Article pubs.acs.org/Langmuir
The Role of Modifying Molecular Chains in the Formation of Organized Molecular Films of Organo-Modified Nanodiamond: Construction of a Highly Ordered Low Defect Particle Layer and Evaluation of Desorption Behavior of Organic Chains Atsuhiro Fujimori,*,† Yusuke Kasahara,‡ Nanami Honda,† and Shuichi Akasaka§ †
Graduate School of Science and Engineering and ‡Department of Functional Material Science, Faculty of Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan § Graduate School of Science and Engineering, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro-ku, Tokyo 152-8550, Japan S Supporting Information *
ABSTRACT: The role of organo-modifying molecular chains in the formation of molecular films of organo-modified nanodiamond is discussed herein based on interfacial chemical particle integration of organo-modified nanodiamond having a particle size of 5 nm. The surface of nanodiamond is known to be covered with a nanolayer of adsorbed water. This water nanolayer was exploited for organo-modification of nanodiamond with longchain fatty acids via adsorption, leading to nanodispersion of nanodiamond in general organic solvents as a mimic of solvency. The organo-modified nanodiamond dispersed “solution” was used as a spreading solution for depositing a mono-“particle” layer on the water surface, and a Langmuir particle layer was integrated at the air/water interface. Multi-“particle” layers were then formed via the Langmuir−Blodgett technique and were subjected to fine structural analysis. The effect of organo-modification enabled integration and multilayer formation of inorganic nanoparticles due to enhancement of the van der Waals interactions between the chains. That is to say, the “encounter” between the organomodifying chain and the inorganic particles led to solubilization of the inorganic particles and enhanced interactions between the particles, which can be regarded as imparting new function to the organic molecules. The morphology of the single-particle layer was maintained after removal of the organic region of the composite via the baking process, whereas the regularity of the layered period was disordered. Thus, the organic chains are essential as modifiers for maintenance of the layered structure.
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ity,27,28 increased conductivity,29,30 and nonphotobleaching fluorescence31,32 of these species. Thus, it has been envisioned that two-dimensional integration of nanodiamond nanoparticles into various materials should effectively enhance several material functionalities. However, it is difficult to obtain regular arrangements of nanodiamond particles because the van der Waals interaction in inorganic materials is relatively weak. To overcome this limitation, surface modification using organic compounds is one prospective means of increasing the affinity between particles. In a previous study, we investigated the formation and structure of molecular films comprising organo-modified clay.33,34 In that study, the organo-modified inorganic material formed an extremely condensed monolayer on the surface of water. Moreover, a highly ordered layer structure along the caxis and two-dimensional packing in the ab-plane have commonly been constructed by the Langmuir−Blodgett (LB) technique.35,36 In addition, the authors have successfully
INTRODUCTION Can new functionality be imparted to organic molecules by an encounter with inorganic particles? In other words, can the functionality of inorganic particles be induced in organic molecules (Figure S1a), such as impartation of the solubilizing ability of nonionic inorganic particles to general organic solvents, enhancement of van der Waals interactions between the particles, and conference of amphiphilic properties, etc.? Two-dimensional integration of nanoparticles has played an important role in the development of modern technology.1−3 Integrated nanoparticles have potential application in numerous technical areas ranging from organic devices to biomaterials.4−7 Furthermore, organic/inorganic hybrid materials8,9 have captured the attention of scientists as well as engineers owing to their remarkably high dimensional stability and gas-barrier performance, in addition to their superior mechanical properties relative to conventional composite materials.10,11 The use of nanodiamonds12,13 in products such as heat spreaders,14,15 photonic crystals,16,17 medical applications,18 application in electronics and sensors,19,20 and biosensors21,22 has also spurred tireless research efforts due to the high thermal conductivity,23,24 high refractive index,25,26 antibacterial activ© 2015 American Chemical Society
Received: January 5, 2015 Revised: February 17, 2015 Published: February 18, 2015 2895
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Figure 1. Characterization of organo-modified nanodiamond: (a) TG curve. (b) Schematic illustration of particle surface. (c) Powder X-ray diffraction profile and resultant calculation of their particle size.
fabricated highly ordered particle assemblies by the synthesis of long-chain fatty acid-modified zirconium oxide (zirconia) by using novel organo-modification methods.37 Khabashesku et al. have reported the organo-modification method of nanodiamond surface.38 In this study, fluoronanodiamond has been used as a precursor of fabrication of the alkyl-, amino-, and amino acid-nanodiamond derivatives. All of these organo-modified nanodiamonds indicated the improvement of solubility in polar organic solvents and a reduction of particle aggregation. Further, Pichot et al. have reported the formation of a single particle layer of organo-modified nanodiamond by the LB method.39 In this case, cetyltrimethylammonium chloride was used in order to form the anionic complex ND-COO−(NH3)+-R with the functional group of nanodiamond. In the present study, high-density, two-dimensional integration and regular three-dimensional lamination of nanodiamonds are performed by an interfacial chemical method (Figure S1b). Ultrathin organo-modified nanodiamond films are constructed by floating Langmuir monolayers. The technique proposed in this study is based on the nanodispersion of insoluble inorganic particles by solubilization in a general organic solvent. In general, the outermost layer of the nanodiamond with single-nanometer diameter is covered by a nanolayer of water for structural stabilization. The challenge of organo-modification of inorganic particles through the surface
nanophase of water is addressed herein. This nanodispersion of fine inorganic particles can be used as a “spreading solvent” for Langmuir monolayers. In other words, the formation of LB multilayers of nanodiamonds is made possible by using the proposed technique. In this study, LB multilayers of organomodified nanodiamond films are characterized by out-of-plane and in-plane X-ray diffraction (XRD) and atomic force microscopy (AFM). The proposed technique should facilitate the development of a new technique for two-dimensional integration of insoluble nanodiamonds that may be widely employed using a simple wet process. Furthermore, the discovery of new possibilities for molecular chain organo-modification is also discussed. Notably, new possibilities arise from functionalization of the inorganic particles based on their encounter with organic molecules via the contact interface in the interfacial integrated technique for generating organo-modified inorganic particles. Solubilization and formation of an interfacial nanofilm by the organomodified inorganic particles is interpreted in light of the functionality conferred by the organic molecules. In addition, to probe the pertinent question of whether the layered periodic structure and mesoscopic morphology of the integrated organization of inorganic particles is maintained after removal of the organo-modifying chain, the layered regularity of the organo-modified inorganic particles is examined by the baking experiment. This experiment answers the question of whether 2896
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Figure 2. (a) Surface pressure−area (π−A) and (b) surface pressure−compression percentage isotherms of monolayers of several materials on the water surface (15 °C). (c) π−A and (d) π−compression percentage isotherms of single-particle layers of organo-modified nanodiamond on the water surface (5, 15, and 25 °C). antisymmetric stretching vibrations assigned to the alkyl chain of the fatty acids were clearly confirmed around 2910−2840 cm−1.42 Both aforementioned bands were simultaneously detected in the IR spectrum of organo-nanodiamond. Thus, it was inferred that organomodification of the nanodiamond particle surface was successful. Structural Estimation in Bulk. Figure 1a shows the thermogravimetry (TG) curve of bulk organo-nanodiamond. TG measurements were performed using an Al container in an atmosphere of nitrogen at a heating rate of 10 °C min−1 using an EXSTAR TG/ DTA6200 (Seiko Instruments) apparatus. Based on the TG analysis, a loss of about 52% of the modified organo-chain occurred with elevation of the temperature. In this case, since adsorbed water layer exists at the surface of the nanodiamond, a gradual reduction in weight also continues after desorption of the modified alkyl chain. Therefore, a major weight loss approximately considers as desorption of the alkyl chain, and the surface coverages have been calculated by the regarding as desorption temperature at 270 °C. Furthermore, considering the surface area calculated based on the nanodiamond particle size, the area occupied per modified chain molecule is calculated to be about 46 Å2, and the modification ratio was 48%. This value is approximately twice the value of the limiting area of the monolayer on the water surface of stearic acid, and it is proposed that a portion of the water nanolayer on the outermost surface of nanodiamond is exposed (Figure 1b). The packing mode of the bare nanodiamond was examined using powder XRD (Rigaku, Rint-Ultima III; Cu Kα radiation, 40 kV, 40 mA, equipped with a graphite monochromator). Figure 1c shows the powder X-ray diffraction profile of the bulk nanodiamond fine particles. Based on the powder diffraction data, the nanodiamond
there is an essential need for the support provided by the organic molecular chains in the highly ordered, inorganic, layered particle aggregations.
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EXPERIMENTAL SECTION
Synthesis and Characterization of Organo-Modified Nanodiamond. Figure S2a presents a schematic illustration of the protocol for organo-nanodiamond synthesis. A dispersion was prepared by combining an aqueous solution of nanodiamond (New Metals and Chemicals Co., Ltd.) with a methanolic solution of stearic acid (for a detailed procedure of organo-modification of nanodiamond surface see refs 37 and 40). Toluene was poured into the nanodiamond dispersion with stirring. In this step, the organo-nanodiamonds migrated from the methanolic dispersion into the toluene phase. Water, methanol, and the remaining unreacted reagent were then removed by rotary evaporation under reduced pressure and decantation. This process changed the surface-absorbed hydronium ions (R−H2O+) in the water nanolayer on the particle surface to long-chain alkyl carboxylates, as indicated by IR analyses (sea Figure S2b). Figure S2b shows the IR spectra of the organo-nanodiamonds, stearic acid, and bare nanodiamonds in the bulk phase. The IR spectra were acquired using a 2000 spectrometer system (PerkinElmer Co., Ltd.). It is well-known that the nanodiamond surface is coated with a water layer that stabilizes the structure.12 In this case, it is proposed that carboxylic ions (COO−) are adsorbed by the hydronium ions on the nanodiamond surface. In the IR spectrum of bare nanodiamond, the band of the O−H stretching vibration assigned to the hydroxyl groups of the adsorbed water layer on the particle surface was confirmed at 3480 cm−1.41 In addition, C−H symmetric and 2897
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Figure 3. (a) Mesoscopic AFM images of Z-type single-particle layer of organo-modified nanodiamond transferred by LB method (5, 15, and 25 °C). (b) Out-of-plane XRD profiles of multiparticle layers of organo-modified nanodiamond transferred by LB method (5, 15, and 25 °C). (c) Schematic illustration of multiparticle layered organization of organo-modified nanodiamond. (d) Photograph of the occurrence behavior of structural colors of stepwise multilayers of organo-modified nanodiamond. nanoparticles crystallize in a cubic diamond lattice (ac = 3.571 Å). In addition, based on proximate analysis of the Schererr equation using the (111) reflection as the maximum intensity peak, the average particle size of nanodiamond was calculated to be 3.5−4.5 nm. Formation of Monolayers on Water Surface and Observation of Molecular Arrangement in Films. It is possible to achieve uniform size dispersion of the generated organo-nanodiamond on the nanometer scale, where this process can essentially be considered as dissolving organo-nanodiamond in an organic solvent. Therefore, it was also possible to prepare a spreading solvent for formation of a monolayer on the water surface of the nanodiamonds. A monolayer of organo-nanodiamond was formed by spreading a toluene solution containing organo-nanodiamond (ca. 1.0 × 10−4 M) on ultrapure water (18.2 MΩ·cm). The concentration of organo-nanodiamond solutions was estimated by using the average weight of the modifiedchain molecules calculated on the basis of the chemical characterization described above. After evaporating the toluene for 30 min, surface pressure−area (π−A) isotherms were recorded at a compression speed of 0.08 mm s−1. The temperature of the air/ water interface was maintained at a constant value of 15 °C by circulating thermostatically controlled water around the trough. Measurements of the monolayer properties and LB film transfer were carried out using a USI-3-22 Teflon-coated LB trough (USI Instruments). The monolayers were transferred onto CaF2 (IR samples) or mica (AFM samples) or glass substrates with a ferric stearate monolayer as a hydrophobic underlayer (out-of-plane XRD and in-plane XRD) at 15 °C using the LB method. Surface Morphology and Particle Arrangement in Organized Films. The surface morphology of the transferred monomolecular films was observed using a scanning probe microscope
(Dynamic Force Mode, Seiko Instruments, SPA300 with a SPI-3800 probe station) and microfabricated rectangular Si cantilevers with integrated rectangular tips; a spring constant of 1.4 N m−1 was applied in this process. The large spacing between the layer structures of the films transferred onto the glass substrates was measured using an outof-plane X-ray diffractometer (Rigaku, Rint-Ultima III; Cu Kα radiation, 40 kV, 40 mA) equipped with a graphite monochromator. The in-plane spacing of the two-dimensional lattice of the films was determined using an X-ray diffractometer with different geometrical arrangements43,44 (Bruker AXS, MXP-BX; Cu Kα radiation, 40 kV, 40 mA, an instrument especially made to order) that was equipped with a parabolic graded multilayer mirror. X-rays were incident at an angle of 0.2°, and the films were slow-scanned at a speed of 0.05°/80 s. Thus, in-plane XRD measurements were carried out at monomolecular resolution.
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RESULTS AND DISCUSSION The interfacial monolayer behavior of organo-modified inorganic fine particles is extremely interesting in terms of elucidation of whether the monolayer is strongly influenced by any of the components. Figure 2a−d shows the π−A isotherm of a single particle layer on the water surface of organonanodiamond and stearic acid as an organo-modifying agent. Figure 2a,b shows a comparison of the monolayer behavior of organo-modified nanodiamond, stearic acid, and Cd stearate. The horizontal axes in Figure 2a,b indicate the “area” and “compression percentage”, where the “area” corresponds to “area/molecule” in the case of stearic acid and stearic acid 2898
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Figure 4. (a) In-plane XRD profiles of multiparticle layers of organo-modified nanodiamond transferred by LB method (5, 15, and 25 °C). (b) Schematic models of two-dimensional lattices formed by long hydrocarbons on organo-modified nanodiamond surface of their LB films transferred at several subphase temperature. (c) Schematic illustration of formation of subcell structure in high-order layered organization of organo-modified nanodiamond based on the contribution of strong van der Waals interaction between alkyl chains.
cadmium and indicates the “mean area per hydrophobic repeating unit” in the case of nanodiamond. In this case, the concept of molecular weight cannot be applied because the total number of atoms of nanodiamond particle units cannot be exactly determined. Therefore, considering the surface conformation as shown in Figure 2e, the repeating units of only the stearate group of the organo-nanodiamond surface are shown in Figure 2a,c. However, it is expected that the most accurate comparison would be derived by using the “compression percentage”, which indicates the mean of the compression ratio versus the total surface area of the LB trough, as the horizontal axis. Notably, the π−A curve of organomodified nanodiamond is clearly different from that of stearic
acid and Cd stearate. From the results of the π−A isotherms of the organo-modified ND monolayer, both expanded and condensed phases were confirmed in the low and high surface pressure regions, respectively. In addition, two-dimensional phase transition from the expanded phase to the condensed phase is indicated by the changes in the inclination of π−A curve of organo-nanodiamond monolayer. The appearance of this phase transition is an effect derived from the organic component, while the appearance of a clear crystalline phase in the high-pressure region is believed to be an effect of the inorganic component. The temperature dependence of the π−A curve was evaluated to confirm the occurrence of the effect derived from the organic 2899
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Figure 5. (a) Schematic illustration of “repeating compression−expansion method”. (b) Hysteresis curves of π−A isotherms of single-particle layers of organo-modified nanodiamond on the water surface (15 °C). (c) AFM image of single-particle layer of organo-modified nanodiamond fabricated by “repeating compression−expansion method” at 6 times. (d) Out-of-plane XRD profiles of multiparticle layers of organo-modified nanodiamond performed “repeating compression−expansion method” at six times.
corresponds to the particle lamination period as shown in Figure 3c. The diffraction peaks in transferred at 15 °C and transferred at 25 °C were comparatively sharper than that in transferred at 5 °C; therefore, more advanced layered structures were formed in the former films. As further evidence, the multilayers fabricated stepwise at 15 °C exhibited a clear structural related color up to wavelengths in the visible light region in response to stacking (Figure 3d). In this case, gradation of structural color has been indicated on the stepwisemultilayers. The violet, indigo, blue, green, yellow, orange, and red colors correspond to 38, 44, 49, 54, 60, 65, and 70 layers of organo-nanodiamond, respectively. Although the d value from the low-angle region of the wide-angle X-ray diffraction profile contains significant uncertainty in terms of the absolute value, the value of the long period is somewhat small when the molecular length of stearic acid is considered. Stearic acid has a molecular length of about 2.5 nm, and the particle diameter of nanodiamond is expected to be about 3.5−4.5 nm. Therefore, it is proposed that the molecular chain is considerably disordered and tilted or that a structure in which the modified parts of the organo-particles are interdigitated is constructed. Figure 4 shows the in-plane X-ray diffraction profiles of multiparticle layers of organo-nanodiamond that were transferred at several temperatures. Unfortunately, the diffraction peak in the low angle region corresponding to the long spacing in the out-of plane XRD pattern was not observed. Based on the AFM results, this observation may be reasonable. The arrangement of the particles in the two-dimensional plane
component (Figure 2c,d). Specific condensation and expansion behavior typical of the π−A isotherms of organic compounds was confirmed with the change of the subphase temperature. This single-particle layer on the water surface was transferred to a mica substrate at various temperatures by using the upstroke LB method. Figure 3a shows AFM images of these Ztype single-particle layers. Formation of an organized molecular film of organo-modified nanodiamond was also confirmed by laser Raman spectroscopy. A diamond-specific 1330 cm−1 Raman shift band45 was confirmed in the Raman spectrum of the organized film, in addition to the C−C band at 1098 cm−1. In a nutshell, it was not possible to obtain a quite homogeneous single particle film at this stage. In particular, because the height is about 3 times the particle diameter in the case of the layer transferred at 5 °C, it seems that there are sites where the particles aggregate and pile up along the height direction. In the case of the single-particle layers transferred at 15 and 25 °C, although the height direction is homogeneous and consistent with single particle size, the tendency toward particle integration in the in-plane direction is not necessarily high. This problem is eliminated by the “repeating compression− expansion method” discussed in an ensuing section. On the other hand, the formation of a quite highly ordered layer arrangement along the height direction was inferable from the data in Figure 3b. The results of out-of-plane X-ray diffraction of the LB multilayers indicates that an organized film was transferred at all subphase temperatures, and the films showed a clear long-period value at around 5 nm. This value 2900
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Figure 6. (a) IR spectra of baked LB films of organo-modified nanodiamond during 10 min at several temperatures. (b) AFM image of baked singleparticle layer of organo-modified nanodiamond at 170 °C during 10 min. (c) Out-of-plane XRD profiles of multiparticle layers of organo-modified nanodiamond before and after baking. (d) IR spectra of baked LB films of organo-modified nanodiamond during few hours at 100 °C. (e) AFM image of baked single-particle layer of organo-modified nanodiamond at 100 °C for 2 h. (f) Out-of-plane XRD profiles of multiparticle layers of organo-modified nanodiamond before and after baking.
would not be highly regular at this stage. However, the modifying long-chain alkyl group was found to have a high degree of order in the particle layers. A single peak corresponding to the isotropic hexagonal (100) plane was apparent at 4.1 Å in the case of the multiparticle layers fabricated at the subphase temperature of 5 °C. Additionally, the appearance of double peaks in the case of the multiparticle layers fabricated at the subphase temperatures of 15 and 25 °C indicates that the modified alkyl chains form a slightly anisotropic orthorhombic system. In view of the ratio of surface modification of the particles by stearic acid, the possibility that the long alkyl chain is densely packed on one particle surface is extremely low. Also considering the longperiod value, it is possible that this value remained unchanged
from 5 nm because the long hydrocarbon chains between the particles form an interdigitated structure. Accordingly, packing of the alkyl chains is expected to generate a two-dimensional crystal array of the alkyl chains between individual particles. In other words, the two-dimensional integration and formation of the layer structure of organo-nanodiamond can be determined, indicating that crystal formation arises from interaction between modified alkyl chains. This inferred model is represented in Figure 4c. Subcell46 formation by the hydrocarbons between the particles is considered to be the origin of the nanoparticle integrated organization in this system. As the next step, the formation of the high-density and lowdefect particle layer was addressed. Figure 5a shows a schematic illustration of the “repeating compression−expansion process” 2901
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Figure 7. Schematic illustration of the role of the modification molecular chain in formation of organized molecular films of organo-modified nanodiamond.
for generation of the single particle layer on the water surface. In a system where the size of the components is large and the interaction between constituent units is relatively weak, a lowdefect layer can be effectively formed from this process. The fact that this technique works effectively reflects the monolayer properties of the inorganic compound. In the case of an organo-modified montmorillonite single particle layer, this technique was effectively applied to fabricate low-defect films.34 Figure 5b illustrates the reversibility and hysteresis of the π−A isotherm at 15 °C. At each step of the repeating process, the difference in the hysteresis during compression−expansion becomes less. When this process is performed 6 times, the fifth and sixth curves of the hysteresis loop almost coincide. Therefore, considering that the highest density films had successfully been attained, the resulting monolayer and LB multilayers transferred to the solid substrate were subjected to AFM observation and out-of plane X-ray diffraction. The results confirm a very low-defect surface morphology (Figure 5c). In addition, the d001 peak in the out-of plane X-ray diffraction pattern became very sharp (Figure 5d). Comparing the magnitude of the D001 for the crystallites of the fabricated films based on the full width at half-maximum before and after performing the sequence of the “repeating compression− expansion process” for six cycles, the diameter of the crystallites clearly increased from 364 to 461 Å (the Scherrer constant K = 0.94 was used). Here, the effect of the organic chain in the layered organization of organo-modified nanodiamond particles was again examined. Based on the TG data shown in Figure 1a, the organic chains of the nanodiamond surface underwent desorption at about 170 °C. Therefore, the effect of the
organic chains on the surface morphology and the particle arrangement was investigated by removal of the organomodifying chain via baking of the low-defect multiparticle layers. First, desorption of the chains was confirmed by monitoring the C−H stretching vibration of the multiparticle layers after baking at each temperature by using IR (Figure 6a). Baking at 170 °C for 10 min resulted in almost complete disappearance of this band; thus, the morphology of the monolayer and the arrangement of the multiparticle layers were evaluated using these baking conditions. The data demonstrate remarkable aggregation of the particles, and the regularity of the layered period was completely destroyed (Figure 6b,c). In the light of these results, milder calcination conditions were employed. The adsorbed long hydrocarbon chain was found to be completely desorbed by holding the sample for 2 h under baking condition at 100 °C (Figure 6d). Assessment of the morphology of the monolayer using the milder conditions confirmed that the morphology of the high-density single particle layer was maintained (Figure 6e). However, it was found that the periodic structure of the layered organization of organo-particles was lost (Figure 6f). This result supports the model presented in Figure 4c. That is to say, the multilayered organization of organo-modified nanodiamond is not maintained when the modified organic chain is lost, indicating that the chain is required to maintain the arrangement order. These results were also corroborated by macroscopic contact angle measurements and the Zisman plot. Figure S3 shows the lowdefect organo-nanodiamond multiparticle layers and the rapidly and slowly baked films. When the organic chain is present, the contact angle of the water droplet is the largest, whereas the γc value is small. The most hydrophilic surface was obtained by 2902
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(3) Khanh, N. N.; Yoon, K. B. Facile Organization of Colloidal Particles into Large, Perfect One- and Two-Dimensional Arrays by Dry Manual Assembly on Patterned Substrates. J. Am. Chem. Soc. 2009, 131, 14228−14230. (4) Fujimori, A.; Sato, N.; Chiba, S.; Abe, Y.; Shibasaki, Y. Surface Morphological Changes in Monolayers of Aromatic Polyamides Containing Various N-Alkyl Side Chains. J. Phys. Chem. B 2010, 114, 1822−1835. (5) Xue, M.; Zhang, Z.; Zhu, N.; Wang, F.; Zhao, X. S.; Cao, T. Transfer Printing of Metal Nanoparticles with Controllable Dimensions, Placement, and Reproducible Surface-Enhanced Raman Scattering Effects. Langmuir 2009, 25, 4347−4351. (6) Lvov, Y.; Munge, B.; Giraldo, O.; Ichinose, I.; Suib, S. L.; Rusling, J. F. Films of Manganese Oxide Nanoparticles with Polycations or Myoglobin from Alternate-Layer Adsorption. Langmuir 2000, 16, 8850−8857. (7) Zakhidov, A. A.; Baughman, R. H.; Iqbal, Z.; Cui, C.; Khayrullin, I.; Dantas, S. O.; Marti, J.; Ralchenko, V. G. Carbon Structures with Three-Dimensional Periodicity at Optical Wavelengths. Science 1998, 282, 897−901. (8) Kim, K. M.; Keum, D. K.; Chujo, Y. Organic-Inorganic Polymer Hybrids Using Polyoxazoline Initiated by Functionalized Silsesquioxane. Macromolecules 2003, 36, 867−875. (9) Naka, K.; Chujo, Y. Control of Crystal Nucleation and Growth of Calcium Carbonate by Synthetic Substrates. Chem. Mater. 2001, 13, 3245−3259. (10) Fujimori, A.; Ninomiya, N.; Masuko, T. Influence of Dispersed Organophilic Montmorillonite at Nanorneter-Scale on Crystallization of Poly(L-lactide). Polym. Eng. Sci. 2008, 48, 1103−1111. (11) Fujimori, A.; Ninomiya, N.; Masuko, T. Structure and Mechanical Properties in Drawn Poly(L-lactide)/Clay Hybrid Films. Polym. Adv. Technol. 2008, 19, 1735−1744. (12) Korobov, M. V.; Avramenko, N. V.; Bogachev, A. G.; Rozhkova, N. N.; O̅ sawa, E. Nanophase of Water in Nano-Diamond Gel. J. Phys. Chem. C 2007, 111, 7330−7334. (13) Osswald, S.; Yushin, G.; Mochalin, V.; Kucheyev, S. O.; Gogotsi, Y. Control of sp2/sp3 Carbon Ratio and Surface Chemistry of Nanodiamond Powders by Selective Oxidation in Air. J. Am. Chem. Soc. 2006, 128, 11635−11642. (14) May, P. W. The New Diamond Age? Science 2008, 319, 1490− 1491. (15) Young, T.-F. Fabrication and Thermal Analysis of a Copper/ Diamond/Copper Thermal Spreading Device. Surf. Coat. Technol. 2007, 202, 1208−1213. (16) Joannopoulos, J. D.; Meade, R. D.; Winn, J. N. Photonic Crystals; Princeton University Press: Princeton, NJ, 1995. (17) Ondic, L.; Dohnalova, K.; Ledinsky, M.; Kromka, A.; Babchenko, O.; Rezek, B. Effective Extraction of Photoluminescence from a Diamond Layer with a Photonic Crystal. ACS Nano 2011, 5, 346−350. (18) Zhou, H.; Xu, L.; Ogino, A.; Nagatsu, M. Investigation into the Antibacterial Property of Carbon Films. Diamond Relat. Mater. 2008, 17, 1416−1419. (19) Zanin, H.; May, P. W.; Fermin, D. J.; Plana, D.; Vieira, S. M. C.; Milne, W. I.; Corat, E. J. Porous Boron-Doped Diamond/Carbon Nanotube Electrodes. ACS Appl. Mater. Interfaces 2014, 6, 990−995. (20) Willey, T. M.; Fabbri, J. D.; Lee, J. R. I.; Schreiner, P. R.; Fokin, A. A.; Tkachenko, B. A.; Fokina, N. A.; Dahl, J. E. P.; Carlson, R. M. K.; Vance, A. L.; Yang, W. L.; Terminello, L. J.; van Buuren, T.; Melosh, N. A. Near-Edge X-ray Absorption Fine Structure Spectroscopy of Diamondoid Thiol Monolayers on Gold. J. Am. Chem. Soc. 2008, 130, 10536−10544. (21) Lam, R.; Chen, M.; Pierstorff, E.; Huang, H.; O̅ hsawa, E.; Ho, D. Nanodiamond-Embedded Microfilm Devices for Localized Chemotherapeutic Elution. ACS Nano 2008, 2, 2095−2102. (22) Krueger, A.; Stegk, J.; Liang, Y.; Lu, L.; Jarre, G. Biotinylated Nanodiamond: Simple and Efficient Functionalization of Detonation Diamond. Langmuir 2008, 24, 4200−4204.
rapid baking since the substrate is partially exposed by disordering of the morphology and arrangement. The contact angle for the surface of pure nanodiamond was only 86°, and γc = 19.6 mN m−1. The findings of this study are summarized in Figure 7. The role of the surface modifying organic chains were discussed based on the two-dimensional integrated layer of organomodified nanodiamond and the formation of a highly ordered multiparticle layered assembly. In the case where an amphipathic long chain organic compound encounters the inorganic particles at the contact interface, new functionality can be imparted to the inorganic particles. Although the presence of an organic chain was essential for layered lamination, the regularity of the two-dimensional integrated organization of the inorganic particles could be maintained as long as the organic chains were slowly desorbed.
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CONCLUSIONS The role of organic chain molecules used for surface modification of inorganic particles was discussed via construction of two-dimensional integration and layered lamination of organo-modified nanodiamond. The “encounter” of an organo-modifying chain with the inorganic particles led to solubilization of the inorganic particles and enhanced interactions between the particles. Multiparticle layered films of organo-nanodiamond were constructed by using the LB technique. Out-of-plane XRD analysis of the single-particle layer of organo-nanodiamond clearly indicated a sharp peak around 5 nm. Mesoscopic-scale AFM images of this singleparticle layer of organo-nanodiamond fabricated by the “repeating compression−expansion process” demonstrated formation of a high density surface with a uniform height of 5 nm. These regular structures are based on the strong van der Waals interactions of the organo-modifying chains. This study could also be simply referred to as an investigation of “new organic−inorganic two-dimensional nanohybrid integration”. However, it is of note that a very unique structure can be obtained that expresses new possibilities for inorganic particles, and indeed, “the occurrence of new possibilities” arises from the amphiphilic long-chain compounds that can be said “to induce novel function of inorganic particles” as a new characteristic of ubiquitous organic molecules.
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ASSOCIATED CONTENT
S Supporting Information *
Figures S1−S3. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Tel and Fax: +81 48 858 3503; e-mail:
[email protected] (A.F.). Notes
The authors declare no competing financial interest.
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REFERENCES
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