Three-Dimensional-Moldable Nanofiber-Reinforced Transparent

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3D-Moldable Nanofiber-Reinforced Transparent Composites with Hierarchically Self-Assembled “Reverse” Nacre-Like Architecture Subir Kumar Biswas, Hironari Sano, Md. Iftekhar Shams, and Hiroyuki Yano ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b09390 • Publication Date (Web): 16 Aug 2017 Downloaded from http://pubs.acs.org on August 17, 2017

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ACS Applied Materials & Interfaces

3D-Moldable Nanofiber-Reinforced Transparent Composites with Hierarchically Self-Assembled “Reverse” Nacre-Like Architecture Subir K. Biswas,† Hironari Sano,† Md. Iftekhar Shams,§ and Hiroyuki Yano*,† †

Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto 611-

0011, Japan §

Forestry and Wood Technology Discipline, Khulna University, Khulna 9208, Bangladesh

KEYWORDS: Pickering emulsion, brick-and-mortar, flexible optoelectronics, contact lens, microlens array, thermal expansion

ACS Paragon Plus Environment

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ABSTRACT: Achieving structural hierarchy and a uniform nanofiller dispersion simultaneously remains highly challenging for obtaining a robust polymer nanocomposite of immiscible components. In this study, a remarkably facile Pickering emulsification approach is developed to fabricate hierarchical composites of immiscible acrylic polymer and native cellulose nanofibers by taking advantage of the dual role of the nanofibers as both the emulsion stabilizer and polymer reinforcement. The composites feature a unique “reverse” nacre-like microstructure reinforced with well-dispersed two-tier hierarchical nanofiber network, leading to a synergistic high strength, modulus, and toughness (20, 50, and 53 times that of neat polymer, respectively), high optical transparency (89%), high flexibility and a drastically low thermal expansion (13 ppm K-1, 1/15th of the neat polymer). The nanocomposites have a 3D-shape moldability, also their surface can be patterned with micro/nanoscale features with high fidelity by in situ compression molding, making them attractive as the substrate for flexible displays, smart contact lens devices, and photovoltaics. The Pickering emulsification approach should be broadly applicable for the fabrication of novel functional materials of various immiscible components.


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INTRODUCTION Hierarchical structural design of materials provides an opportunity for synergistic tailoring of the materials properties.1 Nature exploits this concept very effectively to create nanocomposite materials with superior functionalities composed of inferior components.1−5 For example, nacre, the mollusks shell, is composed of hard but brittle reinforcing aragonite platelets as the major component (95%) surrounded a soft biopolymer matrix as the minor component (5%).3−6 Despite this composition, it displays an anomalous combination of incredible strength and toughness thanks to its highly synergistic load-bearing, stress-dissipating, and crack-deflecting mechanism effected by the hierarchical “brick-and-mortar” structure.3−8 Mimicking of the nacre-structure has proven to be an elegant strategy for synthesizing (nano)composites with an otherwise inaccessible combination of mechanical properties—high strength and toughness.3−5,9−12 Recently, strong cellulose nanofibers (CNFs) with a diameter of approximately 5–60 nm extracted in high abundance from renewable materials such as wood have gained much attention as polymer reinforcements.13 They have excellent material properties: elastic modulus (E) ~140 GPa14,15 and thermal expansion coefficient (CTE) ~0.1 ppm K-1,16 and strong but flexible network-forming ability through hydrogen (H)-bonding, which promotes the mechanical performance of the composites.17,18 Their diameter is perfect for avoiding light scattering.19 However, the poor dispersion of hydrophilic CNFs (owing to surface –OH groups; also typically extracted in water) in a hydrophobic polymer matrix (most polymers are hydrophobic) is a significant barrier; a uniform nanofiller dispersion is a prerequisite for obtaining a robust nanocomposite.20 As a solution, an entangled CNF network, nanopaper21−23 or organogel,24 has been prepared first, followed by impregnation with a curable polymer to replace the air or liquid. The network significantly improved the mechanical and thermal expansion properties of the


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polymer while preserved flexibility.21−24 Refractive index-matched transparent polymers can be used to produce transparent composites, allowing them to serve as a flexible high-performance substrate for optoelectronics.21−23 However, CNF networks contain strong H-bonds (which are also recoverable when unloaded from deformation) that almost lock the fibrils in position,25−27 which substantially increases the stiffness of the network. Therefore, such a network greatly limits the ductility, and hence toughness and three-dimensionally (3D)-shaped moldability of the corresponding composite (hereinafter “impregnated composite”). In the search for an elegant strategy that would eliminate dispersion, ductility and toughness barriers but would still enable the use of a strong and flexible CNF network, we investigated the use of a Pickering emulsion, which is a particle-stabilized colloidal system of immiscible liquids.28 Recently, short CNFs/cellulose nanocrystals have been successfully utilized as the stabilizer of oil-in-water Pickering emulsions, in which the nanofiber/nanocrystal network can encapsulate oil droplets (for protection from coalescence) to produce liquid-core capsules.29,30 Meanwhile, Shams and Yano developed nanocomposites by Pickering emulsifying a polymer in a chitin nanofiber-network.31 Here, we report the encapsulation of UV-polymerizable resin monomer droplets in a two-tier hierarchical network of long (high-aspect ratio) CNFs via a simple Pickering emulsification pathway to fabricate optically transparent polymer nanocomposites. The nanocomposites uniquely feature what may be called a “reverse” nacre-like microstructure where the weak polymer platelets (~84 wt%) are surrounded and interconnected by the hierarchical network of strong CNFs (~16 wt%), and combine a synergistic high strength and toughness that remarkably surpass the neat polymer. The encapsulated resin monomer droplets reduced the extent of H-bonding in the CNF network that enabled us to fabricate


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nanocomposites with 3D complex shapes (e.g., a lens). Furthermore, the surface of the nanocomposites can be patterned with nano/microscale features simply by compression molding. We chose soft type acrylic resin (2.2 bis[4-(acryloxypolyethoxy]phenyl]propane) as the matrix for high flexibility, however, soft polymers generally have extremely large thermal expansion, often exceeding 200 ppm K-1. Our CNF-reinforced transparent nanocomposites possess a glasslike thermal expansion (13 ppm K-1, 1/15th of the neat polymer) and a good flexibility, which are highly desirable substrate properties for the flexible (opto)electronic devices.

RESULTS AND DISCUSSION Figure 1a depicts the fabrication process of the hierarchical polymer nanocomposite with a selfassembled “reverse” nacre-like microstructure from the CNF-stabilized resin-in-water Pickering emulsion. The Pickering emulsion was prepared first by adding a UV-polymerizable acrylic resin monomer in a CNF/water suspension followed by vigorous blending (Figure 1b). We prepared three types of emulsion, i.e., PE1, PE2, and PE3, all containing the same amount of CNF and resin monomer but decreasing water content from PE1 to PE3 (see formulations in Table S1). This resulted in dilute (PE1) and more viscous (PE3) emulsions. The emulsions contained a high number of round resin droplets with an increasing average diameter (1.87, 1.97, and 2.21 µm) and polydispersity from PE1 to PE3 (Figures 1c and S1). The FE-SEM images revealed that the individual droplets were covered by the CNF network, providing protection from coalescence (Figures 1d and S2). It has been proposed that the CNFs/nanocrystals have amphiphilic properties and can adsorb irreversibly at the oil/water interface to give stable Pickering emulsion.32 In this study, we used CNFs with a high-aspect ratio: length >2000 nm and diameter


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~23 nm (Figure S3). Apart from stabilization, the long CNFs produced an interconnecting network of droplets that allowed us to dehydrate the emulsions by vacuum filtration with no apparent resin loss, leaving behind wet CNF/resin nanocomposite mats on the filter membrane. After oven-drying at 40 °C for 3 h, self-standing nanocomposite mats containing liquid resin droplets were obtained (see Figure 1e for the PE3 mat and Figure S4 for the PE1 and PE2 mat). Here, we discovered that the microstructure of the mat corresponded to a “reverse” nacre-like architecture, in which the elliptical resin droplets (deformed during vacuum-filtration) gave rise to a platelet-like structure of the soft resin (E = 0.03 GPa) and their surrounding protective network of CNFs (E ≈ 140 GPa; ~10 wt%) formed the hard moiety (Figures 1f and g). As such, the CNF-network features a unique self-assembled two-tier hierarchy, one being the submicrometer-thick network around the droplets and another being the interconnecting bulk network throughout the mat. The CNF/resin mats were opaque even after UV polymerization and a high proportion of transparent resin (~90 wt%). The magnified image of the fracture surface of the PE3 mat indicated that the opaqueness was owing to the uncompact interfaces among the CNF-covered droplets (Figures 1f and g). The non-polymerized CNF/resin mat was sandwiched between glass slides and hot-pressed at 150 °C and 5 MPa followed by UV polymerization. Eventually, a highly transparent nanocomposite with a much more compact structure was obtained (Figures 1h and i and Figure 2a). The regular and total transmittances of the nanocomposites were 82%–84% and 89% at 600 nm, respectively (Figures 3a and S5). For comparison, impregnated composites with the same resin and a CNF content of ~20 wt% were also prepared.21,22 The CNF content of our transparent nanocomposites was increased to ~16 wt% because ~7 wt% of resin was squeezed out during hot-pressing. The optical transparency was similar to or even higher than the


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impregnated composites prepared in this study and in the literature.23 The addition of CNFs reduced the regular transmittance of the resin by only 7%–9%, whereas the reduction in total transmittance was only 3%. A gradual attenuation of the regular transmittance from PE3 to PE1 nanocomposite can be observed in Figure 3a. For example, the PE3 nanocomposite transmitted 84% light (at 600 nm) compared with 82% for PE1. This might be because the PE1 emulsion contained relatively uniform and smaller resin droplets, which led to a higher number of CNF/resin interfaces and thus higher light scattering even at a similar CNF content. The CNF/resin mat was opaque, with only 14% (600 nm) regular transmittance (Figures 1e and 3a), but with a total transmittance of 85% (600 nm) (Figure S5). This large amount of light scattering was eliminated by: 1) the hot-pressing, which made the CNF/resin interfaces more compact (Figures 1i and 2a); and 2) the better flowability of the resin monomer at the hot-pressing temperature, which penetrated into the CNF-network and formed a continuous matrix and resulted in a uniform dispersion of the CNFs throughout the bulk of the nanocomposite.33 The hot-pressing also flattened the elliptical resin droplets, mimicking platelets of natural nacre but made up of soft resin (Figures 1j, 2 and S6; also see the schematic in Figure 1a). The platelets were surrounded and interconnected by the hierarchical CNF-network as shown in the TEM images in Figures 1j and S6. Figure 3b and Table S2 highlight the extraordinary mechanical properties of our “reverse” nacrelike nanocomposites compared with the impregnated composite and neat acrylic resin film. Specifically, the strengths of the nanocomposites made from PE1, PE2, and PE3 were 40.14 MPa, 35.69 MPa, and 34.61 MPa, respectively. In contrast, the strength of the impregnated composite was 28.35 MPa, even at a ~4 wt% higher CNF content. A large strain-to-failure— 12.49% for PE1, 13.23% for PE2, and 13.35% for PE3 compared with only 2.06% for the


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impregnated composites—indicated that our nanocomposites are flexible, and combined with their high strength significantly increased their toughness. The toughness was approximately 9 times higher than that of the impregnated composites. The elastic modulus of the present nanocomposites (1.50 GPa, 1.28 GPa, and 1.19 GPa for PE1, PE2, and PE3, respectively) was lower than the impregnated composites (2.85 GPa). In an impregnated composite, the CNF nanopaper is laid intact and sandwiched between two thick resin layers (Figure S7); this implies that the highly H-bonded stiff CNF network mainly governs the mechanical properties of the corresponding impregnated composites.21,24 It is likely that the inclusion of the resin platelets in the hierarchical CNF network of the present nanocomposites may reduce H-bonding and lower the stiffness, but clearly, a synergistic strengthening and toughening mechanism is present. In natural nacre, the “brick-and-mortar” arrangement of hard and soft materials synergistically bears the load, dissipates stress across the interfaces through mutual sliding, and impedes crack propagation through crack deflection and crack bridging.3−8 In our “reverse” nacre-like nanocomposites, the two-tier hierarchical CNF-network carries the load, and stress dissipation can occur at the interfaces of the CNF network/resin platelets through mutual sliding and also in the CNF network itself where the soft resin penetrated during hot-pressing. We also observed the occurrence of crack bridging by CNFs and crack deflection by microcrack formation which are known mechanisms of extrinsic toughening (Figure 4). Furthermore, the mechanical properties of our nanocomposite can be tuned easily by varying the droplet size of the resin simply by adjusting the water content in the emulsion. For example, diluted PE1 emulsion, having relatively uniform and tiny resin droplets, produced stronger, tougher and stiffer nanocomposite compared to PE2 and PE3 (Figure 3b and Table S2). This is


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because more uniform and smaller resin platelets in the nanocomposite resulted in much more homogeneous CNF/resin interfaces, thereby an effective transfer of the stress across interfaces. The fabrication of (opto)electronic devices often includes high-temperature processing steps. Therefore, brittle glass substrates are still preferred because of their low thermal expansion, CTE 7–10 ppm K-1.34 The thermal expansion of the present nanocomposites was extremely low, CTE ~13 ppm K-1, which is comparable to glass (Figure 3c and Table S3). The inclusion of CNFs drastically reduced (~15 times) the thermal expansion of the soft acrylic resin. However, the impregnated composite had a lower CTE of 9.9 ppm K-1, which was owing to the intact sandwiched CNF-nanopaper with a CTE of 8.3 ppm K-1 (literature value 8.5 ppm K-1),35 as well as the ~4 wt% higher CNF content. We also measured the CTE of a transparent and thermally stable polyethylene terephthalate film (PET; Lumirror, Toray, Japan) that is being used in the optoelectronics industry. The CTE was much higher than that of our nanocomposites, 38 ppm K1

, which suggests that our high-performance transparent nanocomposite has strong potential to be

used as a substrate material for flexible electronics. Considering the performances of the nanocomposites derived from the “reverse” nacre-like structure, if they could be 3D molded with good precision they could be used in applications such as the substrate for contact lens sensors and curved displays. Recently unveiled smart contact lenses equipped with microelectronic devices can monitor the blood glucose level or capture an image with a blink of the eye.36,37 We placed the non-polymerized mat into a lensshaped molding die and hot-pressed it at 150 °C and 5 MPa followed by UV polymerization (Figure 5a). A perfectly molded lens-like transparent nanocomposite was obtained (Figures 5b and c). This was possible due to the presence of liquid resin droplets in the mat, which also reduced the extent of H-bonding in the bulk CNF network and enabled us to 3D mold the mat


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with good precision. We also attempted to mold an impregnated composite using a hot-press but this inevitably failed (Figure S8). The impregnated composite did not form a perfect lens-like shape and developed many cracks. Evidently, such a 3D molded transparent material with high mechanical performance, low CTE and flexibility could not be obtained by the impregnation method because the strong recoverable H-bonds25−27 make the CNF-nanopaper substantially less deformable. Furthermore, the surface of the present nanocomposites can be patterned with desirable micro/nanoscale features simply by direct compression-molding (150 °C, 5 MPa) of the CNF/resin mat using an oppositely patterned substrate. As evidence, we fabricated a concave microlens array with high fidelity (Figure 5d). The patterned nanocomposites had a rainbow color and light scattering owing to diffraction (Figures 5e and f). Surface-patterned polymeric films have numerous high-tech application in areas such as semiconductor microelectronics, optoelectronics, and as anti-reflection, light-scattering, and light-trapping coatings or substrates for high-performance photovoltaics.38−40 Owing to the high mechanical performance, a CTE similar to that of glass, high flexibility, and ease of fabrication, our polymer nanocomposites are suitable candidates for these applications. Their surface can be patterned in a scalable way, e.g., using a roll-to-roll process; also, multitier pattering is easily possible.

CONCLUSIONS In conclusion, we have developed a simple water-based Pickering emulsification pathway to fabricate hierarchical nanocomposites of immiscible polymer and well-dispersed reinforcing cellulose nanofibers. The nanocomposites featured a unique “reverse” nacre-like microstructure


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made up of soft polymer platelets (84 wt%) surrounded by a strong hierarchical network of nanofibers (16 wt%). The microstructure was self-assembled during vacuum-filtration (dewatering) of the nanofiber-stabilized resin-in-water Pickering emulsion. The microstructure synergistically led to a desirable combination of high strength (40.14 MPa) and toughness (3.69 MJ m-3), which are 20 and 53 times higher than that of neat polymer, respectively. The nanocomposites also possessed a high optical transparency (89%), a high flexibility, and a CTE similar to that of glass (~13 ppm K-1, 1/15th of the neat polymer) owing to the well-dispersed cellulose nanofibers. Moreover, the liquid resin droplets in the vacuum-filtered Pickering emulsion mat minimized the H-bonding in the nanofiber-network, which allowed the otherwise inaccessible molding of the nanocomposite into 3D complex shape. The surface of the nanocomposite could be patterned with micro/nanoscale features with high resolution and fidelity by direct compression-molding. The high mechanical, thermal, and optical performances together with the easy fabrication process indicate that our nanocomposites are suitable candidates as the substrate for high-performance flexible/wearable (opto)electronic devices including displays, smart contact lens sensors, and photovoltaics. The facile Pickering emulsification approach should be easily applicable to a vast range of immiscible polymers and nanoreinforcements for unlocking new class of functional hierarchical composite materials.

MATERIALS AND METHODS Materials. Wood powder of Japanese Cypress sieved through 60 mesh was used as raw material for CNF preparation. UV-curable acrylic resin monomer (2.2 bis[4(acryloxypolyethoxy)phenyl]propane (ABPE-10) refractive index 1.516, Shin-Nakamura


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Chemical, Japan) was used. Photoinitiator 2-hydroxy-2-methylpropiophenone (Wako, Japan) was added (0.25% w/w) to the monomer before use. Preparation of CNFs. CNFs were prepared by grinding (MKCA6-2, Masuko Sangyo, Japan) extractive- and matrix-removed (hemicelluloses and lignin) wood powder suspended in water following the process reported by Abe et al.41 CNFs were obtained in a native state with a length of >2000 nm and a diameter of ~23 nm (Figure S3). Preparation of Resin-in-Water Pickering Emulsions. CNF-stabilized emulsions with three different formulations, PE1, PE2, and PE3, were prepared. The formulations are provided in Table S1. The resin monomer was poured in a CNF/water suspension followed by an initial blending (Vita-Mix Absolute 3, Osaka Chemical, Japan) at 5,000 rpm for 2 min to disperse the resin as much as possible. The speed of the blender was then adjusted to 37,000 rpm and blended for 15 min with a 5-min interval after 7.5 min. The emulsions were stored in the dark to prevent any undesirable polymerization of the liquid resin droplets. Fabrication of Nanocomposites. Emulsions were vacuum-filtered to obtain a CNF/resin mat on a PTFE filter membrane (0.1-µm pore, Advantec, Japan). To keep the CNF content the same, a desired amount of the emulsion was filtered for approximately 8 h (PE1), 5 h (PE2), and 3 h (PE3). The mats were then oven-dried at 40 °C for 3 h to remove residual water. The mats were hot-pressed (150 °C, 5 MPa, 10 min) by either placing them between glass slides or a stainlesssteel die (Figure S8) to fabricate flat or 3D curved composites. For surface micropatterned composites, the mat was placed in between a patterned sapphire substrate (SAMCO, Japan) and a glass slide followed by hot-pressing under the same condition. The materials were UV polymerized immediately after hot-pressing (F300S UV lamp/LC6 conveyer, 20 J cm-2, Fusion UV Systems, USA). Impregnated composites were prepared by immersing CNF nanopaper into


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an acrylic resin monomer under a reduced pressure (–0.1 MPa) for 6 h followed by UV polymerization. Characterizations. FE-SEM imaging was performed using a JSM-6700F or a JSM-7800F Prime (JEOL, USA) after platinum coating. TEM observation was carried out using a JEM-1400 Plus (JEOL, USA) after embedding the ultrathin composite samples in epoxy resin followed by staining with solid osmium tetroxide (OsO4). Total and regular transmittances were measured using a UV-Vis spectrophotometer U-4100 (Hitachi, Japan) by placing the samples at and 25 cm apart from the entrance port of the integrating sphere, respectively. Thermal expansion properties were obtained using a thermomechanical analyzer TMA/SS 6100 (Seiko Instruments, Japan) in tensile mode with a 20-mm span and a ramp of 5 °C min-1 under a N2 atmosphere. The tensile test was carried out using an Instron 3365 universal testing machine (Instron, USA) with a span length of 20 mm, at a crosshead speed of 1 mm min-1. Stress–strain data were recorded for five rectangular nanocomposite specimens (5 mm × 35 mm). The resin droplet diameter was directly analyzed from the FE-SEM images of the UV-cured and oven-dried emulsions using ImageJ software.


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Figure 1.


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Figure 1. From Pickering emulsion to a unique “reverse” nacre-like transparent polymer nanocomposite. (a) Schematic depiction of the fabrication of CNF-reinforced polymer nanocomposite with “reverse” nacre-like microstructure. The change in color from green to blue in the nanocomposite is intended to indicate the penetration of the resin in the CNF-network during hot-pressing. (b) A resin-in-water Pickering emulsion prepared by vigorously blending a CNF/water/liquid-resin-monomer mixture. (c) A digital microscopic image of an emulsion taken immediately after preparation showing its numerous polydispersed but round droplets of resin. (d) A FE-SEM image of a UV polymerized and dehydrated emulsion showing a resin droplet encapsulated by the CNF-network. (e) A self-standing, opaque CNF/resin nanocomposite mat containing liquid resin droplets. (f,g) FE-SEM images of the fracture surface (cross-section) of the mat (UV polymerized) with different magnifications showing the self-assembled “reverse” nacre-like architecture. (h) A highly transparent polymer nanocomposite reinforced with CNFs obtained by hot-pressing the mat. (i) A FE-SEM image of the fracture surface (cross-section) of a transparent nanocomposite showing a compact layered structure. (j) A TEM image of the crosssection of a transparent nanocomposite revealing the “reverse” nacre-like microstructure composed of soft resin platelets (indicated by arrows) surrounded by the hierarchical CNF network. Figures b–j correspond to Pickering emulsion PE3 and its corresponding mat and transparent nanocomposite.


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Figure 2.


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Figure 2. FE-SEM image of the fracture surface of a “reverse” nacre-like nanocomposite (a) and natural nacre (b). The microstructure of the nanocomposite (PE3) shows an architecture that mimics that of natural nacre but contains soft resin platelets (indicated by arrows).


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Figure 3.

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100 10 Present nanocomposite (PE1) Present nanocomposite (PE2) Present nanocomposite (PE3) Impreg. composite CNF nanopaper PET Neat resin

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Figure 3. Material properties of the “reverse” nacre-like nanocomposites. (a) Regular light transmittances of the present nanocomposites, CNF/resin mat (UV polymerized), impregnated composite, and neat acrylic resin film. The present nanocomposites were ~150–180 µm thick and the impregnated composites were ~120–140 µm thick. The transmittances were normalized to


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100-µm thickness of the materials to eliminate the effect of thickness variation. (b) Tensile stress–strain curves of the CNF-reinforced nanocomposites and neat resin film. Compared with the impregnated composite and neat resin film, the present nanocomposites have an extraordinary strength, toughness, and ductility thanks to their synergistic “reverse” brick-andmortar architecture. (c) Thermal expansion curves of nanocomposites, CNF nanopaper, commercial PET film, and neat resin film. The CTE value of each material is derived from the corresponding thermal expansion curve in the range between 20 °C and 150 °C (Table S3).

Figure 4.


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Figure 4. FE-SEM images of the fracture surface of the “reverse” nacre-like nanocomposite after the tensile test. a) Top view of the fracture surface showing protruded CNFs which provided


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crack bridging. b) Side view of the fracture surface showing crack deflection by microcrack formation. c) Zoomed-in image showing CNF bridging inside the microcrack.

Figure 5.


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Figure 5. Fabrication of 3D-macro/micromolded transparent nanocomposites. (a) Schematic depiction of the steps involved in the fabrication of a lens-like nanocomposite from the nonpolymerized CNF/resin mat. (b,c) Photographic images of the big-size (b) and contact-lens-size (c) 3D-molded nanocomposites indicating that they were optically transparent and flexible. (d) FE-SEM images of the surface micropatterned nanocomposites (top view, top; slanting view, bottom) with concave microlens array with high fidelity. The patterned nanocomposite was produced by the same steps as in (a) but by sandwiching a CNF/resin mat in between an oppositely patterned sapphire substrate and glass slide instead of molding die. (e,f) The patterned nanocomposites show a diffraction-induced rainbow color and light scattering. The arrow in (f) indicates the LASER light incidence point.


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ASSOCIATED CONTENT Supporting Information

Figures S1−S8 and Tables S1−S3: Emulsion droplet diameter, FE-SEM image of CNF encapsulated droplets, FE-SEM image of CNFs, photographic images of nanocomposite mats, total light transmittances, cross-sectional TEM image of nanocomposites, FE-SEM image of the fracture surface of an impregnated composite, an attempt at molding an impregnated composite, formulation of emulsions, comparison tables of mechanical and thermal expansion properties (PDF)

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected].

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

The authors thank SAMCO Inc., Japan for providing patterned sapphire substrate. S.K.B gratefully acknowledges the financial support from the Ministry of Education, Culture, Sports, Science and Technology, Japan (Monbukagakusho).


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Graphical ToC


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Three-Dimensional-Moldable Nanofiber-Reinforced Transparent

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