Blooming of Block Copolymer Micelles into Complex Nanostructures

Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

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Blooming of Block Copolymer Micelles into Complex Nanostructures on a Surface Hongyan Zhu,†,‡ Xinyan Wang,⊥ Yan Cui,§ Jiandong Cai,‡,⊥ Feng Tian,*,†,∥ Jie Wang,*,†,∥ and Huibin Qiu*,§ †

Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China University of Chinese Academy of Sciences, Beijing 100049, China § School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China ∥ Shanghai Advanced Research Institute, Zhangjiang Lab, Chinese Academy of Sciences, Shanghai 201204, China ⊥ School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China

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‡

S Supporting Information *

ABSTRACT: Self-assembled block copolymer (BCP) nanostructures are of important utility across a wide field. Here, we report a solution−surface sequential self-assembly approach to tailor amphiphilic BCPs in solution and subsequently on a substrate into complex nanostructures. Spherical micelles that formed in solution transform on a substrate sequentially into toroidal micelles, concentric toroidal micelles, and ring clusters upon alternating annealing in solvents that selectively swell the core but poor for the corona. This process is found in both diblock and triblock copolymer systems and appears to be independent of the nature of substrate and gravity. Thus, BCPs micelles with simple shapes can be further manipulated on a surface in a flexible fashion to constructed novel nanostructures.

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INTRODUCTION Solution self-assembly of amphiphilic block copolymers (BCPs) has been demonstrated to be a versatile route toward core−corona nanoparticles (micelles) with widespread applications.1−4 Numerous efforts have been devoted to realize a precise control of the micellar morphology, where conventional strategies involve delicate manipulation of the chemistry, length, and geometry of BCPs as well as the feature of solvents.2,5 This has enabled the formation of a diverse array of micelles with distinct simple morphologies, such as spheres,2 cylinders,6−8 disks,9−13 toroids,14,15 and vesicles,16,17 with core−shell complexity further diversified by introducing three or more polymer blocks, yielding Janus, patchy, and multicompartment micelles.18−20 In these systems, self-assembly is predominantly driven by the aggregation of core-forming blocks through solvophobic interactions, with the micellar morphology modulated both thermodynamically and kinetically by the balance of core coalescence and corona dissolution.2,16,21 However, the creation of new micellar structures is limited by the factor that the core/corona (corona/solvent) interface tends to adopt less complex topologies to reduce the surface energy. In contrast to the discrete micelles observed in solution, amphiphilic BCPs form long-range ordered nanostructures in bulk or thin film via microphase separation.22−25 Upon thermal26 or solvent vapor annealing,27 the incompatible © XXXX American Chemical Society

blocks segregate into spatially isolated domains. In this case, the interface of these domains emerges in a more diverse fashion with the formation of bicontinuous and other complicated phases (especially for multiblock copolymers).20,28,29 The polymer/substrate interface appears to be critical for the thin films, and hence the microphase separation highly depends on the substrate chemistry30 and can be guided by the surface pattern.31,32 Previous interests in microphase separation majorly focused on relatively large-scale bulk monoliths or thin films, aiming at various potential applications in soft lithography33,34 and porous materials.35 Nevertheless, the segregation of the incompatible blocks in a discrete BCP nanoobject that deposited on a surface was rarely studied, in spite of a few preliminary reports on the transition of spherical micelles to toroidal micelles upon solvent vapor annealing.36−38 Meanwhile, it remains a challenge to understand the motion of chain blocks during the annealing process. Here, we develop a solution−surface sequential selfassembly strategy to design complex nanostructures of amphiphilic BCPs. This involved the preparation of BCP micelles with a core−corona structure in solution and subsequent self-assembly on a surface induced by alternating Received: January 28, 2019 Revised: April 13, 2019

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DOI: 10.1021/acs.macromol.9b00197 Macromolecules XXXX, XXX, XXX−XXX

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room temperature for 24 h, prior to drying for characterization and further annealing experiments. Process 3: The silicon wafer was then placed in a sealed glass bottle filled with ethanol vapor and allowed to anneal at room temperature for 24 h, prior to drying for characterization and further annealing experiments. Process 4: The silicon wafer was then placed in a sealed glass bottle filled with cyclohexane vapor and allowed to anneal at room temperature for 24 h, prior to drying for characterization. To track the intermediates formed during the transition, a small container (vial lid) loaded with a sample was placed in a larger glass bottle filled with a desired solvent vapor, and after a certain period, the small container was took out quickly by a tweezer. The time periods shown in the figures correspond to that when the sample was statically placed in the glass bottle (although the actual solvent annealing process is slightly longer in consideration of the time that used to place and fetch the samples as well as that for the drying process). In consideration of the variable solubility of PS in cyclohexane, the solvent annealing experiments were initially conducted at different temperatures (Figure S6). At 5 °C, which is below the melting point of cyclohexane, little cyclohexane vapor was generated in the chamber, and thus the toroidal micelles hardly transformed. At 20 °C, the BCP micelles only transformed into disklike micelles, and at 30 °C, the transition was poorly controlled. The evolution was well resolved at room temperature (25 °C), and thus this was selected as the optimized temperature for all annealing processes. It should be noted that all the micellar morphologies were found to be stable on the surface in the air, and no obvious change was detected after 20 days. In the air, at room temperature, the possible active component is water vapor. However, the solubility parameter of water (47.9 MPa1/2) is far away from PS (18.6 MPa1/2) and P2VP (20.6 MPa1/2), and consequently water would be hard to induce prominent changes. Moreover, it should be noted that relatively dilute micelle solutions (0.5 mg/mL) were used for the initial spin-coating process to obtain a sparse distribution of the original micelles. The morphology formed by a single micelle upon solvent vapor annealing was found to be apparently different from the continuous phase separation structures derived from the dense arrays (Figure S7). Transition of PS-b-P2VP Spherical Micelles on Silicon Wafer Immersed in Solvent. A 20 μL aliquot of the solution of the PS700b-P2VP960 spherical micelles (0.5 mg/mL in toluene) was spin-coated on a piece of silicon wafer at a spin rate of 6000 rpm. The silicon wafer was then immersed in ethanol, n-butanol, or n-octanol at room temperature for 24 h and subsequently dried in the air prior to characterization (Figure S10). Influence of Gravity on the Transition of PS-b-P2VP Spherical Micelles on Silicon Wafer. A 20 μL aliquot of the solution of the PS700-b-P2VP960 spherical micelles (0.5 mg/mL in toluene) was spin-coated on a piece of silicon wafer at a spin rate of 6000 rpm. The silicon wafer was then horizontally (with the surface coated with spherical micelles facing upward or downward) or vertically placed in a sealed glass bottle filled with ethanol vapor and allowed to anneal at room temperature for 24 h, prior to drying for characterization (Figure S14).

annealing by selective solvents. Through sequential core− corona inversion under different solvent vapors that swell the core but poor for the corona, spherical micelles that immobilized on a substrate transformed successively into toroidal micelles, concentric toroidal micelles, and ring clusters. This process was found to be universal in terms of solvent annealing conditions, BCP chain length, and substrate feature and orientation and appeared to be routine for a variety of diblock and triblock copolymers, where triblock copolymers demonstrated a more complex transition process that ended with patchy structures. Generally, this strategy provides a distinctive method for the fabrication of complex nanostructures of amphiphilic BCPs as well as a deeper insight into the chain motion of BCPs upon solvent annealing.

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EXPERIMENTAL SECTION

Synthesis of Block Copolymers. Polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP), polybutadiene-b-poly(2-vinylpyridine) (PB-bP2VP), polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA), and polystyrene-b-polybutadiene-b-poly(2-vinylpyridine) (PS-b-PB-bP2VP) were synthesized via living anionic polymerization in tetrahydrofuran (THF) using sec-butyllithium as an initiator in an inert argon atmosphere glovebox (see the Supporting Information for experimental details). The molecular structures and features of the resulting PSm-b-P2VPn, PBm-b-P2VPn, PSm-b-PMMAn, and PSm-b-PBnb-P2VPk (the subscripts denote the degree of polymerization) block copolymers are shown in Figure S1 and Table S1, respectively. Preparation of PS-b-P2VP, PB-b-P2VP, and PS-b-PB-b-P2VP Micelles in Toluene. The block copolymer was first dissolved in toluene (0.5 mg/mL) by stirring at 75 °C for ca. 2 h. Afterward, the solution was cooled slowly to room temperature in the heating block and allowed to age for 1 day. PS500-b-P2VP710, PS700-b-P2VP960, PS920b-P2VP1330, PS530-b-P2VP770, PS360-b-P2VP720, PS300-b-P2VP1010, PB220-b-P2VP750, and PS580-b-PB660-b-P2VP920 formed spherical micelles, while PS80-b-P2VP1130 formed wormlike micelles and a mixture of toroidal micelles and vesicles for PS100-b-P2VP3350. Preparation of PS-b-PMMA Micelles in Acetone. PS980-bPMMA630 was dissolved in THF (10 mg/mL) by stirring at room temperature for ca. 1 h. Then, 50 μL of the above solution was added into 950 μL of acetone. The solution (0.5 mg/mL) was stirred at 50 °C for ca. 1 h, cooled slowly to room temperature in the heating block, and allowed to age for 1 day. Eventually, PS980-b-PMMA630 selfassembled into spherical micelles. Transition of PS-b-P2VP, PB-b-P2VP, PS-b-PMMA, and PS-bPB-b-P2VP Micelles on Silicon Wafer under Solvent Vapor. Generally, 20 μL of BCP micelle solution (0.5 mg/mL) was spincoated on a substrate (e.g., silicon wafer, mica, or carbon-coated copper grid) at a spin rate of 6000 rpm. The sample was then placed in a sealed glass bottle (volume of ca. 100 cm3 with 25 mL of solvent at the bottom; the sample was placed ca. 5 mm above the solvent surface) filled with a desired solvent vapor and allowed to anneal at room temperature for 24 h. To eliminate the influence of the original solvents, samples were dried by N2 flow before the next-stage solvent annealing. After drying, the micelles barely changed prior to solvent anneal, indicating a very weak influence from the possibly retained (trace amount of) original solvents. The solubility parameters (δ) of the solvents and polymers used in the annealing experiments are listed in Table S2. A typical set of experiments involved the following: Process 1: A 20 μL aliquot of the solution of the PS700-b-P2VP960 spherical micelles (0.5 mg/mL in toluene) was spin-coated on a piece of silicon wafer at a spin rate of 6000 rpm. The silicon wafer was then placed in a sealed glass bottle filled with ethanol vapor and allowed to anneal at room temperature for 24 h, prior to drying for characterization and further annealing experiments. Process 2: The silicon wafer was subsequently placed in a sealed glass bottle filled with cyclohexane vapor and allowed to anneal at

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RESULTS AND DISCUSSION Solution−Surface Sequential Self-Assembly of PS-bP2VP Diblock Copolymers. PS-b-P2VP diblock copolymers were first studied in consideration of the relatively well-known solubility preferences of the PS and P2VP blocks as well as their high glass transition temperatures (Tg ≈ 100 °C for PS and 106 °C for P2VP),39−41 which makes the nanostructures stable on the surface after drying. Solution self-assembly of these BCPs was conducted in toluene, which is a selective solvent for the PS block, yielding relatively monodisperse spherical micelles with a P2VP core and a PS corona (Figure B

DOI: 10.1021/acs.macromol.9b00197 Macromolecules XXXX, XXX, XXX−XXX

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Figure 1. (a) Schematic diagrams illustrating the solution self-assembly of PS700-b-P2VP960 into spherical micelles with a P2VP core and a PS corona in toluene and the formation of inversed spherical micelles with a PS core and a P2VP corona when being added into ethanol. (b) Schematic diagrams illustrating the transition of spherical micelles of PS700-b-P2VP960 into toroidal micelles, concentric toroidal micelles, and ring clusters upon sequential annealing in ethanol, cyclohexane, and ethanol vapors on a surface. (c−j) Atomic force microscopy (AFM) height images and height profiles of (c, g) spherical micelles on silicon wafer, (d, h) toroidal micelles formed after annealing in ethanol vapor, (e, i) concentric toroidal micelles formed after subsequent annealing in cyclohexane vapor, and (f, j) ring clusters formed after further annealing in ethanol vapor. The scale bars correspond to 50 nm in the inset AFM images.

1a and Figure S2a).42,43 In a typical solvent annealing process (Figure 1b), the resulting spherical micelles were first transferred to a piece of clean silicon wafer by spin-coating, and then the silicon wafer was horizontally placed in a sealed glass bottle filled with a desired solvent vapor (Figure S3a). For PS700-b-P2VP960, the spherical micelles with numberaverage diameter (Dn) measured by dynamic laser scattering (DLS) of ∼68 nm (Figure S2a) collapsed upon drying on the silicon wafer and formed depressed globes (Figure 1c) with Dn of ∼80 nm and number-average height (Hn) of ∼25 nm (Figure 1g). The annealing experiment was initially performed in a vapor of ethanol, which is a good solvent for the P2VP block but poor for the PS block.37,44 Hence, the P2VP core tends to be dissolved out, while the PS corona be gradually frozen. Interestingly, this led to the emergence of toroidal nanostructures (Figure 1d) with overall Dn of ∼80 nm and Hn of ∼10 nm (Figure 1h). It can be seem that the nanoobjects further contracted in the vertical direction. A series of samples with various annealing periods under ethanol vapor were visualized by AFM and scanning electron microscopy (SEM) to track the evolution process (Figure 2a−f and Figure S3). The depressed globes (Figure 2a) immediately collapsed in 2 s (Figure 2b) and formed a relatively flat and concave top in 6 s (Figure 2c). In the following few minutes,

the height of the center further decreased while the periphery retained almost constant. Consequently, the micelle perforated along the vertical direction and eventually transformed into a toroidal structure (Figure 2f). In the whole process, the overall diameter of the nanostructures changed very slightly (Figure 2k), and hence the total volume of the micelle significantly contracted, indicating a more condensed packing of the polymer chains (Figure S4). The transition process was also confirmed by in situ observation on a Cypher VRS video rate atomic force microscope, where the micelles also collapsed and gradually perforated into toroids (Figure S5). Encouraged by the above findings, we next selected cyclohexane, a poor solvent for P2VP, but slightly good for PS,37,44 to trigger a further evolution (Figure 2g−j and Figure S8). The toroidal micelles also collapsed in the initial stage with an apparent decrease in the cavity size and transformed into slightly patchy disks in 60 s (Figure 2h). These flat nanoobjects eventually evolved into concentric duplex toroidal micelles, which consisted of a smaller inner ring and a significantly larger external ring (Figures 1e and 2j). In this case, the nano-objects expanded along the surface with Dn increased to ∼115 nm but further depressed in the vertical direction with Hn decreased to ∼3.5 nm (Figures 1i and 2k, C

DOI: 10.1021/acs.macromol.9b00197 Macromolecules XXXX, XXX, XXX−XXX

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pyridyl groups in the P2VP corona with the hydroxyl groups on the silicon wafer). Thus, the annealing process can be operated directly in a solvent with the substrate fully immersed. This also led to the transition into well-defined toroidal structures, not only in ethanol but also in less volatile solvents, such as n-butanol and n-octanol (Figure 3a and

Figure 3. Transition of spherical micelles into toroidal micelles (a) for PS700-b-P2VP960 with the silicon wafer directly immersed in n-butanol and n-octanol, (b) for PS360-b-P2VP720 and PS300-b-P2VP1010 upon annealing in ethanol vapor, and (c) for PS700-b-P2VP960 on mica and carbon film upon annealing in ethanol vapor. (d) Influence of gravity on the transition of spherical micelles of PS700-b-P2VP960 into toroidal micelles with the silicon wafer vertically (left) and inversely placed (right) in ethanol vapor. Figure 2. AFM height and 3D images (inset) illustrating the transition process of (a) spherical micelles of PS700-b-P2VP960 upon (b−f) ethanol vapor annealing with increasing periods (inside a glass bottle filled with ethanol vapor) into toroidal micelles and subsequent (g−j) cyclohexane vapor annealing with increasing periods (inside a glass bottle filled with cyclohexane vapor) into concentric toroidal micelles. (k) Height profiles for the AFM images shown in (a−j).

Figure S10). We also employed a variety of other solvents with distinct solubility parameters (Table S2) to anneal the spherical micelles (Figure S11). The Flory−Huggins parameters between various polymers and solvents are listed in Table S3. For good solvents for both the PS and P2VP blocks, such as ethyl acetate and chloroform,37 only diffused spots were detected, while for cyclohexane and hexane, which are poor solvents for the P2VP block, no obvious change was observed. Ethyl acetate and chloroform also failed to drive a regular evolution of the toroidal micelles, while under a vapor of hexane, a less good solvent than cyclohexane for PS, porous discotic nanostructures were produced. It appeared that the use of a proper selective solvent is essential to modulate the motion of polymer chains by dissolution and coalescence and thus favor the subsequent transition into complex nanostructures. Notably, such a transition was found in a rich array of PS-b-P2VP BCPs, including PS 530 -b-P2VP 770 , PS 300 -bP2VP1010, PS360-b-P2VP720, PS920-b-P2VP1330, and PS500-bP2VP710 (Figure 3b and Figure S12). The transition from spherical to toroidal micelles was also observed on other substrates, such as micas and carbon-coated copper grids (Figure 3c and Figure S13), indicating that the evolution was independent of the polarity of substrates. Nevertheless, the presence of a substrate was essential for the formation of complex nanostructures. In solution, spherical micelles of PS700-b-P2VP960 (formed in toluene) failed to transform into toroidal micelles with the addition of ethanol

Figure S8). Again, the polymer chains adopted a more compact stacking as the total volume shrank (Figure S4). It seemed that with the simultaneous dissolution of the core and the coalescence of the corona, the micelles splits on the surface, analogous to a fraction process in geometry. Indeed, with subsequent annealing in ethanol vapor, the inner and external rings of the concentric toroids further split and formed circular clusters of fused small rings (Figure 1f). Interestingly, the height of the micelles recovered to ∼7.5 nm, while the overall diameter retained to be ∼115 nm, indicating a swollen structure (Figure 1j). Such ring clusters vanished and incompact spots formed in a continuous annealing process under cyclohexane vapor (Figure S9), probably as a consequence that the relatively diffuse micellar structures presented upon cyclohexane vapor annealing were not able to resolve the splitting of finer nanostructures. Features of the Micellar Morphology Evolution on a Surface. The spherical micelles of PS700-b-P2VP960 were found to stay on the substrate upon rinsing with alcoholic solvents (probably due to the hydrogen bonding between the D

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Macromolecules but only formed spherical micelles with an inverse core/corona structure (Figure 1a and Figure S2b). On the contrary, the substrate imposes the chain motion occur in a localized region and limited dimension and thus prevents a free reconstruction of the core and corona. With the dissolution of the core and the coalescence of the corona, the BCP chains “roll” on the surface and the original micelles split into more complex nanostructures. Notably, the chain motion along the vertical direction was substantially independent of gravity as the sphere-to-toroid transition was retained when the silicon wafer was vertically or inversely placed in ethanol vapor (Figure 3d and Figure S14). Generality of the Solution−Surface Sequential SelfAssembly Approach. In the following attempt, we studied the solution−surface sequential self-assembly of PS-b-PMMA (for PMMA, Tg = 105 °C)45,46 diblock copolymers with a distinct polar block. Typically, solution self-assembly of PS980b-PMMA630 was conducted in acetone, which is a near-θ solvent for the PS block but a good solvent for the PMMA block,18 thus yielding spherical micelles with a PS core and a PMMA corona (Figure 4b). Similarly, upon immobilization on a piece of silica wafer and annealing in cyclohexane vapor, which is a slightly good solvent for PS but poor for PMMA, these micelles transformed into toroidal micelles with a decreased height (Figure 4a,c,d). We also switched the nonpolar block by the synthesis of PBb-P2VP diblock copolymers with a lower Tg (−12 °C) PB block.21 Typically, PB220-b-P2VP750 self-assembled into spherical micelles with a P2VP core and a PB corona in toluene (Figure 4f). After immobilization on a piece of silica wafer, these micelles again transformed into toroidal micelles upon annealing in ethanol vapor (Figure 4e,g). However, the height of the toroidal micelles was apparently lower (∼1.5 nm, Figure 4h), indicating a more collapsed structure, probably as a consequence of the very flexible PB block. Generally, high-Tg polymer blocks form rigid cores and coronas, and this is probably critical for a well-resolved micellar morphology evolution process on a surface. (It should be noted that the final micellar morphology should be predominantly determined by the dissolution of the original core and the coalescence of the original corona, but the high-Tg nature of the polymer blocks would be essential as well, as it endows the micelles with sufficient rigidity upon drying.) We further verified the triblock copolymer system by employing PS580-b-PB660-b-P2VP920 as an example, which also self-assembled into spherical micelles with a P2VP core and a hybrid PS/PB corona in toluene. In an analogous manner, the depressed globes that immobilized on a piece of silicon wafer (Figure 5a,e) transformed to toroids upon annealing in ethanol vapor (Figure 5b,f) and subsequently to concentric toroids in cyclohexane vapor (Figure 5c,g), further to irregular ring clusters in ethanol vapor (Figure 5d,h), and finally to amorphous structures in cyclohexane vapor (Figure S15). Interestingly, the intermediates that were observed during the transition from the depressed globes to the toroidal micelles exhibited more complex structural features (Figure 5i and Figure S16), where perforated disks with protrusions surrounding the hollow emerged in the initial stage (1−10 min) and flat patch rings formed afterward (2−10 h). Apparently, the presence of an additional PB block sophisticates the pace of the chain motion and develops the patches, presumably due to its distinct solvation preference and drastically lower Tg.

Figure 4. (a) Schematic diagrams illustrating the transition of spherical micelles of PS980-b-PMMA630 into toroidal micelles upon annealing in cyclohexane vapor and (b−d) corresponding AFM height images and height profiles. (e) Schematic diagrams illustrating the transition of spherical micelles of PB220-b-P2VP750 into toroidal micelles upon annealing in ethanol vapor and (f−h) corresponding AFM height images and height profiles. The scale bars correspond to 50 nm in the inset AFM images.

We found that PS-b-P2VP diblock copolymers with smaller PS/P2VP block ratios, namely PS80-b-P2VP1130 and PS100-bP2VP3350, formed wormlike and toroidal micelles and vesicles in toluene. These low-curvature micelles should provide additional platforms to trigger unique evolutions into other complex nanostructures. However, preliminary attempts showed that these micelles transformed into amorphous morphologies with highly congregated tiny spherical micelles in ethanol vapor (Figure S17). Thus, the concerted evolution was critically disfavored by the short PS blocks, probably because the newly formed thick P2VP coronas impeded them from coalescing into a larger continuous core (only spherical micelles can form). It seems that for a well-defined morphological evolution the polar and nonpolar blocks should possess comparable chain lengths.

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SUMMARY In summary, we have demonstrated a distinctive method to construct well-defined complex nanostructures through solution−surface sequential self-assembly of amphiphilic BCPs. With the motion of polymer chains restricted in a confined E

DOI: 10.1021/acs.macromol.9b00197 Macromolecules XXXX, XXX, XXX−XXX

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Figure 5. (a−h) AFM height images and height profiles of (a, e) spherical micelles of PS580-b-PB660-b-P2VP920 on silicon wafers, (b, f) toroidal micelles formed after annealing in ethanol vapor, (c, g) concentric toroidal micelles formed after subsequent annealing in cyclohexane vapor, and (d, h) irregular ring clusters after further annealing in ethanol vapor. The scale bars correspond to 50 nm in the inset AFM images. (i) AFM height images illustrating the transition process of spherical micelles of PS580-b-PB660-b-P2VP920 upon ethanol vapor annealing with increasing period.

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space and dimension by the substrate, spherical micelles transform sequentially into toroidal micelles, concentric toroidal micelles, and ring clusters upon annealing in various solvent vapors. This work provides complementary insights into BCP self-assembly and opens a unique avenue to fabricate functional structures on various surfaces.

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(1) Schacher, F. H.; Rupar, P. A.; Manners, I. Functional block copolymers: nanostructured materials with emerging applications. Angew. Chem., Int. Ed. 2012, 51 (32), 7898−7921. (2) Mai, Y.; Eisenberg, A. Self-assembly of block copolymers. Chem. Soc. Rev. 2012, 41 (18), 5969−5985. (3) Walther, A.; Müller, A. H. Janus particles: synthesis, selfassembly, physical properties, and applications. Chem. Rev. 2013, 113 (7), 5194−5261. (4) Tritschler, U.; Pearce, S.; Gwyther, J.; Whittell, G. R.; Manners, I. 50th Anniversary Perspective: Functional Nanoparticles from the Solution Self-Assembly of Block Copolymers. Macromolecules 2017, 50 (9), 3439−3463. (5) Zhang, L.; Eisenberg, A. Multiple Morphologies of Crew-Cut Aggregates of Polystyrene-b-Poly(Acrylic Acid) Block-Copolymers. Science 1995, 268 (5218), 1728−1731. (6) Won, Y.-Y.; Davis, H. T.; Bates, F. S. Giant wormlike rubber micelles. Science 1999, 283 (5404), 960−963. (7) Geng, Y.; Discher, D. E. Hydrolytic degradation of poly(ethylene oxide)-block-polycaprolactone worm micelles. J. Am. Chem. Soc. 2005, 127 (37), 12780−12781. (8) Zhu, J. T.; Hayward, R. C. Wormlike Micelles with MicrophaseSeparated Cores from Blends of Amphiphilic AB and Hydrophobic BC Diblock Copolymers. Macromolecules 2008, 41 (21), 7794−7797. (9) Zhou, Z.; Li, Z.; Ren, Y.; Hillmyer, M. A.; Lodge, T. P. Micellar shape change and internal segregation induced by chemical modification of a tryptych block copolymer surfactant. J. Am. Chem. Soc. 2003, 125 (34), 10182−10183. (10) Lodge, T. P.; Hillmyer, M. A.; Zhou, Z.; Talmon, Y. Access to the superstrong segregation regime with nonionic ABC copolymers. Macromolecules 2004, 37 (18), 6680−6682. (11) Edmonds, W. F.; Li, Z.; Hillmyer, M. A.; Lodge, T. P. Disk micelles from nonionic coil-coil diblock copolymers. Macromolecules 2006, 39 (13), 4526−4530. (12) Walther, A.; André, X.; Drechsler, M.; Abetz, V.; Müller, A. H. E. Janus discs. J. Am. Chem. Soc. 2007, 129 (19), 6187−6198. (13) Deng, R.; Liang, F.; Zhou, P.; Zhang, C.; Qu, X.; Wang, Q.; Li, J.; Zhu, J.; Yang, Z. Janus Nanodisc of Diblock Copolymers. Adv. Mater. 2014, 26 (26), 4469−4472.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.9b00197. Experimental details and additional results (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Huibin Qiu: 0000-0002-4699-6558 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS H.Q. thanks the National Natural Science Foundation of China (21674062, U1632117) and the Science and Technology Commission of Shanghai Municipality (16ZR1422600, 17JC1400700, 18JC1415500) for financial support. The authors thank Ren Zhu (Oxford Instrument Technology (Shanghai) Co. Ltd.) for Cypher VRS video-rate AFM, the Analytical Instrumentation Center (AIC) at School of Physical Science and Technology (SPST) in ShanghaiTech University for Fastscan/Icon AFM (Bruker Co.), and the Centre for High-resolution Electron Microscopy in ShanghaiTech for TEM. F

DOI: 10.1021/acs.macromol.9b00197 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules (14) Pochan, D. J.; Chen, Z.; Cui, H.; Hales, K.; Qi, K.; Wooley, K. L. Toroidal triblock copolymer assemblies. Science 2004, 306 (5693), 94−97. (15) Huang, H.; Chung, B.; Jung, J.; Park, H.-W.; Chang, T. Toroidal micelles of uniform size from diblock copolymers. Angew. Chem., Int. Ed. 2009, 48 (25), 4594−4597. (16) Discher, D. E.; Eisenberg, A. Polymer vesicles. Science 2002, 297 (5583), 967−973. (17) Du, J.; O’Reilly, R. K. Advances and challenges in smart and functional polymer vesicles. Soft Matter 2009, 5 (19), 3544−3561. (18) Gröschel, A. H.; Schacher, F. H.; Schmalz, H.; Borisov, O. V.; Zhulina, E. B.; Walther, A.; Müller, A. H. E. Precise hierarchical selfassembly of multicompartment micelles. Nat. Commun. 2012, 3, 710− 719. (19) Gröschel, A. H.; Walther, A.; Löbling, T. I.; Schacher, F. H.; Schmalz, H.; Müller, A. H. E. Guided hierarchical co-assembly of soft patchy nanoparticles. Nature 2013, 503 (7475), 247−251. (20) Löbling, T. I.; Borisov, O.; Haataja, J. S.; Ikkala, O.; Gröschel, A. H.; Müller, A. H. Rational design of ABC triblock terpolymer solution nanostructures with controlled patch morphology. Nat. Commun. 2016, 7, 12097−12106. (21) Jain, S.; Bates, F. S. On the origins of morphological complexity in block copolymer surfactants. Science 2003, 300 (5618), 460−464. (22) Bates, F. S. Polymer-Polymer Phase-Behavior. Science 1991, 251 (4996), 898−905. (23) Kim, S. H.; Misner, M. J.; Xu, T.; Kimura, M.; Russell, T. P. Highly oriented and ordered arrays from block copolymers via solvent evaporation. Adv. Mater. 2004, 16 (3), 226−231. (24) Lee, J. H.; Kim, Y.; Cho, J.-Y.; Yang, S. R.; Kim, J. M.; Yim, S.; Lee, H.; Jung, Y. S. In Situ Nanolithography with Sub-10 nm Resolution Realized by Thermally Assisted Spin-Casting of a SelfAssembling Polymer. Adv. Mater. 2015, 27 (33), 4814−4822. (25) Löbling, T. I.; Hiekkataipale, P.; Hanisch, A.; Bennet, F.; Schmalz, H.; Ikkala, O.; Gröschel, A. H.; Müller, A. H. E. Bulk morphologies of polystyrene-block-polybutadiene-block-poly(tertbutyl methacrylate) triblock terpolymers. Polymer 2015, 72, 479−489. (26) Majewski, P. W.; Yager, K. G. Rapid ordering of block copolymer thin films. J. Phys.: Condens. Matter 2016, 28 (40), 403002−403041. (27) Sinturel, C.; Vayer, M.; Morris, M.; Hillmyer, M. A. Solvent Vapor Annealing of Block Polymer Thin Films. Macromolecules 2013, 46 (14), 5399−5415. (28) Peinemann, K.-V.; Abetz, V.; Simon, P. F. W. Asymmetric superstructure formed in a block copolymer via phase separation. Nat. Mater. 2007, 6 (12), 992−996. (29) Lynd, N. A.; Meuler, A. J.; Hillmyer, M. A. Polydispersity and block copolymer self-assembly. Prog. Polym. Sci. 2008, 33 (9), 875− 893. (30) Stein, G. E.; Mahadevapuram, N.; Mitra, I. Controlling Interfacial Interactions for Directed Self Assembly of Block Copolymers. J. Polym. Sci., Part B: Polym. Phys. 2015, 53 (2), 96−102. (31) Hu, H.; Gopinadhan, M.; Osuji, C. O. Directed self-assembly of block copolymers: a tutorial review of strategies for enabling nanotechnology with soft matter. Soft Matter 2014, 10 (22), 3867− 3889. (32) Li, W.; Müller, M. Directed self-assembly of block copolymers by chemical or topographical guiding patterns: Optimizing molecular architecture, thin-film properties, and kinetics. Prog. Polym. Sci. 2016, 54−55, 47−75. (33) Luo, M.; Epps, T. H. Directed Block Copolymer Thin Film Self-Assembly: Emerging Trends in Nanopattern Fabrication. Macromolecules 2013, 46 (19), 7567−7579. (34) Ji, S.; Wan, L.; Liu, C.-C.; Nealey, P. F. Directed self-assembly of block copolymers on chemical patterns: A platform for nanofabrication. Prog. Polym. Sci. 2016, 54−55, 76−127. (35) Wang, Y.; Li, F. An emerging pore-making strategy: confined swelling-induced pore generation in block copolymer materials. Adv. Mater. 2011, 23 (19), 2134−2148.

(36) O’Driscoll, S. M.; O’Mahony, C. T.; Farrell, R. A.; Fitzgerald, T. G.; Holmes, J. D.; Morris, M. A. Toroid formation in polystyreneblock-poly(4-vinyl pyridine) diblock copolymers: Combined substrate and solvent control. Chem. Phys. Lett. 2009, 476 (1−3), 65−68. (37) Chen, Z.; He, C.; Li, F.; Tong, L.; Liao, X.; Wang, Y. Responsive micellar films of amphiphilic block copolymer micelles: control on micelle opening and closing. Langmuir 2010, 26 (11), 8869−8874. (38) Xue, F.; Li, H.; An, L.; Jiang, S. Constructional details of polystyrene-block-poly(4-vinylpyridine) ordered thin film morphology. J. Colloid Interface Sci. 2013, 399, 62−67. (39) Wang, Y.; Gösele, U.; Steinhart, M. Mesoporous Block Copolymer Nanorods by Swelling-induced Morphology Reconstruction. Nano Lett. 2008, 8 (10), 3548−3553. (40) Naidu, S.; Ahn, H.; Gong, J.; Kim, B.; Ryu, D. Y. Phase Behavior and Ionic Conductivity of Lithium Perchlorate-Doped Polystyrene-b-poly(2-vinylpyridine) Copolymer. Macromolecules 2011, 44 (15), 6085−6093. (41) Wang, Y.; Tong, L.; Steinhart, M. Swelling-Induced Morphology Reconstruction in Block Copolymer Nanorods: Kinetics and Impact of Surface Tension During Solvent Evaporation. ACS Nano 2011, 5 (3), 1928−1938. (42) Ogawa, H.; Takenaka, M.; Miyazaki, T.; Fujiwara, A.; Lee, B.; Shimokita, K.; Nishibori, E.; Takata, M. Direct Observation on SpinCoating Process of PS-b-P2VP Thin Films. Macromolecules 2016, 49 (9), 3471−3477. (43) Kim, S. H.; Char, K.; Yoo, S. I.; Sohn, B.-H. One-Step Hierarchical Assembly of Spheres-in-Lamellae Nanostructures from Solvent-Annealed Thin Films of Binary Diblock Copolymer Micelles. Adv. Funct. Mater. 2017, 27 (17), 1606715−1606723. (44) Cui, L.; Li, B.; Han, Y. Transformation from ordered islands to holes in phase-separating P2VP/PS blend films by adding triton X100. Langmuir 2007, 23 (6), 3349−3354. (45) Sauer, B. B.; Kim, Y. H. Structural heterogeneity in poly(methyl methacrylate) glasses of different tacticity studied by thermally stimulated current thermal sampling techniques. Macromolecules 1997, 30 (11), 3323−3328. (46) Westlund, R.; Malmström, E.; Lopes, C.; Ö hgren, J.; Rodgers, T.; Saito, Y.; Kawata, S.; Glimsdal, E.; Lindgren, M. Efficient nonlinear absorbing platinum(II) acetylide chromophores in solid PMMA matrices. Adv. Funct. Mater. 2008, 18 (13), 1939−1948.

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DOI: 10.1021/acs.macromol.9b00197 Macromolecules XXXX, XXX, XXX−XXX