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Orthogonal Liquid Crystal Alignment Layer: Templating SpeedDependent Orientation of Chromonic Liquid Crystals Yun Jeong Cha,† Min-Jun Gim,† Hyungju Ahn,‡ Tae Joo Shin,§ Joonwoo Jeong,∥ and Dong Ki Yoon*,† †
Graduate School of Nanoscience and Technology and KINC, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea ‡ Pohang Accelerator Laboratory, POSTECH, Pohang 37673, Republic of Korea § UNIST Central Research Facilities & School of Natural Science, UNIST, Ulsan 44919, Republic of Korea ∥ School of Natural Science, UNIST, Ulsan 44919, Republic of Korea S Supporting Information *
ABSTRACT: Lyotropic chromonic liquid crystals (LCLCs) have been extensively studied because of the interesting structural characteristics of the linear aggregation of their plank-shaped molecules in aqueous solvents. We report a simple method to control the orientation of LCLCs such as Sunset Yellow (SSY), disodium cromoglycate (DSCG), and DNA by varying pulling speed of the top substrate and temperatures during shear flow induced experiment. Crystallized columns of LCLCs are aligned parallel and perpendicular to the shear direction, at fast and slow pulling speeds of the top substrate, respectively. On the basis of this result, we fabricated an orthogonally patterned film that can be used as an alignment layer for guiding rodlike liquid crystals (LCs) to generate both twisted and planar alignments simultaneously. Our resulting platform can provide a facile method to form multidirectional orientation of soft materials and biomaterials in a process of simple shearing and evaporation, which gives rise to potential patterning applications using LCLCs due to their unique structural characteristics. KEYWORDS: lyotropic chromonic liquid crystal (LCLC), pulling speed, self-assembly, multidomain alignment layer coating,16,17 blade coating,18 and roll coating19 use a meniscus to prepare a film on a substrate. By pulling the substrate at a constant speed, the solution can be uniformly coated onto the surface of the substrate, after which evaporation of the solution induces crystallization of the coated film.20 The free-meniscus coating method has been most widely used to produce a thin film having a fine structure with a uniform thickness.21 It has been reported that, when this process is used to prepare an LCLC thin film, a dried film of 1D LCLC aggregates aligned parallel to the shear direction is formed.9−11,15 These dried films have been used as the alignment layer for other LC materials because of their high regularity.22−24 However, there are few studies investigating a multidirectional alignment layer utilizing the dried LCLC film, although Yi and Clark25 showed a multistable alignment of LCLC in the N phase under topographic confinement. However, the alignment state of LCLC was not systematically controlled. Recently, a dramatic improvement was seen in the control of aligned DNA, in which the DNA form periodic zigzag patterns, which resulted
1. INTRODUCTION Orientation control of soft materials has been important for industrial applications as well as scientific research.1,2 The most representative example of these efforts is liquid crystal display (LCD) technology using a mechanically rubbed alignment layer, which is used in handheld display devices such as cellphones.3 Among the various kinds of soft materials, lyotropic chromonic liquid crystals (LCLCs) are well-known for unique structural characteristics such as self-organization by noncovalent interactions, producing complex structures;4 thus, they have been widely used in specific applications such as biosensors,5,6 microelectronic devices,7,8 and polarizing components.9−11 In general, the building blocks of LCLCs have the plank shape that can aggregate to make one-dimensional (1D) structures, forming nematic (N), columnar (Col) LC phases, and columnar crystal phase depending on the concentration and temperature via intra- and interaggregative forces as observed in food dyes,12 drugs,13 and DNA nucleotides.14 Well-oriented structures of LCLCs are easily obtained by mechanical shearing methods such as shear flow induced technique and doctor blade coating,9−11,15 in which the meniscus of the solution slides on a substrate in one direction as the solvent simultaneously evaporates. Compared to other coating methods, free-meniscus coating tehcniques such as dip © 2017 American Chemical Society
Received: March 24, 2017 Accepted: May 10, 2017 Published: May 10, 2017 18355
DOI: 10.1021/acsami.7b04188 ACS Appl. Mater. Interfaces 2017, 9, 18355−18361
Research Article
ACS Applied Materials & Interfaces
urations. Our method is a simple but powerful platform for potential patterning applications beyond current LCD technology.
from the competitive interaction between DNA elasticity and dilative stress during water evaporation.26 Basically, the multidirectional alignment layer is very much required in many applications, such as the patterned retarder for 3D displays,27,28 transflective LCDs,29 tunable gratings for projection displays,30−33 optical interconnection devices,32 and the hybrid alignment layers for polarization converters.34,35 It is well-known that general rubbing methods to fabricate the alignment layer cannot produce multidirectionally aligned patterns. Although the photoalignment process can be used to achieve the multidirectional alignment, it often produces thermally and temporarily unstable LC molecular orientation with weak surface anchoring.28,30 In the present work, we report the formation of an orthogonally patterned alignment layer by adjusting the pulling speed of the top substrate in the shear flow induced method to control the orientation of LCLCs (Figure 1a and b). Micro-
2. RESULTS AND DISCUSSION Preparation and Characterization of Aligned SSY Films. The LCLC used in this experiment was Sunset Yellow FCF (SSY), which is a common food dye.36 The intrinsic structural characteristic including elastic anisotropy-driven chirality and orientation have been extensively studied.37−40 The SSY molecule consists of a hydrophobic core and hydrophilic peripheral groups, which can make SSY molecules spontaneously self-assemble into cylindrical aggregates in aqueous solution.36,41,42 To investigate the assembling behavior of SSY under different pulling speeds, the shear flow induced method was used at 65 °C. Because temperature is also an important factor determining the orientation, we also investigated the effect of temperature systematically. When the upper substrate was moved in one direction, the water in the SSY solution began to evaporate at an exposed air−liquid−solid contact line and the SSY-aggregated film was formed on a bottom substrate just above the contact line (Figure 1a). The orientation of of the SSY is controlled by molecular concentration, temperature, and pulling speed. The two different pulling speeds used in this study are marked as “Slow” (100 μm/s) and “Fast” (300 μm/s) in Figure 1b, in which the relatively slow and fast terminologies were defined based on the transition point where the orientational direction is changed as shown in Figure 3. Ericksen number (Er) is a dimensionless number defined as the ratio of the viscous (here shear) to elastic forces. The viscous force is dominant or the elastic force is dominant when Er is ≫1 or 1, but the phase transition should be considered in our system during the organization of SSYs compared with the previous studies.43 Note that the slow and fast terminologies are simply used to determine which force is dominant to modulate the orientation of SSY columns (see Note S1 in Supporting Information). The aligned SSY films prepared at different pulling speeds were observed by POM (Figure 1c−f). The POM images show the specific orientation of SSY molecules because the transmitted light intensity (I) is proportional to sin2 2ψ depending on the angle ψ between the polarization direction (P) and the principal optic axis of the SSY aggregates (nSSY). Both the slow and fast sheared samples showed a maximum and minimum intensity when the shear direction was tilted diagonally and parallel to the crossed polarizers, respectively (see Figure 1c and e and Figures S1 and S2). To confirm the exact orientation of the SSY aggregates, a first-order retardation plate (λ = 530 nm) was inserted between the sample and analyzer (Figures 1d and f, S1c and d, and S2c and d). This reveals color changes depending on the retardation of the wavefront of the light after passing through the sample and a retardation plate. When the optic axis of the birefringent materials corresponds to two crossed polarizers, magenta color appears. A cyan blue or yellow color appears when the optic axis of the sample is parallel or perpendicular to the slow axis of the retardation plate, respectively. However, the SSY has a negative birefringence because the plank-shaped molecules stack perpendicular to the long axis of the columnar aggregates (nSSY).9 This results in the opposite tendency of
Figure 1. Schematic illustration of the shear flow induced process and POM images of the SSY film. (a, b) Schematic illustrations of the shear flow induced at various pulling speeds and the different orientations of LCLCs. Stacks of plank-shaped molecules indicate SSY aggregates, and the double-headed arrows denote the LC director. SSY columns are aligned perpendicular to the shear direction at a slow pulling speed and parallel with the shear direction at a fast pulling speed. POM images of the SSY films when the pulling speed is (c, d) slow and (e, f) fast. (d, f) Images with the retardation plate (λ = 530 nm) inserted to show nSSY. (Black arrows indicate the shear direction.)
and nanostructures fabricated using this method were thoroughly investigated using various characterization techniques, including polarized optical microscopy (POM), atomic force microscopy (AFM), spectroscopy, and grazing incident Xray diffraction (GIXD). The resulting orthogonal alignment layers could control the N phase of rodlike LCs to make alternating domains of parallel and twisted nematic config18356
DOI: 10.1021/acsami.7b04188 ACS Appl. Mater. Interfaces 2017, 9, 18355−18361
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ACS Applied Materials & Interfaces
Figure 2. Sequential changes of oriented SSYs under different pulling speeds of top substrate: (a−c) 100 μm/s, (d−f) 200 μm/s, and (g−i) 300 μm/ s. The white dashed lines denote the contact line of the meniscus. (j, k) Schematic illustrations representing vertical cross sections of the coating meniscus at slow (j) and fast (k) pulling speeds, cyan and green dotted lines, respectively (a, g).
aggregates aligned parallel with the contact line (Figure 2j). Indeed, this arrangement of SSY aggregates is preferred to the splayed configuration as shown in the viscous forces dominant case at the fast pulling speed (Figure 2k), which means that the orientation of SSY agregates is along with the shear direction.48 During the water evaporation, the slowly pulled sample shows that the SSY columns stayed near the contact line even after the crystallization, aligning perpendicular to the shear direction (Figure 2a−c). However, the SSY columns prepared with a medium pulling speed underwent the translational diffusion due to the competitive interactions between the shearing force and the elastic energy minimization (Figure 2d−f).49 When the pulling speed increased to 300 μm/s, the SSY columns were aligned parallel to the shear direction from the beginning (Figure 2g−i and k) as previously reported.10,11,15,22 Temperature and Pulling Speed Diagram of Different Orientation. To validate our scenario and check the reproducibility of the results, the experiments were performed in the temperature range between 45 and 65 °C for different pulling speeds, ranging from 100 to 300 μm/s (Figure 3). Above this temperature range, the water evaporation rate is too fast to form the regular film. For each temperature−pulling speed combination, we repeated the experiments at least five times, to get the qualitatively same outcomes. Figure 3a shows three typical aligned structures, as detailed below. (1) nSSY aligned perpendicular to the shear direction. Parts b and c of Figure 3 show that slow pulling speed and relatively high temperature (65 °C) led to fast evaporation and
color changes with the retardation plate. The POM results showed that the SSY films revealed a yellow color when prepared at a slow pulling speed and a blue color when prepared at a fast pulling speed with the shear direction perpendicular to the slow axis of the retardation plate (Figure 1d and f). This indicates that nSSY was aligned parallel to the shear direction in the fast pulling speed sample, which is wellknown from previous studies.10,11,15,21 In contrast, nSSY was perpendicular to the shear direction and parallel with the contact line of the meniscus in the slow pulling speed region, which has never been observed in LCLCs, although there are similar reports in the case of drying solution of bacteria phage and the other biomaterials under the specific boundary conditions.44−46 We show that other lyotropic materials exhibit a similar tendency as shown in the SSY sample; disodium cromoglycate (DSCG) (see Figure S3) and DNA (see Figure S4) were also well-aligned by our strategy, which suggests that our platform may be used in a broad family of LCLC materials. To elucidate the mechanism of this unique behavior, we varied the pulling speeds of the SSY solution at 65 °C (Figure 2 and Supporting Information Movies S1, S2, and S3). As shown in the movies and Figure 2a−f, when the pulling speed is slow and medium (100 and 200 μm/s, respectively), nSSY is initially parallel with the contact line, where the solvent evaporation starts.45,47 In the beginning, the SSY solution showed an isotropic phase at 65 °C. When the solution was sheared, the concentration of the SSY solution at the contact line was increased because of the solvent evaporation and the SSY 18357
DOI: 10.1021/acsami.7b04188 ACS Appl. Mater. Interfaces 2017, 9, 18355−18361
Research Article
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contact line region, which is opposite to the higher-temperature case (Figure 3b and c). Even at high temperature, 65 °C, the fast pulling speed can align the nSSY parallel to shear direction because this pulling speed (v ≈ 300 μm/s) condition can be considered as viscous force dominant or shear flow dominant case. Orthogonally Aligned SSY Film. Orthogonally aligned SSY films were prepared based on the results of these temperature−pulling speed experiments (Figure 4). Here, the
Figure 3. Orientation diagram and POM images at each point. (a) Orientation changes of SSYs depending on the pulling speeds and temperatures. Yellow circles, green triangles, and blue squares represent nSSY ⊥ shear direction, the transition point, and nSSY ∥ shear direction, respectively. (b−g) Distinct alignments of SSY are shown, in which the images (c, e, g) were acquired with the retardation plate (λ = 530 nm). POM images (b, c) at nSSY ⊥ shear direction and (f, g) at nSSY ∥ shear direction. (d, e) POM images at the transition state.
Figure 4. Orthogonally aligned SSY film with different pulling speeds. (a) POM image of the SSY film with a slow pulling speed (100 μm/s) and with a fast pulling speed (300 μm/s). (b) Intensity profiles of the polarized light passing through the slow sheared part (red circles) and the fast sheared part (black squares) of the SSY film as a function of the rotational angle (Φ) between the shear direction and the polarizer (P). (c, d) POM images with the retardation plate, in which the shear direction is (c) perpendicular and (d) parallel with respect to the slow axis of the retardation plate (magenta arrow in the inset).
crystallization, resulting in the perpendicularly aligned nSSY (yellow circles). Slow pulling speed means that the molecules are rarely influenced by shear flow induced by the pulling of the upper substrate. At the same time, high temperature caused stronger capillary flow for translocating the molecules to the contact line, which induced the packing of SSY molecules and forming the Col aggregates at the contact line area. The long axis of the aggregates could be considered to assemble perpendicular to the shear direction (Figure 2j) because the direction of the SSY column has no deformation, which is the lowest elastic energy conformation (Figure S5).48 After evaporation, the SSY molecules changed to columnar crystal phases while retaining the initial molecular direction. (2) Intermediate state. As shown in Figure 3d and e, the mixed morphologies of parallel and perpendicularly aligned SSYs were found under the conditions of medium pulling speed at 65 °C and slow pulling speed at 55 and 45 °C (green triangles). At a relatively low temperature, the rate of water evaporation is not fast enough to cause a competition between the self-assembly and the shear orientation of SSY molecules, forming the mixed domains. (3) nSSY aligned parallel to shear direction. Parts f and g of Figure 3 show the parallel aligned nSSY at fast pulling speed and the relatively low temperature of 45 °C (blue squares). In the slow evaporation at 45 °C or lower temperatures, the capillary flow decreases and fewer SSY molecules can move to the
temperature was fixed at 65 °C, which was shown to be the best temperature to induce two different kinds of SSY molecular orientation. Slow and fast pulling speeds were used, 100 and 300 μm/s, respectively. As a result, two kinds of domains were observed with a distinct boundary (white arrow in Figure 4a). This is expected to be the domain boundary between parallel and perpendicularly aligned SSY columns.44 To investigate the orientation of this sample, POM experiments with crossed polarizers and a retardation plate were carried out. In Figure 4c, the slow and fast sheared parts of the SSY film revealed yellow and blue colors and vice versa with the given shear direction (Figure 4d). To quantify the optical property of these SSY films, the transmittance of the film under the single polarizer was measured using a spectrometer, in which the sample was rotated (Figure 4d). Φ was defined as the angle between shear direction and polarizer. In the region of slow shear, the lowest transmission intensity was obtained at Φ = 0, 180°, while the highest was measured at Φ = 90, 270° (red circles). On the contrary, the region of fast shear had the lowest transmittance at Φ = 90, 270° and the highest at Φ = 0, 180° (black squares). This linear polarization-dependent transmittance resulted from the dichroic chracteristics of the aligned SSY aggregates, in which the absorption of the polarized light was maximized and minimized when the P is perpendicular and parallel to the nSSY, respectively, in which the analyzer was removed (Figure 18358
DOI: 10.1021/acsami.7b04188 ACS Appl. Mater. Interfaces 2017, 9, 18355−18361
Research Article
ACS Applied Materials & Interfaces S6).25 The optical anisotropy changed as the angles Φ changed (Figure S6a and b), where the fast and slow sheared parts showed a relatively dark and bright signal, respectively, at Φ = 90° (Figure S6a) and vice versa for Φ = 0° (Figure S6b). The transmittance of each fast (Figure S6c) and slow (Figure S6d) sheared area shown in Figure S6a and b was measured in the visible light range, in which T0 is the transmittance when Φ is 0°, T90 is the transmittance at Φ ≈ 90°, and Tsingle is the mean transmittance of T0 and T90. The wavelength range of the absorbance of the light for SSY is 400−550 nm; thus, the transmittance of this range is relatively lower than the others.15 In the fast sheared part, the T0 is higher than T90 (Figure S6c) and vice versa for the slow sheared part (Figure S6d). The opposite transmittance tendency of the slow and fast sheared areas clearly indicated that the SSY film had an orthogonal orientation in the plane. Further direct examination of the orientation was performed using AFM (Figure S7). The surface morphology of the fast sheared region had streaks parallel with the shear direction (Figure S7a), while we observed elongated patterns vertically aligned to the shear direction on the surface of the slow sheared part (Figure S7c). The boundary between the regions of slow and fast shear had random orientation (Figure S7b). The internal structure of the aligned SSY film was also observed at molecular resolution using GIXD with a synchrotron radiation source. The SSY film was measured while moving the sample stage through the shear direction from the fast to slow shear region, in which the incident beam direction, denoted as a yellow arrow, is perpendicular to the shear direction (Figure S8). In the wide-angle region, two strong diffraction arcs appear at the equator (white arrows in Figure S8a), revealing the face-to-face stacking between the SSY molecules (d1 = 3.4 Å). The intermediate diffraction peak (d2 = 5.0 Å) is from the flexible segments in the azo group, which link the two aromatic rings.50 In the small-angle region, another diffraction peak (d3 = 8.4 Å) at the meridian was observed, which corresponds to the width of the SSY molecule, indicating that nSSY is oriented parallel to the shear direction. In Figure S8b, the XRD peaks revealing π-stacks of SSYs at the wideangle region disappeared while well-defined small-angle diffraction patterns corresponding to the rectangular columnar orientation of SSYs were observed, suggesting that nSSY of the slow region had an uniaxial orientation perpendicular to the shear direction. The two innermost diffraction patterns in the small-angle region (white arrows in Figure S8b) resulted from the coexisting structures of the in-plane and out-of-plane arrangements of SSYs, indicating that a splay deformation of the SSY columns existed by a tilted geometry of the given meniscus as described in Figures 2k and S5b.51 These distinctive GIXD patterns unambiguously indicate that the SSY film had a highly ordered orthogonal orientation. Consequently, we can confirm that changing pulling speeds leads to the tendency of the SSY columns to assemble differently at the air−liquid−solid interface. Hybrid LC Cell with Orthogonally Aligned SSY Film. We used the resultant SSY film in an LC alignment layer application, like previous studies with 1D alignment of LCLC molecules (Figure 5).22−24 First, a sandwich cell was fabricated (with a thickness of 3 μm), in which the orthogonally aligned SSY film was used as a bottom substrate and the top cover glass was coated with a polyimide (PI) layer rubbed in one direction. The rubbing direction (RD) of the top substrate was parallel to nSSY of the fast sheared region, which means that the RD is
Figure 5. Hybrid LC cell with an orthogonal SSY alignment layer. POM images show the N and TN arrangements of 5CB molecules in the cell, in which RD is parallel (a, c) and tilted (b) to the crossed polarizers. (d) Schematic illustration of the hybrid LC cell, in which RD is parallel and perpendicular with nSSY in the N and TN parts, respectively. (e) Intensity profiles from the hybrid LC cell show the transmitted intensities of TN (red triangles) and N parts (blue squares) as a function of the rotation angle (θ) between RD and P.
perpendicular to nSSY of the slow sheared part (Figure 5d). The well-known rodlike LC, 4-cyano-4′-pentylbiphenyl (5CB), was then injected into the cell by capillary forces at isotropic temperature (40 °C). 5CB molecules were oriented parallel to nSSY and the RD; therefore, the resulting LC shows a hybrid orientation, with homogeneous one-directional (N) arrangement in one domain and twisted nematic (TN) arrangement in the other domain (Figure 5d). The hybrid LC cell using an orthogonal SSY alignment layer analyzed by POM showed dramatic birefringence changes when the sample was rotated (Figure 5a−c). When the RD was parallel to either the polarizer or the analyzer, the N domain exhibited a good extinction (Figure 5a and c), while it became bright when the RD was tilted to the crossed polarizers (Figure 5b). The TN region revealed a bright domain during this rotation, although changes of intensity and birefringence color appeared, which was induced by the different orientation of 5CB molecules and underlying polarizer (Figure 5a−c). To evaluate N and TN modes on the SSY film, optical analyses were conducted as a function of the rotation angle (θ) between the RD and the polarizer (Figure 5e), in which two different LC domains showed distinct intensity profiles as a function of θ. In the TN domain, the highest transmittance appeared at θ = 0, 90, 180°, while the N-region showed the highest transmittance at θ = 45, 135°. This can be explained by the phase shift of the incident light. In the TN domain, the light undergoes a phase shift of π/2 after passing through the LC film, called the wave-guiding effect.52 Thus, the cell always shows the bright state under the crossed polarizers. However, a slight decrease of the transmission at the θ ≠ 0, 90, 180° resulted from the elliptically polarized light induced from the LC layer anchored on the SSY film. The highest transmittance appeared at θ = 0, 90, 180° because the plane of the linearly polarized light that passed through the TN LC domain was parallel to the analyzer. On the other hand, in the N domain, light transmission occurred when phase retardation was generated, as shown in the normal N cell.53 Thus, the dark state appeared when molecular directors are parallel or perpendicular to the polarizers (θ = 0, 90, 180°) due to the absence of the phase retardation. 18359
DOI: 10.1021/acsami.7b04188 ACS Appl. Mater. Interfaces 2017, 9, 18355−18361
Research Article
ACS Applied Materials & Interfaces
3. CONCLUSION In summary, we first report that the LCLC materials can be aligned orthogonally, simply by varying the pulling speed of the shear flow induced technique, where nLCLC was not only parallel but also perpendicularly aligned with the shear direction. The competitive interaction between the self-assembly at the air− liquid−solid interface and the shear force can vary the orientation of SSY aggregates. This interesting behavior introduced a simple method for fabricating an orthogonal alignment layer consisting of LCLCs to align guest LCs. The resulting platform would be of special interest for the recently proposed approaches to LCLCs5,42,54 that can control the ordering and orientation of functional biomaterials in the solution system.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Dong Ki Yoon: 0000-0002-9383-8958 Notes
The authors declare no competing financial interest.
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4. EXPERIMENTAL METHODS
ACKNOWLEDGMENTS This study was supported by a grant from the National Research Foundation (NRF) and funded by the Korean Government (MSIP) (2012M3A7B4049802 and 2015R1A2A2A01007613). The experiments at the PLS-II were supported in part by MSIP and POSTECH.
Materials and Sample Preparation. Sunset Yellow FCF (SSY, dye content 90%) purchased from Sigma-Aldrich was dissolved in deionized water at 1 wt % concentration without any further purification. Bare glass or silicon substrates (20 × 30 mm2) were cleaned using acetone, ethanol, and deionized water, and the bottom substrate was treated with O2 plasma for 5 min to remove any organic residue. Two substrates were sandwiched with the 3 μm silica ball spacers, which may be the same dimension with the expected thickness of the SSY solution. The SSY solution was injected between the LC sandwich cell by capillary forces, and then the upper glass piece of the sandwich cell was pulled in the heating stage (Linkam TST350). The temperature range and pulling speeds were 45−65 °C and 100−300 μm/s, respectively, and the film thickness was ∼500 nm (as measured by AFM). To fabricate the hybrid LC cell, two substrates were prepared, where one was an orthogonally aligned SSY film on glass and the other was a glass with a rubbed polyimide layer. These two substrates were sandwiched with 3 μm silica ball spacers. Then 4cyano-4-pentylbiphenyl (5CB, Sigma-Aldrich) thermotropic rodlike liquid crystal material was injected into the cell by capillary forces at its isotropic temperature (∼40 °C). Characterization. Optical textures of the prepared SSY films and LC material were measured using POM (Nikon LV100POL) with a first-order retardation plate (λ = 530 nm). The optical properties of these SSY films were quantitatively measured using a spectrometer (USB-2000+, Ocean Optics) with a light source at 460 nm (SPECTRA X, Lumencor), in which the sample was rotated (Figure 4b). AFM images of the SSY film were observed using the tapping mode with the SiN tip having a cantilever length of 115 μm and a resonant frequency of ∼70 kHz (Bruker, Multimode-8). GIXD experiments were carried out at the 9A beamline of the Pohang Accelerator Laboratory (PAL) in Korea. The incident beam size was 30 (V) × 100 (H) μm2 with a grazing incidence angle of 0.15°. The sample-to-detector distance (SDD) was kept at 224 mm, and the energy was 11.05 keV to observe both the small- and wide-angle regions. The diffraction patterns were recorded using a twodimensional charge-coupled-device detector (Rayonix SX165, U.S.A.).
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Fabrication of SSY films at medium pulling speed (200 μm/s), recorded under cross-polarizers with retardation plate (AVI) Fabrication of SSY films at fast pulling speed (300 μm/ s), recorded under cross-polarizers with retardation plate (AVI)
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REFERENCES
(1) Yoon, D. K.; Deb, R.; Chen, D.; Körblova, E.; Shao, R.; Ishikawa, K.; Rao, N. V.; Walba, D. M.; Smalyukh, I. I.; Clark, N. A. Organization of the Polarization Splay Modulated Smectic Liquid Crystal Phase by Topographic Confinement. Proc. Natl. Acad. Sci. U. S. A. 2010, 107 (50), 21311−21315. (2) Kim, J. H.; Kim, Y. H.; Jeong, H. S.; Srinivasarao, M.; Hudson, S. D.; Jung, H.-T. Thermally Responsive Microlens Arrays Fabricated with the Use of Defect Arrays in a Smectic Liquid Crystal. RSC Adv. 2012, 2 (17), 6729−6732. (3) Geelhaar, T. Liquid Crystals for Display Applications. Liq. Cryst. 1998, 24 (1), 91−98. (4) Tam-Chang, S.-W.; Huang, L. Chromonic Liquid Crystals: Properties and Applications as Functional Materials. Chem. Commun. 2008, 17, 1957−1967. (5) Shiyanovskii, S.; Lavrentovich, O.; Schneider, T.; Ishikawa, T.; Smalyukh, I.; Woolverton, C.; Niehaus, G.; Doane, K. Lyotropic Chromonic Liquid Crystals for Biological Sensing Applications. Mol. Cryst. Liq. Cryst. 2005, 434 (1), 259−270. (6) Shiyanovskii, S. V.; Schneider, T.; Smalyukh, I. I.; Ishikawa, T.; Niehaus, G.; Doane, K.; Woolverton, C. J.; Lavrentovich, O. Real-time Microbe Detection based on Director Distortions Around Growing Immune Complexes in Lyotropic Chromonic Liquid Crystals. Phys. Rev. E 2005, 71 (2), 020702. (7) van de Craats, A. M.; Warman, J. M. The Core-Size Effect on the Mobility of Charge in Discotic Liquid Crystalline Materials. Adv. Mater. 2001, 13 (2), 130−133. (8) Nazarenko, V.; Boiko, O.; Anisimov, M.; Kadashchuk, A.; Nastishin, Y. A.; Golovin, A.; Lavrentovich, O. Lyotropic Chromonic Liquid Crystal Semiconductors for Water-solution Processable Organic Electronics. Appl. Phys. Lett. 2010, 97 (26), 263305. (9) Lavrentovich, M.; Sergan, T.; Kelly, J. Planar and Twisted Lyotropic Chromonic Liquid Crystal Cells as Optical Compensators for Twisted Nematic Displays. Liq. Cryst. 2003, 30 (7), 851−859. (10) Bae, Y.-J.; Yang, H.-J.; Shin, S.-H.; Jeong, K.-U.; Lee, M.-H. A Novel Thin Film Polarizer from Photocurable Non-aqueous Lyotropic Chromonic Liquid Crystal Solutions. J. Mater. Chem. 2011, 21 (7), 2074−2077. (11) Park, S. K.; Kim, S. E.; Kim, D. Y.; Kang, S. W.; Shin, S.; Kuo, S. W.; Hwang, S. H.; Lee, S. H.; Lee, M. H.; Jeong, K. U. PolymerStabilized Chromonic Liquid-Crystalline Polarizer. Adv. Funct. Mater. 2011, 21 (11), 2129−2139. (12) Attwood, T.; Lydon, J.; Jones, F. The Chromonic Phases of Dyes. Liq. Cryst. 1986, 1 (6), 499−507.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b04188. Comparison of viscous and elastic forces depending on the pulling speeds using Ericksen number, POM images, molecular configurations depending on the Ericksen number, dichroism of the SSY film, AFM images, and GIXD patterns (PDF) Fabrication of SSY films at slow pulling speed(100 μm/ s), recorded under cross-polarizers with retardation plate (AVI) 18360
DOI: 10.1021/acsami.7b04188 ACS Appl. Mater. Interfaces 2017, 9, 18355−18361
Research Article
ACS Applied Materials & Interfaces (13) Lydon, J. Chromonic Liquid Crystal Phases. Curr. Opin. Colloid Interface Sci. 1998, 3 (5), 458−466. (14) Nakata, M.; Zanchetta, G.; Chapman, B. D.; Jones, C. D.; Cross, J. O.; Pindak, R.; Bellini, T.; Clark, N. A. End-to-end Stacking and Liquid Crystal Condensation of 6−to 20−Base Pair DNA Duplexes. Science 2007, 318 (5854), 1276−1279. (15) Nastishin, Y. A.; Liu, H.; Schneider, T.; Nazarenko, V.; Vasyuta, R.; Shiyanovskii, S.; Lavrentovich, O. Optical Characterization of the Nematic Lyotropic Chromonic Liquid Crystals: Light Absorption, Birefringence, and Scalar Order Parameter. Phys. Rev. E 2005, 72 (4), 041711. (16) Kim, J.; Novick, B. J.; DeSimone, J. M.; Carbonell, R. G. Ultrathin Film Deposition by Liquid CO2 Free Meniscus Coating Uniformity and Morphology. Langmuir 2006, 22 (2), 642−657. (17) Brinker, C. J. Dip Coating. In Chemical Solution Deposition of Functional Oxide Thin Films; Springer: 2013; pp 233−261. (18) Weinstein, S. J.; Ruschak, K. J. Coating Flows. Annu. Rev. Fluid Mech. 2004, 36, 29−53. (19) Gaskell, P. H.; Savage, M. D. Meniscus Roll Coating. In Liquid Film Coating; Springer: 1997; pp 573−597. (20) Schweizer, P. M.; Kistler, S. Liquid Film Coating: Scientific Principles and their Technological Implications; Springer Science & Business Media: 2012. (21) Diao, Y.; Shaw, L.; Bao, Z.; Mannsfeld, S. C. Morphology Control Strategies for Solution-processed Organic Semiconductor Thin Films. Energy Environ. Sci. 2014, 7 (7), 2145−2159. (22) Sergan, T.; Schneider, T.; Kelly, J.; Lavrentovich, O. Polarizingalignment Layers for Twisted Nematic Cells. Liq. Cryst. 2000, 27 (5), 567−572. (23) Cha, Y. J.; Gim, M.-J.; Oh, K.; Yoon, D. K. In-Plane Switching Mode for Liquid Crystal Displays Using a DNA Alignment Layer. ACS Appl. Mater. Interfaces 2015, 7 (24), 13627−13632. (24) Cha, Y. J.; Gim, M.-J.; Oh, K.; Yoon, D. K. Twisted-nematicmode Liquid Crystal Display with a DNA Alignment Layer. J. Inf. Disp. 2015, 16 (3), 129−135. (25) Yi, Y.; Clark, N. A. Orientation of Chromonic Liquid Crystals by Topographic Linear Channels: Multi-stable Alignment and Tactoid Structure. Liq. Cryst. 2013, 40 (12), 1736−1747. (26) Cha, Y. J.; Yoon, D. K. Control of Periodic Zigzag Structures of DNA by a Simple Shearing Method. Adv. Mater. 2017, 29 (3), 1604247. (27) Wu, Y. J.; Jeng, Y. S.; Yeh, P. C.; Hu, C. J.; Huang, W. M. In 20.2: Stereoscopic 3D Display Using Patterned Retarder, SID Symp. Dig. Tec.; Wiley Online Library: 2008; pp 260−263. (28) Trofimova, A.; Mahilny, U.; Stankevich, A.; Muravsky, A.; Murauski, A. In Paper No 16.2: New Process for Patterned Retarder Fabrication, SID Symp. Dig. Tec.; Wiley Online Library: 2013; pp 258− 261. (29) Zhu, X.; Ge, Z.; Wu, T. X.; Wu, S.-T. Transflective Liquid Crystal Displays. J. Disp. Technol. 2005, 1 (1), 15. (30) Honma, M.; Nose, T. Polarization-independent Liquid Crystal Grating Fabricated by Microrubbing Process. Jpn. J. Appl. Phys. 2003, 42 (11R), 6992. (31) Kapoustine, V.; Kazakevitch, A.; So, V.; Tam, R. Simple Method of Formation of Switchable Liquid Crystal Gratings by Introducing Periodic Photoalignment Pattern into Liquid Crystal Cell. Opt. Commun. 2006, 266 (1), 1−5. (32) Hu, W.; Srivastava, A.; Xu, F.; Sun, J.-T.; Lin, X.-W.; Cui, H.-Q.; Chigrinov, V.; Lu, Y.-Q. Liquid Crystal Gratings based on Alternate TN and PA Photoalignment. Opt. Express 2012, 20 (5), 5384−5391. (33) Hu, W.; Kumar Srivastava, A.; Lin, X.-W.; Liang, X.; Wu, Z.-J.; Sun, J.-T.; Zhu, G.; Chigrinov, V.; Lu, Y.-Q. Polarization Independent Liquid Crystal Gratings based on Orthogonal Photoalignments. Appl. Phys. Lett. 2012, 100 (11), 111116. (34) Ren, H.; Wu, S.-T. Liquid-crystal-based Linear Polarization Rotator. Appl. Phys. Lett. 2007, 90 (12), 121123. (35) Huang, C.-Y.; Tsai, H.-Y.; Wang, Y.-H.; Huang, C.-M.; Lo, K.Y.; Lee, C.-R. Linear Polarization Rotators based on Dye-doped Liquid Crystal Cells. Appl. Phys. Lett. 2010, 96 (19), 191103.
(36) Edwards, D.; Jones, J.; Lozman, O.; Ormerod, A.; Sintyureva, M.; Tiddy, G. Chromonic Liquid Crystal Formation by Edicol Sunset Yellow†. J. Phys. Chem. B 2008, 112 (46), 14628−14636. (37) Tone, C. M.; De Santo, M. P.; Buonomenna, M. G.; Golemme, G.; Ciuchi, F. Dynamical Homeotropic and Planar Alignments of Chromonic Liquid Crystals. Soft Matter 2012, 8 (32), 8478−8482. (38) Jeong, J.; Han, G.; Johnson, A. C.; Collings, P. J.; Lubensky, T. C.; Yodh, A. G. Homeotropic Alignment of Lyotropic Chromonic Liquid Crystals using Noncovalent Interactions. Langmuir 2014, 30 (10), 2914−2920. (39) Jeong, J.; Kang, L.; Davidson, Z. S.; Collings, P. J.; Lubensky, T. C.; Yodh, A. Chiral Structures from Achiral Liquid Crystals in Cylindrical Capillaries. Proc. Natl. Acad. Sci. U. S. A. 2015, 112 (15), E1837−E1844. (40) Nayani, K.; Chang, R.; Fu, J.; Ellis, P. W.; Fernandez-Nieves, A.; Park, J. O.; Srinivasarao, M. Spontaneous Emergence of Chirality in Achiral Lyotropic Chromonic Liquid Crystals Confined to Cylinders. Nat. Commun. 2015, 6, 8067. (41) Lydon, J. Chromonic Review. J. Mater. Chem. 2010, 20 (45), 10071−10099. (42) Lydon, J. Chromonic Liquid Crystalline Phases. Liq. Cryst. 2011, 38 (11−12), 1663−1681. (43) Zhou, S.; Nastishin, Y. A.; Omelchenko, M.; Tortora, L.; Nazarenko, V.; Boiko, O.; Ostapenko, T.; Hu, T.; Almasan, C.; Sprunt, S.; et al. Elasticity of Lyotropic Chromonic Liquid Crystals Probed by Director Reorientation in a Magnetic Field. Phys. Rev. Lett. 2012, 109 (3), 037801. (44) Smalyukh, I. I.; Zribi, O. V.; Butler, J. C.; Lavrentovich, O. D.; Wong, G. C. Structure and Dynamics of Liquid Crystalline Pattern Formation in Drying Droplets of DNA. Phys. Rev. Lett. 2006, 96 (17), 177801. (45) Lin, Y.; Balizan, E.; Lee, L. A.; Niu, Z.; Wang, Q. Self-Assembly of Rodlike Bio-nanoparticles in Capillary Tubes. Angew. Chem., Int. Ed. 2010, 49 (5), 868−872. (46) Chung, W.-J.; Oh, J.-W.; Kwak, K.; Lee, B. Y.; Meyer, J.; Wang, E.; Hexemer, A.; Lee, S.-W. Biomimetic Self-templating Supramolecular Structures. Nature 2011, 478 (7369), 364−368. (47) He, J.; Zhang, Q.; Gupta, S.; Emrick, T.; Russell, T. P.; Thiyagarajan, P. Drying droplets: A Window into the Behavior of Nanorods at Interfaces. Small 2007, 3 (7), 1214−1217. (48) Tortora, L.; Lavrentovich, O. D. Chiral Symmetry Breaking by Spatial Confinement in Tactoidal Droplets of Lyotropic Chromonic Liquid Crystals. Proc. Natl. Acad. Sci. U. S. A. 2011, 108 (13), 5163− 5168. (49) Rahnama, M.; Koch, D. L.; Iso, Y.; Cohen, C. Hydrodynamic, Translational Diffusion in Fiber Suspensions Subject to Simple Shear Flow. Phys. Fluids A 1993, 5 (4), 849−862. (50) Agra-Kooijman, D. M.; Singh, G.; Lorenz, A.; Collings, P. J.; Kitzerow, H.-S.; Kumar, S. Columnar Molecular Aggregation in the Aqueous Solutions of Disodium Cromoglycate. Phys. Rev. E 2014, 89 (6), 062504. (51) Lavrentovich, O. Geometrical Anchoring at an Inclined Surface of a Liquid Crystal. Phys. Rev. A: At., Mol., Opt. Phys. 1992, 46 (2), R722. (52) Kim, J.; Kim, D. W.; Yu, C. J.; Lee, S. D. A New Transflective Geometry of Low Twisted Nematic Liquid Crystal Display Having a Single Cell Gap. J. Inf. Disp. 2004, 5 (3), 14−17. (53) Choi, B.; Song, S.; Jeong, S. M.; Chung, S.-H.; Glushchenko, A. Electrically Tunable Birefringence of a Polymer Composite with Longrange Orientational Ordering of Liquid Crystals. Opt. Express 2014, 22 (15), 18027−18035. (54) Al-Lawati, Z. H.; Alkhairalla, B.; Bramble, J. P.; Henderson, J. R.; Bushby, R. J.; Evans, S. D. Alignment of Discotic Lyotropic Liquid Crystals at Hydrophobic and Hydrophilic Self-assembled Monolayers. J. Phys. Chem. C 2012, 116 (23), 12627−12635.
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DOI: 10.1021/acsami.7b04188 ACS Appl. Mater. Interfaces 2017, 9, 18355−18361
