Janus Nanoparticles of Block Copolymers by Emulsion Solvent

Article pubs.acs.org/Macromolecules

Janus Nanoparticles of Block Copolymers by Emulsion Solvent Evaporation Induced Assembly Renhua Deng,†,‡ Hui Li,§ Jintao Zhu,*,‡ Baohui Li,*,§ Fuxin Liang,† Fan Jia,† Xiaozhong Qu,† and Zhenzhong Yang*,† †

State Key Laboratory of Polymer Physics and Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China ‡ Key Laboratory Materials Chemistry for Energy Conversion and Storage of the Ministry of Education, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China § School of Physics and Key Laboratory of Functional Polymer Materials of the Ministry of Education, Nankai University, Tianjin 300071, China S Supporting Information *

ABSTRACT: We present a facile approach toward straightforward synthesis of Janus nanoparticles (NPs) of poly(4vinylpyridine)-based block copolymers by solvent evaporation induced assembly within emulsion droplets. Formation of the Janus NPs is arisen from the synergistic effect between solvent selectivity and interfacial selectivity. This method is robust without the requisites of narrow molecular weight distribution and specific range of block fraction of the copolymers. Janus NPs can also be achieved from mixtures of copolymers, whose aspect size ratio and thus Janus balance are finely tunable. The Janus NPs are capable to self-assemble into ordered superstructures either onto substrates or in dispersions, whose morphology relies on Janus balance. which are formed by drying emulsion droplets.28 It is noticed that all the aforementioned methods are essentially based on self-assembly/cross-linking/disassembly combinational route. The BCPs should possess specific range of block fraction so as to self-assemble into the expected supramolecular structures. Meanwhile, sufficiently narrow molecular weight distribution is required to ensure the uniformity of the self-assembled structures. It remains challenging to prepare Janus NPs from BCPs with broad range of molecular weight distribution and block fraction. Herein, we demonstrate a robust method to synthesize Janus NPs from P4VP based BCPs through emulsion solvent evaporation (Scheme 1). All the BCPs can convert into a Janus NP after solvent evaporation if the emulsion droplet is sufficiently small. It is significant that P4VP block should be more affinitive to the emulsion interface while the other block is more affinitive to the solvent. During solvent evaporation, P4VP chains start to aggregate while chains of the block keep dissoluble. The aggregated P4VP head tends to migrate toward the interface. After complete evaporation of the solvent, chains of the other block are condensed forming another head at the opposite side. Janus NPs can also be derived from mixtures of BCPs with varying block fraction and molecular weight. The

1. INTRODUCTION Polymeric Janus objects with asymmetric structures have gained growing concerns.1−6 They are highly flexible and responsive to solvent, temperature, pH, or other stimuli.7,8 Especially, Janus nanoparticles (NPs) of block copolymers (BCPs) with different parts covalently bound are tunable in microstructure and composition and thus physicochemical performance.9−11 For example, the Janus NPs are amphiphilic and flexible, which can act as adaptive building units to self-assemble into complex superstructures12,13 or serve as functional solid surfactants.14−16 Although there are several reports on straightforward synthesis of Janus micelles by self-assembly or coassembly of BCPs in solution after carefully controlling experimental parameters,17−19 core−shell or multiple-compartment micelles (MCMs) are usually obtained due to the thermodynamic and dynamic barrier in the self-assembly process.20−23 During the past 15 years after pioneering work by Müller, the technique of disassembly of partially cross-linked supramolecular bulk24−26 or MCMs27 has been extensively employed to synthesize Janus NPs of BCPs. It is effective to tune shape and Janus balance of the Janus NPs by varying block fraction of ABC triblock copolymers with the cross-linkable B-block. However, it is difficult to adopt the route for AB diblock copolymers, since diblock copolymers usually tend to form core−shell NPs rather than Janus ones. Recently, we have successfully achieved Janus NPs from polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers by disassembly of the patchy particles, © XXXX American Chemical Society

Received: November 20, 2015 Revised: January 16, 2016

A

DOI: 10.1021/acs.macromol.5b02507 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules

in the resultant dispersion ensures good dispersion of the Janus NPs in water. Labeling P4VP Head of the Janus NPs with Au. 10 μL of HAuCl4·4H2O aqueous solution (50 mg/mL) was added to the Janus NPs dispersion in water (1 mL). The solution was shaken fully and stood for 2 h at room temperature. Subsequently, the products were separated by centrifugation at 16 000 rpm for 10 min. Cross-Linking P4VP Head of the Janus NPs. 5 μL of DIP was added to the above Janus NPs dispersion in ethanol (1 mL). The dispersion was stored at 35 °C for 3 days to perform a selective crosslinking of P4VP head. After centrifugation at 16 000 rpm for15 min and washing with CTAB ethanol solution and ethanol (2 mg/mL), the cross-linked Janus NPs were dispersed in 2 mL of DCM or THF. Self-Assembly of the Janus NPs. A certain volume of ethanol (or water) was dropwise added into the above dispersion of the crosslinked Janus NPs in DCM (or THF). The dispersion was fully shaken and stood at 30 °C for 2 h. Dialysis was also used to drive the selfassembly of the cross-linked Janus NPs. The cross-linked Janus NPs dispersion in THF in a dialysis bag (molecular weight cutoff: 35 000 Da) was dialyzed against 300 mL of water under stirring at room temperature for 3 days. Characterization. Transmission electron microscopy (TEM) measurement was performed on JEM-1011 TEM operated at an acceleration voltage of 100 kV. Scanning electron microscopy (SEM) images were recorded on S-4800 (JEOL) operated at an acceleration voltage of 20 kV. Size and size distribution of the particles were measured using DLS (Malvern Zetasizer Nano ZS90). AFM images were recorded at a tapping mode under ambient condition using a Digital Instrument Multimode Nanoscope IIIA.

Scheme 1. Illustrative Synthesis of the Janus NPs by Solvent Evaporation Induced Assembly of P4VP-Based Diblock Copolymers in Emulsion Dropletsa

a

The size of the P4VP head (red) and thus Janus balance are tunable by varying P4VP fraction.

aspect size ratio of the Janus NPs and thus Janus balance can be finely tunable across 1:1. The Janus NPs can self-assemble into superstructures whose morphologies are dependent on the Janus balance.

2. EXPERIMENTAL SECTION Materials. PS188K-b-P4VP96K (Mw/Mn = 1.15), PS110K-b-P4VP107K (Mw/Mn = 1.15), PS38K-b-P4VP82K (Mw/Mn = 1.39), and PtBMA80K-bP4VP77K (Mw/Mn = 1.15) were purchased from Polymer Source, Inc. Poly(vinyl alcohol) (PVA) (Mw = 13K−23K g/mol, 87−89% hydrolyzed) and cetyltrimethylammonium bromide (CTAB) were purchased from Aldrich. Pluronic F108 was obtained from BASF. Chloroauric acid (HAuCl4·4H2O), sodium dodecyl sulfate (SDS), chloroform, dichloromethane (DCM), tetrahydrofuran (THF), and ethanol were purchased from Beijing Chemical Works. 1,5Diiodopentane (DIP) was purchased from Tokyo Chemical Industry Co. All the chemicals were used as received without further purification. Preparation of the Janus NPs. The Janus NPs were prepared by solvent evaporation induced assembly of BCPs within emulsion droplets stabilized with PVA aqueous solution. BCPs were initially dissolved in chloroform at a concentration of 0.5 mg/mL. 0.1 mL of the solution was emulsified with 1.0 mL of PVA aqueous solution (5 mg/mL) through membrane extrusion emulsification for 40 times cycle. After the emulsion was collected in a vial (10 mL), chloroform slowly evaporated at 35 °C for 24 h. The products were separated by centrifugation (16 000 rpm, 15 min). A small amount of residual PVA

3. RESULTS AND DISCUSSION Janus NPs of PS-b-P4VP. The formation process of the Janus NPs is shown in Scheme 1. The BCPs solution in chloroform is emulsified to form emulsion droplets stabilized by PVA. P4VP has a poorer solubility in chloroform than PS. During evaporation of chloroform, P4VP first start to aggregate into a cluster in the droplet.29 Owing to the hydrogen bonding between P4VP with PVA or water, the P4VP aggregates tend to expose at the emulsion interface. After the completion of solvent evaporation, Janus NPs form with another newly formed PS head at the opposite side. Janus NPs of PS188K-b-

Figure 1. (a, b) TEM images of PS188K-b-P4VP96K Janus NPs with P4VP head stained by I2 and labeled with Au NPs, respectively. (c) SEM image of PS188K-b-P4VP96K Janus NPs. (d) DLS plot of the Janus NPs in water. B


Article

Macromolecules

Figure 2. SEM images of the PS-b-P4VP Janus NPs with varied f P4VP: (a) PS110K-b-P4VP107K; (b) PS38K-b-P4VP82K; inset TEM images of the Janus NPs labeled with Au NPs at the P4VP head; all the scale bars are 50 nm. (c) Simulative volume ratio (R) of Janus NPs (red dashed curve) and experimental height ratio (r) (blue solid curve) showing Janus balance as a function of f P4VP.

Figure 3. TEM images of the Au NPs labeled Janus NPs from binary mixtures of PS38K-b-P4VP82K/PS188K-b-P4VP96K at varied mass fraction (Φ) of PS38K-b-P4VP82K: (a) 0.2, (b) 0.4, (c) 0.6, and (d) 0.8. (e) Computer simulative head volume ratio of P4VP/PS (R) and experimental height aspect ratio (r) as a function of Φ. (f) TEM image of the Janus NPs from a triple mixture of PS188K-b-P4VP96K/PS110K-b-P4VP107K/PS93K-b-P4VP35K (1:1:1).

P4VP96K (f P4VP ∼ 0.34) were prepared directly using the emulsion solvent evaporation induced assembly. The Janus NPs with a small P4VP head are shown after staining by I2 vapor at room temperature for 2 h (Figure 1a). The Janus structure is also verified by selective labeling the P4VP head with Au NPs (Figure 1b). The average diameter is ∼75 nm. SEM image reveals that the Janus NPs are clearly separated into P4VP and PS heads with a neck (Figure 1c). For a representative particle, P4VP and PS heads are high ∼30 and ∼50 nm, respectively. The P4VP/PS aspect height ratio (r) is 0.6:1, implying that the Janus NPs are more hydrophobic. Average hydrodynamic diameter of the Janus NPs in water is measured ∼96 nm by DLS (Figure 1d).

In order to effectively generate Janus NPs, the particles should be small enough ensuring that each particle contains one PS and one P4VP domain. In addition, the interface should be properly adjusted to ensure that both PS and P4VP blocks can expose onto the surface. In the control experiments, PS188K-bP4VP96K is employed to investigate formation mechanism of the Janus NPs. The polymer NPs are achieved after complete drying the emulsion droplets. The particle size determines if they are Janus or patchy particles with multiple patches, which is decreased with decreasing the initial emulsion droplet diameter (D0) and (or) the initial polymer concentration (c0). According to the Monte Carlo simulation,29 particles with one PS domain and one P4VP domain can form within C


Article

Macromolecules

Further increasing Φ to 0.8 leads to a higher ratio of 1.40:1. Inverted snowman-like Janus NPs are thus obtained (Figure 3d). The aspect volume aspect ratio of the Janus NPs from A4B8/A8B4 mixtures at Φ = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 is computer simulated (red dashed curve, Figure 3e). Experimentally, the aspect height ratio (r) is continuously increased with Φ (blue solid curve, Figure 3e), which is well consistent with the computer simulation result. The synthetic method is robust, and Janus NPs can also be achieved from triple mixtures (Figure 3f). This mixing strategy is advantageous in finely tuning Janus balance of the NPs by simply varying the fraction. Extension of the Synthesis Method. Based on our previous report on the formation of unique pupa-like and patchy particles of PS-b-P4VP after drying emulsion droplets stabilized with PVA, we emphasized the importance of a nearly neutral interface in controlling morphology of particles.28,31,32 However, the nearly neutral interface window is rather narrow in the phase diagram. In most cases, the interface is selective for one block of the BCPs. This is the reason that diblock copolymers always tend to self-assemble into core−shell structures.32,33 It is promising to achieve Janus NPs from selective interface. In fact, in our system, the interface is slightly selective for P4VP. As discussed above, P4VP blocks first aggregate into a cluster while PS blocks remain soluble during solvent evaporation, since the solvent chloroform (solubility parameter, δ = 19.0 MPa1/2) is more selective for PS (δ = 18.6 MPa1/2) than P4VP (δ = 22.2 MPa1/2).34 The P4VP cluster is more affinitive to the emulsion interface and tend to expose there. That is the main reason that Janus NPs rather than a core−shell structure can form under the condition of a slightly selective interface. It is expected that the approach can be extended to other soluble polymeric blocks beyond PS block. In comparison with P4VP block, the other block should be preferentially dissoluble in the solvent but less affinitive to the emulsion interface. A large family of hydrophobic polymer blocks can easily satisfy both requirements. It is feasible to achieve Janus NPs from droplets with a selective interface beyond a neutral one. PtBMA80K-b-P4VP77K is used as an example since PtBMA is preferentially dissoluble in chloroform (δ = 16.9 MPa1/2) while the interface is more selective for P4VP. Indeed, individual Janus NPs can be obtained (Figure 4a). The Janus NPs become crescent after prolonged electron

sufficiently small droplets. The critical emulsion droplet radius forming the Janus NPs of A8B4 (A: PS block; B: P4VP block) is 7 when c0 = 15%. When the radius is larger, for example 18, the particle contains multiple B-patches on the surface (Figure S1a). When the radius is 6, a Janus NP can be obtained (Figure S1b). Experimentally, decreasing D0 is easily realized by simply increasing extrusion cycle number during the emulsion preparation. After extrusion for 10 cycles, most of the emulsion droplets are large with the diameter of 1.5−2.0 μm (Figure S1c1). As a result, the polymer particles contain multiple P4VP patches onto their surface (Figure S1d1). Few smaller snowman-like Janus NPs with single P4VP patch are found. When the extrusion cycle number is increased to 20, the emulsion droplets become smaller with the diameter of 0.9−1.5 μm (Figure S1c2). A fraction of the Janus NPs are greatly increased (Figure S1d2). Further increasing the extrusion number to 40, the emulsion droplets become much smaller (diameter: 0.8−1.1 μm) and relatively uniform (Figure S1c3). In this case, nearly all the polymer particles are Janus NPs. Therefore, in all the experiments, the extrusion number is fixated at 40. Surfactants also play a very important role in forming the Janus NPs. When another nonionic surfactant, e.g., Pluronic F108, is used to replace PVA, Janus NPs can be achieved (Figure S2a). It is understandable that F108 has no selective interaction with either PS or P4VP. When a P4VP selective surfactant such as SDS is used, core−shell NPs form with the P4VP shell (Figure S2b). When a PS selective surfactant such as CTAB is used,30 core−shell NPs form but with the PS shell (Figure S2c). To achieve the Janus NPs, it is significant that neither block is soluble in water. Otherwise, the NPs would be core−shell structure. P4VP is pH responsive with a pKa ∼ 4.8. At lower pH, for example ∼3, P4VP is protonated and becomes soluble in water, and PS/P4VP core/shell micelles are indeed formed (Figure S3a). At higher pH for example ∼9, P4VP is water insoluble yet more affinitive to the interface than PS block. Janus NPs can be always achieved (Figure S3b). Synthesis Robustness. In principle, our method is feasible for PS-b-P4VP with nearly full range of f P4VP. Therefore, it is effective to tune Janus balance of the NPs by varying f P4VP. When a symmetric PS110K-b-P4VP107K (f P4VP ∼ 0.49) is used, dumbbell-like Janus NPs are achieved (Figure 2a). Both heads are almost equal in size. When PS38K-b-P4VP82K ( f P4VP ∼ 0.68) is used, Janus NPs are formed with a larger P4VP head (Figure 2b). The Janus NPs of PS38K-b-P4VP82K should be more hydrophilic. The aspect height ratio (r) increases with f P4VP (blue solid curve, Figure 2c). Computer simulation predicts that Janus NPs can always be achieved from A9B3, A8B4, A6B6, A4B8, and A3B9, and the P4VP/PS head volume ratio (R) is increased continuously with f P4VP, which can cross the critical ratio of 1:1 at f P4VP = 0.5 (red dashed curve, Figure 2c). The validity of this method is independent of molecular weight distribution of BCPs. As proof of the concept, PS38K-bP4VP82K and PS188K-b-P4VP96K are mixed at an arbitrary ratio. As a result, Janus NPs are always achieved at varied mass fraction of PS38K-b-P4VP82K (Φ). At Φ = 0.2, snowman-like Janus NPs are achieved (Figure 3a). The P4VP/PS aspect height ratio (r) is 0.78:1, implying that they are more hydrophobic. When Φ is increased from 0.4 to 0.6, dumbbell-like Janus NPs are achieved (Figures 3b,c). The aspect height ratio is also increased from 0.93:1 to 1.15:1, crossing the critical ratio of 1:1. This implies that the Janus NPs is transformed from more hydrophobic to more hydrophilic.

Figure 4. TEM images of PtBMA80K-b-P4VP77K Janus NPs (a) and (b) the crescent NPs by long electron beam irradiation during observation. Both samples are stained with I2.

beam irradiation during TEM observation (Figure 4b), which is attributed to the PtBMA degradation by electron beam.27 Our method can be expanded to other copolymers to derive those Janus NPs with tunable physical/chemical properties. Self-Assembly of PS-b-P4VP Janus NPs. The PS-b-P4VP Janus NPs are amphilphilic with hydrophilic P4VP and hydrophobic PS heads distinctly compartmentalized onto D


Article

Macromolecules

Figure 5. (a) TEM, (b, c) SEM and (d) AFM images of the self-assembled superstructures from PS188K-b-P4VP96K Janus NPs onto a hydrophobic substrate.

Figure 6. TEM images of the superstructures by PS188K-b-P4VP96K Janus NPs after adding varied amount of ethanol into 1 mL of dispersion in DCM: (a) 0.25 mL; (b) 0.8 mL. (c) TEM image of the superstructures formed after adding 0.8 mL of ethanol into 1 mL of PS38K-b-P4VP82K Janus NPs dispersion in DCM. (d) SEM image of the superstructures after PS188K-b-P4VP96K Janus NPs dispersion in THF is dialyzed against water; inset a TEM image.

cross-linked P4VP heads maintain isolated and direct toward air (Figure 5a). A capillary force among the Janus NPs during solvent evaporation can drive the Janus NPs to stack into an ordered monolayer. Since the dispersion is highly diluted, the monolayer is composed of some patchy domains with varied particle number. All the domains are highly ordered. SEM (Figure 5b,c) and AFM images (Figure 5d) of the monolayer reveal that all the isolated P4VP heads direct upwardly to air. However, when the inverted snowman-like Janus NPs of PS38Kb-P4VP82K with a larger hydrophilic P4VP head are used, disordered individual particles instead of monolayer are observed after solvent (e.g., DCM) evaporation from the dispersion on carbon substrate (Figure S4b). Formation of the

both sides. They can further self-assemble into superstructures. Morphology of the superstructures is dominated by Janus balance of the NPs. The snowman-like Janus NPs of PS188K-bP4VP96K are selected, whose hydrophobic PS head is larger than the hydrophilic P4VP head. In order to strengthen the Janus NPs, the P4VP head is cross-linked with diiodopentane. In a good solvent, for example dichloromethane (DCM) or tetrahydrofuran (THF), the cross-linked Janus NPs can well preserve their integrity rather than dissolved (Figure S4a). When spreading 5 μL of the dilute dispersion onto a hydrophobic substrate such as carbon film, the hydrophobic PS heads are preferentially adhered onto carbon substrate and coalesce into a film after drying within 30 s. Meanwhile, the E


Article

Macromolecules Notes

monolayer is suppressed by the steric hindrance of larger P4VP heads. The Janus NPs can self-assemble into superstructures by adding P4VP selective solvents such as ethanol and water. After a small amount of ethanol (0.25 mL) is added into 1 mL of PS 188K -b-P4VP 96K Janus NPs dispersion in DCM, no aggregation is found in the dispersion. Upon the mixture solvent evaporation, some aggregates form (Figure 6a). P4VP sides tend to segregate inwardly while the PS chains are located outwardly. Meanwhile, PS chains tend to coalesce with each other. When the amount of ethanol is increased to 0.8 mL, the Janus NPs self-assemble into patchy particles with P4VP heads onto the surface (Figure 6b). In this case, P4VP is more affinitive to the mixture solvent. Similar behavior has been observed for the PS110K-b-P4VP107K Janus NPs.28 Interestingly, after adding 0.8 mL of ethanol into PS38K-b-P4VP82K Janus NPs (with larger P4VP heads) dispersion in DCM (1.0 mL), the self-assembled superparticles contain smaller number of Janus NPs (Figure 6c). Some dimers and trimers coexist. Besides, the self-assembly can occur by dialyzing the Janus NPs dispersion in THF against water. For the Janus NPs of PS38K-b-P4VP82K, the superparticles contain a small number of the Janus NPs (Figure S4c), while PS188K-b-P4VP96K Janus NPs (with larger PS heads) can self-assemble into hollow spheres after THF is substituted with water (Figure 6d). The coarsening exterior surface of the sphere wall is covered with the hydrophilic P4VP heads. The interior surface is smooth by the coalescence of PS chains (Figure S4d). The wall thickness is comparable with the Janus NP size, implying that the wall is a monolayer selfassembled of the Janus NPs.

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Z.Y. acknowledges NSFC (51233007 and 51173191), J.Z. acknowledges NSFC (51525302), and B.L. acknowledges NSFC (91227121).

■

(1) Walther, A.; Müller, A. H. E. Chem. Rev. 2013, 113, 5194−5261. (2) Wurm, F.; Kilbinger, A. F. M. Angew. Chem., Int. Ed. 2009, 48, 8412−8421. (3) Pang, X.; Wan, C.; Wang, M.; Lin, Z. Angew. Chem., Int. Ed. 2014, 53, 5524−5538. (4) Nie, L.; Liu, S.; Shen, W.; Chen, D.; Jiang, M. Angew. Chem., Int. Ed. 2007, 46, 6321−6324. (5) Nie, Z.; Li, W.; Seo, M.; Xu, S.; Kumacheva, E. J. Am. Chem. Soc. 2006, 128, 9408−9412. (6) Hu, J.; Zhou, S. X.; Sun, Y. Y.; Fang, X. S.; Wu, L. M. Chem. Soc. Rev. 2012, 41, 4356−4378. (7) Gröschel, A. H.; Walther, A.; Löbling, T. I.; Schacher, F. H.; Schmalz, H.; Müller, A. H. E. Nature 2013, 503, 247−251. (8) Gao, L.; Zhang, K.; Chen, Y. M. ACS Macro Lett. 2012, 1, 1143− 1145. (9) Erhardt, R.; Zhang, M.; Böker, A.; Zettl, H.; Abetz, C.; Frederik, P.; Krausch, G.; Abetz, V.; Müller, A. H. E. J. Am. Chem. Soc. 2003, 125, 3260−3267. (10) Ruhland, T. M.; Groschel, A. H.; Ballard, N.; Skelhon, T. S.; Walther, A.; Müller, A. H. E.; Bon, S. A. F. Langmuir 2013, 29, 1388− 1394. (11) Deng, R. H.; Liang, F. X.; Zhou, P.; Zhang, C. L.; Qu, X. Z.; Wang, Q.; Li, J. L.; Zhu, J. T.; Yang, Z. Z. Adv. Mater. 2014, 26, 4469− 4472. (12) Walther, A.; Drechsler, M.; Rosenfeldt, S.; Harnau, L.; Ballauff, M.; Abetz, V.; Müller, A. H. E. J. Am. Chem. Soc. 2009, 131, 4720− 4728. (13) Cheng, L.; Zhang, G. Z.; Zhu, L.; Chen, D. Y.; Jiang, M. Angew. Chem., Int. Ed. 2008, 47, 10171−10174. (14) Walther, A.; Hoffmann, M.; Müller, A. H. E. Angew. Chem., Int. Ed. 2008, 47, 711−714. (15) Gröschel, A. H.; Löbling, T. I.; Petrov, P. D.; Müllner, M.; Kuttner, C.; Wieberger, F.; Müller, A. H. E. Angew. Chem., Int. Ed. 2013, 52, 3602−3606. (16) Xu, J.; Wang, K.; Li, J.; Zhou, H.; Xie, X.; Zhu, J. Macromolecules 2015, 48, 2628−2636. (17) Voets, I. K.; Keizer, A.; Waard, P.; Frederik, P. M.; Bomans, P. H. H.; Schmalz, H.; Walther, A.; King, S. M.; Leermakers, F. A. M.; Stuart, M. A. C. Angew. Chem., Int. Ed. 2006, 45, 6673−6676. (18) Li, X.; Yang, H.; Xu, L.; Fu, X.; Guo, H.; Zhang, X. Macromol. Chem. Phys. 2010, 211, 297−302. (19) Higuchi, T.; Tajima, A.; Motoyoshi, K.; Yabu, H.; Shimomura, M. Angew. Chem., Int. Ed. 2008, 47, 8044−8046. (20) Kubowicz, S.; Baussard, J. F.; Lutz, J. F.; Thünemann, A. F.; von Berlepsch, H.; Laschewsky, A. Angew. Chem., Int. Ed. 2005, 44, 5262− 5265. (21) Pochan, D. J.; Zhu, J. H.; Zhang, K.; Wooley, K. L.; Miesch, C.; Emrick, T. Soft Matter 2011, 7, 2500−2506. (22) Moughton, A. O.; Hillmyer, M. A.; Lodge, T. P. Macromolecules 2012, 45, 2−19. (23) Du, J.; Armes, S. P. Soft Matter 2010, 6, 4851−4857. (24) Erhardt, R.; Boker, A.; Zettl, H.; Kaya, H.; Pyckhout-Hintzen, W.; Krausch, G.; Abetz, V.; Müller, A. H. E. Macromolecules 2001, 34, 1069−1075. (25) Liu, Y.; Abetz, V.; Müller, A. H. E. Macromolecules 2003, 36, 7894−7898. (26) Walther, A.; Andre, X.; Drechsler, M.; Abetz, V.; Müller, A. H. E. J. Am. Chem. Soc. 2007, 129, 6187−6198.

4. CONCLUSION In summary, we have proposed an easy approach toward Janus NPs of P4VP-based BCPs by solvent evaporation induced assembly within small emulsion droplets. The synergistic effect between solvent selectivity and interface selectivity determines the formation of Janus NPs. The method is straightforward and robust without any strict requisites for narrow molecular weight distribution and specific range of block fraction of BCPs. The approach is general and valid for mixtures of BCPs. It is effective to continuously adjust Janus balance across 1:1 by simply changing either the block fraction (f P4VP) of one copolymer or the relative content (Φ) in a mixture. The Janus NPs are capable to self-assemble into ordered superstructures either on substrates or in dispersions. Functional composite Janus NPs are easily derived after preferential growth of functional species at the P4VP head. A new way is open to organize functional NPs into ordered superstructures using the Janus composite ones.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.5b02507. Figures S1−S4 (PDF)

■

REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (J.Z.). *E-mail: [email protected] (B.L.). *E-mail: [email protected] (Z.Y.). F


Article

Macromolecules (27) Gröschel, A. H.; Walther, A.; Löbling, T. I.; Schmelz, J.; Hanisch, A.; Schmalz, H.; Müller, A. H. E. J. Am. Chem. Soc. 2012, 134, 13850−13860. (28) Deng, R. H.; Liang, F. X.; Qu, X. Z.; Wang, Q.; Zhu, J. T.; Yang, Z. Z. Macromolecules 2015, 48, 750−755. (29) Deng, R. H.; Li, H.; Liang, F. X.; Zhu, J. T.; Li, B. H.; Xie, X. L.; Yang, Z. Z. Macromolecules 2015, 48, 5855−5860. (30) Klinger, D.; Wang, C. X.; Connal, L. A.; Audus, D. J.; Jang, S. G.; Kraemer, S.; Killops, K. L.; Fredrickson, G. H.; Kramer, E. J.; Hawker, C. J. Angew. Chem., Int. Ed. 2014, 53, 7018−7022. (31) Deng, R. H.; Liang, F. X.; Li, W. K.; Yang, Z. Z.; Zhu, J. T. Macromolecules 2013, 46, 7012−7017. (32) Yu, B.; Li, B.; Jin, Q.; Ding, D.; Shi, A. C. Macromolecules 2007, 40, 9133−9142. (33) Jeon, S. J.; Yi, G. R.; Koo, C. M.; Yang, S. M. Macromolecules 2007, 40, 8430−8439. (34) Brandrup, J., Immergut, E. H., Grulke, E. A., Eds.; Polymer Handbook; Wiley: New York, 1999; Section VII, pp 675−714.

G


Janus Nanoparticles of Block Copolymers by Emulsion Solvent

Recommend Documents