pubs.acs.org/Langmuir © 2010 American Chemical Society
Sonochemical Synthesis of Magnetic Janus Nanoparticles Boon M. Teo,† Su Kyung Suh,‡ T. Alan Hatton,*,‡ Muthupandian Ashokkumar,*,† and Franz Grieser*,† †
Particulate Fluids Processing Centre, School of Chemistry, University of Melbourne, Victoria 3010, Australia, and ‡Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States Received October 26, 2010. Revised Manuscript Received November 29, 2010
The sonochemical synthesis of nanosized surface-dissymmetrical (Janus) particles is described. The Janus particles were composed of silica and polystyrene, with the polystyrene portion loaded with nanosized magnetite particles. It is shown that the Janus particles can be used to form kinetically stable oil-in-water emulsions that can be spontaneously broken on application of an external magnetic field. The one-pot synthetic process used to prepare the Janus particles has several advantages over other conventional methods of producing such particles.
Introduction Ever since the fabrication of surface-dissymmetrical particles was first reported in the 1980s by Casagrande and Veyssie,1,2 there has been a surge of interest in these structures because of the wealth of promising applications that such particles have to offer. These Janus particles, a term first used by de Gennes3 in deference to the Roman double-faced god of gateways, are usually micro- or nanosized spheres with hemispherical amphiphilicity, that is, onehalf or a section of the sphere is polar and the other is nonpolar.4-17 Such particles are expected to be especially effective in stabilizing mixtures of immiscible liquids (Pickering effect) and in other applications such as biosensors and two-colored Janus particles for use in electronic paper or other display applications.18,19 Several articles have already been published on Janus particles, *Corresponding authors. (T.A.H.) E-mail:
[email protected]. (M.A. and F.G.) E-mail:
[email protected],
[email protected]. Tel: þ61383446476. Fax: þ61393475180.
(1) Wurm, F.; Kilbinger, A. F. M. Angew. Chem., Int. Ed. 2009, 48, 8412. (2) Casagrande, C.; Veyssie, M. C. R. Acad. Sci. 1988, 306, 1423. (3) de Gennes, P. G. Croat. Chem. Acta 1998, 71, 833. (4) Perro, A.; Reculusa, S.; Ravaine, S.; Bourgeat-Lami, E.; Duguet, E. J. Mater. Chem. 2005, 15, 3745. (5) Binks, B. P. Curr. Opin. Colloid Interface Sci. 2002, 7, 21. (6) Binks, B. P.; Fletcher, P. D. I. Langmuir 2001, 17, 4708. (7) Isojima, T.; Suh, S. K.; Vander Sande, J. B.; Hatton, T. A. Langmuir 2009, 25, 8292. (8) Isojima, T.; Lattuada, M.; Vander Sande, J. B.; Hatton, T. A. ACS Nano 2008, 2, 1799. (9) Lattuada, M.; Hatton, T. A. J. Am. Chem. Soc. 2007, 129, 12878. (10) Yin, Y.; Lu, Y.; Xia, Y. J. Am. Chem. Soc. 2001, 123, 771. (11) Giersig, M.; Ung, T.; Liz-Marzan, L. M.; Mulvaney, P. Adv. Mater. 1997, 9, 570. (12) Chen, T.; Yang, M. X.; Wang, X. J.; Tan, L. H.; Chen, H. Y. J. Am. Chem. Soc. 2008, 130, 11858. (13) Liu, B.; Wei, W.; Qu, X. Z.; Yang, Z. H. Angew. Chem., Int. Ed. 2008, 47, 3973. (14) Hu, S. H.; Gao, X. H. J. Am. Chem. Soc. 2010, 132, 7234. (15) Petit, L.; Sellier, E.; Duguet, E.; Ravaine, S.; Mingotaud, C. J. Mater. Chem. 2000, 10, 253. (16) Gu, H.; Yang, Z.; Gao, J.; Chang, C. K.; Xu, B. J. Am. Chem. Soc. 2005, 127, 34. (17) Yu, H.; Chen, M.; Rice, P. M.; Wang, S. X.; White, R. L.; Sun, S. Nano Lett. 2005, 5, 379. (18) McNaughton, B. H.; Agayan, R. R.; Wang, J. X.; Kopelman, R. Sens. Actuators, B 2007, 121, 330. (19) Roh, K. H.; Yoshida, M.; Lahann, J. Langmuir 2007, 23, 5683. (20) Lu, W.; Chen, M.; Wu, L. M. J. Colloid Interface Sci. 2008, 328, 98. (21) Cayre, O.; Paunov, V. N.; Velev, O. D. Chem. Commun. 2003, 18, 2296. (22) Koo, H. Y.; Yi, D. K.; Yoo, S. J.; Ki, D. Y. Adv. Mater. 2004, 16, 274.
30 DOI: 10.1021/la104284v
with particular focus on the synthesis methods.20-24 However, most of these methods are template-assisted or require a multiplestep procedure. Hence, it is of practical interest to synthesize such particles by a simple, effective one-pot process. Herein, we report a convenient one-pot process to illustrate the technical simplicity and efficacy of using ultrasound irradiation to prepare magnetic Janus particles. We have previously demonstrated the ease of synthesizing magnetite latex nanoparticles via an effective and innocuous sonochemical miniemulsion polymerization method.25 The current work is a novel extension to the encapsulation of inorganic materials into polymeric Janus particles. It is based on the strategy that during polymerization reactions at elevated temperature the elastic stress driven by the entropy change in the swollen networks can cause phase separation resulting in two-phase nonspherical particles.26 In addition, as a proof of concept, we demonstrate the potential of these magnetic Janus particles as emulsion stabilizers for oil/water systems and the ability to induce reversible macroscopic phase separation upon the application of an external magnetic field.
Experimental Details Chemicals. Tetraethoxysilane (98%), (3-aminopropyl)trimethoxysilane (97%), benzyl ether (99%), iron tri(acetylacetonate) (97%), oleic acid (90%), oleyl amine (70%), 1,2-tetradecanediol (90%), and styrene (g99%) were purchased from SigmaAldrich. Methanol (99.8%) was purchased from Mellinkrod, and ammonia (28 wt % aqueous solution) was purchased from ChemSupply. The monomer was filtered twice through basic aluminum oxide to remove the inhibitor, hydroquinone. The purified monomer was then sealed and stored below 4 °C until further use. High-purity (99%, AR grade) sodium dodecylsulfate (SDS) was purchased from BDH. Milli-Q-filtered water (18 MΩ cm-1) was used to prepare all aqueous solutions. High-purity nitrogen gas, provided by BOC Gases, was used for sparging solutions without further purification. (23) Okubo, M.; Fujibayashi, T.; Yamada, M.; Minami, H. Colloid Polym. Sci. 2005, 283, 1041. (24) Zhao, N.; Gao, M. Y. Adv. Mater. 2009, 21, 184. (25) Teo, B. M.; Chen, F.; Hatton, T. A.; Grieser, F.; Ashokkumar, M. Langmuir 2009, 25, 2593. (26) Sheu, H. R.; El-Aasser, M. S.; Vanderhoff, J. W. J. Polym. Sci., Part A: Polym. Chem. 1990, 28, 629.
Published on Web 12/06/2010
Langmuir 2011, 27(1), 30–33
Teo et al.
Letter
Figure 1. Schematic diagram of the procedure for the synthesis of magnetic asymmetric Janus particles by the sonochemically driven miniemulsion polymerization pathway.
Apparatus. The equipment employed for the sonochemical polymerization reactions comprised a 20 kHz Branson 450 ultrasound generator equipped with a sonotrode of 19 mm in diameter with a stainless steel tip. A custom-made glass reaction cell was surrounded by a water jacket through which circulated thermostatted water maintained a constant temperature of 60 °C. Synthesis of Materials. Monodisperse 10-nm-diameter (
