Large-surface-area BN nanosheets and their utilization in polymeric composites with improved thermal and dielectric properties
© Wang et al.; licensee Springer. 2012
Received: 15 November 2012
Accepted: 19 November 2012
Published: 30 November 2012
High-throughput few-layered BN nanosheets have been synthesized through a facile chemical blowing route. They possess large lateral dimensions and high surface area, which are beneficial to fabricate effectively reinforced polymeric composites. The demonstrated composites made of polymethyl methacrylate and BN nanosheets revealed excellent thermal stability, 2.5-fold improved dielectric constant, and 17-fold enhanced thermal conductivity. The results indicate multifunctional practical applications of such polymeric composites in many specific fields, such as thermoconductive insulating long-lifetime packaging for electrical circuits.
KeywordsBN nanosheet Polymeric composite Thermal conductivity Dielectric constant
Honeycomb-like mono-/few-layered hexagonal boron nitride (h-BN; also called ‘white’ graphene) is a structural analogue of graphene, which may serve as one of the outstanding representatives of 2D crystals due to its unique physics and diverse functionalities [1, 2]. The robust B-N bonding within a BN layer, even stronger than C-C bonding in graphene, makes mono-/few-layered BN nanosheets highly thermoconductive (ca. thermal conductivity of 100 to 1,000 W/mK), mechanically strong and elastic, and thermally and chemically stable [3, 4]. Partially ionic B-N bonds, different from pure covalent bonds in graphene, make BN nanosheets an intrinsic insulator with a wide band gap (ca. 5.5 eV) valuable for dielectric applications and deep ultraviolet luminescence. Besides, the weak van der Waals bonds out of planes of few-layered BN nanosheets are advantageous for good solid-state lubricants.
Quick heat-releasing and good electrical insulation are required in the packaging materials in high-speed electronics, and polymer materials with a high dielectric constant are attractive for large capacitors and high-k gate in flexible electronics [5–7]. The standard polymer materials normally have low thermal conductivity. One approach toward preparing highly thermal conductive polymeric materials is to embed fillers with high thermal conductivity, such as traditional silicon nitride, aluminum nitride, and boron nitride microparticles. Nanomaterials are more effective fillers for the so-called nanocomposites due to their developed surfaces and high aspect ratios. The polymers embedded with graphenes or other conductive fillers may exhibit high thermal conductivities and dielectric constants before the percolation threshold ; however, the possible electrical current leakage is undesired. BN materials exhibit good electrical insulation to deal with these drawbacks. Comparing with 0D BN nanoparticles  and 1D BN nanofibers/tubes [10–14], 2D BN nanosheets maximally expose their basal (002) crystal planes; therefore, the regarded excellent in-plane properties become dominant because both directions parallel to the (002) planes substantially work for phonon transport in a BN sheet. Intrinsic thermal conductivity of BN nanosheets is notably higher than the reported values of AlN powders and BN powders/nanotubes . BN nanosheets are thus envisaged to be one of the best fillers in composites owing to the highly insulating and thermoconductive properties.
Filling of BN nanosheets into polymeric or ceramic composites requires a sufficient mass of BN nanosheets. The current methods, such as mechanical cleavage, solution exfoliation [16–18], high-energy electron beam irradiation, reaction of boric acid and urea , unwrapping nanotubes , and chemical vapor deposition [20–24], have been utilized to successfully fabricate BN nanosheets; however, mass quantities of BN nanosheets via those methods are still not available on the market due to many problems in reliable chemical intercalations and exfoliations. Recently, a new strategy, the so-called ‘chemical blowing’, has been developed by us [25, 26], which relies on making large bubbles with atomically thin B-N-H polymer walls starting from a precursor ammonia borane compound (AB, which is relatively cheap) and then annealing polymer bubbles into BN ones having ultra-thin BN walls, i.e., BN nanosheets. Here, we use the regarded chemical blowing technology to prepare large amount of BN nanosheets (gram-level) and reveal their high surface area. Based on the high throughput, high surface area, and unique 2D-crystal properties, the produced BN nanosheets effectively perform as excellent fillers in polymeric composites for improving thermal stability, thermal conductivity, and dielectric properties.
Commercial fresh AB (Sigma-Aldrich Corporation, St. Louis, USA) was first pre-treated at 80°C for 1 h. Using a 8°C/min heating rate, the precursors were heated to 1,300°C to obtain the BN products. The products were characterized by scanning electron microscopy (SEM, Hitachi S-4800, Tokyo, Japan), high-resolution transmission electron microscopy (HRTEM, JEOL JEM-3000F, Tokyo, Japan), atomic force microscopy (AFM, JEOL JSPM-5200), electron energy loss spectroscopy (EELS, attachment in TEM), and nitrogen adsorption-desorption measurements carried out at liquid nitrogen temperature (Quantachrome Autosorb-1, Boynton Beach, FL, USA). Brunauer-Emmett-Teller (BET) surface area was estimated over a relative pressure range of 0.05 to 0.3 P/P0. Pore distributions were analyzed using a Barrett-Joyner-Halenda method.
To fabricate polymer/BN composites, as-grown BN products were dispersed in a polymethyl methacrylate (PMMA)/chloroform solution with a controlled weight ratio. The mixture was then spread on a glass plate; this made the solvent naturally volatilized. The residual solvent was removed by further drying at 50°C. The composites were studied by thermogravimetry (TG; Rigaku Thermo plus TG 8120, Tokyo, Japan) and differential scanning calorimetry (DSC; Rigaku Thermo plus EVO DSC8230), thermoconductivity analysis (thermal constant analyzer of Kyoto Electronics Manufacturing Co., Ltd., Kyoto, Japan) following a hot disk method, and dielectric constant analysis (Wayne Kerr precision component analyzer, West Sussex, UK).
Results and discussion
where λc, λf, and λm are the thermal conductivities of composites, BN fillers, and PMMA matrices, respectively; ϕ is the volume fraction of BN fillers. Parameter C1 relates to structures of polymer matrix; and C2 means the difficulty level in forming conductive chains of fillers. In this fitting, C1 = 0.94; C2 = 3.9. The C2 is generally larger than that of powder fillers, implying an easily constructed thermal conductive path, which results from the large lateral size of BN nanosheets grown using chemical blowing technology (tens of μm lateral size of BN nanosheets dispersed in a solution). Together with the abundant interfaces and strong interfacial interactions, the heat in a polymer matrix can, thus, be easily collected and conducted by BN fillers, resulting in a high thermoconductive of the composites.
To sum up, mass production of meso-/macro-porous large-SSA few-layered BN nanosheets is realized; the sheets have successfully been integrated into PMMA polymeric composites. The outstanding (002)-crystal plane properties and abundant interfaces of BN nanosheets are utilized to increase the thermal stability, thermal conductivity, and dielectric properties of the composites, i.e., 17-fold gained thermal conductivity, 2.5-fold increased dielectric constant, and a 18°C increased glass transition temperature were documented. The fabricated PMMA/BN composite plastics are, thus, envisaged to be valuable for diverse functional applications in many fields, especially for the new-generation thermoconductive insulating long-lifetime packaging materials.
XW is a junior researcher of MANA, NIMS, as well as a Ph.D. candidate of Waseda University (Japan) under the supervision of Prof. YB. He obtained his bachelor and master degrees at Nanjing University. At present, he focuses on the syntheses and applications of 2D sp2 hybrid crystals, such as BN nanosheets and graphenes. CZ is a scientist of MANA, NIMS, and is moving to City University of Hong Kong (China) as an assistant professor. He is an expert in the fields of inorganic nanomaterials and functional polymeric composites. DG and YB are two group leaders and professors in MANA, NIMS.
The authors thank Dr. A. Nukui, Dr. N. Kawamoto, Dr. I. Yamada, and Ms. Y. Hirai for the experimental support, and also the MANA support staff for the technical assistance. Financial support from the WPI-MANA, NIMS, Tsukuba, Japan is gratefully acknowledged.
- Pakdel A, Zhi CY, Bando Y, Golberg D: Low-dimensional boron nitride nanomaterials. Mater Today 2012, 15: 256–265. 10.1016/S1369-7021(12)70116-5View ArticleGoogle Scholar
- Zeng HB, Zhi CY, Zhang ZH, Wei XL, Wang XB, Guo WL, Bando Y, Golberg D: White graphenes: boron nitride nanoribbons via boron nitride nanotube unwrapping. Nano Lett 2010, 10: 5049. 10.1021/nl103251mView ArticleGoogle Scholar
- Li C, Bando Y, Zhi CY, Huang Y, Golberg D: Thickness-dependent bending modulus of hexagonal boron nitride nanosheets. Nanotechnology 2009, 20: 385707. 10.1088/0957-4484/20/38/385707View ArticleGoogle Scholar
- Ghassemi HM, Lee CH, Yap YK, Yassar RS: In situ TEM monitoring of thermal decomposition in individual boron nitride nanotubes. JOM 2010, 62: 69.View ArticleGoogle Scholar
- Zhi CY, Bando Y, Terao T, Tang CC, Kuwahara H, Golberg D: Towards thermoconductive, electrically insulating polymeric composites with boron nitride nanotubes as fillers. Adv Funct Mater 2009, 19: 1857–1862. 10.1002/adfm.200801435View ArticleGoogle Scholar
- Li Y, Zhou J, Luo Z, Tung S, Schneider E, Wu J, Li X: Investigation on two abnormal phenomena about thermal conductivity enhancement of BN/EG nanofluids. Nanoscale Res Lett 2011, 6: 443. 10.1186/1556-276X-6-443View ArticleGoogle Scholar
- Martin-Gallego M, Verdejo R, Khayet M, Zarate JM, Essalhi M, Lopez-Manchado MA: Thermal conductivity of carbon nanotubes and graphene in epoxy nanofluids and nanocomposites. Nanoscale Res Lett 2011, 6: 610. 10.1186/1556-276X-6-610View ArticleGoogle Scholar
- Romasanta LJ, Hernandez M, Lopez-Manchado MA, Verdejo R: Functionalised graphene sheets as effective high dielectric constant fillers. Nanoscale Res Lett 2011, 6: 508. 10.1186/1556-276X-6-508View ArticleGoogle Scholar
- Tang CC, Bando Y, Huang Y, Zhi CY, Golberg D: Synthetic routes and formation mechanisms of spherical boron nitride nanoparticles. Adv Funct Mater 2008, 18: 3653–3661. 10.1002/adfm.200800493View ArticleGoogle Scholar
- Huo KF, Hu Z, Chen F, Fu JJ, Chen Y, Liu BH, Ding J, Dong ZL, White T: Synthesis of boron nitride nanowires. Appl Phys Lett 2002, 80: 3611–3613. 10.1063/1.1479213View ArticleGoogle Scholar
- Tang CC, Bando Y, Sato T, Kurashima K: A novel precursor for synthesis of pure boron nitride nanotubes. Chem Commun 2002, 12: 1290–1291.View ArticleGoogle Scholar
- Wang JS, Lee CH, Yap YK: Recent advancements in boron nitride nanotubes. Nanoscale 2028, 2010: 2.Google Scholar
- Li L, Li LH, Chen Y, Dai XJ, Xing T, Petravic M, Liu X: Mechanically activated catalyst mixing for high-yield boron nitride nanotube growth. Nanoscale Res Lett 2012, 7: 417. 10.1186/1556-276X-7-417View ArticleGoogle Scholar
- Zhong B, Huang X, Wen G, Yu H, Zhang X, Zhang T, Bai H: Large-scale fabrication of boron nitride nanotubes via a facile chemical vapor reaction route and their cathodoluminescence properties. Nanoscale Res Lett 2011, 6: 36.View ArticleGoogle Scholar
- Lee GW, Park M, Kim J, Lee JI, Yoon HG: Enhanced thermal conductivity of polymer composites filled with hybrid filler. Compos Part A-Appl S 2006, 37: 727. 10.1016/j.compositesa.2005.07.006View ArticleGoogle Scholar
- Lin Y, Williams TV, Connell JW: Soluble, exfoliated hexagonal boron nitride nanosheets. J Phys Chem Lett 2010, 1: 277–283. 10.1021/jz9002108View ArticleGoogle Scholar
- Lin Y, Williams TV, Xu TB, Cao W, Elsayed-Ali HE, Connell JW: Aqueous dispersions of few-layered and monolayered hexagonal boron nitride nanosheets from sonication-assisted hydrolysis: critical role of water. J Phys Chem C 2011, 115: 2679–2685.View ArticleGoogle Scholar
- Zhi CY, Bando Y, Tang CC, Kuwahara H, Golberg D: Large-scale fabrication of boron nitride nanosheets and their utilization in polymeric composites with improved thermal and mechanical properties. Adv Mater 2009, 21: 2889–2893. 10.1002/adma.200900323View ArticleGoogle Scholar
- Nag A, Raidongia K, Hembram KPSS, Datta R, Waghmare UV, Rao CNR: Graphene analogues of BN: novel synthesis and properties. ACS Nano 2010, 4: 1539. 10.1021/nn9018762View ArticleGoogle Scholar
- Ci L, Song L, Jin C, Jariwala D, Wu D, Li Y, Arivastava S, Wang ZF, Storr K, Balicas L, Liu F, Ajayan PM: Atomic layers of hybridized boron nitride and graphene domains. Nature Mater 2010, 9: 430. 10.1038/nmat2711View ArticleGoogle Scholar
- Shi Y, Hamsen C, Jia X, Kim KK, Reina A, Hofmann M, Hsu AL, Zhang K, Li H, Juang ZY, Dresselhaus MS, Li LJ, Kong J: Synthesis of few-layer hexagonal boron nitride thin film by chemical vapor deposition. Nano Lett 2010, 10: 4134. 10.1021/nl1023707View ArticleGoogle Scholar
- Pakdel A, Zhi CY, Bando Y, Nakayama T, Golberg D: Boron nitride nanosheet coatings with controllable water repellency. ACS Nano 2011, 5: 6507–6515. 10.1021/nn201838wView ArticleGoogle Scholar
- Pakdel A, Wang XB, Zhi CY, Bando Y, Watanabe K, Sekiguchi T, Nakayama T, Golberg D: Facile synthesis of vertically aligned hexagonal boron nitride nanosheets hybridized with graphitic domains. J Mater Chem 2012, 22: 4818–4824. 10.1039/c2jm15109jView ArticleGoogle Scholar
- Gao R, Yin LW, Wang CX, Qi YX, Lun N, Zhang L, Liu YX, Kang L, Wang XF: High-yield synthesis of boron nitride nanosheets with strong ultraviolet cathodoluminescence emission. J Phys Chem C 2009, 113: 15160–15165. 10.1021/jp904246jView ArticleGoogle Scholar
- Wang XB, Zhi CY, Li L, Zeng HB, Li C, Mitome M, Golberg D, Bando Y: Chemical blowing of thin-walled bubbles: high-throughput fabrication of large-area, few-layered BN and Cx-BN nanosheets. Adv Mater 2011, 23: 4072–4076. 10.1002/adma.201101788View ArticleGoogle Scholar
- Wang XB, Pakde A, Zhi CY, Watanabe K, Sekiguchi T, Golberg D, Bando Y: High-yield boron nitride nanosheets from chemical blowing: towards practical applications in polymer composites. J Phys: Condens Matter 2012, 24: 314205. 10.1088/0953-8984/24/31/314205Google Scholar
- Perdigon-Melon JA, Auroux A, Cornu D, Miele P, Toury B, Bonnetot B: Porous boron nitride supports obtained from molecular precursors: influence of the precursor formulation and of the thermal treatment on the properties of the BN ceramic. J Organomet Chem 2002, 657: 98. 10.1016/S0022-328X(02)01589-9View ArticleGoogle Scholar
- Grassie N, Melville HW: The mechanism of the thermal degradation of polymethyl methacrylate. Faraday Soc Disc 1947, 2: 378.View ArticleGoogle Scholar
- Peterson JD, Vyazovkin S, Wight CA: Stabilizing effect of oxygen on thermal degradation of poly (methyl methacrylate). Macromol Rapid Commun 1999, 20: 480–483. 10.1002/(SICI)1521-3927(19990901)20:9<480::AID-MARC480>3.0.CO;2-7View ArticleGoogle Scholar
- Zhi CY, Bando Y, Terao T, Tang CC, Golberg D: Dielectric and thermal properties of epoxy/boron nitride nanotube composites. Pure Appl Chem 2010, 82: 2175–2183. 10.1351/PAC-CON-09-11-41View ArticleGoogle Scholar
- Lunkenheimer P, Fichtl R, Ebbinghaus SG, Loidl A: Nonintrinsic origin of the colossal dielectric constants in CaCu3Ti4O12. Phys Rev B 2004, 70: 172102.View ArticleGoogle Scholar
- Zhou W, Qi S, An Q, Zhao H, Liu N: Thermal conductivity of boron nitride reinforced polyethylene composites. Mater Res Bull 2007, 42: 1863–1873. 10.1016/j.materresbull.2006.11.047View ArticleGoogle Scholar
- Zhi CY, Bando Y, Wang WL, Tang CC, Kuwahara H, Golberg D: Mechanical and thermal properties of polymethyl methacrylate-BN nanotube composites. J Nanomater 2008, 2008: 642036.Google Scholar
- Agari Y, Ueda A, Tanaka M, Nagai S: Thermal conductivity of a polymer filled with particles in the wide range from low to super-high volume content. J Appl Polym Sci 1990, 40: 929–941. 10.1002/app.1990.070400526View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.