Well-Ordered Inorganic Nanoparticle Arrays Directed by Block

May 24, 2019 - (41,42) To the best of our knowledge, the formation of a flat BCP sheet ... Plot shows the dependence of interfacial tension (γ) for t...
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Well-Ordered Inorganic Nanoparticle Arrays Directed by Block Copolymer Nanosheets Nan Yan,† Xuejie Liu,† Jintao Zhu,*,‡ Yutian Zhu,*,†,§ and Wei Jiang†

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State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, China ‡ Key Laboratory of Materials Chemistry for Energy Conversion and Storage, Ministry of Education (HUST), School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), Wuhan, Hubei 430074, China § College of Materials, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou, Zhejiang 311121, China S Supporting Information *

ABSTRACT: Precise control over the spatial arrangement of inorganic nanoparticles on a large scale is desirable for the design of functional nanomaterials, sensing, and optical/electronic devices. Although great progress has been recently made in controlling the organization of nanoparticles, there still remains a grand challenge to arrange nanoparticles into highly-ordered arrays over multiple length scales. Here, we report the directed arrangement of inorganic nanoparticles into arrayed structures with long-range order, up to tens of microns, by using hexagonally-packed cylindrical patterns of block copolymer nanosheets self-assembled within collapsed emulsion droplets as scaffolds. This technique can be used to generate nanoparticle arrays with various nanoparticle arrangements, including hexagonal honeycomb structures, periodic nanoring structures, and their combinations. This finding provides an effective route to fabricate diverse nanoparticle arrayed structures for the design of functional materials and devices. KEYWORDS: inorganic nanoparticle array, block copolymers, self-assembly, flat emulsion droplet, soft confinement

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small molecules, and functional polymers) can be used to induce the precise organization of NPs into nanostructured arrays.17−19 Among others, block copolymers (BCPs), consisting of two or more chemically distinct polymer segments linked by covalent bonds, are attractive as scaffolds to assist the assembly of NPs because they can spontaneously assemble into diverse well-defined nanostructures.20−30 When NPs are incorporated into BCPs, both the enthalpic and entropic interactions are involved in the NP assembly process, enabling greater control over the assembly nanostructures and the spatial arrangement of the NPs.31−34 For example, Xu and co-workers demonstrated that precise control over the spatial organization of NPs over multiple length scales could be achieved by tailoring the interactions between BCP and NPs.31 Nevertheless, in spite of great advances made in recent years, it remains challenging to arrange NPs into highly-ordered arrays over multiple length scales. Here, we report the controlled arrangement of AuNPs into large-scale (up to tens of microns) arrays with various wellordered structures, including ring-like, hexagonal honeycomb, and their combinations. Two-dimensional structures as-

recise organization of inorganic nanoparticles (NPs) into addressable arrays is the prerequisite for the fabrication of various functional materials and devices.1−12 Lithographic technology has been progressively developed toward the fabrication of NP arrays with higher density and smaller feature size. This technique is, however, costly and time-consuming for fabricating structures with feature sizes below ∼80 nm.13 Nevertheless, there are strong incentives to generate well-defined NP arrays with nanoscale resolution because at this length scale quantum effects dominate the optical, electronic, or magnetic properties of materials and devices.14−16 For instance, two-dimensional (2D) arrays of closely spaced metallic NPs could drastically enhance the Raman signal in the detection of trace amounts of multiphase analytes.14 Superlattice monolayer of noncloselypacked polystyrene (PS)-tethered gold NPs (AuNPs) could act as a nanofloating-gate in memory devices with a higher memory ratio (over 105) than traditional devices based on amorphous AuNP monolayer even after the devices are operated over 10 years.15 Therefore, there is an urgent demand for a facile and effective strategy for the generation of highly-ordered NP arrays. Templated assembly of NPs into ordered arrays has been developed to fabricate large-scale NP arrays with controllable collective properties. Various templates or scaffolds (e.g., DNA, © 2019 American Chemical Society

Received: February 1, 2019 Accepted: May 24, 2019 Published: May 24, 2019 6638

DOI: 10.1021/acsnano.9b00940 ACS Nano 2019, 13, 6638−6646

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Figure 1. Neat PS27k-b-P4VP17k BCP scaffolds generated by the FEDCA strategy. (a−c) TEM images of PS27k-b-P4VP17k scaffolds under different magnification, in which P4VP domains are selectively stained with iodine vapor. The inset in (c) is the associated FFT of hexagonally-packed phase-separated nanostructures of PS27k-b-P4VP17k. (d) SEM image of the PS27k-b-P4VP17k sheets from the side view. (e) AFM phase image of the scaffold. (f) AFM height profile of the scaffold structure, giving the height variation along the red line on a sheet with a diameter of 1.6 μm (inset image).

transform (FFT) of the phase-separated nanostructure (inset in Figure 1c) demonstrates a regular character of the nanostructure of the BCP scaffold. The P4VP cylinders (37.8 ± 1.5 nm) possess a very narrow size distribution (Figure S1d), owing to the inherent nature of the phase-separation of BCPs. The P4VP cylinders appear as hexagonally-packed dimples on the surface of the BCP sheet, as shown in the magnified SEM image (Figure S1c). The side-view SEM images of the PS27k-b-P4VP17k sheets clearly show that the sheet-like particles possess uniform thickness (Figures 1d and S1b). The thickness of the nanosheets varies slightly with the particle size, as indicated by the atomic force microscopy (AFM) topology phase image (Figure 1e and inset in Figure 1f).35 The thickness of a typical BCP sheet is estimated to be ∼123 nm (Figure 1f). Furthermore, the fluorescence microscopy image (Figure S2a) of the BCP scaffold loaded with Nile Red clearly shows that the sheet-like BCP particles can be massively produced via this facile method. The diameters of the PS27k-b-P4VP17k sheets from low-magnification TEM images are measured to be in the range of ∼1−40 μm (Figure S2b,c). The confined assembly of BCPs within the oil-in-water emulsion droplets has been widely applied to fabricate nanostructured polymer particles, owing to its convenience and controllability.36−40 Generally, the formed polymer particles are spherical in shape because of interfacial tension between the oil/water.41,42 To the best of our knowledge, the formation of a flat BCP sheet over multiple length scales has rarely been reported in the emulsion-confined assembly of BCPs. To reveal the formation mechanism of the nanostructured BCP sheet, we used optical microscopy (OM) to

sembled from PS-block-poly(4-vinylpyridine) (PS 27k -bP4VP17k, the subscripts refer to the number-average molecular weights of PS and P4VP blocks) in emulsion droplets are used as scaffolds to direct the organization of NPs. Unlike BCP scaffolds generated by other approaches, the 2D scaffolds with hexagonally-packed P4VP cylindrical nanodomains in the PS matrix are fabricated by the “flat-emulsion-droplet confined assembly” (FEDCA) strategy, which can direct AuNPs into ordered arrays on BCP scaffolds. The FEDCA method provides an isolated and 2D soft space for BCPs, which can gradually assemble into ordered BCP scaffolds inside the flat emulsion droplet. This FEDCA strategy allows us to precisely localize NPs arrays over tens of microns in a facile manner, providing an efficient route to design and fabricate various functional devices with ordered NP arrays.

RESULTS AND DISCUSSION Typically, PS27k-b-P4VP17k is first dissolved in chloroform at a concentration of 0.5 wt %. Subsequently, 0.1 mL of the resulting solution is emulsified in a 1.0 mL aqueous surfactant solution of cetyltrimethylammonium bromide (CTAB, 12 mg/ mL) via stirring (450 rpm, 4 min). After the slow evaporation of organic solvent, the glassy PS27k-b-P4VP17k particles are collected by repeated centrifugation and redispersed in deionized water. As shown in Figure 1, well-defined BCP sheets with long-range ordered nanostructures are formed. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images (Figures 1a−d and S1a− c) show that cylindrical P4VP nanodomains are hexagonally organized in the PS matrix over multiple length scales, thus forming the sheet-like BCP scaffold. Associated fast Fourier 6639

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Figure 2. OM images (top) showing the morphological evolution of the emulsion droplet from the rugged emulsion droplet to the flat droplet as chloroform evaporates. Initial time (i.e., 0 s) is regarded as the moment of capturing the droplet by OM after rapidly adding the freshly prepared emulsion into aqueous solution containing a high dose of CTAB surfactant (12 mg/mL). The surface of the emulsion droplet quickly becomes smooth within 30 s. The contour of the emulsion droplet remains roughly unchanged while the height of the droplet is decreased with the sustained volatilization of the organic phase, indicating the spontaneous vertical collapse of the emulsion droplet. The scale bar in the first image applies to the others. The bottom image is the illustration for the formation of sheet-like BCP particles via deformation of the emulsions.

monitor the morphological evolution of the emulsion droplets containing BCPs. Figure 2 (top images) shows a series of OM images of the morphological evolution of the emulsion droplets at the initial stage of solvent evaporation. On the basis of the in situ observation of the evaporation process, the formation mechanism of the BCP sheets was proposed and illustrated in Figure 2 (bottom image). At the beginning, the freshly prepared chloroform emulsion droplet presents a rugged surface after rapidly adding the emulsion droplet into the CTAB/water solution. Notably, the surface of the emulsion droplet becomes smooth within 30 s, and then, its contour remains roughly unchanged during the evaporation process. The height of the droplet is decreased with the continuous volatilization of the organic phase, whereas the contour of the droplet remains roughly unchanged, leading to the formation of glassy PS-b-P4VP sheets after complete evaporation of chloroform (Figures S3 and S4). A complete phase separation of PS and P4VP domains occurs after the collapse of droplets, since the deformation process is so fast and there is still sufficient chloroform inside the droplets. Therefore, we assume that, in the evaporation process of chloroform, the BCPs/ chloroform emulsion droplets are collapsed along the vertical direction to form a flat droplet in the presence of high-content surfactants which reduce the interfacial tension of the emulsion droplets to an extremely low value. We quantitatively measured the interfacial tension (γ) of the emulsion droplets as a function of CTAB concentration (CCTAB) (Figure 3). Some representative self-assemblies at different CCTAB values are presented in Figures 3 and S5. Clearly, there is a significant decrease in γ after the addition of CTAB into water because of the adsorption of CTAB molecules to the oil/water interface. For example, γ decreases rapidly from 11.3 to 3.2 mN/m with the increase of CCTAB from 0.1 to 12 mg/mL for the BCP/ chloroform droplets containing 0.5 wt % PS27k-b-P4VP17k. At

Figure 3. Plot shows the dependence of interfacial tension (γ) for the chloroform/water interface (■) and chloroform (containing 0.5 wt % PS27k-b-P4VP17k)/water interface (●) as a function of CCTAB. The interfacial tension is measured by the pendant drop method. Scale bar for the TEM images is 200 nm. Error bars represent the standard deviation.

CCTAB = 0.1 mg/mL (γ = 11.3 mN/m), spherical BCP particles with a large number of P4VP cylinders and dots surrounded by PS continuous phase are obtained. As CCTAB is increased to 2 mg/mL (γ = 7.2 mN/m), irregular complex particles with uneven surface are observed. At CCTAB = 12 mg/mL (γ = 3.2 mN/m), uniform BCP sheets with well-defined nanostructures are generated. In recent reports, the nonspherical structures (e.g., oblates) are also obtained from the self-assembly of BCPs within the emulsion droplets.35,43 Kim et al. proposed that the BCP molecular chain rearrangement induced the deformation of the emulsion droplets during solvent evaporation,43 which was mainly due to the neutralization of the interfacial tension between the A/surrounding media and B/surrounding media 6640

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Figure 4. (a) Dark field STEM image of the large-scale arrayed Au nanorings on the PS27k-b-P4VP17k scaffold. (b) Magnified TEM image (top) and corresponding STEM (bottom) image. (c) EDX elemental mapping of Au on the PS27k-b-P4VP17k scaffold, where red nanorings indicated the incorporation of Au NPs. (d) SEM image of the gold rings on the PS27k-b-P4VP17k scaffold. (e) The size distribution of inner (DI) and outer diameters (DO) of the gold nanorings on the PS27k-b-P4VP17k scaffold (shown in image a). (f) Schematic illustration showing the formation mechanism of the array of the AuNP nanorings on the PS-b-P4VP scaffold.

18.9 vol % (Figure S6b) or 21.5 vol % (Figure S6c), the deformation of the emulsions occurs and lens-shaped ellipsoids with a thick center and thin margin are obtained. As φP4VP increases to 30.6 vol % (Figure S6d) or 38.6 vol % (Figure S6e), typical sheet-like particles with uniform thickness are fabricated. Multilayered spherical particles with PS located at the outmost layer are obtained when the symmetric BCP (PS9.8k-b-P4VP10k, 50.5 vol % P4VP) is used (Figure S6f). The results above suggest that only PS-b-P4VP BCPs with a specific block ratio (namely, “cylinder-forming” BCPs) can induce the spontaneous deformation of emulsion droplets and hence generate the oblate or sheet-like BCP particles.35,43 Interestingly, the generated BCP sheets with long-range hexagonally-packed cylindrical nanostructure can direct the assembly of inorganic NPs. Usually, in situ deposition of NPs on a prefabricated BCP scaffold is a facile strategy to organize NPs.44,45 In general, electrostatic interaction exists between Au precursors and P4VP monomers, making Au precursors selectively adsorb on P4VP chains.44 Specifically, the

for the A-b-B diblock copolymer. We measured the interfacial tensions of PS/CTAB (γ PS/CTAB ) and P4VP/CTAB (γP4VP/CTAB) (Table S1) at different concentrations of CTAB (i.e., 0.1, 2.0, and 12 mg/mL). Clearly, γPS/CTAB is larger than γP4VP/CTAB when the CTAB concentration is below 2 mg/mL. As the CTAB content increases to 12 mg/mL, γPS/CTAB and γP4VP/CTAB drop rapidly to close values (2.9 ± 0.2 and 2.8 ± 0.2 mN/m, respectively), thus triggering the deformation of the emulsion droplets and generating the sheet-like particles. We further investigated the effect of block ratio of the BCPs on the shape and internal structures of the obtained particles. PS-b-P4VP BCPs with different volume fractions of P4VP (φP4VP) are used to perform the confined self-assembly through the same procedure as described above (Figure S6). At φP4VP = 7.2 vol %, typical spherical particles are formed, indicating that the emulsions always remain in a spherical shape during the solvent evaporation (Figure S6a). In this case, the PS block dominates the shape and morphology of the assemblies since φP4VP is too low. When φP4VP is increased to 6641

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Figure 5. TEM images of the AuNP arrangement prepared by incubating the BCP scaffolds in the Au precursor solution (5 mM) for different times: (a) 1 h (corresponding STEM image is inserted in the lower right position); (b) 3 h; (c) 7 h; (d) 24 h.

Figure 6. (a) TEM image of the AuNPs arranged in a long-range hexagonal honeycomb structure within the PS27k-b-P4VP17k scaffold by confined coassembly of the ∼1.7 nm PS-tethered AuNPs (∼8.2 vol %) and PS27k-b-P4VP17k in the emulsion droplets. (b,c) The magnified TEM and corresponding STEM image of the AuNP arrays. (d) TEM image of the hybrid nanosheet where P4VP domains are selectively stained with iodine vapor to further illustrate the location of the AuNPs. (e) Illustration showing that the AuNPs are preferentially located at the center of the triangle formed by three adjacent P4VP cylinders. (f) TEM image and inset cartoon showing that the AuNPs are arranged in a combined structure of hexagonal honeycomb and ring-like structures on the BCP scaffold.

prefabricated long-range ordered PS27k-b-P4VP17k sheets are redispersed in the tetrachloroaurate trihydrate (HAuCl4·3H2O, 5 mM) aqueous solution and then incubated for 24 h. After removal of the unabsorbed Au precursors by centrifugation, PS27k-b-P4VP17k sheets adsorbed with Au precursors are irradiated by an electron to reduce Au precursors into

AuNPs under electron microscopy investigation. Scanning transmission electron microscopy (STEM) and TEM images (Figures 4a,b, and S7) show that the reduced AuNPs are arranged into nanorings with periodic arrangement on the BCP scaffold. The formation of Au ring arrays is further confirmed by an energy-dispersive X-ray (EDX) elemental mapping 6642

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distribution (Figure 6a), which resembles the carbon atom skeleton structure of graphene. The hexagonal honeycomb arrangement of AuNPs within PS27k-b-P4VP17k sheets is further confirmed by the magnified TEM image (Figure 6b) and corresponding STEM image (Figure 6c). To further elucidate the spatial localization of the AuNP arrays, the P4VP domains of the polymeric scaffold are stained dark by iodine (Figure 6d). As expected, the AuNPs are located in the light-colored PS domain because of the enthalpic interaction between the PS ligands on AuNPs and PS blocks. More interestingly, all the AuNPs are precisely located at the centers of the triangles formed by the three adjacent P4VP cylinders rather than having random distribution in the PS domain (Figure 6e). This can be attributed to the minimization of the entropic penalty arising from the deformation of PS chains by selectively locating AuNPs at the triangle center from three adjacent PS/P4VP interfaces.50−52 Moreover, we also investigate the edges of the hybrid sheet-like particles to explore the distribution of AuNPs along the height direction of the hybrid particles (Figure S10). Notably, most of the AuNPs are enriched in the domain near the surface of the polymer sheet rather than having uniform distribution along its height direction. We conclude that this uneven distribution of AuNPs in the height direction is attributed to the entropic and enthalpic effects. Enrichment of AuNPs close to the BCP surface can effectively reduce the conformational entropy loss of the PS blocks. On the other hand, the affinity between the PS-coated AuNPs and the CTAB surfactant in the aqueous phase may also attract PScoated AuNPs to surface microdomains. Moreover, the hexagonal honeycomb array with a single AuNP as the skeleton can be generated when the Au3.5S (3.5 is the diameter of the core of the AuNPs) is loaded (Figure S11). The reason can be ascribed to the limited space at the triangle center, which can only accommodate a single Au3.5S rather than their clusters. When the BCP sheet containing a hexagonal honeycomb array of Au1.7S NPs is used as the scaffold for in situ deposition of AuNPs, more complex arrays of AuNPs can be produced (Figure 6f). In the resulting structure with a combination of two types of arrays, the PS-coated AuNPs are arranged as a long-range hexagonal honeycomb structure, while the reduced AuNPs can form a ring exactly in the center of the hexagon (Figures 6f and S12).

image (Figure 4c), where the Au-ring contours appear red. The magnified SEM image indicates that Au NPs are deposited along the ring-shaped interface of the PS and P4VP phases (Figure 4d). The inner (DI) and outer (DO) diameters of the nanorings are 27.0 ± 0.5 and 42.1 ± 0.5 nm, respectively, demonstrating an extremely narrow size distribution of the Au nanorings (Figure 4e). Usually, solvent evaporation, nanodroplet template, colloidal lithography, and magnetic dipolar interaction methods have been employed to generate inorganic nanorings.46−49 However, there still remains a big challenge to fabricate high-quality NP rings with uniform sub-100 nm size. Our facile strategy enabled the in situ arrangement of NPs on the BCP scaffold to generate periodic arrays of uniform Au nanorings at a very long-range scale. The TEM image of the sample stained with iodine vapor shows that Au nanorings are precisely located at the PS/P4VP interface (Figure S8). We propose that the formation mechanism of Au nanoring arrays on the PS27k-b-P4VP17k scaffold involves three main steps (Figure 4f): (1) the adsorption of anion [AuCl4]− onto the protonated P4VP chains on the surface of BCP sheets through electronic interaction after the incubation of the sheets in the Au precursor solution (Notably, the protonated P4VP blocks bonded with [AuCl4]− form a dense brush on the P4VP domain, preventing further adsorption of [AuCl4]− onto the deeper unprotonated P4VP blocks.); (2) the collapse of originally protonated P4VP blocks that are saturated with a large number of [AuCl4]− toward the PS/P4VP interfaces to form ring-like domains of P4VP/[AuCl4]− complexes on the surface of the BCP sheets; (3) the reduction of bonded Au precursors to produce AuNP nanorings upon the irradiation of electron beams. The aforementioned results suggest that protonation of the surface layer of the P4VP domain is crucial to the formation of ring structure. We, therefore, investigated the effect of the protonation time (i.e., incubation time of the BCP scaffolds in the Au precursor solution) on the arrangement of AuNPs on the PS27k-b-P4VP17k scaffold (Figure 5). When the incubation time is short (1 h), the surface of P4VP nanodomains is randomly covered by AuNPs to produce hexagonal arrays (Figure 5a). This is ascribed to the insufficient protonation of P4VP chains located on the surface of the scaffolds. With the increase of protonation time, the circle edge is darker than the interior area, indicating that the vast majority of the AuNPs are enriched at the interface of PS and P4VP domains (Figures 5b,c). Further increase of protonation time to 24 h triggers the precise localization of AuNPs at the PS/P4VP interface to form the ordered array of Au nanorings (Figure 5d). Furthermore, coassembly of BCPs and NPs is another effective strategy to direct the arrangement of NPs. Specifically, the PS coated AuNPs (Au1.7S, 1.7 is the diameter of the core of AuNPs, S represents PS-SH ligand) are mixed with PS27k-bP4VP17k in chloroform and then emulsified with CTAB aqueous solution (CCTAB: 12 mg/mL). During chloroform evaporation, BCPs spontaneously assemble into ordered BCP sheets and simultaneously assist the spatial organization of AuNPs. Figures 6 and S9 show that the AuNPs are successfully incorporated into the polymeric scaffolds to form sheet-like BCP/AuNPs hybrid particles, while the overall shape of the scaffold remains unchanged at a volume fraction of ∼8.2 vol % for Au1.7S (see Table S2 for the detailed calculation). More interestingly, it is observed that the introduced AuNPs arrange into a highly-ordered hexagonal honeycomb structure (∼32.7 nm on a side) within the BCP sheet instead of having random

CONCLUSIONS In summary, we have developed a facile yet effective approach to localize the AuNPs into highly-ordered arrays by using phase-separated BCP sheets as scaffolds. The key of this approach is the formation of large-scale sheet-like BCP scaffolds via asymmetric collapse of an emulsion droplet containing BCPs at an extremely low interfacial tension. We demonstrated the use of this technique for the fabrication of polymer sheets with well-ordered NP arrays at a large scale (up to tens of microns), including the hexagonal honeycomb array, patterned nanoring array, and their combinations. This approach provides an effective route to design hybrid NP arrays with applications in advanced optical/electronic devices. METHODS Materials. PS27k-b-P4VP17k (the subscripts are Mn of each block, Mw/Mn = 1.15) and thiol terminated polystyrene (PS2k-SH, Mw/Mn = 1.15, thiol functionality >95%) were purchased from Polymer Source, Inc. Cetyltrimethylammonium bromide (CTAB; purity: 98%) and 6643

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Characterization. TEM and scanning transmission electron microscopy (STEM) measurements were performed on an FEI Tecnai G2 S-Twin instrument with the operation voltage of 200 kV. A drop of the aqueous sample dispersion was deposited on the carboncoated copper grids, followed by being blown dry with a blowpipe. To distinguish the PS and P4VP domains, the P4VP phase was stained with iodine vapor for 2 h. Atomic force microscopy (AFM) images were recorded using a Bruker instrument with tapping mode. Scanning electron microscope (SEM) measurements were performed on a Hitachi S-4800 operating at 10 kV. The evaporation of the emulsion droplets was observed in bright-field or epifluorescence mode by an optical microscope (Olympus, IX 71) to monitor the evolution of shrinking emulsion droplets. Typically, 50 μL of freshly prepared emulsion droplets was quickly transformed into a special homemade cell which had a flat bottom containing the CTAB aqueous solution (1 mL, 12 mg/mL). The interfacial tension of the emulsion droplets was measured on a JC2000C1 (Dataphysics Instruments Shanghai Zhongchen Digital Technic Apparatus Co., Ltd.) at room temperature.

tetraoctylammonium bromide (TOAB; purity: 98%) were obtained from Aladdin. Nile Red (NR) was purchased from Aldrich. Hydrogen tetrachloroaurate trihydrate (HAuCl4·3H2O; purity: 99.99%) was supplied by Alfa Aesar. Trisodium citrate and sodium borohydride (NaBH4) were purchased from Sinopharm Chemical Reagent. Other chemicals were supplied by Beijing Chemical Factory. All of the materials were used directly without further purification. The glassware used for synthesizing AuNPs was cleaned by aqua regia and rinsed with deionized water prior to the experiments. BCP Sheet Preparation. The PS-b-P4VP was first dissolved in chloroform to fabricate a 0.5 wt % stock solution and stirred overnight. Then, the polymer solution (0.1 mL) was emulsified with aqueous solution containing 1.2 wt % CTAB by magnetic stirring for 4 min at 450 rpm. The organic solvent was allowed to evaporate at room temperature for 48 h without stirring. The sample was washed with DI water by repeated centrifugations (10 000 rpm, 30 min) to remove the residual surfactant, followed by redispersion in DI water for further characterization. Synthesis of Size-Controlled AuNPs. PS2k-SH-coated AuNPs (AuxS, S represents PS ligands, and x is the diameter of the AuNPs core) were applied in the current study. For Au1.7S, the traditional Brust two-phase method was used.53 Typically, the prepared HAuCl4· 3H2O (0.3 mL, 30 mM) aqueous solution and TOAB (0.8 mL, 50 mM) in toluene solution were mixed together and stirred vigorously until all the HAuCl4 was transferred into the organic phase. Thiol terminated PS2k-SH (18 mg, 9 μmol) was then added to the toluene phase, followed by dropwise addition of the fresh ice-cold NaBH4 aqueous solution with continuous stirring. The reaction was continued for 3 h before ethanol was added into the organic phase to precipitate the AuNPs. The AuNPs were separated by centrifugation (10 000 rpm, 30 min), washed with ethanol (5−6 times), and then redispersed in chloroform with a final concentration of 10 mg/mL. Au3.5S was synthesized by the two-step ligand exchange approach.54 The citrate-stabilized Au3.5NPs were first synthesized and used as the starting material. To synthesize the citrate-stabilized NPs, a 20 mL aqueous solution containing HAuCl4·3H2O (0.25 mM) and trisodium citrate (0.25 mM) was prepared and stirred gently. Subsequently, prepared ice-cold NaBH4 (0.6 mL, 0.1 M) was injected into the solution. Then, the solution was kept stirring for 3 min, and the obtained NPs were used as starting materials within 2−5 h. The Au3.5S was further synthesized by the ligand exchange process.55 Typically, the prepared aqueous solution of citrate-stabilized Au3.5NPs (200 mL) was added into the THF solution (200 mL) containing PS2k-SH (mole ratio Au/SH = 1:0.3). The mixture was then sonicated for 3 h. After incubating for 24 h, the Au3.5S NPs were collected by centrifugation (10 000 rpm, 30 min) and redissolved in chloroform PS2k-SH (mole ratio Au/SH = 1:0.15) for the secondary grafting process. The AuNPs with high PS grafting density were then washed with ethanol (5−6 times) and redispersed in chloroform with a final concentration of 10 mg/mL. Directed Assembly of AuNPs by BCP Sheet Scaffold. The hexagonal honeycomb AuNP array was prepared by the coassembly of Au1.7S and PS-b-P4VP confined within emulsion droplets. First, 30 μL of Au1.7S/chloroform solution (10 mg/mL) was added into a vial and dried in nitrogen flow. Then, 0.25 mL of the PS27k-b-P4VP17k/ chloroform solution (0.5 wt %) was added into the vial. After stirring for 12 h, 0.1 mL of the PS27k-b-P4VP17k/Au1.7S solution was emulsified in 1.0 mL of deionized water containing 1.2 wt % CTAB by magnetic stirring for 4 min at 450 rpm. The following experimental process was the same as that of the preparation of the BCP sheet. For the synthesis of the AuNP ring-structured array, 0.05 wt % PSb-P4VP sheet particles were redispersed into 5 mM HAuCl4·3H2O aqueous solution (1 mL) to allow a preferential absorption of Au precursor with protonated P4VP chains for 24 h. After centrifugation (10 000 rpm, 30 min) for 3−5 times, the particles were redispersed in deionized water (1 mL) for transmission electron microscopy (TEM) characterization. Then, the Au nanorings were in situ formed at the surface of the BCP scaffold by the electron irradiation under TEM investigation.

ASSOCIATED CONTENT S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.9b00940. Figures S1−S12: SEM images, TEM images and fluorescence microscopy images of PS27k-b-P4VP17k sheets, size statistics of the P4VP domain, the deformation process of the emulsion droplet, effect of interfacial tension and block ratio on the self-assembled structures, and the AuNP arrangement; Tables S1 and S2: the interfacial tension values of PS and P4VP homopolymers at various CTAB concentrations and characterization of the ligand-coated AuNP (PDF)

AUTHOR INFORMATION Corresponding Authors

*E-mail: [email protected] (J.Z.). *E-mail: [email protected] (Y.Z.). ORCID

Jintao Zhu: 0000-0002-8230-3923 Yutian Zhu: 0000-0002-7092-0086 Wei Jiang: 0000-0003-4316-880X Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China for Major Program (51433009), Youth Science Funds (51703224), General Program (21774126), Jilin Provincial science and technology development program (20190103119JH), Open Research Fund of State Key Lab of Polymer Physics & Chemistry, CIAC, CAS (2017-27), Program for HUST Academic Frontier Youth Team (2015-01), and the start-up fund from Hangzhou Normal University. REFERENCES (1) Dong, A.; Chen, J.; Vora, P. M.; Kikkawa, J. M.; Murray, C. B. Binary Nanocrystal Superlattice Membranes Self-Assembled at the Liquid−Air Interface. Nature 2010, 466, 474−477. (2) Liu, K.; Nie, Z.; Zhao, N.; Li, W.; Rubinstein, M.; Kumacheva, E. Step-Growth Polymerization of Inorganic Nanoparticles. Science 2010, 329, 197−200. 6644

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Its Application for Release in Chronological Order. Angew. Chem., Int. Ed. 2018, 57, 3578−3582. (22) Ku, K. H.; Shin, J. M.; Kim, M. P.; Lee, C.-H.; Seo, M.-K.; Yi, G.-R.; Jang, S. G.; Kim, B. J. Size-Controlled Nanoparticle-Guided Assembly of Block Copolymers for Convex Lens-Shaped Particles. J. Am. Chem. Soc. 2014, 136, 9982−9989. (23) He, Y.; Zhang, Y.; Yan, N.; Zhu, Y.; Jiang, W.; Shi, D. SelfAssembly of Block Copolymers into Sieve-Like Particles with Arrayed Switchable Channels and as Scaffolds to Guide the Arrangement of Gold Nanoparticles. Nanoscale 2017, 9, 15056−15061. (24) Lu, X.; Song, D.-P.; Ribbe, A.; Watkins, J. J. Chiral Arrangements of Au Nanoparticles with Prescribed Handedness Templated by Helical Pores in Block Copolymer Films. Macromolecules 2017, 50, 5293−5300. (25) Lee, J.; Ku, K. H.; Kim, M.; Shin, J. M.; Han, J.; Park, C. H.; Yi, G.-R.; Jang, S. G.; Kim, B. J. Stimuli-Responsive, Shape-Transforming Nanostructured Particles. Adv. Mater. 2017, 29, 1700608. (26) Jung, H.; Leibfarth, F. A.; Woo, S.; Lee, S.; Kang, M.; Moon, B.; Hawker, C. J.; Bang, J. Efficient Surface Neutralization and Enhanced Substrate Adhesion through Ketene Mediated Crosslinking and Functionalization. Adv. Funct. Mater. 2013, 23, 1597−1602. (27) Bang, J.; Bae, J.; Lowenhielm, P.; Spiessberger, C.; Given-Beck, S. A.; Russell, T. P.; Hawker, C. J. Facile Routes to Patterned Surface Neutralization Layers for Block Copolymer Lithography. Adv. Mater. 2007, 19, 4552−4557. (28) Bang, J.; Jeong, U.; Ryu, D. Y.; Russell, T. P.; Hawker, C. J. Block Copolymer Nanolithography: Translation of Molecular Level Control to Nanoscale Patterns. Adv. Mater. 2009, 21, 4769−4792. (29) Jung, H.; Hwang, D.; Kim, E.; Kim, B.-J.; Lee, W. B.; Poelma, J. E.; Kim, J.; Hawker, C. J.; Huh, J.; Ryu, D. Y.; Bang, J. ThreeDimensional Multilayered Nanostructures with Controlled Orientation of Microdomains from Cross-Linkable Block Copolymers. ACS Nano 2011, 5, 6164−6173. (30) Bang, J.; Kim, S. H.; Drockenmuller, E.; Misner, M. J.; Russell, T. P.; Hawker, C. J. Defect-Free Nanoporous Thin Films from ABC Triblock Copolymers. J. Am. Chem. Soc. 2006, 128, 7622−7629. (31) Zhao, Y.; Thorkelsson, K.; Mastroianni, A. J.; Schilling, T.; Luther, J. M.; Rancatore, B. J.; Matsunaga, K.; Jinnai, H.; Wu, Y.; Poulsen, D.; Frechet, J. M. J.; Alivisatos, A. P.; Xu, T. Small-MoleculeDirected Nanoparticle Assembly Towards Stimuli-Responsive Nanocomposites. Nat. Mater. 2009, 8, 979−985. (32) Yan, N.; Liu, H.; Zhu, Y.; Jiang, W.; Dong, Z. Entropy-Driven Hierarchical Nanostructures from Cooperative Self-Assembly of Gold Nanoparticles/Block Copolymers under Three-Dimensional Confinement. Macromolecules 2015, 48, 5980−5987. (33) Yan, N.; Zhang, Y.; He, Y.; Zhu, Y.; Jiang, W. Controllable Location of Inorganic Nanoparticles on Block Copolymer SelfAssembled Scaffolds by Tailoring the Entropy and Enthalpy Contributions. Macromolecules 2017, 50, 6771−6778. (34) Kao, J.; Bai, P.; Chuang, V. P.; Jiang, Z.; Ercius, P.; Xu, T. Nanoparticle Assemblies in Thin Films of Supramolecular Nanocomposites. Nano Lett. 2012, 12, 2610−2618. (35) Ku, K. H.; Lee, Y. J.; Kim, Y.; Kim, B. J. Shape-Anisotropic Diblock Copolymer Particles from Evaporative Emulsions: Experiment and Theory. Macromolecules 2019, 52, 1150−1157. (36) Xu, J.; Wu, Y.; Wang, K.; Shen, L.; Xie, X.; Zhu, J. The Generation of Polymeric Nano-Bowls through 3D Confined Assembly and Disassembly. Soft Matter 2016, 12, 3683−3687. (37) Ku, K. H.; Kim, Y.; Yi, G.-R.; Jung, Y. S.; Kim, B. J. Soft Patchy Particles of Block Copolymers from Interface-Engineered Emulsions. ACS Nano 2015, 9, 11333−11341. (38) 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, 4469−4472. (39) Yang, H.; Ku, K. H.; Shin, J. M.; Lee, J.; Park, C. H.; Cho, H.H.; Jang, S. G.; Kim, B. J. Engineering the Shape of Block Copolymer Particles by Surface-Modulated Graphene Quantum Dots. Chem. Mater. 2016, 28, 830−837.

(3) Song, K.; Huang, P.; Yi, C.; Ning, B.; Hu, S.; Nie, L.; Chen, X.; Nie, Z. Photoacoustic and Colorimetric Visualization of Latent Fingerprints. ACS Nano 2015, 9, 12344−12348. (4) Liu, Y.; He, J.; Yang, K.; Yi, C.; Liu, Y.; Nie, L.; Khashab, N. M.; Chen, X.; Nie, Z. Folding Up of Gold Nanoparticle Strings into Plasmonic Vesicles for Enhanced Photoacoustic Imaging. Angew. Chem., Int. Ed. 2015, 54, 15809−15812. (5) Kim, S.; Yoo, M.; Kang, N.; Moon, B.; Kim, B. J.; Choi, S.-H.; Kim, J. U.; Bang, J. Nanoporous Bicontinuous Structures via Addition of Thermally-Stable Amphiphilic Nanoparticles within Block Copolymer Templates. ACS Appl. Mater. Interfaces 2013, 5, 5659−5666. (6) Yoo, M.; Kim, S.; Lim, J.; Kramer, E. J.; Hawker, C. J.; Kim, B. J.; Bang, J. Facile Synthesis of Thermally Stable Core-Shell Gold Nanoparticles via Photo-Cross-Linkable Polymeric Ligands. Macromolecules 2010, 43, 3570−3575. (7) Yoo, M.; Kim, S.; Jang, S. G.; Choi, S.-H.; Yang, H.; Kramer, E. J.; Lee, W. B.; Kim, B. J.; Bang, J. Controlling the Orientation of Block Copolymer Thin Films using Thermally-Stable Gold Nanoparticles with Tuned Surface Chemistry. Macromolecules 2011, 44, 9356−9365. (8) Dai, Q.; Nelson, A. Magnetically-Responsive Self Assembled Composites. Chem. Soc. Rev. 2010, 39, 4057−4066. (9) Dai, Q.; Rettner, C. T.; Davis, B.; Cheng, J.; Nelson, A. Topographically Directed Self-Assembly of Goldnanoparticles. J. Mater. Chem. 2011, 21, 16863−16865. (10) Dai, Q.; Frommer, J.; Berman, D.; Virwani, K.; Davis, B.; Cheng, J. Y.; Nelson, A. High-Throughput Directed Self-Assembly of Core-Shell Ferrimagnetic Nanoparticle Arrays. Langmuir 2013, 29, 7472−7477. (11) Dai, Q.; Chen, Y.; Liu, C.-C.; Rettner, C. T.; Holmdahl, B.; Gleixner, S.; Chung, R.; Pitera, J. W.; Cheng, J.; Nelson, A. Programmable Nanoparticle Ensembles via High-Throughput Directed Self-Assembly. Langmuir 2013, 29, 3567−3574. (12) Dai, Q.; Berman, D.; Virwani, K.; Frommer, J.; Jubert, P.-O.; Lam, M.; Topuria, T.; Imaino, W.; Nelson, A. Self-Assembled Ferrimagnet Polymer-Composites for Magnetic Recording Media. Nano Lett. 2010, 10, 3216−3221. (13) McMillan, R. A.; Paavola, C. D.; Howard, J.; Chan, S. L.; Zaluzec, N. J.; Trent, J. D. Ordered Nanoparticle Arrays Formed on Engineered Chaperonin Protein Templates. Nat. Mater. 2002, 1, 247−252. (14) Cecchini, M. P.; Turek, V. A.; Paget, J.; Kornyshev, A. A.; Edel, J. B. Self-Assembled Nanoparticle Arrays for Multiphase Trace Analyte Detection. Nat. Mater. 2013, 12, 165−171. (15) Wang, K.; Ling, H.; Bao, Y.; Yang, M.; Yang, Y.; Hussain, M.; Wang, H.; Zhang, L.; Xie, L.; Yi, M.; Huang, W.; Xie, X.; Zhu, J. A Centimeter-Scale Inorganic Nanoparticle Superlattice Monolayer with Non-Close-Packing and its High Performance in Memory Devices. Adv. Mater. 2018, 30, 1800595. (16) Halpern, A. R.; Corn, R. M. Lithographically Patterned Electrodeposition of Gold, Silver, and Nickel Nanoring Arrays with Widely Tunable Near-Infrared Plasmonic Resonances. ACS Nano 2013, 7, 1755−1762. (17) Kim, P. Y.; Oh, J.-W.; Nam, J.-M. Controlled Co-Assembly of Nanoparticles and Polymer into Ultralong and Continuous OneDimensional Nanochains. J. Am. Chem. Soc. 2015, 137, 8030−8033. (18) Benn, F.; Haley, N. E. C.; Lucas, A. E.; Silvester, E.; Helmi, S.; Schreiber, R.; Bath, J.; Turberfield, A. J. Chiral DNA Origami Nanotubes with Well-Defined and Addressable Inside and Outside Surfaces. Angew. Chem., Int. Ed. 2018, 57, 7687−7690. (19) Li, W.; Liu, S.; Deng, R.; Zhu, J. Encapsulation of Nanoparticles in Block Copolymer Micellar Aggregates by Directed Supramolecular Assembly. Angew. Chem., Int. Ed. 2011, 50, 5865−5868. (20) Xu, J.; Li, J.; Yang, Y.; Wang, K.; Xu, N.; Li, J.; Liang, R.; Shen, L.; Xie, X.; Tao, J.; Zhu, J. Block Copolymer Capsules with StructureDependent Release Behavior. Angew. Chem., Int. Ed. 2016, 55, 14633−14637. (21) Wu, M.; Zhu, Y.; Jiang, W. Disassembly of Multicompartment Polymer Micelles in Spatial Sequence Using an Electrostatic Field and 6645

DOI: 10.1021/acsnano.9b00940 ACS Nano 2019, 13, 6638−6646

Article

ACS Nano (40) Shin, J. M.; Lee, Y. J.; Kim, M.; Ku, K. H.; Lee, J.; Kim, Y.; Yun, H.; Liao, K.; Hawker, C. J.; Kim, B. J. Development of Shape-Tuned, Monodisperse Block Copolymer Particles through Solvent-Mediated Particle Restructuring. Chem. Mater. 2019, 31, 1066−1074. (41) Xu, J.; Wang, K.; Li, J.; Zhou, H.; Xie, X.; Zhu, J. ABC Triblock Copolymer Particles with Tunable Shape and Internal Structure through 3D Confined Assembly. Macromolecules 2015, 48, 2628− 2636. (42) 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. Striped, Ellipsoidal Particles by Controlled Assembly of Diblock Copolymers. J. Am. Chem. Soc. 2013, 135, 6649−6657. (43) Ku, K. H.; Shin, J. M.; Yun, H.; Yi, G.-R.; Jang, S. G.; Kim, B. J. Multidimensional Design of Anisotropic Polymer Particles from Solvent-Evaporative Emulsion. Adv. Funct. Mater. 2018, 28, 1802961. (44) Cha, S. K.; Mun, J. H.; Chang, T.; Kim, S. Y.; Kim, J. Y.; Jin, H. M.; Lee, J. Y.; Shin, J.; Kim, K. H.; Kim, S. O. Au-Ag Core-Shell Nanoparticle Array by Block Copolymer Lithography for Synergistic Broadband Plasmonic Properties. ACS Nano 2015, 9, 5536−5543. (45) Shin, D. O.; Mun, J. H.; Hwang, G.-T.; Yoon, J. M.; Kim, J. Y.; Yun, J. M.; Yang, Y.-B.; Oh, Y.; Lee, J. Y.; Shin, J.; Lee, K. J.; Park, S.; Kim, J. U.; Kim, S. O. Multicomponent Nanopatterns by Directed Block Copolymer Self-Assembly. ACS Nano 2013, 7, 8899−8907. (46) Tripp, S. L.; Pusztay, S. V.; Ribbe, A. E.; Wei, A. Self-Assembly of Cobalt Nanoparticle Rings. J. Am. Chem. Soc. 2002, 124, 7914− 7915. (47) Bao, Y.; Witten, T. A.; Scherer, N. F. Self-Organizing Arrays of Size Scalable Nanoparticle Rings. ACS Nano 2016, 10, 8947−8955. (48) Lin, G.; Zhu, X.; Anand, U.; Liu, Q.; Lu, J.; Aabdin, Z.; Su, H.; Mirsaidov, U. Nanodroplet-Mediated Assembly of Platinum Nanoparticle Rings in Solution. Nano Lett. 2016, 16, 1092−1096. (49) Yan, J.; Chaudhary, K.; Bae, S. C.; Lewis, J. A.; Granick, S. Colloidal Ribbons and Rings from Janus Magnetic Rods. Nat. Commun. 2013, 4, 1516. (50) Thompson, R. B.; Ginzburg, V. V.; Matsen, M. W.; Balazs, A. C. Predicting the Mesophases of Copolymer-Nanoparticle Composites. Science 2001, 292, 2469−2472. (51) Liu, Y.; Li, Y.; He, J.; Duelge, K. J.; Lu, Z.; Nie, Z. EntropyDriven Pattern Formation of Hybrid Vesicular Assemblies Made from Molecular and Nanoparticle Amphiphiles. J. Am. Chem. Soc. 2014, 136, 2602−2610. (52) Huang, J.; Xiao, Y.; Xu, T. Achieving 3-D Nanoparticle Assembly in Nanocomposite Thin Films via Kinetic Control. Macromolecules 2017, 50, 2183−2188. (53) Brust, M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. Synthesis of Thiol-Derivatised Gold Nanoparticles in a Two-Phase Liquid-Liquid System. J. Chem. Soc., Chem. Commun. 1994, 0, 801− 802. (54) Li, W.; Liu, S.; Deng, R.; Zhu, J. Encapsulation of Nanoparticles in Block Copolymer Micellar Aggregates by Directed Supramolecular Assembly. Angew. Chem., Int. Ed. 2011, 50, 5865−5868. (55) Nie, Z.; Fava, D.; Kumacheva, E.; Zou, S.; Walker, G. C.; Rubinstein, M. Self-Assembly of Metal-Polymer Analogues of Amphiphilic Triblock Copolymers. Nat. Mater. 2007, 6, 609−614.

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DOI: 10.1021/acsnano.9b00940 ACS Nano 2019, 13, 6638−6646