly(NIPAAm-co-[Fe(bpy)3]) for different concentrations of the BZ substrates are shown. As shown in Figure 3, the oscillation amplitudes were almost the same for all concentrations of the BZ substrate, demonstrating that NaBrO3 concentration hardly affected the amplitude of the soluble−insoluble self-oscillation. In contrast, the amplitude of poly(NIPAAm-co[Ru(bpy)3]) was much affected by the initial concentrations of the BZ substrates.45 When the concentration of HNO3 for poly(NIPAAm-co-[Fe(bpy)3]) was varied, it was demonstrated that the soluble−insoluble self-oscillation occurred only for [HNO3] = 0.3 M at 12 °C. Self-oscillation was not observed when [HNO3] = 0.1, 0.2, 0.4, or 0.5 M, together with [NaBrO3] = 0.5 M and [MA] = 0.1 M. Evidently, the self-oscillation in transmittance of poly(NIPAAm-co-Fe(bpy)3) is strongly dependent on the concentration of nitric acid. Figure 4 shows the logarithmic plots of the period of selfoscillation against the initial concentration of one of the three BZ substrates, while the initial concentrations of the other two substrates of the BZ reaction were fixed at 12 °C. As can be seen in the figure, the logarithmic plots were straight lines. Therefore, the period (T (s)) of self-oscillation can be calculated as a[substrate]b: a and b are experimental constants, and the square brackets denote the initial concentration of the BZ substrates. As shown in Figure 4a, when the initial concentration of NaBrO3 was varied, the period of self-oscillation decreased with increasing [NaBrO3]. In contrast, as shown in Figure 4b, the period of the self-oscillation was hardly affected by the concentration of malonic acid, [MA]. These results demonstrate that the controlling factor of T for the optical self-oscillation of the poly(NIPAAm-co-[Fe(bpy)3]) solution is the concentration of sodium bromate. In order to understand the details of the self-oscillating transmittance behavior of poly(NIPAAm-co-[Fe(bpy)3]), we evaluated
■
EXPERIMENTAL METHODS Polymerization Reactions. The self-oscillating polymer chain with the Fe catalyst moiety (Figure 1) was synthesized as
Figure 1. Chemical structure of the self-oscillating polymer chain.
follows.44 NIPAAm (9.0 g), [Fe(bpy)3] (1.0 g), and 2,2′-azobis(2-methylbutyronitrile) (0.01 g), for use as an initiator, were mixed in ethanol (40 g). To synthesize poly(NIPAAm-co[Fe(bpy)3]) (Figure 1), we conducted free-radical polymerization at 80 °C for 5 h under N2 bubbling. Finally, we dialyzed the reaction mixture solution with ethanol for 30 days while changing ethanol frequently, and then freeze-dried after we changed ethanol into water. Measurement of Transmittance Self-Oscillation. The poly(NIPAAm-co-[Fe(bpy)3]) solutions were adjusted by dissolving the polymer (0.5 wt %) and the three BZ reaction substrates (MA, NaBrO3, and HNO3) in an aqueous solution.44 The evaluation of the self-oscillating behavior of the polymer was carried out while stirring the solution at a constant temperature (12 °C). A wavelength of 444 nm was adopted to detect optical transmittance self-oscillation because this wavelength is associated with the isosbestic point of the reduced and oxidized states of [Fe(bpy)3].44 In other words, we measured the transmittance change originating from the conformational change in the polymer chain, and found that this measurement was not affected by the color changes in the polymer solution. A temporal change in the optical transmittance of the polymer was measured at 444 nm using a spectrophotometer (JASCO, model V-630, Tokyo, Japan). 6932
dx.doi.org/10.1021/jp500824e | J. Phys. Chem. B 2014, 118, 6931−6936
The Journal of Physical Chemistry B
Article
Figure 2. Profiles of transmittance self-oscillation at 12 °C for a 0.5 wt % poly(NIPAAm-co-[Fe(bpy)3]) solution with fixed initial concentrations of nitric acid, [HNO3] = 0.3 M, and malonic acid, [MA] = 0.1 M, and varied concentrations of sodium bromate: (a) [NaBrO3] = 0.1 M; (b) [NaBrO3] = 0.2 M, (c) [NaBrO3] = 0.3 M; (d) [NaBrO3] = 0.4 M; (e) [NaBrO3] = 0.5 M.
where Fela(α) and Fint(α) are the free energies resulting from the elasticity of a polyelectrolyte chain and the interaction between Kuhn segments, respectively, while B and C are the second and third virial coefficients, respectively, which describe the two-body and three-body interactions.49 In the present case, these interactions are those between two Kuhn segments and between three Kuhn segments, respectively. ρ is the density of Kuhn segments, and O(ρ4) is the surplus term. α is the ratio of the size of a polymer chain (R) to that of a Gaussian chain (RG):
the behavior of the polymer chain using theoretical methods. To explain the detailed dynamics of the self-oscillating polymer chain, we first examined the first-order phase transition of a semiflexible polymer chain, as summarized from findings of our previous studies. We describe the free energy Fsingle(α) by virial expansion as follows:47,48 Fsingle(α) ∼ Fela(α) + Fint(α) ∼
3 2 (α + α −2) + Bρ2 V + Cρ3 V + O(ρ 4 ) 2
α = R /R G
(2)
Here,
(1) 6933
dx.doi.org/10.1021/jp500824e | J. Phys. Chem. B 2014, 118, 6931−6936
The Journal of Physical Chemistry B
Article
R ∼ αlKN1/2
(4)
Considering that the Kuhn segments are parallel to each other with a cross angle, eq 1 is reformulated as Fsingle(α) ∼ (3/2)(α 2 + α −2) + C*α −6 ⎡ λ ⎤ − N ln⎢1 − 1/2 3 ⎥ + O(ρ 4 ) ⎣ N α ⎦
(5)
where the first term is the conformational energy, the second is the (attractive or repulsive) interaction between the Kuhn segment varied by solvent quality, and the third is conveniently introduced into the equation to describe the excluded volume effect and to avoid the anomaly of Fsingle(α) → −∞ when α → 0. The last term contains the higher-order terms. The second term in eq 5 plays a significant role in the representation of the discrete conformational change as the term of three-body interaction with another third virial coefficient C*. This coefficient means solvent quality as explained below. Here, we treated that the conformational change is caused by the three-body interaction because ρ3V in eq 1 is proportional to α−6 using the relationships between V and R of a polymer chain of V ∝ R3 and R = αRG = αlKN1/2 (eq 4) in the Kuhn model.51 C* is described as
Figure 3. Dependence of the self-oscillation amplitude for the polymer solution at 12 °C with changes in concentration of one BZ substrate while the concentrations of the other two BZ substrates were fixed: variable [MA] = 0.03, 0.04, 0.05, and 0.06 M with fixed [NaBrO3] = 0.5 M and fixed [HNO3] = 0.3 M; variable [NaBrO3] = 0.1, 0.2, 0.3, 0.4, and 0.5 M with fixed [MA] = 0.1 M and fixed [HNO3] = 0.3 M.
C* = λ 3(1 + στ /lp)
(6)
where λ is the aspect ratio of the Kuhn segment (λ = a/lp, with a as the diameter of the Kuhn segment and lp as the persistent length), σ is the characteristic length of the attractive potential, and τ is the reduced temperature (τ = (T − TC)/TC). If C* > 0 (or C* < 0), the solvent quality is good (or poor).49 When the polymer is in a good solvent environment, the polymer chain assumes the elongated state. On the other hand, when it is in a poor solvent environment, the chain is the collapsed state. This term is the origin of the first-order phase transition. In this theoretical framework, the change in the valence of the metal catalyst corresponds to a change in C*, with the Fe3+-rich condition (Fe2+-rich condition) being a good solvent (poor solvent). C* is equal to z, the normalized [Fe2+], in the two-parameter Oregonator model shown later. On the other hand, stable states of the polymer chain with changing solvent quality, C*, can be determined from ∂Fsingle[α]/ ∂α = 0: ⎡ ⎤ 3 λ 2C* = α8 − α 4 − N1/2⎢λ + ⎥α 1/2 3 − − ⎣ 1 − λN α ⎦
(7)
In the case of a semiflexible polymer chain (λ ≪ 1), the stable α is obtained from 2C* = α8 − α 4 −
(8)
From the symmetry of eq 8, it is understood that the size of the collapsed chain and the width of the hysteresis are determined by λN−1/2 and λN1/2, respectively. First, this means that a stiff and long polymer chain forms smaller collapsed chains, and then, the volume change in α is larger than that for the case of a flexible polymer chain. Next, it means that the stiff and long chain shows wide hysteresis and the phase transition occurs under good solvent conditions. In other words, the flexible and short polymer chain shows a smaller volume change under poor solvent conditions. Since the mass of Fe(bpy)3 is less than that of Ru(bpy)3, it may be noted that the polymer chain with Fe(bpy)3 is flexible in comparison to that with Ru(bpy)3, because the Brownian
Figure 4. Logarithmic plots of period T(s) as a function of the molar concentration of one of the three substrates of the BZ reaction at 12 °C, with the other two substrate concentrations being fixed: (a) [MA] = 0.1 M and [HNO3] = 0.3 M; (b) [NaBrO3] = 0.5 M and [HNO3] = 0.3 M.
R G ∼ lKN1/2
λN1/2α 3 1 − λN −1/2α −3
(3)
where lK is the Kuhn length (twice the persistent length lp) and N is the number of Kuhn segments in the chain, which means that the single polymer chain itself is a small number system.50 From eqs 2 and 3, R is obtained as 6934
dx.doi.org/10.1021/jp500824e | J. Phys. Chem. B 2014, 118, 6931−6936
The Journal of Physical Chemistry B
Article
discretely on the level of a single polymer chain; however, it has been clarified that the ensemble average of the change is rather continuous because of fluctuations in the small number system, i.e., a deviation from the law of large numbers.53,54 As a result, the ensemble average in the conformational change occurs along the change in concentration of Fe3+. Therefore, this theoretical framework sufficiently explains the experimental result of the optical self-oscillation in the polymer solution.
motion of Fe(bpy)3 is larger than that of Ru(bpy)3. This is in turn reflected in the values of λ; i.e., λ for Fe(bpy)3 is relatively larger than that for Ru(bpy)3 (λ = 0013).50 This may be the reason for the amplitude in α of the polymer chain with the Fe catalyst being smaller than that with the Ru catalyst. Figure 5 shows the calculated result with λ = 0.02 and N = 9.
■
CONCLUSIONS We have demonstrated the effect of BZ substrate concentrations on the self-oscillating behavior of poly(NIPAAm-co-[Fe(bpy)3]). The amplitude of the polymer system’s soluble−insoluble selfoscillation was significantly smaller than that of the corresponding NIPAAm-based self-oscillating polymer chain with a Ru catalyst. This difference in behavior (between the Fe and Ru systems) originates from the relatively small difference in C* values in the reduced and oxidized states of the Fe catalyst. In addition, the self-oscillation depended strongly on the concentration of HNO3. The controlling factor of the transmittance selfoscillation period for the poly(NIPAAm-co-[Fe(bpy)3]) solution was the concentration of sodium bromate. The oscillation period was quite insensitive to the concentration of malonic acid.
Figure 5. Numerical relationship between α and solvent quality (−C*). Here, λ = 0.02 and N = 9.
■
To depict the BZ reaction, we have adopted a two-parameter Oregonator model. The temporal changes in chemical species in the BZ reaction can be described by x−q dx ε = x(1 − x) − fz dt x+q (9)
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
and dz =x−z dt
AUTHOR INFORMATION
ACKNOWLEDGMENTS This work was supported by the auspices of the New Energy and Industrial Technology Development Organization (NEDO) of Japan under the Industrial Technology Research Grant Program in 2011. We were also supported by Grants-in-Aid (KAKENHI) for Challenging Exploratory Research (24656178) and Scientific Research on Innovative Area (25104501) from the Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT).
(10)
where x and z correspond to the normalized concentrations of bromous acid (HBrO2) and Fe3+, respectively; f is the stoichiometric factor between bromic malonic acid (BrCH(COOH)2, BrMA) and Fe3+; and ε is the tuning parameter.52 We treated z as the normalized concentration of Fe3+, and the concentration of Fe2+ was obtained from ([Fe2+] + [Fe3+])/[Fe2+] (t = 0) = constant. Figure 6 shows the numerical results of temporal
■
REFERENCES
(1) Tanaka, T. Gels. Sci. Am. 1981, 244, 110−116. (2) Suzuki, A.; Tanaka, T. Phase transition in polymer gels induced by visible light. Nature 1990, 346, 345−347. (3) Ilmain, F.; Tanaka, T.; Kokufuta, E. Volume transition in a gel driven by hydrogen bonding. Nature 1991, 349, 400−401. (4) Steinberg, I. Z.; Oplatka, A.; Kachalsky, A. Mechanochemnical engines. Nature 1966, 210, 568−571. (5) Oguro, K.; Kawami, Y.; Takenaka, H. An actuator element of polyelectrotyte gel membrane-electrode composite. Bull. Gov. Ind. Res. Inst., Osaka 1992, 43, 21. (6) Fukushima, T.; Asaka, K.; Kosaka, A.; Aida, T. Fully Plastic Actuator through Layer-by-Layer Casting with Ionic-Liquid-Based Bucky Gel. Angew. Chem., Int. Ed. 2005, 44, 2410−2413. (7) Yeghiazarian, L.; Mahajan, S.; Montemagno, C.; Cohen, C.; Wiesner, U. Directed Motion and Cargo Transport Through Propagation of Polymer-Gel Volume Phase Transitions. Adv. Mater. 2005, 17, 1869−1873. (8) Ebara, M.; Hoffman, J. M.; Hoffman, A. S.; Stayton, P. S.; Lai, J. J. A photoinduced nanoparticle separation in microchannels via pHsensitive surface traps. Langmuir 2013, 29, 5388−5393. (9) Peppas, N. A.; Hilt, J. Z.; Khademhosseini, A.; Langer, R. Hydrogels in Biology and Medicine: From Molecular Principles to Bionanotechnology. Adv. Mater. 2006, 18, 1345−1360.
Figure 6. Changes in x, z, and the conformation of a single polymer chain resulting from the BZ reaction.
changes in the chemical species, where ε = 0.01, q = 0.0008, x(t = 0) = 0.001 927, z(t = 0) = 0.004 487, and Fe2+ + z = 0.28.52 Here, it should be noted that the conformational change occurs 6935
dx.doi.org/10.1021/jp500824e | J. Phys. Chem. B 2014, 118, 6931−6936
The Journal of Physical Chemistry B
Article
(36) Maeda, S.; Hara, Y.; Yoshida, R.; Hashimoto, S. Control of the dynamic motion of a gel actuator driven by the Belousov-Zhabotinsky reaction. Macromol. Rapid Commun. 2008, 29, 401−405. (37) Maeda, S.; Hara, Y.; Yoshida, R.; Hashimoto, S. Peristaltic Motion of Polymer Gels. Angew. Chem., Int. Ed. 2008, 120, 6792. (38) Hara, Y.; Yoshida, R. Self-oscillating polymer fueled by organic acid. J. Phys. Chem. B 2008, 112, 8427−8429. (39) Hara, Y.; Yoshida, R. Self-oscillation of polymer chains induced by the Belousov-Zhabotinsky reaction under acid-free conditions. J. Phys. Chem. B 2005, 109, 9451−9454. (40) Hara, Y.; Yoshida, R. Influence of a Positively Charged Moiety on Aggregation-Disaggregation Self-Oscillation Induced by the BZ Reaction. Macromol. Rapid Commun. 2009, 30, 2160−2166. (41) Hara, Y.; Yoshida, R. A viscosity self-oscillation of polymer solution induced by the BZ reaction under acid-free condition. J. Chem. Phys. 2008, 128, 224904. (42) Hara, Y.; Yoshida, R. Control of oscillating behavior for the selfoscillating polymer with pH-control site. Langmuir 2005, 21, 9773. (43) Hara, Y.; Yamaguchi, Y.; Mayama, H. Switching the BelousovZhabotinsky reaction with a Strong-Acid-Free Gel. J. Phys. Chem. B 2014, 118 (2), 634−638. (44) Hara, Y.; Fujimoto, K.; Mayama, H. Self-Oscillation of Polymer Chains with an Fe(bpy)3 Catalyst Induced by the BelousovZhabotinsky Reaction. J. Phys. Chem. B 2014, 118 (2), 608−612. (45) Hara, Y.; Takenaka, Y. Autonomous Oscillation of Polymer Chains Induced by the Belousov−Zhabotinsky Reaction. Sensors 2014, 14 (1), 1497−1510. (46) Hara, Y.; Jouhan, A. R. Activation Energy of AggregationDisaggregation Self-Oscillation of Polymer Chain. Int. J. Mol. Sci. 2012, 13 (12), 16281−16290. (47) Mayama, H.; Nakai, T.; Takushi, E.; Tsujii, K.; Yoshikawa, K. Marked differences in volume phase transitions between gel and single molecule in DNA. J. Chem. Phys. 2007, 127, 034901. (48) Sato, Y. T.; Watanabe, S.; Kenmotsu, T.; Ichikawa, M.; Yoshikawa, Y.; Teramoto, J.; Imanaka, T.; Ishihama, A.; Yoshikawa, K. Structural change of DNA induced by nucleoid proteins: growth phase-specific Fis and stationary phase-specific Dps. Biophys. J. 2013, 105, 1037−1044. (49) Mayama, H.; Nakai, T.; Takushi, E.; Tsujii, K.; Yoshikawa, K. Marked Differences in Volume Phase Transitions Between Gel and Single Molecule in DNA. J. Chem. Phys. 2007, 127, 034901. (50) Hara, Y.; Mayama, H.; Yamaguchi, Y.; Takenaka, Y.; Fukuda, R. Direct Observation of Periodic Swelling and Collapse of Polymer Chain Induced by the Belousov-Zhabotinsky Reaction. J. Phys. Chem. B 2013, 117 (46), 14351−14357. (51) Grosberg, A. Y.; Khokhlov, A. R. Statistical Physics of Macromolecules; AIP Press: New York, 1994; Chapter 1. (52) Hara, Y.; Mayama, H.; Morishima, K. Generative Force of SelfOscillating Gel. J. Phys. Chem. B 2014, 118 (9), 2576−2581. (53) Ueda, M.; Yoshikawa, K. Discrete Phase Transition and Phase Segregation in a Single Double-Stranded DNA Molecule. Phys. Rev. Lett. 1996, 77, 2133. (54) Takahashi, M.; Yoshikawa, K.; Vasilevskaya, V. V.; Khokhlov, A. R. Discrete Coil−Globule Transition of Single Duplex DNAs Induced by Polyamines. J. Phys. Chem. B 1997, 101, 9396−9401.
(10) Hirokawa, Y.; Tanaka, T. Volume phase transition in a nonionic gel. J. Chem. Phys. 1984, 81, 6379−6380. (11) Nakayama, M.; Yamada, N.; Kumashiro, Y.; Kanazawa, H.; Yamato, M.; Okano, T. Thermoresponsive poly(N-isopropylacrylamide)-based block copolymer coating for optimizing cell sheet fabrication. Macromol. Biosci. 2012, 12, 751−760. (12) Imran, A. B.; Seki, T.; Ito, K.; Takeoka, Y. Facile Synthesis of Sliding Poly(NIPA) Gels Using a Vinyl Modified Polyrotaxane as a Cross-Linker. Macromolecules 2010, 43, 1975−1980. (13) Yoshida, R.; Uchida, K.; Kaneko, Y.; Sakai, K.; Kikuchi, A.; Sakurai, Y.; Okano, T. Comb-type grafted hydrogels with rapid deswelling response to temperature changes. Nature 1995, 374, 240. (14) Hoffmann, J.; Plö tner, M.; Kuckling, D.; Fischer, W.-J. Photopatterning of thermally sensitive hydrogels useful for microactuators. Sens. Actuators, A 1999, 77, 139−144. (15) Yeghiazarian, L.; Mahajan, S.; Montemagno, C.; Cohen, C.; Wiesner, U. Directed Motion and Cargo Transport Through Propagation of Polymer-Gel Volume Phase Transitions. Adv. Mater. 2005, 17, 1869−1873. (16) Ishiwatari, T.; Kawaguchi, M.; Mitsuishi, M. Oscillatry reactions in polymer. Systems. J. Polym. Sci., Part A: Polym. Chem. 1984, 22, 2699. (17) Yoshida, R.; Sakai, T.; Ito, S.; Yamaguchi, T. Self-oscillation of polymer chains with rhythmical soluble-insoluble changes. J. Am. Chem. Soc. 2002, 124, 8095−8098. (18) Yoshida, R.; Takahashi, T.; Yamaguchi, T.; Ichijo, H. Selfoscillating gel. J. Am. Chem. Soc. 1996, 118, 5134−5135. (19) Nakagawa, H.; Hara, Y.; Maeda, S.; Hashimoto, S. A Novel Design of Nanofibrous Gel Actuator. Polymers 2011, 3, 405−412. (20) Hara, Y.; Maeda, S.; Mikanohara, T.; Nakaagwa, H.; Nakamaru, S.; Hashimoto, S. In Novel Self-Oscillating Polymer Actuators for Soft Robot, Smart Actuation and Sensing Systems - Recent Advances and Future Challenges; Berselli, G., Ed.; In Tech: Croatia, 2012. (21) Maeda, S.; Hara, Y.; Nakamaru, S.; Nakagawa, H.; Hashimoto S. In Chemical Robots, On Biomimetics; Pramatarova, L., Ed.; In Tech: Croatia, 2011. (22) Yoshida, R.; Okano, T. Stimuli-Responsive Hydrogels and Their Application to Functional Materials. In Biomedical Applications of Hydrogels Handbook; Ottenbrite, R. M., Park, K., Okano, T., Eds.; Springer: Berlin/Heidelberg, Germany, 2010; pp 19−43. (23) Belousov, B. P. Sb. Ref. Radiat. Med. (Collections of Abstracts on Radiation Medicine, Medgiz, Moscow) 1959, 1, 145. (24) Zaikin, A. N.; Zhabotinsky, A. M. Concentration Wave Propagation in Two-dimensional Liquid-phase Self-oscillating System. Nature 1970, 225, 535−537. (25) Nicolis, G.; Prigogine, I. Self-Organization in Nonequilibrium Systems; John Wiley & Sons: New York, 1977. (26) Reusser, E. J.; Field, R. J. The Transition from Phase Waves to Trigger Waves in a Model of the Zhabotinskii Reaction. J. Am. Chem. Soc. 1979, 101, 1063−1094. (27) Field, R. J.; Burger, M. Oscillations and Traveling Waves in Chemical Systems; John Wiley & Sons: New York, 1985. (28) Tyson, J. J.; Fife, P. C. Target Patterns in a Realistic Model of the Belousov-Zhabotinskii Reaction. J. Chem. Phys. 1980, 73, 1−14. (29) Wood, P. M.; Ross, J. A Quantitative Study of Chemical Waves in the Belousov-Zhabotinsky Reaction. J. Chem. Phys. 1985, 82, 1−13. (30) Kuhnert, L.; Krug, H. J. Kinetics of Chemical Waves in the Acidic Bromate-malonic acid-tris(bipyridine)ruthenium(2+) System in Comparison with the Ferroin System. J. Phys. Chem. 1987, 91, 730−733. (31) Murray, J. D. Mathematical Biology; Springer-Verlag: Berlin, Germany, 1990. (32) Scott, S. K. Chemical Chaos, 1st ed.; Oxford University Press: Oxford, U.K., 1991. (33) Moriand, H.; Kuramoto, Y. Dissipative Structures and Chaos; Springer-Verlag: Berlin, Germany, 1997. (34) Hara, Y.; Maeda, S.; Hashimoto, S.; Yoshida, R. Molecular Design and Functional Control of Novel Self-Oscillating Polymers. Int. J. Mol. Sci. 2010, 11, 704−718. (35) Maeda, S.; Hara, Y.; Sakai, T.; Yoshida, R.; Hashimoto, S. SelfWalking Gel. Adv. Mater. 2007, 19, 3480−3484. 6936
dx.doi.org/10.1021/jp500824e | J. Phys. Chem. B 2014, 118, 6931−6936
