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Structural Colored Balloons Consisting of Polystyrene Microcapsules in Water Fumiyoshi Ikkai* L’Oreal Recherche, Nihon L’Oreal K.K., KSP R&D-D637, 3-2-1 Sakado, Takatsu-ku, Kawasaki, Kanagawa 213-0012, Japan ReceiVed April 10, 2007. In Final Form: September 9, 2007 Structural colored balloons (SCBs) consisting of polystyrene microcapsules in water were prepared and characterized. SCBs were produced by the solvent evaporation method of W/O/W-type double emulsion. Because the surface thickness of SCB was controlled to be comparable to a visible-light wavelength, SCB developed various structural colors from violet to red depending on the surface thickness. SCB characterization revealed that (1) the surface thickness was independent of SCB size, (2) the developing color distribution was random, and (3) the surface thickness was strongly related to the developing color. The relationship between surface thickness, developed color, and capsule size can be predicted by an optical theory. Scanning electron microscopy (SEM) images proved the validity of the theoretical calculation.
Introduction Structural color development is potentially one of the most important techniques in industrial fields concerned with color, especially in cosmetics and paints. Because structural color is developed by an optical effect (i.e., diffraction, reflection, interference, etc.) that does not involve pigments, it has received attention as a new kind of color-developing material. The word structural color/colour was used in 1901 at the latest by Johnson,1 who discussed the structural color of layered tapetum developed in the eyes of animals. In 1913, the first emulsions exhibiting a wide range of structural colors were prepared by Bodroux.2 In the 1920s, structural colors of birds, insects, and trees were thoroughly investigated,3-9 and later on fish in the 1970s1980s.10-13 However, when artificial colloidal crystals were reported in the 1950s,14 many researchers were interested in the structural color of colloidal crystals,15-18 and their manufacturing process prompted many studies.19-25 Since the late 1990s, whereas the methods described above can be considered to be static as far as the developing colors are * E-mail:
[email protected]. Tel: +81-44-812-2013. Fax: +81-44812-2033. (1) Johnson, G. L. Philos. Trans. R. Soc. London, Ser. B 1901, 194, 1. (2) Bodroux, F. Compt. Rend. 1913, 156, 772. (3) Hayes, W. P. Trans. Am. Micro. Soc. 1922, 41, 1. (4) Mason, C. W. J. Phys. Chem. 1923, 27, 201. (5) Bancroft, W. D. J. Phys. Chem. 1924, 28, 351. (6) Bancroft, W. D. J. Phys. Chem. 1926, 30, 521. (7) Mason, C. W. J. Phys. Chem. 1926, 30, 383. (8) Merritt, E. J. Opt. Soc. Am. ReV. Sci. Inst. 1925, 11, 93. (9) Rayleigh, L. Proc. R. Soc. London, Ser. A 1930, 128, 624. (10) Rohrlich, S. T. J. Cell Biol. 1974, 62, 295. (11) Lythgoe, J. N.; Shand, J. EnViron. Biol. Fish. 1983, 8, 249. (12) Clothier, J.; Lythgoe, J. N. J. Cell Sci. 1987, 88, 663. (13) Shand, J. J. Fish Biol. 1988, 32, 625. (14) Alfrey, T. J.; Bradford, E. B.; Vanderhoff, J. W.; Oster, G. J. Opt. Soc. Am. 1954, 44, 603. (15) Luck, W.; Klier, M.; Wesslau, H. Ber. Bunsen-Ges. Phys. Chem. 1963, 67, 75. (16) Krieger, I. M.; O’Neill, F. M. J. Am. Chem. Soc. 1968, 90, 3114. (17) Hiltner, P. A.; Krieger, I. M. J. Phys. Chem. 1969, 73, 2386. (18) Clark, N. A.; Hurd, A. J.; Ackerson, B. J. Nature 1979, 281, 57. (19) Dushkin, C. D.; Nagayama, K.; Miwa, T.; Kralchevsky, P. A. Langmuir 1993, 9, 3695. (20) Asher, S. A.; Holtz, J.; Liu, L.; Wu, Z. J. Am. Chem. Soc. 1994, 116, 4997. (21) Mayoral, R.; Requena, J.; Moya, J. S.; Lopez, C.; Cintas, A.; Miguez, H.; Meseguer, F.; Vazquez, L.; Holgado, M.; Blanco, A. AdV. Mater. 1997, 9, 257. (22) Dimitrov, A. S.; Miwa, T.; Nagayama, K. Langmuir 1999, 15, 5257. (23) Hattori, H. Thin Solid Films 2001, 385, 302. (24) Sullivan, M.; Zhao, K.; Harrison, C.; Austin, R. H.; Megens, M.; Hollingsworth, A.; Russel, W. B.; Cheng, Z.; Mason, T.; Chaikin, P. M. J. Phys.: Condens. Matter 2003, 15, S11.
entirely decided by initial preparation conditions, dynamic structural color development using polymer gels was published. For example, Asher et al.26-28 enclosed polymer particles in an environment-responsive polymer gel and controlled the structural color by changing the interparticle distance through the gel swelling behavior. In addition, Fudouzi et al.29 enclosed silica colloidal particles into rubber and controlled the structural color by physical stimulation. Hu et al.30,31 prepared monosized microgel particles consisting of a temperature-sensitive polymer (i.e., N-isopropylacrylamide) with a diameter in the range of a visible-light wavelength. The size of those microgel particles changes depending on temperature, resulting in a change in the color of concentrated solutions containing microgel particles. Takeoka et al.32 made temperature-sensitive porous gels by using regularly packed silica colloidal crystals as microstructure templates. The gel pore size and the distance between pores can change quickly depending on temperature, resulting in a change in structural color. In this article, we studied a kind of soap bubble. A soap bubble is the simplest but one of the oldest and most attractive materials used in developing structural colors. The fact that the principle of structural color development by soap bubbles is due to an optical thin layer interference phenomenon occurring at the bubble surface was discussed in 1704 by Newton.33 The scene of the structural color change with decreasing surface thickness by drying is fascinating. The initial idea for this study came from immobilizing the structural color of these soap bubbles. Here, we introduce a new type of soap-bubble-like structural colored material (i.e., a structural colored balloon (SCB)) that consists of nonaqueous polymers in water, and we discuss the relationship between the developing color and balloon structure. Experimental Section Materials. Polystyrene (Mw ) 200 000), gelatin, and dichloromethane were purchased from Wako Chemical Co. Ltd., Tokyo. They were used without further treatment. (25) Palberg, T.; Biehl, R. Faraday Discuss. 2003, 123, 133. (26) Holtz, J. H.; Asher, S. A. Nature 1997, 389, 829. (27) Weissman, J. M.; Sunkara, H. B.; Tse, A. S.; Asher, S. A. Science 1996, 274, 959. (28) Pan, G.; Kesavamoorthy, R.; Asher, S. A. Phys. ReV. Lett. 1997, 78, 3860. (29) Fudouzi, H. J. Colloid Interface Sci. 2004, 275, 277. (30) Hu, Z.; Lu, X.; Gao, J. AdV. Mater. 2001, 13, 1708. (31) Hu, Z.; Huang, G. Angew. Chem., Int. Ed. 2003, 42, 4799. (32) Takeoka, Y.; Watanabe, M. Langmuir 2003, 19, 9554. (33) Newton, I. Optics or a Treatise of the Reflections, Refractions, Inflections and Colours of Light; Impensis S. Smith & B. Walford: London, 1706.
10.1021/la701044b CCC: $40.75 © 2008 American Chemical Society Published on Web 03/04/2008
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Figure 2. Relative reflectance spectra of the interference light on the surfaces of arbitrary chosen colored SCBs.
Figure 1. (a) As-prepared second emulsified solution and micrographs of structural colored balloons (SCB) filtered using four types of sieves with different pore sizes: (b)
