Article pubs.acs.org/Macromolecules
Reversible Transformation of Nanostructured Polymer Particles Renhua Deng,† Fuxin Liang,‡ Weikun Li,† Zhenzhong Yang,*,‡ and Jintao Zhu*,† †
Key Laboratory of Large-Format Battery Materials and Systems of the Ministry of Education, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China ‡ State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China S Supporting Information *
ABSTRACT: A reversible transformation of overall shape and internal structure as well as surface composition of nanostructured block copolymer particles is demonstrated by solvent-adsorption annealing. Polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) pupa-like particles with PS and P4VP lamellar domains alternatively stacked can be obtained by self-assembly of the block copolymer under 3D soft confinement. Chloroform, a good solvent for both blocks, is selected to swell and anneal the pupa-like particles suspended in aqueous media. Reversible transformation between pupa-like and onion-like structures of the particles can be readily tuned by simply adjusting the particle/aqueous solution interfacial property. Interestingly, poly(vinyl alcohol) (PVA) concentration in the aqueous media plays a critical role in determining the particle morphology. High level of PVA concentration is favorable for pupa-like morphology, while extremely low concentration of PVA is favorable for the formation of onion-like particles. Moreover, the stimuli-response behavior of the particles can be highly suppressed through selective growth of Au nanoparticles within the P4VP domains. This strategy provides a new concept for the reversible transformation of nanostructured polymer particles, which will find potential applications in the field of sensing, detection, optical devices, drug delivery, and smart materials fabrication. and surface composition.29−33 Each emulsion droplet acts as a soft and deformable compartment for the confined assembly, which allows to finely tune the overall shape and internal structure by controlling the interfacial dynamics and the commensurability of the BCPs. Thermal annealing treatment can further adjust their internal structures.34,35 However, the internal structural transformation is irreversible. Different from thermal annealing, solvent vapor annealing is effective to tailor BCP nanostructures in a reversible manner.36−38 Reversible transformations of BCP films among different morphologies or orientations become feasible by solvent vapor annealing.39 However, a question has arisen about how to apply the vapor annealing approach to BCP particles since the particles may become coalesced in the presence of the annealing solvents. A new approach is proposed to avoid the coalescence among the particles by simply using an aqueous suspension system as a confined environment for each particle.40,41 The structure changes from concentric lamellae to cylindrical microdomains and then to spherical structures after slightly varying the solvent selectivity. Yet, the transformation is only one-way. It is a prerequisite that the annealing solvent should be slightly soluble in water and possess an appropriately high vapor pressure as well as different selectivity for BCP.
1. INTRODUCTION Responsive polymer materials are adaptive to external stimuli, such as solvent, pH, temperature, and light, which can undergo shape, structure, and performance changes.1−5 If the responses (or switches) are reversible, the materials will be more promising in detection, memory storage, optical systems, and self-healing.6−10 Nowadays, the reversibly responsive polymer materials focus on polymer films, brushes, capsules, and micelles.11−14 For example, multivesicular assemblies with pH on/off reversibly responsive transmembrane channels are prepared by self-assembly of poly(acrylic acid)-co-poly(distearin acrylate).11 Although the response is reversible at the surface of the assembly, it is hard to induce the internal structure to transform. The shape and internal structure of nanostructured polymer particles play critical roles in determining their functions and for this reason are interesting.15−17 How to simply and reversibly tailor their internal structure is decisive to exploit their applications.18 Well-defined and functional block copolymers (BCPs) have been extensively utilized to construct the nanostructures.19−23 In order to control the internal structures, self-assembly of BCPs under 3D confinement is usually employed.24−28 Generally, the morphologies are essentially dependent on external forces (confinement effect and boundary interaction) at a given molecular composition. As an example, when BCPs are confined in emulsion droplets, colloidal particles are created with tunable internal structure, shape, © 2013 American Chemical Society
Received: July 4, 2013 Revised: August 13, 2013 Published: August 29, 2013 7012
dx.doi.org/10.1021/ma401398h | Macromolecules 2013, 46, 7012−7017
Macromolecules
Article
Scheme 1. Illustration Showing 3D Confined Self-Assembly of PS-b-P4VP in Emulsion Droplet (Chloroform Solution Droplet in PVA Aqueous Solution) and Switchable Morphological Transformation of the Particles as Responses to External Environment Assisted by Solvent Annealing
was gently stirred for 4 h. Finally, the composite particles were separated by centrifugation at 14 000 rpm for 8 min. Characterization. The internal structure of the particles was observed by using a JEM-1011 TEM (JEOL Ltd., Japan) operated at an accelerated voltage of 100 kV. Before TEM characterization, the samples were stained with iodine vapor for 2 h. The size distribution of the polymer particles was measured using DLS (Malvern Zetasizer Nano ZS90). The UV−vis absorption spectra of dispersions were collected in the range of 400−800 nm on a TU-1901 UV−vis spectrophotometer.
Until now, reversible structural transformation of the nanostructured BCP particles remains challenging. Herein, we demonstrate a reversible morphological transformation of BCP particles by adjusting the particle/aqueous solution interfacial interaction based on solvent-adsorption annealing in an aqueous suspension system (see Scheme 1). We first prepared polystyrene-b-poly(4-vinylpyridine) (PS-bP4VP) ellipsoidal pupa-like particles through the emulsionsolvent evaporation method. Reversible transformation between pupa-like and onion-like structures of the particles is readily tuned by simply adjusting the particle/aqueous solution interfacial property. Moreover, the stimuli-response behavior of the particles can be highly suppressed through the introduction of Au NPs. This represents a new approach for the formation of novel nanostructured polymer particles and reversible transformation of the particles.
3. RESULTS AND DISCUSSION PS-b-P4VP particles are prepared by the emulsion-solvent evaporation method. In a typical experiment, PS9.8K-b-P4VP10K is first dissolved in chloroform to form a polymer solution, which is then emulsified in poly(vinyl alcohol) (PVA) aqueous solution using a membrane-extrusion approach.30 When organic solvent diffuses through the aqueous phase and evaporates, the emulsion droplets will shrink, and eventually this leads to the solidification of block copolymer and segregation of the different blocks within the confined spaces. After complete removal of the organic solvent, ellipsoidal pupalike particles form with PS and P4VP lamellar domains alternatively stacked (Figure 1a). The alternative arrangement is also preserved on the particle surface. Formation of this unique morphology can be understandable that the interactions of the two blocks with the particle−aqueous solution interface are comparable.27,29 In the current emulsion system, PVA plays dual roles in both stabilizing the droplets and creating a nearly neutral interface for PS and P4VP microdomains. After minimizing the surface free energy and fitting the commensurability of the BCPs, the unique morphology is expected. Ellipsoid having low curvature boundaries (side) is superior to spherical shape since the entropic penalty associated with bending of BCPs is minimized.29 It is worth noting that the two poles (high curvature) of the ellipsoids are covered with P4VP onto the outermost layer due to their slight selectivity.27 The structure of the solid pupa-like particles is kinetically frozen in water at room temperature (∼30 °C), which can be transformed into different morphologies upon adsorption of organic solvent, such as chloroform. The absorbed solvent in the particles can not only provide the driving force for movement of the polymer segments but also swell the particles, providing more space for the rearrangement of the polymer chains. Notably, PVA is removed from the pupa-like particle suspension by centrifugation, and the particles were dispersed again in deionized water prior to solvent-adsorption annealing. Chloroform, a good solvent for both blocks and slightly soluble
2. EXPERIMENTAL SECTION Materials. Diblock copolymer PS9.8K-b-P4VP10K (Mw/Mn = 1.08) was purchased from Polymer Source, Inc. Poly(vinyl alcohol) (PVA, average Mw: 13K−23K g/mol, 87−89% hydrolyzed) was purchased from Aldrich. All of the materials were used as received without further purification. Preparation of PS-b-P4VP Particles. The polymer particles were prepared by dissolving PS-b-P4VP in chloroform at a concentration of 0.3 wt %. Subsequently, 0.1 mL of the PS-b-P4VP solution was emulsified with 1.0 mL of PVA aqueous solution (3 mg/mL) by using a membrane-extrusion emulsification.30,42 The resulting emulsions were diluted by adding another 0.3 mL of PVA aqueous solution. Organic solvent was then allowed to slowly evaporate for 48 h at 30 °C. Finally, the particles were separated by centrifugation (14 000 rpm, 8 min) to remove the PVA. Solvent-Adsorption Annealing. 500 μL of the polymer particle aqueous suspension (or PVA aqueous solution suspension) with particle content of ∼0.4 mg/mL in a small vial (5 mL) was placed inside a large vial (25 mL) with 1.0 mL of the chloroform at 30 °C for a certain time. Afterward, the inner small vial was taken out to the ambient atmosphere to release the absorbed chloroform for 12 h at 30 °C. This annealing procedure is shown in Scheme S1 of the Supporting Information. Subsequently, the structure of the particles is kinetically frozen after removal of chloroform, and the particles were separated by centrifugation (14 000 rpm, 8 min) to remove the PVA (if the aqueous phase contains PVA). In Situ Growth of Au NPs. The polymer particles were dispersed in an aqueous solution of HAuCl4·4H2O (0.25 mg/mL) to allow HAuCl4 to be preferentially absorbed by P4VP segment for ∼4 h and then separated by centrifugation at 14 000 rpm for 8 min. The resultant particles were dispersed in deionized water (∼0.4 mg/mL, 1 mL); a freshly prepared solution of NaBH4 cooled to 0 °C (0.5 mg/ mL, 20 μL) was added dropwise while stirring. Afterward, the mixture 7013
dx.doi.org/10.1021/ma401398h | Macromolecules 2013, 46, 7012−7017
Macromolecules
Article
particles (Figure 1b). The onion-like particles are predicted after considering the preferential interfacial interaction of one block for the bulk lamellar-forming diblock copolymers.25,27,43 In our soft confinement system, removal of PVA from the aqueous media will induce moderate P4VP/aqueous solution interfacial interaction due to the slight hydrophilicity and relatively strong polarity of P4VP. A slightly weak acidic environment (pH of distilled water in our experiment ∼6) is conducive to increase the hydrophilicity. A layer of P4VP is thus formed on the external surface of the swollen particle in order to reduce the interfacial energy. The lamellar phases start to rearrange along the outermost layer, and the concentric shell structure is achieved while the spherical shape is adopted to minimize the surface free energy. Based on the above conjecture, a reversible transformation from onion-like particles to pupa-like particles should be feasible if PVA is added back to the annealing environment. As expected, pupa-like particles (Figure 1c) are indeed derived from the onion-like particles after chloroform annealing for 12 h in PVA aqueous solution (3 mg/mL). In order to facilitate understanding the reversible transformation in more details, a schematic illustration is provided (Scheme S2) to show the possible mechanism. The obtained pupa-like structure can switch back to the onion-like structure after removal of PVA and chloroform annealing treatment (Figure 1d). In order to understand the transformation dynamics, morphological evolution of the particles with annealing time is recorded. At early stage, the transformation starts from one pole of the pupa-like particles (Figure 2a). One pole becomes
Figure 1. TEM images of PS9.8K-b-P4VP10K particles with switchable shape and internal structure induced by solvent-adsorption annealing: (a) initial pupa-like particles prepared by emulsion-solvent evaporation method; (b) is derived from (a) after chloroform annealing in water; (c) is derived from (b) after chloroform annealing in PVA aqueous solution; (d) is derived from (c) after chloroform annealing in water again. Blue arrows show P4VP monolayer on both poles of the ellipsoids or outermost layer of the spheres. Insets in (a) and (b) are the cartoons showing their structures. After staining with iodine vapor, P4VP domains become black while the PS domains keep gray.
in water (0.776 wt %), is selected to swell and anneal the pupalike particles suspended in aqueous media. The solvent adsorption annealing procedure is shown in Scheme S1. Generally, the solvent annealing occurs by vapor−aqueous phase exchange of chloroform and water, allowing both the aqueous and organic phase to approach saturation state within each other. In the aqueous suspension, chloroform molecules will diffuse into the polymer particles, swelling both blocks until the chemical potentials of chloroform are equal in each BCP microdomain and in the aqueous phase.40 After absorbing chloroform molecules, polymer segments will rearrange to adapt to new external environment. This condition is kept for a certain time which is recorded as the annealing time for all polymer segments rearrangement to achieve a new thermodynamic equilibrium structure. Afterward, the absorbed chloroform is allowed to release completely and the new structure of the finial particles is kinetically frozen again. Dynamic light scattering (DLS) is used to monitor swelling of the BCP particles in the chloroform-saturated aqueous system. DLS analysis indicates that average diameter of the particles increases ∼1.35 times from 227 nm (Figures S1a) to 306 nm after absorbed chloroform at early stage of 1 h (Figures S1b). When chloroform is released completely, the mean diameter of the particles decreases to 235 nm (Figures S 1d). The size change of the particles induced by solvent swelling is also reflected by the suspension color change. The initial suspension is light blue (inset in Figure S1a), while it changed to bluewhite after absorbing chloroform (insets in Figure S1b,c) and changed back to light blue after releasing the absorbed chloroform (inset in Figure S1d). After 12 h solvent annealing treatment, followed by removal of chloroform (same procedure is also carried out in the following part, unless noted), all pupalike particles have completely transformed into onion-like
Figure 2. TEM images showing the evolution process of nanostructured particles induced by solvent-adsorption annealing for different time: (a) 1 , (b) 2, (c) 4, and (d) 8 h.
flattened while the other pole keeps the tip structure. BCPs in the pole layers have a high mobility owing to the surface effect since BCPs thereby are more exposed to the particle surface. In addition, the pole layers are more unstable because they consist of individual segment layer.34 Internal stress during chains rearrangement is allowed to release after one pole becomes flattened. Transient bud-like particles form after annealing for 2 h (Figure 2b). Similar structure is also reported in thermal 7014
dx.doi.org/10.1021/ma401398h | Macromolecules 2013, 46, 7012−7017
Macromolecules
Article
Figure 3. TEM images of the PS-b-P4VP particles by solvent annealing of pupa-like particles in suspensions with various PVA concentration (mg/ mL): (a) 0.05, (b) 0.1, (c) 0.2, (d) 0.3, (e) 0.5, and (f) 1.0. Insets in (b−d) are histograms of nanoparticles with different morphologies, in which different morphologies are indicated by different colors: onion-like particles (red), bud-like particles (green), and pupa-like particles (blue).
annealing-induced phase transition.34 Interestingly, these kinds of particles are Janus-like morphology where PS and P4VP lamellae are exposed alternately at the high curvature pole forming a terrace-like morphology, while only P4VP blocks are exposed at the low curvature pole. When the annealing time is increased to 4 h, the transformation is complete such that all the pupa-like particles have evolved into the onion-like particles (Figure 2c). Further increasing the annealing time to 8 h for example produces minimal changes in the onion-like morphology (Figure 2d). The morphological transformation is closely related to the PVA concentration. At low level of PVA concentration of 0.05 mg/mL, almost all the pupa-like particles are transformed into onion-like particles after annealing treatment (Figure 3a). This can be understood that PVA is insufficient to neutralize the particle interface, and the outmost layer P4VP segments play a major role in the surface free energy. Presumably, there exists a competition between outmost layer P4VP segments and PVA in determining the particle morphology. With the increase of PVA concentration, the competitive advantage of PVA in minimizing surface free energy is significantly increased. When PVA concentration increases to 0.1 mg/mL, a majority of the final particles are onion-like particles, while some bud-like particles coexisted (Figure 3b). The formation of bud-like particles is a result of the nonuniform distribution of PVA on their surfaces, since PVA is insufficient to neutralize the full surface. Further increasing PVA concentration to 0.2 mg/mL will trigger the formation of pupa-like particles, coexisting with bud-like particles and onion-like particles (Figure 3c). At sufficiently high level of PVA concentration of 0.3 mg/mL, very few onion-like particles are observed while almost all the pupalike particles survive (Figure 3d). It implies that there exists a transition region of PVA concentration (0.1−0.3 mg/mL) at which bud-like and onion-like particles coexist with pupa-like particles. In this region, PVA is insufficient for neutralization of all particle surfaces; therefore, the particles absorbed relatively more PVA may keep the pupa-like structure, while those who absorbed few PVA may transform into bud-like or even onion-
like structures. Therefore, in order to adopt pupa-like morphology for the particles, it is always necessary to have a high level of PVA concentration (usually exceeds 0.5 mg/mL) in the aqueous solution (Figure 3e,f). Decreasing PVA concentration will induce morphology transformation from pupa-like structure to onion-like structure. Extremely low concentration of PVA (under 0.05 mg/mL) is favorable for the formation of onion-like particles. These nanostructured PS-b-P4VP colloidal particles can be further functionalized after selective growth of functional NPs. Specific interaction of P4VP with metallic precursors can induce a favorable growth of NPs within the P4VP domains through in situ reduction. Lamellar structure of pupa-like particle becomes more discerned after growth of Au NPs without staining with iodine vapor (Figure 4a). The Au
Figure 4. TEM images of Au/polymer composite particles: composite pupa-like particles before (a) and after (b) chloroform annealing treatment in water. The particles were not stained by iodine vapor before TEM investigation.
particles are ∼3.0 nm in diameter. The absorption peak of Au particles in the composite particles is at ∼550 nm (Figure S2), which is red-shifted with respect to the position of the characteristic peak (∼520 nm) for isolated Au NPs of ∼3.0 nm diameter. This is explained by the plasmon coupling of the densely stacked Au NPs. This idea can be easily extended to 7015
dx.doi.org/10.1021/ma401398h | Macromolecules 2013, 46, 7012−7017
Macromolecules
Article
Winnik, F.; Zauscher, S.; Luzinov, I.; Minko, S. Nat. Mater. 2010, 9, 101−113. (2) Russell, T. P. Science 2002, 297, 964−967. (3) Luzinov, I.; Minko, S.; Tsukruk, V. V. Prog. Polym. Sci. 2004, 29, 635−698. (4) Roy, D.; Cambre, J. N.; Sumerlin, B. S. Prog. Polym. Sci. 2010, 35, 278−301. (5) Jochum, F. D.; Theato, P. Chem. Soc. Rev. 2013, 42, 7468−7483. (6) Bae, Y.; Fukushima, S.; Harada, A.; Kataoka, K. Angew. Chem., Int. Ed. 2003, 42, 4640−4643. (7) Motornov, M.; Roiter, Y.; Tokarev, I.; Minko, S. Prog. Polym. Sci. 2010, 35, 147−211. (8) Hu, J. M.; Liu, S. Y. Macromolecules 2010, 43, 8315−8330. (9) Kelley, E. G.; Albert, J. N. L.; Sullivan, M. O.; Epps, T. H. Chem. Soc. Rev. 2013, 42, 7057−7071. (10) Habault, D.; Zhang, H. J.; Zhao, Y. Chem. Soc. Rev. 2013, 42, 7244−7256. (11) Chiu, H.; Lin, Y.; Huang, Y.; Chuang, C.; Chern, C. Angew. Chem., Int. Ed. 2008, 47, 1875−1878. (12) Dong, R.; Zhu, B.; Zhou, Y.; Yan, D.; Zhu, X. Angew. Chem., Int. Ed. 2012, 51, 11633−11637. (13) Li, L.; Rosenthal, M.; Zhang, H.; Hernandez, J. J.; Drechsler, M.; Phan, K. H.; Rütten, S.; Zhu, X.; Ivanov, D. A.; Möller, M. Angew. Chem., Int. Ed. 2012, 51, 11616−11619. (14) Xu, W.; Choi, I.; Plamper, F. A.; Synatschke, C. V.; Müller, A. H. E.; Tsukruk, V. V. ACS Nano 2013, 7, 598−613. (15) Moon, J. J.; Suh, H.; Bershteyn, A.; Stephan, M. T.; Liu, H. P.; Huang, B.; Sohail, M.; Luo, S.; Um, S. H.; Khant, H.; Goodwin, J. T.; Ramos, J.; Chiu, W.; Irvine, D. J. Nat. Mater. 2011, 10, 243−251. (16) Lu, Z. H.; Liu, G. J.; Phillips, H.; Hill, J. M.; Chang, J.; Kydd, R. A. Nano Lett. 2001, 1, 683−687. (17) Pham, H. H.; Gourevich, I.; Oh, J. K.; Jonkman, J.; Kumacheva, E. Adv. Mater. 2004, 16, 516−520. (18) Staff, R. H.; Gallei, M.; Mazurowski, M.; Rehahn, M.; Berger, R.; Landfester, K.; Crespy, D. ACS Nano 2012, 6, 9042−9049. (19) Zhu, J. T.; Ferrer, N.; Hayward, R. C. Soft Matter 2009, 5, 2471−2478. (20) Liu, G. J. Chin. J. Polym. Sci. 2000, 18, 255−262. (21) Orilall, M. C.; Wiesner, U. Chem. Soc. Rev. 2011, 40, 520−535. (22) Zhu, J. T.; Jiang, W. Mater. Chem. Phys. 2007, 101, 56−62. (23) Hanisch, A.; Gröschel, A. H.; Förtsch, M.; Drechsler, M.; Jinnai, H.; Ruhland, T. M.; Schacher, F. H.; Müller, A. H. E. ACS Nano 2013, 7, 4030−4041. (24) Arsenault, A. C.; Rider, D. A.; Tétreault, N.; Chen, J. I. L.; Coombs, N.; Ozin, G. A.; Manners, I. J. Am. Chem. Soc. 2005, 127, 9954−9955. (25) Yu, B.; Li, B.; Jin, Q.; Ding, D.; Shi, A. Macromolecules 2007, 40, 9133−9142. (26) Higuchi, T.; Tajima, A.; Motoyoshi, K.; Yabu, H.; Shimomura, M. Angew. Chem., Int. Ed. 2008, 47, 8044−8046. (27) Chi, P.; Wang, Z.; Li, B.; Shi, A. Langmuir 2011, 27, 11683− 11689. (28) Chai, A. H.; Zhang, L. X. Chin. J. Polym. Sci. 2011, 29, 684−691. (29) Jeon, S.; Yi, G.; Yang, S. Adv. Mater. 2008, 20, 4103−4108. (30) Deng, R. H.; Liu, S. Q.; Li, J. Y.; Liao, Y. G.; Tao, J.; Zhu, J. T. Adv. Mater. 2012, 24, 1889−1893. (31) Deng, R. H.; Liang, F. X.; Li, W. K.; Liu, S. Q.; Liang, R. J.; Cai, M. L.; Yang, Z. Z.; Zhu, J. T. Small 2013, DOI: 10.1002/smll. 201300271. (32) Jang, S. G.; Audus, D. J.; Klinger, D.; Krogstad, D. V.; Kim, B. J.; Cameron, A.; Kim, S. W.; Delaney, K. T.; Hur, S. M.; Killops, K. L.; Fredrickson, G. H.; Kramer, E. J.; Hawker, C. J. J. Am. Chem. Soc. 2013, 135, 6649−6657. (33) McKenzie, B. E.; Nudelman, F.; Bomans, P.; Holder, S. J.; Sommerdijk, N. J. Am. Chem. Soc. 2010, 132, 10256−10259. (34) Higuchi, T.; Motoyoshi, K.; Sugimori, H.; Jinnai, H.; Yabu, H.; Shimomura, M. Macromol. Rapid Commun. 2010, 31, 1773−1778. (35) Higuchi, T.; Shimomura, M.; Yabu, H. Macromolecules 2013, 46, 4064−4068.
other functional NPs such as palladium, platinum, or iron oxide.31,44 Moreover, Au NPs addition will highly suppress the phase transformation due to the strong interaction between P4VP and Au NPs. In this case, Au NPs act as cross-linkers and P4VP segments are “cross-linked”, resulting in the constraint of the polymer chain rearrangement and suppression of the phase transformation. After chloroform annealing in water for 12 h, their aspect ratio decreases, and the particles tend to be spherical shape (Figure 4b and Figure S3a) while keeping their internal axially stacked lamellae structure. These pudgy composite particles cannot change back to the initial spindle ones even after annealing in PVA aqueous solution (3 mg/mL) again (Figure S3b). This transition is irreversible since the selective existence of Au NPs in P4VP microdomain destroyed the balance of PS and P4VP domains to the PVA solution at the particle surface.
4. CONCLUSIONS In summary, we have demonstrated the reversible morphological transformation of nanostructured polymer particles by using solvent-adsorption annealing. After solvent adsorption, the swelled particles can simultaneously undergo shape and structure changes to response new external environment. The transformation can be well controlled in a reversible manner by tailoring the particle/aqueous solution interfacial properties. As far as we know, this is the first report on the reversible transformation of block copolymer nanostructured particles. The polymer particles can be further functionalized after selective growth of functional materials, for example Au NPs. Moreover, the stimuli-response behavior of the composited particles can be highly suppressed through the introduction of Au NPs. This strategy provides a new concept for the reversible transformation of the responsive nanostructured polymer particles, which may offer new opportunities in the area of detection, sensors, drug delivery, catalysis, and smart materials formation.
■
ASSOCIATED CONTENT
S Supporting Information *
Additional data and figures. This material is available free of charge via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected] (Z.Y.). *E-mail
[email protected] (J.Z.). Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We gratefully acknowledge National Basic Research Program of China (2012CB821500), National Natural Science Foundation of China (51173056 and 91127046), and Excellent Youth Foundation of Hubei Scientific Committee (2012FFA008). We also thank Prof. X. H. He at Tianjin University for fruitful discussions. J.Z. thanks HUST Analytical and Testing Center for allowing us to use its facilities.
■
REFERENCES
(1) Stuart, M. A. C.; Huck, W. T. S.; Genzer, J.; Müller, M.; Ober, C.; Stamm, M.; Sukhorukov, G. B.; Szleifer, I.; Tsukruk, V. V.; Urban, M.; 7016
dx.doi.org/10.1021/ma401398h | Macromolecules 2013, 46, 7012−7017
Macromolecules
Article
(36) Kim, S. H.; Misner, M. J.; Xu, T.; Kimura, M.; Russell, T. P. Adv. Mater. 2004, 16, 226−231. (37) Albert, J.; Epps, T. H. Mater. Today 2010, 13, 24−33. (38) Jeong, J. W.; Park, W. I.; Kim, M.; Ross, C. A.; Jung, Y. S. Nano Lett. 2011, 11, 4095−4101. (39) Sidorenko, A.; Tokarev, I.; Minko, S.; Stamm, M. J. Am. Chem. Soc. 2003, 125, 12211−12216. (40) Li, L.; Matsunaga, K.; Zhu, J. T.; Higuchi, T.; Yabu, H.; Shimomura, M.; Jinnai, H.; Hayward, R. C.; Russell, T. P. Macromolecules 2010, 43, 7807−7812. (41) Mei, S. L.; Wang, L.; Feng, X. D.; Jin, Z. X. Langmuir 2013, 29, 4640−4646. (42) Tangirala, R.; Revanur, R.; Russell, T. P.; Emrick, T. Langmuir 2007, 23, 965−969. (43) Saito, N.; Takekoh, R.; Nakatsuru, R.; Okubo, M. Langmuir 2007, 23, 5978−5983. (44) Kim, M. P.; Kang, D. J.; Jung, D. W.; Kannan, A. G.; Kim, K.; Ku, K. H.; Jang, S. G.; Chae, W. S.; Yi, G. R.; Kim, B. J. ACS Nano 2012, 6, 2750−2757.
7017
dx.doi.org/10.1021/ma401398h | Macromolecules 2013, 46, 7012−7017
