7520
Langmuir 1999, 15, 7520-7529
Multilayered Clay Films: Atomic Force Microscopy Study and Modeling Bart van Duffel and Robert A. Schoonheydt* Centrum voor Oppervlaktechemie en Katalyse, K.U. Leuven, Kardinaal Mercierlaan 92, 3001 Leuven, Belgium
Cees P. M. Grim and Frans C. De Schryver Afdeling Fotochemie en Spectroscopie, Departement Scheikunde, K.U. Leuven, Celestijnenlaan 200 F, 3001 Leuven, Belgium Received February 2, 1999. In Final Form: June 15, 1999 Self-assembled natural and synthetic clay-polymer films have been prepared by sequential adsorption of poly(diallyldimethylammonium chloride) (PDDA) and clay particles onto mica. The influence of pH, polymer concentration, and clay particle size on the building and roughness of mono- and multicycle depositions was investigated. The monocyclic deposition gives a submonolayer of clay particles. The thickness of the films increases linearly with the number of cycles in the deposition process, thus giving an average increase of thickness per cycles which depends on clay particle size and PDDA concentration. The film roughness is affected by the same parameters and increases with particle size of the clay and PDDA concentration. Optimal conditions for the deposition of smooth multilayer films consist of the combined use of a 0.05-0.5% (w/w) aqueous solution of PDDA and a 0.05% (w/w) clay suspension at pH ) 9-10. The film formation was modeled assuming a deposition of homogeneous layers partially covering the surface. The model indicates that Laponite films are characterized by significantly higher surface coverages than natural clay films.
Introduction Smectite-type clay minerals are very versatile materials, which find industrial application in a broad range of activities such as adsorption, ion exchange, and catalysis.1 This versatility originates from their unique combination of properties: submicrometer platelike particles, ion exchange, and swelling.2,3 Thus, they can be dispersed in water, and clay mineral films are prepared by simple gravitational sedimentation processes.4,5 Organic cations can be ion exchanged, giving the clay particles a hydrophobic character.4,6,7 If one can control the ordering of these molecules on the surface and if the organization of the clay particles into films can be controlled too, then organized materials are obtained, which by proper choice of clay particles and molecules may exhibit unique electronic, optical, and electrochemical properties. Molecules confined in the interlamellar space of clay mineral particles exhibit specific photophysical and photochemical properties. Among these are photocatalysis, luminescence, photochemical hole burning, nonlinear optics, and others.8-10 At extremely low loadings of methylene blue (MB) on Laponite in aqueous suspension, the hyperpolarizability of MB is increased by a factor of 11 with respect to its solution value.11 Engineering of new * Corresponding author. (1) Murray, H. H. Proceedings of the 10th International Clay Conference; CSIRO Publishing: Melbourne, Australia, 1993; pp 4955. (2) Theng, B. K. G. The Chemistry of Clay Organic Reactions; Wiley: New York, 1974. (3) Sato, T.; Watanabe, T.; Otsuka, R. Clays Clay Miner. 1992, 40, 103-113. (4) Isyama, M.; Sakata, K.; Kunitake, T. Trans. Mater. Res. Soc. Jpn. 1993, 15A, 591-594. (5) De´ka´ny, I.; Haraszti, T. Colloids Surf. 1997, 123-124, 391-401. (6) Stul, M. S.; Maes, A.; Uytterhoeven, J. B. Clays Clay Miner. 1978, 26, 309-317. (7) Ogawa, M.; Shirai, H.; Kuroda, K.; Kato, C. Clays Clay Miner. 1992, 40, 485-490.
materials based on these findings remains difficult, because of the lack of knowledge and of control of the organization of molecules and clay mineral particles. For the organization of particles Langmuir-Blodgett (LB)12-23 and self-assembling (SA) methods have been proposed. The reported SA methods most often consist of the successive deposition of an organic polyelectrolyte and the inorganic colloid particle. In this way films have been prepared using smectites,24-29 zirconium phosphate,30-33 (8) Usami, H.; Takagi, K.; Sawaki, Y. Bull. Chem. Soc. Jpn. 1991, 64, 3395-3401. (9) Tapia Este´vez, M. J.; Lo´pez Arbeloa, F.; Lo´pez Arbeloa, T.; Lo´pez Arbeloa, I.; Schoonheydt, R. A. Clay Miner. 1994, 29, 105-113. (10) Ogawa, M.; Kuroda, K. Chem. Rev. 1995, 95, 399-438, and references cited therein. (11) Boutton, C.; Kauranen, M.; Persoons, A.; Keung, M. P.; Jacobs, K. Y.; Schoonheydt, R. A. Clays Clay Miner. 1997, 45, 483-485. (12) Inukai, K.; Hotta, Y.; Taniguchi, M.; Tomura, S.; Yamagishi, A. J. Chem. Soc., Chem. Commun. 1994, 959. (13) Kotov, N. A.; Meldrum, F. C.; Fendler, J. H.; Tomba´cz, E.; De´ka´ny, I. Langmuir 1994, 10, 3797-3804. (14) Ewins, C. T.; Stewart, B. Thin Solid Films 1996, 284-285, 4952. (15) Hotta, Y.; Taniguchi, M.; Inukai, K.; Yamagishi, A. Langmuir 1996, 12, 5195-5201. (16) Dultsev, F. N.; Sveshnikova, L. L. Thin Solid Films 1996, 288, 103-107. (17) Li, L. S.; Hui, Z.; Chen Y.; Zhang, X. T.; Peng X.; Liu, Z.; Li, T. J. J. Colloid. Interface. Sci. 1997, 192, 275-280. (18) Mayya, K. S.; Patil, V.; Sastry, M. Langmuir 1997, 13, 25752577. (19) Li, L. S.; Qu, L.; Wang, L.; Lu, W.; Peng, X.; Zhao, Y.; Li, T. J. Langmuir 1997, 13, 6183-6187. (20) Mayya, K. S.; Patil, V.; Kumar, P. M.; Murali, S. Thin Solid Films 1998, 312, 300-305. (21) Schurr, M.; Brugger, A.; Schopman, Ch.; Voit, H. Thin Solid Films 1998, 324, 253-256. (22) Sastry, M.; Patil, V.; Mayya, K. S.; Paranjape, D. V.; Singh, P.; Sainkar, S. R. Thin Solid Films 1998, 324, 239-244. (23) Vitta, S.; Metzger, T. H.; Major, S. S.; Dhanabalan, A.; Talwar, S. S. Langmuir 1998, 14, 1799-1803. (24) Kleinfeld, E. R.; Ferguson, G. S. Science 1994, 265, 370-373. (25) Ferguson, G. S.; Kleinfeld, E. R. Adv. Mater. 1995, 7, 414-416.
10.1021/la990110n CCC: $18.00 © 1999 American Chemical Society Published on Web 08/31/1999
Multilayered Clay Films
and graphite oxide.34 The success of the SA method can be traced back to the plateletlike particles, which tend to organize spontaneously into films. However, SA film preparation is also reported for spherical colloidal particles of gold,35-40 cadmium and lead sulfide,41-43 titanium oxide,44 and silicon oxide.45 A fast and simple SA method is the sequential adsorption of poly(diallyldimethylammonium chloride) (PDDA) and Laponite clay particles on a silicon substrate. This procedure, first reported by Kleinfeld and Ferguson,24 is based on the Coulombic interaction between the anionic colloid platelets and the cationic polymer. In this paper we extend this procedure to the incorporation of natural clay particles and investigate the influence of parameters such as particle size, pH, and polymer concentration on the film formation. A primitive model is proposed to describe film formation. Experimental Section (1) Materials. As a cationic polymer PDDA (Aldrich, medium molecular weight) was used. The synthetic clay was Laponite (Laporte Industries), which is chemically analogous to Hectorite. The particles of this clay are considered to be disk shaped with an average diameter of 30 nm. Its cation exchange capacity (CEC) is 568 µequiv/g. The two natural clays were Hectorite (particle size fractions < 0.5 µm and < 0.05 µm; CEC ) 525 µequiv/g) and Saponite (particle size fraction < 0.05 µm; CEC ) 738 µequiv/g) from the Source Clay Minerals Repository of the Clay Minerals Society. The natural clays were Na+-saturated by repeated (three times) exchange with 1 M NaCl solutions followed by dialysis with water until Cl- free (AgCl test). The different particle size fractions were prepared by centrifugation after which the clays were freeze-dried and stored in a dark room. The CEC’s were determined with the 22Na method.46 The water used in all (26) Kleinfeld, E. R.; Ferguson, G. S. Chem. Mater. 1995, 7, 23272331. (27) Lvov, Y.; Ariga, K.; Ichinose, I.; Kunitake, T. Thin Solid Films 1996, 284-285, 797-801. (28) Kotov, N. A.; Haraszti, T.; Turi, L.; Zavala, G.; Geer, R. E.; De´ka´ny, I.; Fendler, J. H. J. Am. Chem. Soc. 1997, 119, 6821-6832. (29) Hotta, Y.; Inukai, K.; Taniguchi, M.; Yamagishi, A. J. Colloid Interface Sci. 1997, 188, 404-408. (30) Lee, H.; Kepley, L. J.; Hong, H.; Akhter, S.; Mallouk, T. E. J. Phys. Chem. 1988, 92, 2597-2601. (31) Vermeulen, L. A.; Snover, J. L.; Sapochak, L. S.; Thompson, M. E. J. Am. Chem. Soc. 1993, 115, 11767-11774. (32) Byrd, H.; Whipps, S.; Pike, J. K.; Ma, J.; Nagler, S. E.; Talham, D. R. J. Am. Chem. Soc. 1994, 116, 295-301. (33) Hanken, D. G.; Naujok, R. R.; Gray, J. M.; Corn, R. M. Anal. Chem. 1997, 69, 240-248. (34) Kotov, N. A.; De´ka´ny, I.; Fendler, J. H. Adv. Mater. 1996, 8, 637-641. (35) Griffith, F. R.; Grabar, K. C.; Allison, K. J.; Bright, R. M.; Davis, J. A.; Guthrie, A. P.; Hommer, M. B.; Jackson, M. A.; Smith, P. C.; Walter, D. G.; Natan, M. J. Science 1995, 267, 1629-1632. (36) Grabar, K. C.; Freeman, G. R.; Hommer, M. B.; Natan, M. J. Anal. Chem. 1995, 67, 735-743. (37) Feldheim, D. L.; Grabar, K. C.; Natan, M. J.; Mallouk, T. E. J. Am. Chem. Soc. 1996, 118, 7640-7641. (38) Grabar, K. C.; Allison, K. J.; Baker, B. E.; Bright, R. M.; Brown, K. R.; Freeman, R. G.; Fox, A. P.; Keating, C. D.; Musick, M. D.; Natan, M. J. Langmuir 1996, 12, 2353-2361. (39) Bandyopadhyay, K.; Patil, V.; Vijayamohanan, K.; Sastry, M. Langmuir 1997, 13, 5244-5248. (40) Schmitt, J.; Decher, G.; Dressick, W. J.; Brandow, S. L.; Geer, R. E.; Shashidhar, R.; Calvert, J. M. Adv. Mater. 1997, 9 (1), 6165. (41) Kotov, N. A.; De´ka´ny, I.; Fendler, J. H. J. Phys. Chem. 1995, 99, 13065-13069. (42) Gao, M.; Zhang, X.; Yang, B.; Li, F.; Shen, J. Thin Solid Films 1996, 284-285, 242-245. (43) Nanda, K. K.; Sarangi, S. N.; Mohanty, S.; Sahu, S. N. Thin Solid Films 1998, 322, 21-27. (44) Huang, D.; Xiao Z.-D.; Gu, J.-H.; Huang, N.-P.; Yuan, C.-W. Thin Solid Films 1997, 305, 110-115. (45) Lvov, Y.; Ariga, K.; Onda, M.; Ichinose, I.; Kunitake, T. Langmuir 1997, 13, 6195-6203.
Langmuir, Vol. 15, No. 22, 1999 7521 experiments was deionized, distilled water. As a substrate for the films, freshly cleaved mica was used. (2) Methods. Preparation of Clay Suspensions. Clays were suspended in LiOH and NaOH solutions at a clay concentration of 0.05 wt %. The LiOH and NaOH concentrations ranged from 10-7 M (pH ) 7) to 10-2 M (pH ) 12). The particle size fractions of the natural clays were
