Directed Self-Assembly of Block Copolymer Micelles onto

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Directed Self-Assembly of Block Copolymer Micelles onto Topographically Patterned Surface Dong-Eun Lee, Nam Jin Je, Seong Il Yoo, and DONG HYUN LEE Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b03419 • Publication Date (Web): 05 Nov 2015 Downloaded from http://pubs.acs.org on November 10, 2015

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Directed Self-Assembly of Block Copolymer Micelles onto Topographically Patterned Surface

Dong-Eun Lee1, Nam Jin Je2, Seong Il Yoo2* and Dong Hyun Lee1*

1

Department of Polymer Science and Engineering, Dankook University, 152 Jukjeon-ro, Suji-gu, Yongin-si, Gyeonggi-do, 448-701, Republic of Korea

2

Department of Polymer Engineering, Pukyong National University, 365 Sinseon-ro, Nam-gu, Busan 608-739, Korea.

Corresponding Authors: *To whom correspondence should be addressed. E-mail: [email protected]; Telephone: +82-31-8005-3589; Fax: +82-31-8021-7218. E-mail: [email protected]; Telephone: +82-51-629-6456; Fax: +81-51-629-6429.

Keywords: Block Copolymers, Spherical Micelles, Solvent-Annealing, Self-Assembly, and Nanoparticles.

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ABSTACT: We report a facile method to control directed self-assembly (DSA) of spherical micelles of block copolymers (BCPs) by topographically patterned surface. A cylinder-forming polystyrene-block-poly(2-vinylpyrdine) copolymer (Mn,PS = 175 kg/mol, Mn,P2VP = 70 kg/mol, and PDI = 1.08) was phase-separated on a thin film of poly(vinyl alcohol) (PVA) by solvent-annealing. By additional treatment with ethanol as a preferential solvent for P2VP block, the surface of BCP thin film was reconstructed to produce nanopores. The nanoporous structures in BCP thin films were transferred to the underlying hydrophilic PVA film by reactive ion etching (RIE). Then, spherical BCP micelles were quickly self-assembled within the nanopores in the PVA layer due to topographical contrast and surface energy difference during spin-coating. Consequently, the site-selective array of BCP micelles was utilized as templates to achieve heterogeneous organization of nanoparticles and organic fluorescent dyes over large area. In addition, it was observed that those heterogeneous assemblies showed remarkable decrease in fluorescence intensity of organic dyes.


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1. Introduction High density arrays of nanometer-scale objects including nanoparticles (or nanorods), quantum dots, and carbon nanotubes etc. have been attracting considerable attention for the past decades due to their potential applications in various areas such as templates, photonics, sensors, and plasmonics.1-7 There are basically two different types of approaches to generate ordered nanostructures in large area. Top-down techniques such as photolithography, which has mainly applied to semiconductor manufacturing, can easily access to ordered nanostructures in large area even though there exist some drawbacks that these techniques not only essentially need chemically modified photoresists and exquisitely fabricated masks, but also should undergo multiple steps of complex processes.8-10 In addition, these are not still free from intrinsic optical resolution limit. In contrast, it is known that bottom-up techniques including self-assembly of colloidal particles, block copolymers and self-assembled monolayers etc. can provide facile methods to fabricate nanostructures with evasion of restrict processing that were mentioned earlier.11-14 Among the materials applied to bottom-up approaches, it is concerned that block copolymers (BCPs), which are consisted of two or more chemically distinct polymers linked by covalent bond, can be particularly one of the most feasible choices because of their various self-assembled nanostructures arisen from immiscibility between two blocks.15 They also can offer laterally ordered nanopatterns as integrated with conventional photolithography.16,17 Recently, it is aware that the self-assembly of block copolymers having functional groups can be applied to generate the array of functional nanomaterials, whose abilities would be strongly dependent on their lateral ordering.18-20 However, in fact, dimension and inter-spacing of self-assembled BCP


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nanostructures certainly would be faithfully fixed and unchangeable despite the necessity to control them since their chain length (or molecular weights) and composition (or volume fraction) that are principal parameters to change their nanostructures are determined once they are chemically synthesized.21 Therefore, taking nanostructures to desired placements in well-defined order is still remained unfulfilled in patterning approaches based on conventional BCP self-assembly. In the present study, we demonstrate a versatile and reproducible method to control directed self-assembly (DSA) of nanostructures assisted by patterned surface as a template. A BCP thin film was spin-coated on a hydrophilic poly(vinyl alcohol) (PVA) film and solvent-annealed in organic vapor to induce BCP phase separation. The resulting morphology, cylinders oriented parallel to the surface, was directly used as a mask for reactive ion etching (RIE) in order to transfer nanostructures to the PVA film. As a different type of BCP micelles was introduced on the underlying PVA line patterns, the directed self-assembly (DSA) of spherical BCP micelles within the periodic length scale of PVA line patterns was spontaneously achieved in large area because they were registered due to topographical contrast and surface energy difference into empty regions formed by two different PVA line patterns. The spatial arrangement of BCP micelles by topographically patterned surface in this study clearly exhibits flexibility for many applications that need effectively to control geometry of nanostructures, but may not be achieved by existing BCP patterning process. Consequently, these BCP micelles array was used as a template either to synthesize different types of nanoparticles or to load organic dyes into the cores of BCP micelles. With the aid of combined BCP assemblies, heterogeneous organization of Au nanoparticles (NPs) and fluorescence dyes was further


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demonstrated, which also provided a modality in studying NP-dye interaction in the assembled structures.

2. Experimental Section 2.1. Materials Polystyrene-block-poly(2-vinyl pyridine) (S2VP245, Mn,PS = 175,000 g/mol, Mn,P2VP = 70,000 g/mol, PDI = 1.08) and polystyrene-block-poly(4-vinyl pyridine) (S4VP69, Mn,PS = 51,000 g/mol, Mn,P4VP = 18,000 g/mol, PDI = 1.15) were purchased from Polymer Source and used as received. Poly(vinyl alcohol) (Mw = 13,000 ~ 23,000 g/mol, SigmaAldrich) was also used as a sacrificial template to guide block copolymer (BCP) micelles. Hydrolysis degree of the PVA was about 98 %. Chloroform and toluene were purchased from Sigma-Aldrich and used without any further purification. Si wafers (p-type, Si) were purchased from LG Siltron Inc. The pieces were 1.5 cm long and 1.5 cm wide. Quartz substrates were provided from JNC QUARTZ. CO. 2.2. Fabrication of Nanostructures on Polymer Thin Films The whole process to fabricate nanostructures on polymer thin films in this study was showed in Scheme 1. Aqueous PVA solution (2 wt%) was spin-coated at 2000 ~ 5000 rpm on substrates. To remove residual water, PVA thin films were placed on a heating plate at 180 oC for 5 min. Then, S2VP245 was spin-coated directly on the PVA films from its toluene solution (1 wt%) at 2000 rpm. To generate cylindrical nanostructures of poly(2-vinylpyridine) (P2VP) of S2VP245 oriented parallel to the surface, BCP thin films were put on the stage of a chamber containing 0.2 mL of chloroform for various annealing time. It is noted that the solvent-annealing chamber was covered with an


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aluminum foil having a pinhole in its center, which can allow chloroform to be evaporated and released slowly through the hole. The surface of S2VP245 thin films on a PVA film was reconstructed by immersion into pure ethanol, a selective solvent to P2VP, for 30 min. Then ethanol was removed by air blowing so that line patterns having about 10 nm in depth and 82 nm in width were produced. By using oxygen plasma treatment, line patterns were transferred to underlying PVA films. 2.3. Directed Self-Assembly of Block Copolymer Micelles The spherical micelles of S4VP69 were spin-coated on PVA line patterns at various rates. Owing to topographical contrast and surface energy of PVA line patterns, the spherical micelles could self-assemble into the only empty spaces between two adjacent PVA lines. Gold chloride tetrahydrate (HAuCl4) was introduced into S4VP69/toluene solutions. Then the solutions were vigorously agitated for 1 day. It is noted that HAuCl4 only located in P4VP cores of S4VP69 micelles. Once S4VP69 micelles containing HAuCl4 were spin-coated on line patterns of PVA, they were selectively positioned in nanopores of the PVA layer. To reduce gold nanoparticles from HAuCl4, oxygen plasma treatment was conducted for 30 min. 2.4. Encapsulation of Fluorescent Dyes and Synthesis of Au NPs Rhodamine 123 (R123, Sigma-Aldrich), fluorescent dye, was added to a 1.0 wt% toluene solution of S4VP69 micelles with a molar ratio of [R123]/[4VP] = 0.005 and then the solution was vigorously stirred for at least 7 days for a selective encapsulation of R123 into the P4VP cores. The resulting solution was filtered through PTFE membrane (pore size = 0.45 µm) and then diluted to 0.15 wt% toluene solution. In order to synthesize Au NPs on the PVA lines, PVA patterns on solid substrates were immersed into a 1.0 wt%


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ethanol solution of HAuCl4 for 1 hr, then thoroughly rinsed with ethanol several times. Subsequently, the PVA patterns loaded with HAuCl4 was dipped into 1.0 wt% aqueous solution of NaBH4 for 5 min to reduce HAuCl4 to Au NPs, followed by rinsing with ethanol again. 2.5. Characterization Surface topography including micelle diameter and pattern width of samples used in this study was assessed by operating the tapping mode of atomic force microscopy (AFM, Digital Instruments Inc., Nanoscope III) in both the height and phase contrast. The ndoped Si tips (1-10 Ohm cm) of Vecco were used to scan the surface of thin films in an area of 3 µm x 3 µm at a typical scan rate of 6 µm per second. The images obtained from all specimens were constructed using 512 scan lines. Field-emission scanning electron microscopy (FE-SEM) was performed by JSM-6700F JEOL operating at 15kV. UV-Vis absorbance was collected using a JASCO V-670 spectrophotometer. Steady-state fluorescence was measured using a UniPL-300 system composed of Andor Shamrock SR-303i-A spectrograph and CCD camera (DV420A-OE) coupled with a He-Cd laser as an excitation source.

3. Results and Discussion Figure 1 first presents the ordering evolution of block copolymer (BCP) thin films upon solvent-annealing process. Figure 1(a) displays a flat surface of a PVA thin film prepared on a Si substrate by spin-coating method from its water solution. Surface roughness of the PVA film was about 11.58 nm according to AFM measurement. To fabricate nanostructures on the PVA surface for guiding spherical BCP micelles, a thin film of a


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cylinder-forming block copolymer (S2VP245) was directly spin-coated at 2000 rpm from its 1 wt% solution of toluene and sequentially solvent-annealed in chloroform vapor, which is a good solvent for both blocks, to enhance the mobility of polymer chains and to induce its phase separation for certain time. It should be noted that the underlying PVA film was not damaged by organic solvents used in this study during spin-coating or solvent-annealing process because of its poor solubility in both toluene and chloroform. Since S2VP245 was dissolved in toluene, which was a selective solvent for PS blocks, spherical micelles having P2VP cores and PS shells were formed in the toluene media.20 Therefore, the as-spun film exhibited ill-defined spherical micelles (diameter ~ 38 nm) deposited on flat Si wafers due to fast solvent evaporation as shown in Figure 1(b). Upon solvent-annealing in chloroform vapor, significant morphological changes in the S2VP245 thin film were observed with increasing time. As displayed in Figure 1(c), the perpendicular and parallel orientations of P2VP cylinders coexisted on film surface after 30 min of annealing time. Because of its asymmetry, we can confirm that the darker regions represent P2VP cylinders embedded in the brighter PS matrix. The preferential orientation of P2VP cylinders against the surface could be effectively tuned by changing solvent-annealing conditions like soaking time, film thickness, or types of solvents. In our study, to control the orientation of P2VP cylinders, the BCP thin films were soaked for various times from 30 min to 2 hrs. In Figure 1(d), P2VP cylinders oriented vertically to the surface were mainly generated at 1 hr of annealing time. With further annealing, it was found that the parallel orientation of P2VP cylinders was preferentially produced as displayed in Figure 1(e) and 1(f).

Finally, well-defined cylinders of P2VP blocks

oriented parallel to the substrate were obtained at the late stage (2 hr of annealing time) of


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solvent-annealing process. (Figure 1(f)) According to our AFM measurements, the center-to-center distance and the diameter of P2VP cylinders in S2VP245 on the PVA layer were about 80 nm and about 30 nm, respectively. To reconstruct the surface of BCP thin films, the BCP thin film displayed in Figure 1(f) was immersed into ethanol, which is a selective solvent for P2VP blocks but a poor solvent for PS blocks, for 30 min.22,23 Once the specimen was pulled off, nanoporous line-type patterns of BCP thin films were generated on the PVA film as residual ethanol was removed by air flowing as exhibited in Figure 2(a). To transfer the line structures of BCP thin films to the underlying PVA layer, the reactive ion etching (RIE) process was performed by exposing the specimen to oxygen plasma.24 After the RIE process, welldefined nanostripes of PVA (the height of 30 nm and the width of 40 nm) were obtained over the whole surface area. (Figure 2(b)) The relative etching contrast of a PVA homopolymer to oxygen plasma was determined by measuring the film thickness with etching times and compared to other homopolymers of polystyrene and poly(2-vinyl pyridine) in Figure 2(c). According to our observation, since etching rate (0.43 nm/sec) of the PVA thin film was relatively faster than those (0.31 nm/sec) of PS and PVP thin films from our RIE condition, the porous structures of BCP thin films were successfully transferred to the underlying PVA films. (Figure 2(b)) These PVA nanostripes can provide topographical difference and chemical contrast for DSA of BCP micelles. Scheme 1 depicts our strategy for producing large-area DSA of BCP micelles in this study. BCP micelles were spin-coated on the PVA layer and solvent-annealed in order to generate well-ordered cylinders oriented parallel to the surface. (Scheme (a) and (b)) By immersion of the film into ethanol which is selective solvent for P2VP chains, the P2VP


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chains exist within thin films were protruded to PS-air interface with its bonding was maintained. Consequentially, the surface of BCP thin film was reconstructed to produce nanoporous structures on the surface and nanoporous structures were produced. (Scheme (c)) As the nanoporous BCP thin film was used as a lithographic mask, those nanostructures were transferred to the underlying PVA layer by drying etching process. (Scheme (d)) Then once another set of BCP micelles whose diameter could be fit with the spacing between two PVA nanostripes was spin-coated, they penetrated into the trough and aligned along the axial direction of PVA nanostripes due to capillary force originated from their topographical difference as well as surface energy difference as seen in Scheme (e). It is well-known that the micelles of amphiphilic block copolymers can used as templates to contain other substances like metal precursors, organic dyes, and biomolecules etc. in their cores.25,26 So, large-area assembly of nano-objects could be finally generated in Scheme (f) after loading metal precursors or organic dyes in the cores of BCP micelles. A different type of BCPs micelles (S4VP69) was directly spin-coated on the nanoporous PVA layer from its toluene solutions with various BCP concentrations ranging from 0.1 wt% to 0.5 wt%. It is noted that the diameter of micelles of S4VP69 was about 38 nm and a little smaller than the width of troughs between two PVA nanostripes. Since the spherical micelles of S4VP69 were formed in toluene, which was a selective solvent for PS, their shells were consisted of PS blocks having lower surface energy than it of PVA while their cores were composed of P4VP blocks. Thus, these micelles would avoid immediately the underlying PVA nanostripes during spin-coating process. Figure 3(a) shows a AFM image of the S4VP69 micelles deposited from 0.1 wt% solution in toluene


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on nanoporous PVA layer. This result clearly indicates that the micelles positioned selectively in the trough of PVA nanostripes even though the center-to-center distance between the micelles was about 75 nm. In addition, since the amounts of BCP micelles deposited on the substrates were increased with BCP concentrations, the BCP micelles should be more closely packed by increasing their contents in the solutions. As displayed in Figure 3(b), the BCP micelles were not only aligned along PVA nanostripes but also filled uniformly into the empty space for more closely accessing each other. Furthermore, the separation distance of the BCP micelle assemblies in the trough of PVA nanostripes was around 80 nm, which is exactly same with it of S2VP245 cylinders observed in Figure 1(f) while the center-to-center distance between the micelles was about 59 nm. It was confirmed that the DSA of S4VP69 micelles with the center-to-center distance of about 52 nm from 2.0 wt% solution could be produced in large area (8 µm x 8 µm) by AFM measurement as seen in Figure 3(c). Therefore, the effect of PVA nanostripes on the guidance of nano-objects in large area is clearly identified in our results. In contrast, over 2.0 wt% of BCP concentrations, it was observed that BCP micelles covered the whole surface area and did not show the preferential DSA because of too many micelles on the surface as shown in Figure 3(d) and 3(e). We consider that these phenomena were originated from the combination of two factors that are the capillary force induced from height variation during evaporation of solvents and the surface energy difference between a PVA nanostripe and a PS corona of a BCP micelle.27-31 Moreover, it is noted that the diameter (38 nm) of S4VP69 micelles was matched with the width of the empty channel, so that only one spherical micelle could be sandwiched between the channels (nanoporous region) formed by two PVA nanostripes.


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To prove our idea, the surface reconstruction of the assembly of S4VP69 micelles were conducted by using the method previously depicted. The assembly of S4VP69 micelles gained in Figure 3(b) was again immersed in ethanol to reconstruct their surfaces. As displayed in Figure 4(a), because of the good solubility of P4VP core for ethanol, the cores of S4VP69 micelles were only reconstructed and nanopores were formed on the film surface. As a result, the nanopores of BCP micelles were aligned along the axial direction of PVA nanostripes while their lateral separation distance kept in the periodic length of the original S2VP245 cylinders. In addition, by rinsing the PVA nanostripes with water, which was a good solvent for PVA, they were completely stripped off and the array of micelles was remained as shown in Figure 4(b). Therefore, according to our observation, we can prove the preferential DSA of the BCP micelles guided by nanostripes of PVA. Micelles of amphiphilic BCPs have been served as nano-reactors (or templates) either to synthesize or to load a variety of nanomaterials because of specific affinity of core blocks against electrically charged molecules.19,32 Since nitrogen atoms of pyridine rings attached to P4VP cores of S4VP69 micelles used in this study could supply unpaired electrons, which could interact with the electrically charged molecules, the array of S4VP69 micelles also could be used as templates for generating well-defined array of nanoparticles. In present study, the S4VP69 micelles were first formed in toluene. Then, small amount of HAuCl4, a precursor of gold (Au) nanoparticles, was introduced into the BCP solution with mechanical agitation in order to integrate the precursors into P4VP cores. Once the BCP micelles containing Au precursors were spin-coated on PVA nanostripes, they exhibited selective displacement in the troughs. (Figure 4(c)) To create


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the array of gold (Au) nanoparticles (NPs), the samples were irradiated by oxygen plasma for 30 min. The assembly of naked Au nanoparticles with certain separation distance of around 66 nm was successfully formed on bare Si wafers while organic components were removed during RIE process as displayed in Figure 4(d). Confirming the general procedure of our assembling method, we further anticipated that the presence of chemically different S4VP69 micelles and PVA nanostripes in the same assembled structure of Figure 3 can eventually assist the placement of different functions in specific sites. In this context, heterogeneous assemblies composed of metal nanoparticles (NPs) and fluorescent dyes are of great interests because the fluorescence of dye molecules can be strongly influenced by the presence of metal NPs in the assembled structure.34-40 To produce heterogeneous assemblies of dyes and metal NPs, we first encapsulated fluorescent dyes, rhodamine 123 (R123), into the core of micelles. To this end, R123 was added to the toluene solution of S4VP69 micelles (molar ratio of [dye]/[4VP] = 0.005). Even though R123 having an ionic character is not soluble in toluene, the dye molecules can be still incorporated into hydrophilic PVP cores of micelles after prolonged stirring (at least ~7 day) to prevent unfavorable contacts with toluene.38 As a result, homogenous solutions of micelles with R123 in the core can be prepared, the UV-Vis (dashed) and fluorescence (solid) spectra of which are shown in Figure 5(a). In a parallel procedure, Au NPs were synthesized in the PVA patterns. Here, PVA nanostripes in Figure 2(b) were prepared on quartz substrates, which was then immersed into an ethanol solution of HAuCl4 (1.0 wt%). Since HAuCl4 can be selectively coordinated to the PVA polymer, subsequent reduction with NaBH4 allowed the selective synthesis of Au NPs in the PVA nanostripes. After NaBH4 treatment, we noticed that the


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color of quartz substrate slightly turned into reddish, indicating the synthesis of Au NPs. In addition, as shown in the FE-SEM (field-emission scanning electron microscopy) image of Figure 5(b), bright spots having an average diameter of approximately 12 nm are homogeneously distributed on the PVA patterns. Since the FE-SEM image was collected without Pt coating, the bright spots in the image correspond to the synthesized Au NPs. To combine R123 and Au NPs in the assembled structures, we spin-coated S4VP69 micelles (0.15 wt%) containing R123 in the core onto the NP-synthesized PVA patterns. As confirmed from AFM result in Figure 5(c), R123-encapsulated micelles are selectively positioned in the trench region so as to be aligned along PVA patterns as in the previous cases. Subsequently, we investigated the effect of Au NPs on the R123 fluorescence in their nanoscale organization. Here, the fluorescence spectrum from micelles with R123 on the bare PVA pattern (green solid) is compared with that from the same micelles on the NP-synthesized PVA pattern (gray dotted) in Figure 5(d). From the comparison, it is quite obvious that R123 fluorescence is strongly quenched by the presence of Au NPs. The quenching behavior of R123 on the heterogeneous assemblies can be explained by the plasmonic effect of Au NPs in terms of (a) the extinction property of Au NPs, (b) the spectral properties of dyes, and (c) the distance between NPs and dyes. In principle, the conduction electrons in metal NPs can be resonantly oscillated by light of a specific frequency. Owing to these phenomena, known as localized surface plasmon resonance, metal NPs strongly absorb and scatter light at the resonant frequency, which constitutes the optical extinction of metal NPs. In general, metal NPs having a strong absorption


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property tend to couple with fluorophores in a non-radiative manner to quench the fluorescence, while metal NPs with a superior scattering enhance the fluorescence by radiative-coupling process.34-36 In this context, we calculated the extinction spectrum of Au NPs with constituent absorption and scattering components by using open-source Mieplot v4400 program.41 In the calculation, we specified the diameter of Au NP = 12 nm and the refractive index of the medium (n = 1.50 for PVA polymer). As shown in Figure 5(e), the extinction of Au NPs (black solid) is mostly composed of the absorption (green dotted) with negligible scattering (red dotted) component. In addition, the extinction of Au NPs in Figure 5(e) strongly overlap with the absorption/fluorescence of R123 in Figure 5(a), which is a clear indication of the strong NP-R123 interaction. Therefore, the Au NPs in the PVA patterns have a strong tendency to quench R123 fluorescence. However, in order to induce substantial quenching effect, the mutual NPR123 distance has to be further engineered. In general, fluorescent dyes have to be placed in the proximity to the NP surface within ~ 30 nm for an effective NP-dye interaction.37-40 In our experiment, R123-encapsulated micelles are positioned in the center of trench between adjacent PVA nanostripes. Therefore, by assuming that Au NPs are homogenously synthesized throughout PVA nanostripes, the average NP-dye distance can be taken as the half value of the distance between adjacent PVA nanostripes (40 nm (= 80 nm/2) from Figure 2(b)). Hence, it can be validated that Au NPs in the PVP patterns strongly quenches R123 fluorescence by plasmonic effects in Figure 5.

4. Conclusion


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In summary, large scale assembly of BCP micelles were achieved by utilizing the patterned PVA surfaces fabricated by combining well-ordered BCP templates and the RIE technique. As the nanostructures of phase-separated BCP thin films were served as a mask for RIE, well-defined nanostripes of PVA were generated in large area. Due to capillary force and surface energy difference during evaporation of solvents, BCP micelles were preferentially located in the empty channels between two PVA nanostripes within original periodic length of the initial BCP thin film. The BCP micelles could become a useful template either to synthesize nanoparticles or to load organic dyes into their cores. In addition, heterogeneous assemblies of metal NPs and fluorescent dyes can be further prepared from the BCP patterns, at which R123 fluorescence was quenched by plasmonic Au NPs. Considering that typical fluorescence-based assay utilizes the change of fluorescence intensity or wavelength by a given chemical reaction, the underlying principles in the quenched fluorescence by the combination with BCP pattern could find interesting opportunities in sensing applications. Overall, this study exemplifies how nanoscale functionalities can be organized into a specific arrangement with the aid of combined BCP assemblies.

Acknowledgement D.H.L gratefully acknowledges the National Research Foundation of Korea (NRF) grant funded by the Korean Government (2011-0013084) and Gyeonggi Regional Research Center (GRRC) Program (GRRC DANKOOK 2014-B01). S.I.Y. acknowledges the support by Brain Busan 21 program.


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Figure Captions Figure 1. AFM images (height mode, 3 µm × 3 µm) of (a) bare PVA surface; (b) S2VP as-spun film on PVA layer by spin-coating and morphology transition of S2VP thin films via solvent annealing in THF vapor as a function of time [after (c) 30 min, (d) 1 hr (e) 1hr 30 min, and (f) 2hr, respectively.] Figure 2. AFM images (height mode, 3 µm × 3 µm) of (a) surface reconstructed S2VP thin film on the PVA layer, (b) PVA nanostripes transferred from S2VP patterns by oxygen plasma treatment, and (c) a plot of etching rates of three different homopolymers with various times [polystyrene (red), poly(2-vinyl pyridine) (green), and poly(vinyl alcohol) (blue)]. All homopolymers initially were spin-coated from 2 wt% solution of toluene at 2000 rpm. Figure 3. AFM images (height mode, (a) ~ (e) : 1.5 µm × 1.5 µm , (c) : 8 µm × 8 µm ) of S4VP micelle arrays spontaneously placed in nano-porous region between two PVA nanostripes by spin-coating in large areas: (a) 0.1 wt%; (b) 0.15 wt%; (c) 0.2 wt%; (d) 0.3 wt%; and (e) 0.5 wt%, respectively. Figure 4. AFM images (height mode, 1.5 µm × 1.5 µm) of S4VP micelles guided by PVA due to its chemical and physical contrast. [(a) reconstructed with ethanol , (b) after removing PVA by rinsing with water which is a good solvent for PVA. (c) BCP micelles with HAuCl4 in their core and (d) Au NPs synthesized from BCP features after oxygen plasma treatment, respectively. Figure 5. (a) UV-Vis (dashed) and fluorescence (solid) spectra from a toluene solution of S4VP micelles containing R123 in the cores, (b) FE-SEM image of Au NPs synthesized in the PVA pattern, (c) AFM images of R123-encapsulated S4VP


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micelles placed along with NP-synthesized PVA pattern, (d) Fluorescence spectra from R123-encapsulated S4VP micelles on the bare (green solid) and the NP-synthesized (gray dotted) PVA patterns, (e) Calculated extinction (black solid), absorption (green dotted), and scattering (red dotted) spectra of Au NP synthesized in PVA patterns. Scheme 1. Schematic illustration of fabrication of various micelle arrays guided by PVA templates: (a) a BCP thin film spin-coated on a PVA layer, (b) solventannealing of the BCP thin film in THF vapor, (c) surface reconstruction by ethanol, (d) plasma etching, (e) spin-coating of BCP micelles, (f) removing PVA templates, (g) BCP micelles containing Au precursors, (h) plasma etching for producing Au NPs, respectively.


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Figure 1


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Figure 2


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Figure 3


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Figure 4


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Figure 5


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Scheme 1


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Table of Content (TOC)

Directed Self-Assembly of Block Copolymer Micelles onto Topographically Patterned Surface

Dong-Eun Lee1, Nam Jin Je2, Seong Il Yoo2* and Dong Hyun Lee1*

1

Department of Polymer Science and Engineering, Dankook University, 152 Jukjeon-ro, Suji-gu, Yongin-si, Gyeonggi-do, 448-701, Republic of Korea

2

Department of Polymer Engineering, Pukyong National University, 365 Sinseon-ro, Nam-gu, Busan 608-739, Korea.

Spherical micelles of block copolymers containing organic fluorescent dyes were prepared on PVA nano-stripes, which were composed of Au nanoparticles (NPs) in large area. In the assembled structures, the fluorescence of dyes was strongly quenched by plasmonic effect of Au NPs.

*This should be use only for the table of content (TOC).


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Directed Self-Assembly of Block Copolymer Micelles onto

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