Macroscopic Alignment of Cylinders via Directional Coalescence of

Article pubs.acs.org/Macromolecules

Macroscopic Alignment of Cylinders via Directional Coalescence of Spheres along Annealing Solvent Permeation Directions in Block Copolymer Thick Films Guanghui Cui,† Masamichi Fujikawa,† Shusaku Nagano,‡ Keisuke Shimokita,§ Tsukasa Miyazaki,§ Shinichi Sakurai,∥ and Katsuhiro Yamamoto*,† †

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan ‡ Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan § Nitto Denko Corporation, 1-1-2, Shimohozumi, Ibaraki, Osaka 567-8680, Japan ∥ Department of Biobased Materials Science, Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan S Supporting Information *

ABSTRACT: We reported the long-range perpendicular and horizontal orientation of polystyrene cylinders in polystyrene-bpoly(methyl acrylate) (PS-b-PMA) films with thickness scale from hundreds micrometers to millimeters. Dissolving block copolymer (BCP) in selective solvents forms PS micelles in solution, which could be trapped in films after ordinary solvent casting. Controllable alignment of perpendicular and horizontal cylinders from the directional coalescences of PS spheres along permeation directions of annealing solvent into the film was achieved, i.e., solvent permeating from surface of film led to perpendicular PS cylinders while from edge resulted in horizontal cylinders. Polarizing optical micrographs and μbeam SAXS confirmed the directional coalescences mechanism during the orientation process and that the cylindrical structure was achieved throughout a macroscopic scale. Solvent components influenced the orientation behavior, and the mixed solvents containing 25− 40% (volume fraction) methanol were favorable to form highly oriented cylinders. branes for viruses and proteins for medical applications.33,38 Up to now, vertically oriented cylinders in various BCPs matrixes have been achieved via diverse techniques, for example, external applied fields,29,42−46 chemically modified and/or topographically patterned substrates,31,47−55 microwave assisted,56,57 thermal annealing and solvent annealing,35,39,58−65 solvent evaporation,66 and shear-induced67,68 have been used to orient cylinders in various BCP thin films. However, spontaneously assembling in the vertical orientation is often known to be achieved mostly in a thickness scale up to a few micrometers, and the practical applications for these self-assembled structures required the suitable substrates to support the thin films because of the weak mechanical strength. Thus, a facile method to control the self-assembly over large thickness scales to endow the BCP films with acceptable mechanical strength is still worth exploring.

1. INTRODUCTION Block copolymer (BCP) films with nanoscale periodic selfassembled patterns have attracted considerable attention,1−11 which are widely applied as a methodology to surmounting the size limitation of the lithography technique for nanofabrications in microelectronics and semiconductor industry12−31 and sizeselective separation for biomedical molecules and proteins nanoparticles.2,32−38 The degree of polymerization, volume fractions of blocks, and the Flory−Huggins interaction parameter are usually considered as the parameters to dominate the phase separation behaviors of BCPs films.5,6,39,40 In terms of two blocks BCPs, diverse morphologies, e.g., sphere, cylinder, gyroids, and lamellar, etc., have been achieved in both computational simulation and practical experiments.41 Despite the morphological diversity, controlling the orientation behaviors of these morphologies is of great interest, especially, formation of vertical oriented cylinders in BCPs films makes them templates and scaffolds for nanofabrication such as ordered metal and metal oxides arrays, growth of magnetic metal nanowires,23−25,29,31 and size-selective separation mem© 2014 American Chemical Society

Received: May 18, 2014 Revised: August 9, 2014 Published: August 22, 2014 5989

dx.doi.org/10.1021/ma501033a | Macromolecules 2014, 47, 5989−5999

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procedure, 36.7 mL of styrene, 0.21 mL of BrEB, 0.22 g of CuBr, a little CuBr2, 0.31 mL of PMDETA, and about 12 mL of anisole were added in a round-bottomed flask. After degassing by freeze−pump− thaw cycles for three times, the flask was sealed in vacuum and immersed into oil bath at 90 °C to conduct the polymerization. After a prescribed time, the flask was exposed to air and the solution was diluted with toluene. Active aluminum powders were used to remove the catalysts. After that, the polymer was precipitated in large amount of methanol followed by filtration and dried under vacuum at room temperature. The molecular weight (Mn) of this PS is 8100, and the polydispersity (PDI) is 1.06. Chain extensions were performed in a similar procedure. Then 35 mL of methyl acrylate monomers, 3 g of PS macroinitiator as synthesized above, 0.053 g of CuBr, a little CuBr2, 0.04 mL of PMDETA and about 12 mL of anisole were added into a round-bottomed flask. After three freeze−pump−thaw cycles, the flask was sealed in vacuum and immersed into an oil bath at 100 °C. After a prescribed time and removal of catalysts, the block copolymer of PS-bPMA was precipitated in a large amount of methanol and dried under vacuum at room temperature. The characteristics of synthesized PS-bPMA (SMA1 and SMA2) were summarized in Table 1. Difference in

There are only a few works that explore the fabrication of vertically oriented cylinders in thick (from hundreds of micrometers to 1 mm) BCP films. Osuji presented a solvent vapor permeation (SVP) method69 for facile vertical alignment of self-assembled cylinders in BCP films with a thickness of approximately 1 mm, during which a solvent in the vapor phase was pressure-driven through a film and hence resulted in longrange ordered and vertical alignment PS cylinders (parallel to direction of the vapor permeation) in the poly(styrene-bethylene/butylene-b-styrene) films. In our previous work, vertical coalescence of spheres via thermal annealing was reported to prepare vertically aligned cylinders in thick films.70 In that work, spherical nanostructures in a nonequilibrium state were formed from the normal cast or spin-cast of BCPs in mixed solvent which was good for the major block and poor for the minor block. After that, thermal annealing by heating (especially T-jump) the films under vacuum over glass transition temperatures (Tg) of two blocks enhanced the mobility of polymer chains and induced the vertical coalescence of nonequilibrium spheres to reach the equilibrium morphologies in the films. However, high annealing temperature and long annealing time were required. More recently, we reported that the directional coalescence process of spheres embedded in a blend thin film (up to a few micrometers in thickness) from polystyrene-b-poly(4-hydroxyl styrene) (PS-b-PHS) and PEG could be achieved via solvent annealing within 1 h.71 In addition, dissolving of PEG in water led to the formation of sub-10 nm nanochannels throughout the thin films. However, whether or not solvent annealing could be efficient to orient ordered structures in much thicker films still remains unclear. Herein, we extended the solvent annealing method to control the alignment of PS cylinders in much thicker films from hundreds micrometers to 1 mm, and they could be achieved in a couple of hours at room temperature. Dissolving the PS-bPMA in the mixed solvents of methanol and acetone could make PS chains shrink into micelles in the solution. After casting and evaporation of solvents at room temperature, PS spherical microdomains could be trapped and remain in films. Both highly perpendicularly and horizontally oriented PS cylinders were prepared simply by changing solvent annealing directions, i.e., solvent permeating into the thick films from the surface can lead to perpendicular cylinders while permeating from the edge can result in horizontal cylinders. The orientation of cylinders along the permeation direction of annealing solvent was first proposed and demonstrated here by POM and μ-beam SAXS. Besides, the effect of component of selective solvents on the orientation was investigated. This strategy, for the first time, provides a novel and simple methodology to fabricate highly oriented cylinders in both perpendicular and horizontal manners in BCP films in macroscopic scale, which would obviously endow the resultant films with anisotropy and robust mechanical property.

Table 1. Characteristics of PS-b-PMA Synthesized by ATRP precursor PS

SMA1 SMA2 a b

PS-b-PMA

Mna

Mwa

PDIa

Mnb

PDIa

PS volume fraction (%)b

8.1k 7.8k

8.6k 8.4k

1.06 1.07

37.2k 38.2k

1.51 1.56

22.0 20.0

Determined by SEC columns calibrated with polystyrene standards. Determined by 1H NMR and mass density of components.

refractive index between PS (1.598) and PMA (1.479) is relatively large among polymers simply synthesized by a block copolymerization. A large difference in refractive index is advantageous for polarized optical microscopic (POM) observation. 2.3. Preparation of Thick Films. Polymer solutions were prepared by dissolving the BCPs in mixed solvents of methanol and acetone with various volume fractions of methanol which are summarized in Table 1. According to the solubility parameter δ, acetone (δ = 10 (cal/cm3)1/2) is a good solvent for PMA (δ = 10.7 (cal/cm3)1/2) and poor for PS (δ = 8.6 (cal/cm3)1/2),36 while methanol (δ = 14.5 (cal/cm3)1/2) is a poor solvent for PMA and nonsolvent for PS.73 It is a slightly difficult to dissolve BCPs in the mixture and to obtain clear solution. Thus, to enhance solubility, dichloromethane (DCM, δ = 9.7 (cal/cm3)1/2), which is a common good solvent for both PS and PMA, was used as the cosolvent in the volume fraction ratio of 1:1. Dichloromethane can volatilize rapidly at room temperature from the mixed solution. After complete evaporation of dichloromethane, most methanol and acetone still remain in solution. First, the copolymer was dissolved in DCM under magnetic stirring, and after totally being dissolved, mixed solvents of methanol and acetone were added into the DCM solution. The mixture solution was stirred overnight prior to film preparation in order to make sure the total dissolution. Unless otherwise stated, the polymer concentration in the mixed solutions was about 5 wt %. To prepare thick films, polymer solutions (19 g) were poured into a polytetrafluoroethylene (PTFE) Petri dish. After slow and complete evaporation of solvents (it took a week at room temperature), casted films with the thickness of about a few hundred micrometers to 1 mm were obtained. The film samples were completely dried in a vacuum desiccator at room temperature for a week. Subsequently, the thick films were cut into small pieces and subjected to thermal and solvent annealing. The thermal annealing was conducted at 250 °C for 48 h under vacuum. The solvent annealing of the films on a glass plate was done as the films were put in a box filled with saturated THF vapor for 15 min to 2 h. Ordinarily, solvent molecules mainly penetrate from a sample surface and propagate into the film inside in case of a film sample that has a generally large top-surface area compared with an edge surface.

2. EXPERIMENTAL SECTION 2.1. Materials. Bis(2-dimethylaminoethyl)methylamine (PMDETA) and (1-bromoethyl)benzene (BrEB) were purchased from SigmaAldrich Co., Ltd. Styrene, methyl acrylate, CuBr, CuBr2, anisole, acetone, methanol, acetone, dichloromethane (DCM), tetrahydrofuran (THF), and toluene were purchased from Nacalai Tesque. Styrene and methyl acrylate monomers were purified by mixing it with aluminum oxide granules to remove inhibitors before polymerization. Other reagents were used as received (analytically pure). 2.2. Synthesis of PS-b-PMA Block Copolymer. Synthesis of PSb-PMA by ATRP was reported elsewhere.72 Herein, as a typical 5990


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Figure 1. Two-dimensional SAXS patterns from the edge view for the (a−d) as-cast films and (e−h) the corresponding thermal annealed films obtained from SMA1 solutions with (a) and (e) 0 vol %, (b) and (f) 25 vol %, (c) and (g) 33 vol %, and (d) and (h) 50 vol % methanol in the mixed solvents. Azimuthal angle (φ) is defined in (g) in order to obtain sector-averaged 1D profiles.

Figure 2. One-dimensional SAXS profiles for (a) the as-cast and (b) thermally annealed films obtained from SMA1 solutions with 0, 25, 33, and 50 vol % methanol in the mixed solvents. The profiles were converted from corresponding 2D SAXS patterns shown in Figure 1 by circular averaging. The dotted lines were obtained by calculation using paracrystalline distortion theory. from the neighbor. When two scan positions are 20 μm away from each other, it is safely said that the overlap in structural information obtained by scattering data from step to step can be negligible because the overlapping area of the X-ray between the scans is less than one percent in our experiment. For the transmission electron microscope (TEM) observation, the samples were previously embedded in epoxy resin (Quetol-812, Nissin EM). After curing, the sample is microtomed using an Ultracut N microtome, Reichert−Nissei. Diamond knives (ultra 35°, DIATOME) were used for both the trimming and cutting process at RT. From the ultramicrotoming process, ca. 200 nm thick slices were obtained and placed over carbon coated copper grids (grid 75/300 mesh Cu, Veco). The thin sections were picked up onto copper grids and stained in RuO4 vapor for ca. 10 min. TEM (H-800, HITACHI Co.) was performed with electron beam energy of 100 keV. To confirm optical anisotropy on a macroscopic length scale, polarized optical microscopic (POM: Olympus BX51) observation was performed under cross-polarizing conditions at room temperature.

2.4. Characterization. The microphase separated structures were observed using small-angle X-ray scattering (SAXS) that were conducted at BL6A and BL9C in the Photon Factory of KEK, Tsukuba, Japan, and BL40B2 and BL03XU in SPring-8, Hyogo, Japan.74,75 At BL9C, an imaging plate (FUJI BAS2500) was used as a detector that was set at a position of 110 cm apart from sample position. At BL6A, BL03XU, and BL40B2, the charge-coupled device with an image intensifier (II-CCD, Hamamatsu Photonics Co., Ltd.) was used as a detector that was set at a position of 250−300 cm apart from sample position. The wavelength λ of X-rays was 0.15 (PF) and 0.10 (SPring-8) nm in the stations. Additionally, laboratory SAXS was conducted using a Rigaku Nano-Viewer (camera length, 1.5 m; X-ray source, Cu Kα) equipped with an R-Axis IV (Imaging Plate) as a detector. Collagen (chicken tendon) was used as a standard specimen to calibrate the SAXS detectors. SAXS measurement using μ beam (9 μm in diameter) X-ray was conducted in BL03XU. The X-ray was collimated with three slits system. Scan step size of 10 μm was used. Intensity profile of the direct beam of the collimated X-ray was confirmed to be presented by Gaussian distribution. Taking into account for the intensity profile, in this case, the structural information from an each scan includes a few percent overlapping information 5991


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where φ is the azimuthal angle that is defined in Figure 1g. Figure 3 shows the scattering intensity of the first-order peak as

3. RESULTS AND DISCUSSION 3.1. Equilibrate Morphology in Thick Films after Thermal Annealing. SAXS data was collected from edge view to investigate inside structures of the thick films. The geometrical relationships of the edge view are illustrated in Figure S1 (Supporting Information). Figure 1 shows twodimensional (2D) SAXS patterns of both as-cast and thermally annealed films. For all as-cast films, ellipsoidally deformed patterns were observed. To understand the structures inside films, the azimuthal averaging (circular average) of 2D-SAXS patterns was conducted to obtain 1D SAXS profiles as shown in Figure 2. The dotted lines are calculated profiles by using paracrystalline distortion theory76−79 (parameters used for calculation are listed in Supporting Information, Table S1). The experimental profiles for as-cast films from mixed solvents were well-fitted with a model calculation of BCC spherical structure but in an almost lattice disordered state (disordered micelles).80 The spherical domains were considered to be randomly distributed in a cast film (domain spacing d given by 2π/qm simply reads the distance between nearest spheres in lattice disorder). The profile obtained for the sample cast from acetone solution cannot be fitted with the BCC model but the hexagonally (HEX) packed cylindrical model (1D profile in Figure 2a bottom shows peaks at 1,√3, and 2 times of main peak qm at ∼0.21 nm−1; q denotes the magnitude of the scattering vector as defined by q = (4π/λ) sin(θ/2), where λ and θ are the wavelength of X-ray and the scattering angle, respectively). The disordered spherical structure casted from mixed solvents was in a nonequilibrium state because the shrinking PS domains in selective solvents were trapped in the glassy state during solvent evaporation. Although acetone is still selective for PS, PS block can be partially dissolved in acetone because Mn of PS in BCP was relatively low. As-cast film from THF solution (good solvent for BCP) gave a HEX cylindrical morphology that was stable structure. After thermal annealing, several scattering rings or arches in all SAXS patterns appeared to be assigned to hexagonally packed cylinders with long-range ordering that was equilibrium morphology over glass transition temperature of PS because of the characteristic SAXS profiles (many diffraction peaks at 1,√3, 2, √7, and 3 times of main peak qm at ∼0.21 nm−1 in Figure 2b). The broad peak at qf = 0.6 nm−1 marked with arrows can be attributed to the form factor of the particles (spheres or cylinders), which can be used to evaluate radius (R) of spherical domains (R = 5.765/qf) and cylinder domains (R = 4.98/qf), as summarized in Supporting Information, Table S1 (precisely obtained by fitting). The radius (R) of spheres in as cast film was approximately 10 nm. All calculations indicated volume fractions of the particles were around 22−25 vol %, which corresponds to the composition of BCPs estimated from NMR. 3.2. Effects of Components of Mixed Solvents on Orientation. From azimuthal-angle dependence of the scattering intensity of the first-order peaks, the orientation factors ( f) which show the degree of orientation can be calculated according to eqs 1 and 2, f=

3⟨cos2 φ⟩ − 1 2 2

⟨cos φ⟩ =

∫0

π /2

∫0

Figure 3. Scattering intensities of the first-order peaks as a function of the azimuthal angle φ with various volume fractions of methanol in the mixed solvent. The definition of φ is shown in Figure 1g.

a function of the azimuthal angle φ corresponding to the 2D SAXS patterns in Figures 1e−h. In theory, for fully perpendicularly and parallel oriented structures, the orientation factors f should be 1 and −0.5, while isotropic and randomly oriented structures yield an orientation factor of 0, as illustrated in Figure 4. Films cast from BCP solutions with different methanol volume fractions, as summarized in Table 2, were prepared and analyzed. The orientation factors showed trend depending on quality of casting solvent (methanol fraction) after annealing, as shown in Figure 4. Specifically, orientation factors for films after thermal annealing decreased as methanol composition increased and reached the bottom point at 40 vol % methanol composition, where vertical cylinders was dominant (region 2). Further increasing methanol composition to 50 vol % soared up the orientation factors, indicating that degree of orientation decreased. Thermal annealing the spheres containing films above glass transition temperatures liberated PS spheres from a frozen state and induced a directional coalescence of spheres to from cylinders vertical to the film surface because of the memory of chemical potential gradient induced by solvent evaporation, as reported in our previous work.70 When solvent was less selective or much more selective, the oriented cylindrical morphology was not obtained effectively (regions 1 and 3 indicated in Figure 4). In the case of using acetone as solvent (region 1), the selectivity of the solvent is not strong enough to form tight PS micelles in solution and the spherical structures in films were dismissed after cast and the morphology had already been cylinder in the as-cast film as shown in Figures 1a and 2a. Once the relatively stable structure close to equilibrium state was generated, it was difficult to achieve a highly orientated structure except for improvement of lattice ordering by thermal annealing without any external directional field. On the other hand, in the case of using a much more selective solvent (50% methanol in solvent, region 3), the solubility was quite low for BCP, resulting in a turbid solution and an opaque cast film. Only a part of spherical domains formed incidentally showed up in SAXS measurement, and some BCPs might be partially macrophase-separated in the cast film.

(1)

I(q , φ)cos 2 φsin φ dφ π /2

I(q , φ)sin φ dφ

(2) 5992


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Figure 4. Orientation factors of cylinders in films after thermal (SMA1) and solvent (SMA2) annealing as a function of methanol contents in mixed solvents. The broken lines are guide to eyes. Schematic illustrations show theoretical relationships between orientation factors and orientation state of cylinders inside the films.

Table 2. Components, Solubility Parameters, and Selectivity for PMA of Mixed Solvents solvents components (volume fraction, vol %)

methanol acetone

0 100

25 75

29 71

33 67

40 60

50 50

solubility parameter (cal/cm3)1/2

mixed solvents PS PMA

10 8.6 10.7

11.1

11.3

11.5

11.8

12.3

low

−−−

−−−

−−−

−−−

high

selectivity of mixed solvents for PMA

3.3. Highly Vertical Orientation Induced by Solvent Annealing from Surface. Solvent annealing has been widely used to control the vertical orientation and lateral ordering of nanostructures in BCP thin films with thickness up to a few micrometers, however, whether this technique is suitable for the orientation in thick films is still unknown. Figure 5 shows the SAXS data collected from the films after cast from SMA2 solutions with methanol of 33 vol % in the mixed solvents and after THF annealing for 2 h. As shown in Figure 5a, the SAXS profile of the as-cast film (obtained by circular averaging 2DSAXS pattern) was assigned to be spherical morphology by the same manner as mentioned above. After THF solvent vapor annealing, the multiple reflection peaks appeared at the relative q positions of 1,√3, 2, √7, and 3 times of the main peak (qm) were the characteristic peaks of hexagonally packed PS cylinders, which means that THF vapor annealing induced morphology transition from sphere to cylinder effectively. Figure 5b is the 2D SAXS pattern from the edge view for the film after THF annealing for 2 h. It is obvious that several scattering spots which heavily concentrated intensity along the qy direction indicated that the long axes of cylinders are preferentially parallel to the qz direction, i.e., vertical to the surface of films. Figure 5c is the azimuthal angle dependence of the first-order peak intensity corresponding to the 2D SAXS pattern in Figure 5b. It shows a very narrow peak (width at half height) that yields an orientation factor of −0.45. The TEM micrographs in parts d and e of Figure 5 also show vertically arranged stripy and hexagonally arrayed patterns, respectively, which are strong and visible evidence for our conclusion here. However, TEM images can only tell us the structure in a very small area (ca. 1.6 μm × 1.6 μm in Figure 5d and 2 μm × 2 μm

in Supporting Information, Figure S3), thus we used polarized optical microscopic (POM) and μ-beam SAXS to confirm the long-range ordered structures in a macroscopic scale (from 200 μm to 1 mm), which will be discussed in detail later. The orientation factors of other films cast from SMA2 solutions with methanol of 25, 29, and 40 vol % in the mixed solvent were −0.41, −0.44 and −0.42, respectively, as shown in Figure 4 and Supporting Information, Figure S2. All these values were very close to that of the fully perpendicular orientation. In contrast, Figure 5e perpendicular orientation cannot be achieved when the film was made from acetone solution even after solvent annealing. This is the consistent result as thermal annealing. Thus, we concluded that selective solvents containing about methanol of 25−40 vol % in the mixed solvent were favorable to form oriented cylinders after proper annealing. The solvent annealing method exhibited more effectiveness for the perpendicular orientation of the cylindrical domains as compared with the thermal annealing. Cussler et al. reported that the orientation mechanism in block copolymer thin film upon solvent evaporation governed by solvent quality (selectivity) and rate of evaporation.66 Using selective solvent for major component of block copolymer, fast evaporation induced perpendicular cylinders. During evaporation of selective solvent, the cylinders grow through a spherical intermediate. The spheres in the solution can coalesce epitaxially from the vapor−solution interface into vertical cylinders along with the solvent concentration profile which developed due to solvent evaporation. Indeed, Wang et al. obtained the highly ordered perpendicularly aligned cylinders by the same mechanism.53 In our case, the spherical structure still remained inside films even after solvent casting because of 5993


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Figure 5. (a) One-dimensional SAXS profiles for as cast and solvent annealed films from SMA2 solutions with methanol of 33 vol % in mixed solvents. Dashed lines are obtained by calculation using paracrystal distortion theory (upper, BCC; bottom, HEX cylinder). (b) 2D SAXS pattern from the edge view after solvent annealing (intensity in logarithmic scale). (c) Intensities of first-order peaks as a function of the azimuthal angle φ in the corresponding image (b), and the orientation factor is −0.45. (d,e) TEM micrographs of edge (d) and through (e) views indicate the perpendicular orientation of PS cylinders inside the films after solvent annealing.

Figure 6. Two-dimensional SAXS patterns of the film from SMA2 solution with methanol of 33 vol % in mixed solvents: (a) edge and (b) through views after solvent annealing from edge side. Circularly averaged 1D SAXS profiles are shown in the patterns. Symbol n and red arrows represent direction normal to film surface. X-ray (black arrows), THF permeation directions (green arrows), and sample coordinates are shown schematically.

solvent molecules can permeate from a film surface accompanying with swelling of the film and travel toward bottom of the film during solvent annealing. At the same time, a nonequilibrium structure (spheres) can transfer to an equilibrium structure (cylinders) along the solvent penetration direction. Thus, perpendicular orientation of the cylinder by solvent annealing was efficiently achieved. To check whether or not this mechanism for the perpendicular orientation is true, we tried the solvent annealing from sample edge sides. First, an as-

the slow evaporation of solvents and generation of glassy PS spheres. The THF vapor annealing was followed by epitaxial morphological transition from spheres to cylinders, which was initiated from the vapor−polymer interface. The epitaxial transition occurring during solvent vapor annealing in our case was a different process from during solvent evaporation although it is analogous that cylinders come from spheres. 3.4. Horizontal Orientation Induced by Solvent Annealing from Edge. It is a reasonable consideration that 5994


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Figure 7. Polarizing optical micrographs of the SMA1 film obtained by solvent casting from SMA1 solution with 40 vol % methanol in mixed solvents and after THF vapor annealing for 60 min under the crossed polarizing condition. (a) The area (film corner) with circle was measured for POM and μ-beam SAXS. (b) A 530 nm retardation plate was inserted in between polarizer and analyzer. (c) POM image at the SAXS experiment in the X-ray Hutch. Beam size of X-ray was 9 μm in diameter. X-ray scan direction and positions are marked with light-pink arrow. Transmittance of Xray at each position is shown in the picture. White broken line is the sample edge. 2D SAXS patterns at the positions 1−9 are shown in Figure 8

cast film (thickness ∼1 mm) obtained from SMA2 solution with methanol of 33 vol % in mixed solvents was cut into small pieces with roughly 1 cm in length, 1 mm in thickness, and 2 mm in width. The pieces were stacked together as one surface attached to another (or bottom surface) without clearances. In this way, the stacked sample has a large area (surface) consisting of the original edge surface of the as-cast film. The newly obtained top surface was large enough for checking an effect of solvent annealing direction on the orientation. During solvent annealing, solvent molecules can penetrate eventually from the original edge side of the as-cast film. This operation was interpreted with illustrations in Supporting Information (Figure S4) including a geometrical definition. Figure 6 shows 2D SAXS patterns and corresponding circularly averaged 1D profiles in edge (a) and through (b) views for the film annealed from the edge side. The geometrical relationship of the sample film, solvent annealing direction, and the X-ray incidence for measurements were schematically shown together. Three peaks in 1D profiles at relative q positions of 1, √3, and 3 times of the main peak were the characteristic peaks of the hexagonally packed PS cylinders. A six-spot-like pattern was observed in edge view (a), and the strong scattering spots appeared at meridian direction in the through view (b). The orientation factor was calculated to be −0.23 from Figure 6b. The experimental results in Figure 6 indicated that long axes of the cylinders preferentially aligned along solvent permeating direction, i.e., horizontal to the original surface of the film. But the degree of orientation was relatively low as compared to the film obtained by annealing from surface as mentioned in section 3.3 where the orientation factor was −0.45. The vertical penetration of solvent molecules showed high efficiency for the directional coalescence of neighboring spheres, which might be attributed to a spatial distance between neighboring spheres, that is, the vertical distance of neighboring spheres was closer than the lateral ones in an as-cast film, as manifested in the vertical-ellipsoid 2D SAXS patterns of as-cast films. 3.5. Alignment of Cylinders along Solvent Permeation Directions in Macroscopic Scale. Among phase separated nanostructures in block copolymers, cylindrical or

lamellar structures should perform anisotropic properties because of the anisotropic shape of inside particles. For example, the refractive indices parallel and perpendicular to the anisotropic particles are different from each other, which gives rise to the so-called form birefringence.81 During THF vapor annealing, PS spheres near sample edge in a film were affected by THF vapor permeation from two surfaces (normal direction to the sample surface (n) and edge surfaces, x and y axis in Figure 7a). To confirm optical anisotropy in macroscopic scale, polarized optical microscopic (POM) observation under cross polarizing condition at room temperature for a SMA1 film after THF vapor annealing for 60 min was conducted. A 530 nm retardation plate was inserted in between polarizer and analyzer. Figure 7b shows POM image (through view) of the annealed SMA1 film obtained from a corner of the film in Figure 7a. Three almost homogeneous colored regions were observed. No retardation (purple color) where it was optically isotropic was found substantially in through view except for the sample edge regions, suggesting perpendicular cylinders formed after solvent annealing. The purple area in the film was relative far from the edge and PS spheres were essentially influenced by solvent vapor penetrated only from the sample surface. On the other hand, both blue and yellow colored regions near the sample edge sides showed different orientation from the purple colored region. Blue and yellow areas indicate the uniaxially orientated cylinders, but the orientation angle of cylinders in the blue area is perpendicular to that in the yellow area. To be more exact, the PS sphere near the edge region was affected by THF solvent vapor from two sides (sample surface and edge surface). That is, horizontal cylinders reasonably formed at the bottom side in the film edge, while perpendicular and horizontal cylinders might coexist at the top side (or randomly oriented cylinders). The length scale of the blue and yellow regions in POM image was ca. 204 and 172 μm from the edge sides as marked in Figure 7b, which represents the depth affected by solvent vapor from the edges, respectively. We also used μ-beam SAXS to confirm our previous interpretation for POM results. Figure 7c shows the positions chosen for μ-beam SAXS measurement based on the POM observation. The beam size of μ-beam SAXS was 9 μm in 5995


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Figure 8. 2D SAXS patterns measured at the positions 1−9 in Figure 7

Figure 9. 2D SAXS patterns (a−f) and cross-sectional POM images (g, h) after THF vapor annealing for 60 min under the crossed polarizing condition. (g) POM image at the SAXS experiment in the X-ray Hutch. X-ray scan direction and positions are marked with blue arrow. Transmittance of X-ray at each position is shown in the picture. Azimuthal angle is defined as shown in (a) in order to obtain sector-averaged 1D profiles (SAXS intensity was azimuthally averaging in the range 80−100°).

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diameter (full width at half-maximum of the beam intensity with Gaussian distribution), and X-ray scan direction and irradiated positions (line scan) are indicated along the lightpink arrow in Figure 7c. Transmittances dependence on positions for the μ-beam SAXS measurement are shown as well. Here, it is noted that a scan step width of 10 μm was conducted so that each step included the overlap information with a few percent to the next scan. 2D SAXS patterns of representative positions are shown in Figure 8. On the 2D SAXS patterns of positions of 1, 2, and 3, the scattering intensities concentrated along with the y-axis, while scattering intensities of positions of 6, 7, and 8 concentrated along with the x-axis. These results indicated that the long axis of cylinders preferentially aligned parallel to the x-axis in positions 1, 2, and 3, while parallel to the y-axis in the positions 6, 7, and 8, i.e., oriented directions of cylinders parallel to the solvent vapor permeation directions, respectively. However, some spots were also observed in each position because of perpendicular cylinders or spherical structures remaining (not affected yet by the annealing). Thus, it can be considered that both directed cylinders (and spheres) coexisted in the edge regions of the annealed sample. In contrast, it can be judged that the cylinders in the positions of 4, 5, and 9 were vertically oriented to the surface because ring- and spot-like patterns were observed in the corresponding 2D SAXS patterns. The positions 4 and 5 are near the borderline between anisotropic and isotropic area as indicated in the POM image in Figure 7. Although it seems that scattering intensities still concentrated on both y- and x-axes, perpendicular oriented cylinders were much predominant in comparison to the sample edge. The μ-beam SAXS results were fully consistent with the POM observation. Figure 9 shows POM images (g, h) and corresponding μbeam SAXS patterns measured from the cross-section view of the annealed film in a thickness scale of about 300 μm. The observed images (g) and (h) are not completely the same position. In Figure 9h, the blue area with the thickness of 206 μm represents anisotropic structure, meaning vertically aligned cylinders to the film surface, while the purple area with a thickness of about 80 μm indicated optically isotropic structure (far from the surface). The POM experiment shows that solvent vapors affected from surface toward bottom of a film. Effects of the vapor annealing did not reach the bottom yet during 60 min solvent annealing process. Parts a−f of Figure 9 are the representative 2D SAXS patterns selected from the POM image (Figure 9g). The cylinders near the surface indicated most oriented, and the orientation gradually decreased with deepening into the film. The scattering pattern near the substrate was ellipsoid that was essentially similar to the pattern of the as-cast film. Probably, the structure near the substrate was still unaffected, i.e., the spherical domain remained. The depth of oriented region was estimated to be ca. 206 μm as revealed by POM observation, which was fairly coincident with the depth of solvent permeation region from the sample edge observed in POM image of Figure 7. Figure 10 shows the sector-averaged 1D profiles obtained from 2D SAXS patterns in Figure 9. They clearly showed that inside structures were dependent on the depth of the film. The dashed lines indicate the simulated profiles of HEX cylinders, which were fairly fitted to experimental results well. At the deeper side in the film, although the experimental profile can be fitted with the HEX cylindrical model with a low degree of ordering (large lattice distortion) as shown in Supporting Information, Figure S5, the volume fraction of PS in the sample

Figure 10. Sector-averaged 1D SAXS profiles obtained from 2D patterns in Figure 9. Numerical numbers indicate the depth from the surface. Dashed-lines are obtained by calculation using paracrystal distortion theory of HEX cylindrical morphology.

deviates to small from molecular composition. Moreover, the BCC spherical model did not fit well to the SAXS profiles (Supporting Information, Figure S5 and Table S2). It can be considered that the structure at the deeper positions was in a transient state from spheres to cylinders. The nanostructures were assigned to cylinder in the range from near the surface to ca. 170−180 μm in depth, but spherical domain or a transient structure was found to remain near the substrate. The morphology transition from sphere to cylinder accompanying with the cylinder orientation started to occur from the surface and grew along the solvent permeation direction. The area of the oriented cylinder observed by the μ-beam SAXS was considerably identical with that in the edge view POM in Figure 9h. Because, strictly speaking, the observed area in Figure 9g was slightly different from that in Figure 9h but they were the same edge view of the identical sample, the data showed somewhat of a discrepancy in length scale of both pictures. However, the phenomenon of the orientation behavior mentioned in this paper was a convincing result. For the more thick film with thickness of 1 mm, the siteselective SAXS results were shown in Supporting Information, Figure S6, which demonstrated that the oriented cylinders were achieved throughout the thickness scale of 1 mm. Thus, the SAXS and POM experiments indicated that long-range ordering (macroscopic scale) of the cylindrical structure can be achieved via the solvent annealing method.

4. CONCLUSIONS Both thermal and solvent annealing induced phase transition from nonequilibrium spherical morphology to equilibrium cylindrical structure accompanying the perpendicular orientation to the sample surface. The solvent quality used for casting influenced the subsequent orientation factor of the cylindrical 5997


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(11) Singh, G.; Batra, S.; Zhang, R.; Yuan, H.; Yager, K. G.; Cakmak, M.; Berry, B.; Karim, A. ACS Nano 2013, 7, 5291−5299. (12) Jung, Y. S.; Lee, J. H.; Lee, J. Y.; Ross, C. A. Nano Lett. 2010, 10, 3722−3726. (13) Alabi, T. R.; Yuan, D.; Das, S. Nanoscale 2013, 5, 3912−3917. (14) Hong, A. J.; Liu, C. C.; Wang, Y.; Kim, J.; Xiu, F.; Ji, S.; Zou, J.; Nealey, P. F.; Wang, K. L. Nano Lett. 2009, 10, 224−229. (15) Seifarth, O.; Krenek, R.; Tokarev, I.; Burkov, Y.; Sidorenko, A.; Minko, S.; Stamm, M.; Schmeiβer, D. Thin Solid Films 2007, 515, 6552−6556. (16) Cheng, J. Y.; Mayes, A. M.; Ross, C. A. Nature Mater. 2004, 3, 823−828. (17) Wang, Y.; Becker, M.; Wang, L.; Liu, J.; Scholz, R.; Peng, J.; Gösele, U.; Christiansen, S.; Kim, D. H.; Steinhart, M. Nano Lett. 2009, 9, 2384−2389. (18) Jung, Y. S.; Jung, W.; Tuller, H. L.; Ross, C. A. Nano Lett. 2008, 8, 3776−3780. (19) Pavan, S. C.; Devon, A. S. ACS Nano 2011, 5, 450−456. (20) Cho, H.; Park, H.; Russell, T. P.; Park, S. J. Mater. Chem. 2010, 20, 5047. (21) Cheng, J. Y.; Zhang, F.; Chuang, V. P.; Mayes, A. M.; Ross, C. A. Nano Lett. 2006, 6, 2099−2103. (22) Watanabe, S.; Nakano, S.; Imai, C.; Laskar, I. R.; Komura, T.; Hadano, S.; Iyoda, T. Chem. Lett. 2010, 39, 902−904. (23) Ghoshal, T.; Fleming, P. G.; Holmes, J. D.; Morris, M. A. J. Mater. Chem. 2012, 22, 22949. (24) Milliron, D. J.; Caldwell, M. A.; Wong, H. S. P. Nano Lett. 2007, 7, 3504−3507. (25) Li, J.; Kamata, K.; Iyoda, T. Thin Solid Films 2008, 516, 2577− 2581. (26) Lei, K. W.; West, T.; Zhu, X. Y. J. Phys. Chem. B 2012, 117, 4582−6. (27) Wakayama, H.; Yonekura, H.; Kawai, Y. ACS Macro Lett. 2013, 2, 284−287. (28) Ruiz, R.; Kang, H.; Detcheverry, F. A.; Dobisz, E.; Kercher, D. S.; Albrecht, T. R.; de Pablo, J. J.; Nealey, P. F. Science 2008, 321, 936−939. (29) ThurnAlbrecht, J. S. T.; Krusin-Elbaum, K. L.; Black, C. T.; Tuominen, M. T.; Russell, T. P. Science 2000, 290, 2126−2129. (30) Bates, C. M.; Maher, M. J.; Janes, D. W.; Ellison, C. J.; Willson, C. G. Macromolecules 2013, 47, 2−12. (31) Kim, B. H.; Kim, J. Y.; Jeong, S. J.; Hwang, J. O.; Lee, D. H.; Shin, D. O.; Choi, S. Y.; Kim, S. O. ACS Nano 2010, 4, 5464−5470. (32) Yamamoto, T.; Kimura, T.; Komura, M.; Suzuki, Y.; Iyoda, T.; Asaoka, S.; Nakanishi, H. Adv. Funct. Mater. 2011, 21, 918−926. (33) Kim, E. S.; Jang, D. S.; Yang, S. Y.; Lee, M. N.; Jin, K. S.; Cha, H. J.; Kim, J. K.; Sung, Y. C.; Choi, K. Y. Nanoscale 2013, 5, 4262−4269. (34) Sageshima, Y.; Arai, S.; Noro, A.; Matsushita, Y. Langmuir 2012, 28, 17524−17529. (35) Lee, D. H.; Park, S.; Gu, W.; Russell, T. P. ACS Nano 2011, 5, 1207−1214. (36) Seung, Y.; Yang, I. R.; Hwang, Y. K.; Jin, K.; Russell, T. P. Adv. Mater. 2006, 18, 709−712. (37) Jeong, U.; Ryu, D. Y.; Kim, J. K.; Kim, D. H.; Wu, X.; Russell, T. P. Macromolecules 2003, 36, 10126−10129. (38) Seung, Y. Y.; Jinhwan, J. P.; Moonhor, R.; Jang, S. K.; Jin, K. K. Adv. Funct. Mater. 2008, 18, 1371−1377. (39) Bates, C. M.; Seshimo, T.; Maher, M. J.; Durand, W. J.; Cushen, J. D.; Dean, L. M.; Blachut, G.; Ellison, C. J.; Willson, C. G. Science 2012, 338, 775−779. (40) Matsen, M. W.; Bates, F. S. Macromolecules 1996, 29, 1091− 1098. (41) Wang, Q.; Nealey, P. F.; de Pablo, J. J. Macromolecules 2001, 34, 3458−3470. (42) Goldberg-Oppenheimer, P.; Kabra, D.; Vignolini, S.; Hüttner, S.; Sommer, M.; Neumann, K.; Thelakkat, M.; Steiner, U. Chem. Mater. 2013, 25, 1063−1070. (43) Olszowka, V.; Hund, M.; Kuntermann, V.; Scherdel, S.; Tsarkova, L.; Böker, A. ACS Nano 2009, 3, 1091−1096.

structures, and the mixed solvents of acetone and methanol with methanol of about 25−40 vol % was favorable to form highly oriented cylinders. The solvent annealing was found to be a more effective way to obtain perpendicularly oriented cylinders than thermal annealing. Controllable alignment of perpendicular and horizontal cylinders from directional coalescence of spheres along solvent permeation directions in BCP thick films in the scale of over 200 μm to 1 mm was first achieved. Solvent annealing from the surface led to highly perpendicular PS cylinders to the film surface, of which the orientation factor was −0.45, while from the edge resulted in horizontal cylinders. Both POM and μ-beam SAXS results demonstrated that the oriented cylindrical structure could be achieved in a macroscopic scale via the solvent annealing method. The concepts provided here can open up a novel methodology to fabricate highly oriented and hexagonally packed cylinders with controllable direction in BCP films in a large size and thickness scale.

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ASSOCIATED CONTENT

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AUTHOR INFORMATION

S Supporting Information *

Geometrical figures to the SAXS measurements and procedure to conduct solvent annealing from the film edge, figure to show azimuthal angle, and tables to show parameters used for calculation based on paracrystalline distortion. This material is available free of charge via the Internet at http://pubs.acs.org. Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japan, Grant-in-Aid for Scientific Research (C) (22550193, 2010) (26410132, 2014). A part of this work was conducted in Nagoya University, supported by Nanotechnology Platform Program (Molecular and Material Synthesis) of MEXT. SAXS and GISAXS measurements were performed at the Photon Factory of High Energy Accelerator Research Organization (approvals 2010G028, 2011G029) and at the SPring-8 (approvals 2010A1180 (BL40B2), 2012A7216, 2012B7266, 2013A7216, 2013B7264 (BL03XU)).

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REFERENCES

(1) Darling, S. B. Prog. Polym. Sci. 2007, 32, 1152−1204. (2) Gong, Y.; Joo, W.; Kim, Y.; Kim, J. K. Chem. Mater. 2008, 20, 1203−1205. (3) Huang, E.; Rockford, L.; Russell, T. P.; Hawker, C. J. Nature 1998, 395, 757−758. (4) Albert, J. N. L.; Epps, T. H., III. Mater. Today 2010, 13, 24−33. (5) Mai, Y.; Eisenberg, A. Chem. Soc. Rev. 2012, 41, 5969−5985. (6) Park, S.; Lee, D. H.; Russell, T. P. Adv. Mater. 2010, 22, 1882− 1884. (7) Shi, A. C.; Li, B. Soft Matter 2013, 9, 1398−1412. (8) Schacher, F. H.; Rupar, P. A.; Manners, I. Angew. Chem., Int. Ed. 2012, 51, 7898−7921. (9) Park, S.; Wang, J. Y.; Kim, B.; Xu, J.; Russell, T. P. ACS Nano 2008, 2, 766−772. (10) 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. ACS Nano 2013, 7, 8899−8907. 5998


Macromolecules

Article

(44) Ruppel, M.; Pester, C. W.; Langner, K. M.; Sevink, G. J. A.; Schoberth, H. G.; Schmidt, K.; Urban, V. S.; Mays, J. W.; Böker, A. ACS Nano 2013, 7, 3854−3867. (45) Cho, K. Y.; Hwang, S. S.; Yoon, H. G.; Baek, K. Y. J. Polym. Sci., Polym. Chem. 2013, 51, 1924−1932. (46) Raman, V.; Bose, A.; Olsen, B. D.; Hatton, T. A. Macromolecules 2012, 45, 9373−9382. (47) Xu, J.; Russell, T. P.; Ocko, B. M.; Checco, A. Soft Matter 2011, 7, 3915−3919. (48) Dessí, R.; Pinna, M.; Zvelindovsky, A. V. Macromolecules 2013, 46, 1923−1931. (49) Han, E.; Kim, M.; Gopalan, P. ACS Nano 2012, 6, 1823−1829. (50) Ji, S.; Nagpal, U.; Liu, G.; Delcambre, S. P.; Müller, M.; de Pablo, J. J.; Nealey, P. F. ACS Nano 2012, 6, 5440−5448. (51) Maher, M. J.; Bates, C. M.; Blachut, G.; Sirard, S.; Self, J. L.; Carlson, M. C.; Dean, L. M.; Cushen, J. D.; Durand, W. J.; Hayes, C. O.; Ellison, C. J.; Willson, C. G. Chem. Mater. 2014, 26, 1471−1479. (52) Kim, S.; Bates, C. M.; Thio, A.; Cushen, J. D.; Ellison, C. J.; Willson, C. G.; Bates, F. S. ACS Nano 2013, 7, 9905−9919. (53) Yin, J.; Yao, X.; Liou, J. Y.; Sun, Y. S.; Wang, Y. ACS Nano 2013, 7, 9961−9974. (54) Park, S. H.; Shin, D. O.; Kim, B. H.; Yoon, D. K.; Kim, K.; Lee, S. Y.; Choi, S. W.; Jeon, S. C.’; Kim, S. O. Soft Matter 2010, 6, 120− 125. (55) Kim, B. H.; Lee, D. H.; Kim, J. Y.; Shin, D. O.; Jeoung, H. Y.; Hong, S.; Yun, J. M.; Koo, C. M.; Lee, H.; Kim, S. O. Adv. Mater. 2011, 23, 5618−5622. (56) Borah, D.; Senthamaraikannan, R.; Rasappa, S.; Kosmala, B.; Holmes, J. D.; Morris, M. A. ACS Nano 2013, 7, 6583−6596. (57) Jin, C.; Murphy, J. N.; Harris, K. D.; Buriak, J. M. ACS Nano 2014, 8, 3979−3991. (58) Olayo-Valles, R.; Guo, S.; Lund, M. S.; Leighton, C.; Hillmyer, M. A. Macromolecules 2005, 38, 10101−10108. (59) Ho, R.-M.; Tseng, W.-H.; Fan, H.-W.; Chiang, Y.-W.; Lin, C.-C.; Ko, B.-T.; Huang, B.-H. Polymer 2005, 46, 9362−9377. (60) Wu, N. L. Y.; Zhang, X.; Murphy, J. N.; Chai, J.; Harris, K. D.; Buriak, J. M. Nano Lett. 2012, 12, 264−268. (61) Park, S.; Kim, B.; Xu, J.; Hofmann, T.; Ocko, B. M.; Russell, T. P. Macromolecules 2009, 42, 1278−1284. (62) Sinturel, C.; Vayer, M.; Morris, M.; Hillmyer, M. A. Macromolecules 2013, 46, 5399−5415. (63) Park, S.; Wang, J. Y.; Kim, B.; Chen, W.; Russell, T. P. Macromolecules 2007, 40, 9059−9063. (64) Bates, C. M.; Pantoja, M. A. B.; Strahan, J. R.; Dean, L. M.; Mueller, B. K.; Ellison, C. J.; Nealey, P. F.; Willson, C. G. J. Polym. Sci., Polym. Chem. 2013, 51, 290−297. (65) Cushen, J. D.; Otsuka, I.; Bates, C. M.; Halila, S.; Fort, S.; Rochas, C.; Easley, J. A.; Rausch, E. L.; Thio, A.; Borsali, R. ACS Nano 2012, 6, 3424−3433. (66) Philips, W. A.; Hillmyer, M. A.; Cussler, E. L. Macromolecules 2010, 43, 7763−7770. (67) Chremos, A.; Chaikin, P. M.; Register, R. A. Macromolecules 2012, 45, 4406−4415. (68) Hong, Y. R.; Adamson, D. H.; Chaikin, P. M.; Register, R. A. Soft Matter 2009, 5, 1687−1691. (69) Osuji, C. O. Macromolecules 2010, 43, 3132−3135. (70) Shinichi, S.; Hidekazu, Y.; Ryoko, F.; Masahiro, M.; Katsuhiro, Y.; Shigeru, O. Macromolecules 2009, 42, 2115−2121. (71) Cui, G.; Ohya, S.; Matsutani, T.; Nagano, S.; Dohi, T.; Nakamura, S.; Sakurai, S.; Miyazaki, T.; Yamamoto, K. Nanoscale 2013, 5, 6713−6719. (72) Matyjaszewski, K.; Xia, K. Chem. Rev. 2001, 101, 2921−2990. (73) Hansen, C. M. Hansen Solubility Parameters: A User’s Handbook, Senond ed.; CRC Press: Boca Raton, FL, 2007. (74) Ogawa, H.; Masunaga, H.; Sasaki, S.; Goto, S.; Tanaka, T.; Seike, T.; Takahashi, S.; Takeshita, K.; Nariyama, N.; Ohashi, H.; Ohata, T.; Furukawa, Y.; Matsushita, T.; Ishizawa, Y.; Yagi, N.; Takata, M.; Kitamura, H.; Takahara, A.; Sakurai, K.; Tashiro, K.; Kanaya, T.; Amemiya, Y.; Horie, K.; Takenaka, M.; Jinnai, H.; Okuda, H.; Akiba, I.;

Takahashi, I.; Yamamoto, K.; Hikosaka, M.; Sakurai, S.; Shinohara, Y.; Sugihara, Y.; Okada, A. Polym. J. 2013, 45, 109−116. (75) Masunaga, H.; Ogawa, H.; Takano, T.; Sasaki, S.; Goto, S.; Tanaka, T.; Seike, T.; Takahashi, S.; Takeshita, K.; Nariyama, N.; Ohashi, H.; Ohata, T.; Furukawa, Y.; Matsushita, T.; Ishizawa, Y.; Yagi, N.; Takata, M.; Kitamura, H.; Sakurai, K.; Tashiro, K.; Takahara, A.; Amamiya, Y.; Horie, K.; Takenaka, M.; Kanaya, T.; Jinnai, H.; Okuda, H.; Akiba, I.; Takahashi, I.; Yamamoto, K.; Hikosaka, M.; Sakurai, S.; Shinohara, Y.; Okada, A.; Sugihara, Y. Polym. J. 2011, 43, 471−477. (76) Hosemann, R.; Bagchi, S. N.; Direct Analysis of Diffraction by Matter; North-Holland: Amsterdam, 1966. (77) Matsuoka, H.; Tanaka, H.; Hashimoto, T.; Ise, N. Phys. Rev. B 1987, 36, 1754−1765. (78) Matsuoka, H.; Tanaka, H.; Iizuka, N.; Hashimoto, T.; Ise, N. Phys. Rev. B 1990, 41, 3854−3856. (79) Hashimoto, T.; Kawamura, T.; Harada, M.; Tanaka, H. Macromolecules 1994, 27, 3063−30. (80) Han, C. C.; Vaidya, N. V.; Kim, D.; Shin, G.; Yamaguchi, D.; Hashimoto, T. Macromolecules 2000, 33, 3767−3780. (81) Folkes, M. J.; Keller, A. Polymer 1971, 12, 222−236.

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Macroscopic Alignment of Cylinders via Directional Coalescence of

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