Article pubs.acs.org/crystal
Synthesis of Monodisperse Single Crystalline Ag Microcubes via Seed-Mediated Growth Seog-Jin Jeon,§ Sadegh Yazdi, Ramathasan Thevamaran, and Edwin L. Thomas* Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, United States S Supporting Information *
ABSTRACT: A multitude of complex-shaped nano- and microparticles have been synthesized due to their interesting size- and shape-dependent properties. However, a number of applications require reliable methods for making nonspherical particles from the nanoscale up to the microscale. Shape control of metal nanoparticles has been studied extensively by utilizing their preferred growth normal to low-surface-energy planes, but their size is typically limited to less than a few hundred nanometers. Here, we report a method to control the size of cubic Ag single crystals in a broad range from 100 nm to 2 μm while maintaining flat faces and sharp edges and vertices. To our knowledge, this is the first report on synthesis of monodisperse nonspherical single crystals from the nano- to micrometer scale, which enables an exploration of size- and shapedependent behaviors of materials.
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typically over 10 μm due to the resolution limit of photolithography. Another synthetic approach is seed-mediated growth with shape-controlled nanoparticles as seeds. There have been many of studies concerning shape control of metal nanoparticles utilizing their controlled crystal growth direction by wet chemical synthesis.13,14 For example, polyvinylpyrrolidone (PVP) which selectively adsorbs onto the {100} planes of Ag enables the directional growth along the directions, resulting in nanocubes.23−25 For the control of particle size, there are relatively few reports, and the maximum particle size achieved thus far is ∼200 nm. For example, Zhang et al. reported seed-mediated growth of Ag nanocubes with the maximum size of grown particles approximately 200 nm.26 Pietrobon et al. reported seed growth of Ag nanodecahedrons up to 120 nm.27 There have been reports on nanowires and nanorods which have micrometer scale length utilizing seed growth, but the other two dimensions, width and thickness, remain at the nanoscale.28,29 Precipitation approaches,30−32 sol−gel,33 surfactant-assisted synthesis,34 and supersaturation strategy35 have also been attempted for the synthesis of nonspherical particles, but the precise and broad range of control of targeted particle size is not easily achieved. Thus, monodisperse nonspherical particles between 200 nm and 10 μm are not easily fabricated by current state-of-the-art synthesis techniques. Here, we report a seed growth method which can grow cubic Ag single nanocrystals up to 2 μm in edge length while
INTRODUCTION
For decades, precise control of particle size has enabled various useful applications in photonics,1−3 energy,4,5 biomedical,6,7 and mechanical composites research fields.8−10 Typically, monodispersed silica and polystyrene spheres with a broad range of well-defined sizes from the nano- to microscale have been used as model systems, serving as building blocks and templates for many applications.11,12 On the other hand, studies on nonspherical particles are mostly biased to the particular application, for example, surface plasmonics of metal nanoparticles of size less than 200 nm.13,14 Recently some new studies have been conducted on other applications of nonspherical particles. For example, the well-ordered structure of uniform dumbbell particles shows omnidirectional photonic bandgaps15 and exhibits combined optical properties of photonic bandgaps and birefringence.16 A three dimensionally interconnected hollow rod structure has been fabricated for particular applications which need anisotropic transport, electric, or optical properties,17 and a hollow cubic structure exhibited superior properties to its hollow spherical counterpart in use as drug delivery capsules18 because the cubic geometry acts as a self-reinforcing mechanical frame. One way to control particle size and shape is to use a topdown approach such as template or microfluidic approaches.19 For example, Choi et al. fabricated nonspherical particles by controlled wetting of the polymer fluid in a polydimethylsiloxane (PDMS) mold,20 and Dendukuri et al. fabricated particles with various shapes by exposing nonmetallic precursors to UV light through masks while flowing inside microfluidic devices.21,22 However, features of such particles are essentially two-dimensional, and the minimum size of the particles is © 2016 American Chemical Society
Received: October 17, 2016 Revised: December 4, 2016 Published: December 12, 2016 284
DOI: 10.1021/acs.cgd.6b01523 Cryst. Growth Des. 2017, 17, 284−289
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Figure 1. (a) SEM images of the initial 100 nm Ag seed nanocubes and (b−d) 400, 450, and 550 nm cubes prepared by first seed growth for various different seed concentrations of 48, 24, and 12 μL/mL. (e−f) 1.2 and 2.0 μm cubes made by second seed growth. For 2.0 μm cubes, one-half the concentration of seed solution and a two times higher concentration of the silver precursor were used compared to that for the 1.2 μm cubes. color. Growth occurs over another 35 min to result in nanocubes with 106 nm edge length. The product is quenched in a water bath at room temperature for minimum 20 min. It is washed with acetone once and with water several times to remove EG and PVP. The final product is dispersed in 1 mL of EG for seed growth. First Seed Growth. Three milliters of EG is preheated at 160 °C for 10 min under Ar introduction, and 60 μL of 600 mM HCl solution in EG is added into the vial. A glass pipet was used to introduce a continuous flow of Ar gas above the reaction solution. After 2 min, 1 mL of 0.8 M AgNO3 in EG was injected dropwise into the vial. After another 2 min, 1 mL of 0.4 M PVP solution in EG is added dropwise. Seed particles were injected 3 min after the PVP injection. Addition of 240, 120, and 60 μL of seed solution resulted in 399, 449, and 546 nm edge length of cubes, respectively. For a closed system, we initially introduced continuous flow of Ar gas (500 SCM) during the 10 min of preheating, and then the reaction vial was closed with a cap which includes a tube with a valve for the addition of reagents. The other experimental conditions were the same with the open system with continuous flow of Ar gas throughout the reaction. The pH of the liquid drops on the reactor inner wall was measured using pH paper (Fisher). The reaction vial was quenched in a water bath at room temperature 35 min after the seed injection. The product is washed with acetone once and with water several times and filtered to remove the small portion of wires (∼5%). The final product was dispersed in 1 mL of EG for further seed growth. Second Seed Growth. For the synthesis of 1.2 μm cubes, 3 mL of EG was preheated 10 min under Ar introduction, and 90 μL (120 μL for 2.0 μm cubes) of 600 mM HCl solution in EG was added into the vial. After 2 min, 1 mL of 0.8 M (1.6 M for 2.0 μm cubes) AgNO3 in EG was injected dropwise into the vial for 20 s. After another 2 min, 1 mL of 0.4 M (0.8 M for 2.0 μm cubes) PVP solution in EG was added dropwise for 20 s. Seed particles with edge length of 449 nm obtained in the first seed growth were injected 3 min after the PVP injection. Addition of 250 μL and 125 μL of first seed grown particles resulted in 1.2 and 2.0 μm edge length of cubes, respectively. The reaction vial was quenched in a water bath at room temperature 35 min after the seed injection. The product was washed with acetone once and with water several times and filtered to remove the small portion of wires. Characterization of Nanocubes and Nanowires. To determine the average size of nanocubes and the number of nanocubes and nanowires, at least 500 particles were analyzed by imaging software (Image-Pro) from scanning electron microscopy (SEM) images. On the basis of this data, the standard deviation σ in size of nanocubes and fA/C was calculated.
precisely maintaining the original shape. We chose Ag cubes as a target material because we can easily obtain seed nanoparticles of Ag with various shapes and well-controlled size due to well-developed synthesis methods.13,14 This work opens up new possibilities for further study on the development of microparticles with various shapes and internal crystal structures for studying the size and shape effects on the mechanical properties of metals. For example, single crystals are unique model systems for studies concerning mechanical deformation as the changes in crystal structure can directly be correlated to the deformation characteristics. The simple and cost-effective synthesis technique is useful to prepare large quantity of specimens for such studies. The well-defined size, shape, and defect-free nature of the single crystal at the micron scale is particularly useful for interpretation of strain rate36 and size effects37 on mechanical properties. For example, an Ag microcube can be launched at supersonic velocities due to its appropriate size that allows imaging to determine its velocity and momentum, and its initial single crystalline nature that enables clear interpretation of the modes and mechanisms of deformation due to the high velocity impact.36
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EXPERIMENTAL SECTION
Materials. Ethylene glycol (EG, Cl < 5 ppm and Fe < 0.2 ppm, Macron Fine Chemicals), hydrochloric acid (HCl, 37%, ACS reagent, Aldrich), silver nitrate (AgNO3, ≥ 99.0%, ACS reagent Aldrich), polyvinylpyrrolidone (PVP, Mw = 55 000 g/mol, Aldrich), and polyvinylpyrrolidone (PVP, Mw = 1 300 000 g/mol, Aldrich) were used as received. A 22 mL vial and Teflon coated spin bar (15.9 mm × 6.4 mm) were purchased from VWR international. Ultra high purity grade oxygen and argon gas were purchased from Matheson. Synthesis of Seed Nanocubes. We followed our previous procedure of nanocube synthesis in a controlled atmosphere. Details are provided in ref 25. Typically, 1 mL of EG is preheated at 140 °C for 10 min with stirring (∼900 rpm) in 22 mL vial, and 50 μL of 60 mM HCl solution in EG is added into the vial. We used fresh HCl solution prepared within 10 h for reproducibility. After 2 min, 1 mL of 0.2 M AgNO3 in EG is injected dropwise into the vial for 20 s. After another 3 min, 1 mL of 0.12 M PVP solution in EG is added dropwise for 20 s. Four hours after the addition of PVP solution, the vial is capped. Then, seeding starts in an hour with the change to a yellow 285
DOI: 10.1021/acs.cgd.6b01523 Cryst. Growth Des. 2017, 17, 284−289
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Instrumentation. The SEM images were taken using a fieldemission scanning electron microscope (FEI Quanta 400) operated at an accelerating voltage of 10−20 keV. A focused ion beam (FIB) cross-section of a seed-grown cube was prepared in an FEI Helios NanoLab 660 DualBeam system equipped with a micromanipulator. To protect the sample from direct Ga ion damage during FIB milling, a layer of electron-beam deposited Pt followed by a thick layer of ionbeam deposited Pt was coated on the sample (Figure S3a) prior to the milling at 30 keV. Finally, a less than 100 nm thick cross-sectional transmission electron microscopy (TEM) specimen was prepared from the middle of the Ag cube (Figure S3b), and the specimen surfaces were polished by a 2 kV Ga ion beam to minimize the damage caused by the initial 30 keV FIB milling. High angle annular dark field scanning transmission electron microscope (HAADF STEM) images and selected area electron diffraction (SAED) patterns of the section were obtained by an FEI Titan Themis STEM operated at 300 keV.
experiments and a large number of wires were still observed. We speculate that accumulated gaseous species such as NO238 and glycolaldehyde39 or uncontrolled insertion of their condensed drops into the reaction batch causes seed dissolution and generation of wires because they form an Ag etchant, HNO3, and act as a reductant, respectively. For example, the formation of HNO3 was evidenced by low pH (2−3) of condensed liquid drops at the inner wall of the reactor. On the other hand, continuous flow of Ar gas rules out the effects of the gaseous species by eliminating the gaseous species and maintaining the reaction atmosphere inert, and, consequently, makes the reaction reproducible and controllable. We found that at least 500 SCM of Ar flow rate was required to prevent seed dissolution and to obtain high purity cubes. Therefore, we used this flow rate consistently in all of our seed growth experiments. Another important factor for success of seed growth reaction is to inhibit the generation of new seeds. To this end, we employed a 10× greater amount of HCl, namely, 36−72 μmol than that of normal seed synthesis (3 μmol). For this much higher HCl content, the selectivity of injected seeds to newly generated seeds is greatly enhanced, leading to a uniform size distribution of Ag cubes. The result is highly reproducible when EG with low chlorine (Cl) and iron (Fe) content is used as the reaction medium.24−26 We verified the reproducibility from six repeated reactions using the experimental conditions employed for the 449 nm cubes (Figure 1c). For the optimized conditions for Ar flow rate and HCl content, the quality of products is highly reproducible in different reactions (Table S1). To check the crystal perfection of the seed grown particles, we employed HAADF STEM and SAED analysis of thin cross sections of the micron size cubes. We used FIB to cut a thin cross section parallel to one of the cube faces and near the center of the cube (Figure S3b). The particular cube was prepared by two iterations of seed growth, and its length and height are almost identical (1.60 and 1.58 μm, respectively), as seen in the HAADF STEM image in Figure 2a taken along the [100] zone axis for valid comparison of the section dimensions. The crystal is quite perfect and uniform throughout its whole area, as shown, for example, in the HAADF STEM lattice image (Figure 2b) and the SAED patterns from multiple regions of the cube, one of which is presented in Figure 2c. The lattice parameter determined from carefully calibrated SAED is 0.408 nm, which is in quite good agreement with the literature value (0.4079 nm) for fcc silver.40 The radius of curvature at the cube edge-corner is ∼25 nm as indicated as a dashed circle in Figure 2d. The thickness of the adsorbed PVP layer can be estimated by measuring the gap between the cube and either the substrate or the deposited Pt-coated side wall, which is 2−5 nm from Figure 2b. In order to understand the role of HCl, we compared products resulting from different contents of HCl. Without any HCl, rounded particles (40−80 nm) smaller than the injected seeds (106 nm) were observed along with large, irregularly shaped aggregates (>500 nm) as shown in Figure 3a. With the addition of a small amount of HCl (12 μmol), the large aggregates were completely eliminated, but a few edge-rounded dimers and trimers were still observed as shown in Figure 3b. From image analysis, an average size (d) of the cubes, standard deviation (σ) in edge length, and σ/d were 462 nm, 63 nm, and 0.136, respectively. For 36 μmol of HCl, σ/d was greatly reduced to 0.05 (Figure 3c), which strongly supports the role of HCl as an agent inhibiting the generation of new seeds. At this
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RESULTS AND DISCUSSION Seed nanocubes were prepared by the synthesis method of our previous work.25 The initial edge length (d) of the nanocubes is 106 nm with standard deviation (σ) of 4.5 nm (Figure 1a), and the concentration is 1.1 vol %. Since there is a good method26 with regard to the synthesis of Ag nanocubes smaller than 200 nm, here we focus on Ag cubes larger than 200 nm. We found that the size of cubes was easily controlled by the seed concentration. For a seed cube concentration (Cc) of 48 μL/ ml, we added 240 μL of seed solution to 5 mL of total batch and observed an average size of 399 nm with σ = 25 nm after seed growth (Figure 1b). For Cc = 24 μL/ml, the size increased to 449 nm with σ = 24 nm as shown in Figure 1c and was further increased to 546 nm with σ = 29 nm for Cc = 12 μL/ml as shown in Figure 1d. To compare the uniformity in size between batches obtained at different seed concentrations, the ratio σ/d corresponds to 0.063, 0.054, and 0.054 with the aspect ratio of the upper “square” surface of the cube width to cube length equal to 1.02, 1.03, and 1.03 for Cc = 48, 24, and 12 μL/mL, respectively. Of course, the cube height is nearly the same as the other two dimensions, as seen in Figure 1d in which the cube, numbered as “1”, with a smaller width and length shows a smaller height than the other same sized cubes, numbered as “2−7”. By repeating the seed growth two times, cubes with edge lengths of approximately 1 and 2 μm were prepared as shown in Figure 1e,f. For example, one-quarter of the 449 nm cube solution was regrown by another seed growth to make approximately 1 μm cubes (Figure 1e). In order to obtain 2 μm cubes, we used one-eighth of the seed solution and a 2× larger amount of silver precursor, namely, 1.6 mmol (Figure 1f). The average size of cubes in Figure 1e,f is 1.2 and 2.0 μm, respectively, and even the 2 μm cubes maintain sharp edges and vertices and the aspect ratio is ∼1.05. Key factors resulting in the success of seed growth of up to 2 μm cubes with precise cube geometry are the well-controlled reaction atmosphere and the use of hydrochloric acid (HCl). Under air atmosphere, most of the injected seeds are dissolved right after the injection, as revealed by fading of the solution color from green ocher (the color of seeds) to the whitish color of AgCl crystals. Consequently, on growth, many silver wires are generated along with a few cubes of 300−500 nm edge length (Figure S1) due to seed dissolution mainly by the too high oxygen concentration in air. To exclude the effect of oxygen, we conducted the same experiment in a closed system under Ar atmosphere by substituting reaction atmosphere with Ar gas and closing off the system with a cap, but the size and size distribution of the cubes were not reproducible in repeated 286
DOI: 10.1021/acs.cgd.6b01523 Cryst. Growth Des. 2017, 17, 284−289
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for cubes from the reaction condition of 36 μmol of HCl, which was one-fourth fA/C = 0.13 of the reaction condition using 12 μmol of HCl. We suggest that there might be enhanced stabilization, i.e., electrosteric stabilization, by HCl induced protonation of the PVP chains adsorbed onto the surfaces of the particles. For higher content of HCl (60 μmol), even injected seeds were dissolved due to the increased concentration of HNO3, a silver etchant formed by the reaction of AgNO3 and HCl. As a result, a large number of wires with nonuniform diameter and length formed along with a small number of cubes and bipyramids (Figure 3d). This result is almost the same as the result for the same reaction condition but without seed injection (Figure S2). According to the above observation, the role of HCl is 2-fold: (i) it acts as an agent inhibiting generation of new seeds, and (ii) HCl is a colloidal stabilization promoter. For a broad range of PVP content, the edges of the cubes maintained their sharpness at the optimized HCl content, even for very low PVP content. Thus, for 0.1 mmol of PVP, which is one-eighth of the silver precursor content, the cube edges are still sharp, but the population of aggregates has increased ( fA/C = 0.13) similar to the result for a lower HCl content (Figure 3e). It is obvious that insufficient stabilization accounts for the large number of aggregates. There has been a report that truncation was observed for cubes for low PVP content,41 but truncation of cubes was not observed in our experiments. For 0.4 mmol of PVP, uniform cubes with the highest uniformity (σ/d = 0.054), the lowest number of aggregates ( fA/C = 0.03), and the lowest aspect ratio (1.03), were observed (Figure 3c). At a higher content of PVP (1.6 mmol), the number of wires in the final product was increased as reported in our previous paper (Figure 3f).25 Because PVP is not only a surface stabilizer but also acts as a reducing agent, the higher content of PVP results in a faster reducing rate and thus induces the large amount of wires. Reducing conditions are easily noted by a color change of the batch. The initial whitish color of the reaction solution (due to AgCl) gradually turned into orange
Figure 2. (a) A low magnification HAADF STEM image of a (100) plane thin cross section of a cube prepared by two iterations of seed growth. (b) A highly magnified image of the cube using high resolution HAADF STEM to image the silver lattice. Inset is a schematic of potential projection of Ag showing the fcc lattice of Ag with the unit cell dimension. The horizontal black region at the bottom of the image is the PVP layer. (c) SAED of the thin section reveals the defect free, single crystal nature. Successive SAED patterns taken over the section are essentially identical. (d) HAADF STEM image of the edge-corner region of the cube is very sharp as shown by the dashed circle, which has a radius of curvature ∼25 nm.
synthesis condition, the number of aggregates was also greatly reduced. To compare the population of aggregates, we define fA/C as number of aggregates (A) versus cubes (C). fA/C = 0.03
Figure 3. (a−d) SEM images of particles prepared from different amounts of HCl added (0−60 μmol) but with all at the same amount of PVP (0.4 mmol). (a) Without HCl, (b) 12 μmol of HCl, (c) 36 μmol of HCl, and (d) 60 μmol of HCl. Small rounded particles with irregular shapes as well as large aggregates form in the absence of HCl. (e−f) SEM images of particles grown using different PVP contents (0.1 and 1.6 mmol) but with the same HCl volume (36 μmol). (e) 0.1 mmol and (f) 1.6 mmol PVP contents. The most monodisperse sample in both shape and size arises from condition (c): 36 μmol of HCl and 0.4 mmol of PVP. 287
DOI: 10.1021/acs.cgd.6b01523 Cryst. Growth Des. 2017, 17, 284−289
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CONCLUSION In conclusion, nearly monodisperse, single crystal Ag cubes, a typical and useful example of nonspherical metal particles, with sizes from 100 nm to 2 μm, have been synthesized by a seed growth approach. Key factors for the success of the seed growth process are the well-controlled reaction atmosphere and the use of HCl. Ar introduction was effective for inhibiting seed dissolution by oxygen at the reaction temperature ∼160 °C, leading to a high yield of monodisperse cubes. HCl plays two important roles for obtaining uniform Ag cubes: (i) as an agent inhibiting generation of new seeds and (ii) as a colloidal stabilization promoter. If there is a sufficient amount of HCl, cubes maintain their sharp edges even for very low content of PVP (0.1 mmol). The crystal perfection of the seed grown particles was confirmed by high resolution imaging of the Ag lattice and SAED of a thin cross section of a cube. The use of higher molecular weight PVP (1300 kg/mol vs 55 kg/mol) greatly reduced the number of aggregates (less than 0.1% by number). To further enhance product quality, even finer control of the molecular weight distribution of PVP may be necessary to attain shape isotropy and monodispersity of the cubes. Our seed growth scheme can be used for the seed growth of Ag nanoparticles with different shapes other than cubes and possibly give inspiration for how to grow other nonspherical metal particles, boosting the exploration on the size- and shape-dependent properties of 100 nm−micron nonspherical particles.
due to the reduction of Ag after PVP injection at lower PVP content, but the color change is more precipitous at higher content of PVP. For example, the time for the transition from whitish to yellowish is around 3 min for 0.4 mmol of PVP, but it is within 30 s for 1.6 mmol of PVP. Typically, there are ∼5% aggregates and wires by number in the final products, but since the wires are of very different dimensions compared to the cubes, they are easily separated out from the products by filtering. However, aggregates such as dimers (Figure 4a) and trimers (Figure 4b) are not easily
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.6b01523. SEM image of the products by seed growth in air atmosphere, SEM image of the products by same experimental conditions for seed growth including Ar introduction except injection of seeds, SEM images for STEM specimen preparation using FIB, and reproducibility in six sets of syntheses (PDF)
Figure 4. SEM images of (a) a dimer and (b) a trimer along with cubes. (c) E-beam sensitive behavior of cubes sampled in the middle of seed growth (10 min) as indicated by white arrows. (d) Cubes prepared using high molecular weight PVP (∼1300 kg/mol).
separated out from the product, which reduces the quality of the final products. The formation of aggregates in the polyol synthesis of Ag nanocubes based on AgCl formation have been reported by Peng et al.,42 but the size of the aggregates in our product is much larger than in their aggregates. To understand the reason why the aggregates are formed, we sampled small amounts of products at the midpoint of the reaction. Interestingly, if we focus the e-beam onto the cubes formed at 10 min, some are unstable under the electron beam. This behavior is likely the reduction of AgCl shells surrounding the seeds into Ag due to the e-beam irradiation (see regions indicated by arrows in Figure 4c).42 There are also stable cubes which are likely pure Ag, and these are slightly larger than the unstable cubes. Thus, we speculate that initially AgCl deposits onto the surface of the seed Ag cubes and is subsequently converted into Ag during growth. PVP chains adsorbing onto the AgCl shell do not provide sufficient stabilization, leading to the formation of aggregates. The use of much higher molecular weight PVP (Mw ≈ 1 300 000 g/mol) greatly reduced the population of aggregates (less than 0.1% by number), and cubes with sharp edges were successfully synthesized by the enhanced stabilization (Figure 4d). The cubes showed a slightly larger aspect ratio, 1.13, than that of the cubes made with the lower molecular weight PVP, σ/d = 1.05, but this may be accounted for by the broad molecular weight distribution of the PVP. The use of monodisperse high molecular weight PVP will likely be able to improve the isotropy of the cubes.
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AUTHOR INFORMATION
Corresponding Author
*Address: Rice University, George R. Brown School of Engineering, Duncan Hall Room 1016, 6100 Main Street Houston, Texas 77005. Phone: 713-348-4955. Fax: 713-3485300. E-mail:
[email protected]. Web: http://elt.rice.edu. ORCID
Ramathasan Thevamaran: 0000-0001-5058-6167 Present Address §
(S.-J.J.) Department of Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts 01003. Funding
This work was financially supported by the William and Stephanie Sick Chair in the George R. Brown School of Engineering at Rice University. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Kim, S. H.; Lee, S. Y.; Yang, S. M.; Yi, G. R. NPG Asia Mater. 2011, 3, 25−33. 288
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(37) Dimiduk, D. M.; Uchic, M. D.; Parthasarathy, T. A. Acta Mater. 2005, 53, 4065−4077. (38) Zhang, Q.; Cobley, C.; Au, L.; McKiernan, M.; Schwartz, A.; Wen, L.-P.; Chen, J.; Xia, Y. ACS Appl. Mater. Interfaces 2009, 1, 2044−2048. (39) Skrabalak, S. E.; Wiley, B. J.; Kim, M.; Formo, E. V.; Xia, Y. Nano Lett. 2008, 8, 2077−2081. (40) Davey, W. P. Phys. Rev. 1925, 25, 753−761. (41) Xia, X.; Zeng, J.; Oetjen, L. K.; Li, Q.; Xia, Y. J. Am. Chem. Soc. 2012, 134, 1793−1801. (42) Peng, S.; Okasinski, J. S.; Almer, J. D.; Ren, Y.; Wang, L.; Yang, W.; Sun, Y. J. Phys. Chem. C 2012, 116, 11842−11847.
(2) Sacanna, S.; Pine, D. J. Curr. Opin. Colloid Interface Sci. 2011, 16, 96−105. (3) Galisteo-Lopez, J. F.; Ibisate, M.; Sapienza, R.; Froufe-Perez, L. S.; Blanco, A.; Lopez, C. Adv. Mater. 2011, 23, 30−69. (4) Doherty, C. M.; Caruso, R. A.; Smarsly, B. M.; Drummond, C. J. Chem. Mater. 2009, 21, 2895−2903. (5) Hu, L.; Yan, N.; Chen, Q.; Zhang, P.; Zhong, H.; Zheng, X.; Li, Y.; Hu, X. Chem. - Eur. J. 2012, 18, 8971−8977. (6) Champion, J. A.; Katare, Y. K.; Mitragotri, S. J. Controlled Release 2007, 121, 3−9. (7) Prow, T. W.; Grice, J. E.; Lin, L. L.; Faye, R.; Butler, M.; Becker, W.; Wurm, E. M. T.; Yoong, C.; Robertson, T. A.; Soyer, H. P.; Roberts, M. S. Adv. Drug Delivery Rev. 2011, 63, 470−491. (8) Unland, G.; Al-Khasawneh, Y. Miner. Eng. 2009, 22, 220−228. (9) Mordehai, D.; Lee, S. W.; Backes, B.; Srolovitz, D. J.; Nix, W. D.; Rabkin, E. Acta Mater. 2011, 59, 5202−5215. (10) Lee, J. H.; Veysset, D.; Singer, J. P.; Retsch, M.; Saini, G.; Pezeril, T.; Nelson, K. A.; Thomas, E. L. Nat. Commun. 2012, 3, 1164. (11) Stein, A.; Wilson, B. E.; Rudisill, S. G. Chem. Soc. Rev. 2013, 42, 2763−2803. (12) Vogel, N.; Retsch, M.; Fustin, C.-A.; del Campo, A.; Jonas, U. Chem. Rev. 2015, 115, 6265−6311. (13) Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E. Angew. Chem., Int. Ed. 2009, 48, 60−103. (14) Xia, Y.; Xia, X.; Wang, Y.; Xie, S. MRS Bull. 2013, 38, 335−344. (15) Hosein, I. D.; Lee, S. H.; Liddell, C. M. Adv. Funct. Mater. 2010, 20, 3085−3091. (16) Forster, J. D.; Park, J.-G.; Mittal, M.; Noh, H.; Schreck, C. F.; O’Hern, C. S.; Cao, H.; Furst, E. M.; Dufresne, E. R. ACS Nano 2011, 5, 6695−6700. (17) Fu, M.; Chaudhary, K.; Lange, J. G.; Kim, H. S.; Juarez, J. J.; Lewis, J. A.; Braun, P. V. Adv. Mater. 2014, 26, 1740−1745. (18) Shchepelina, O.; Kozlovskaya, V.; Kharlampieva, E.; Mao, W. B.; Alexeev, A.; Tsukruk, V. V. Macromol. Rapid Commun. 2010, 31, 2041−2046. (19) Dendukuri, D.; Doyle, P. S. Adv. Mater. 2009, 21, 4071−4086. (20) Choi, C. H.; Lee, J.; Yoon, K.; Tripathi, A.; Stone, H. A.; Weitz, D. A.; Lee, C. S. Angew. Chem., Int. Ed. 2010, 49, 7748−7752. (21) Dendukuri, D.; Pregibon, D. C.; Collins, J.; Hatton, T. A.; Doyle, P. S. Nat. Mater. 2006, 5, 365−369. (22) Jang, J.-H.; Dendukuri, D.; Hatton, T. A.; Thomas, E. L.; Doyle, P. S. Angew. Chem., Int. Ed. 2007, 46, 9027−9031. (23) Sun, Y.; Xia, Y. Science 2002, 298, 2176−2179. (24) Im, S. H.; Lee, Y. T.; Wiley, B.; Xia, Y. N. Angew. Chem., Int. Ed. 2005, 44, 2154−2157. (25) Jeon, S.-J.; Lee, J. H.; Thomas, E. L. J. Colloid Interface Sci. 2014, 435, 105−111. (26) Zhang, Q.; Li, W.; Moran, C.; Zeng, J.; Chen, J.; Wen, L.-P.; Xia, Y. J. Am. Chem. Soc. 2010, 132, 11372−11378. (27) Pietrobon, B.; Kitaev, V. Chem. Mater. 2008, 20, 5186−5190. (28) Jana, N. R.; Gearheart, L.; Murphy, C. J. Adv. Mater. 2001, 13, 1389−1393. (29) Pietrobon, B.; McEachran, M.; Kitaev, V. ACS Nano 2009, 3, 21−26. (30) Holt, B.; Lam, R.; Meldrum, F. C.; Stoyanov, S. D.; Paunov, V. N. Soft Matter 2007, 3, 188−190. (31) Cheng, B.; Lei, M.; Yu, J. G.; Zhao, X. J. Mater. Lett. 2004, 58, 1565−1570. (32) Janekovic, A.; Matijevic, E. J. Colloid Interface Sci. 1985, 103, 436−447. (33) Rossi, L.; Sacanna, S.; Irvine, W. T. M.; Chaikin, P. M.; Pine, D. J.; Philipse, A. P. Soft Matter 2011, 7, 4139−4142. (34) Zhang, X.; Dong, C.; Zapien, J. A.; Ismathullakhan, S.; Kang, Z.; Jie, J.; Zhang, X.; Chang, J. C.; Lee, C.-S.; Lee, S.-T. Angew. Chem., Int. Ed. 2009, 48, 9121−9123. (35) Lin, H.; Lei, Z.; Jiang, Z.; Hou, C.; Liu, D.; Xu, M.; Tian, Z.; Xie, Z. J. Am. Chem. Soc. 2013, 135, 9311−9314. (36) Thevamaran, R.; Lawal, O.; Yazdi, S.; Jeon, S.-J.; Lee, J.-H.; Thomas, E. L. Science 2016, 354, 312−316. 289
DOI: 10.1021/acs.cgd.6b01523 Cryst. Growth Des. 2017, 17, 284−289
