Aqueous Dispersions of Silane-Functionalized Laponite Clay Platelets. A First Step toward the Elaboration of Water-Based Polymer/Clay Nanocomposites Norma Negrete Herrera, † Jean-Marie Letoffe, ‡ Jean-Luc Putaux, § Laurent David, | and Elodie Bourgeat-Lami* ,† Laboratoire de Chimie et Proce ´ de ´ s de Polyme ´ risation - UMR 140 CNRS/CPE, Ba ˆ t. 308F, 43, Bd. du 11 Nov. 1918, BP 2077, 69616 Villeurbanne Cedex, France, Laboratoire des Multimate ´ riaux et Interfaces - UMR CNRS 5615 - Universite ´ Claude Bernard Lyon 1, 69622 Villeurbanne Cedex, France, Centre de Recherches sur les Macromole ´ cules Ve ´ ge ´ tales - UPR 5301 CNRS, BP 53, F-38041 Grenoble Cedex 9, France, and Laboratoire des Mate ´ riaux Polyme ` res et Biomate ´ riaux - UMR CNRS 5627 IMP, Ba ˆ t. ISTIL, Universite ´ Claude Bernard Lyon 1, 69622 Villeurbanne Cedex, France Received May 28, 2003. In Final Form: December 3, 2003 Mono- and trifunctional organo alcoxysilane derivatives carrying a terminal reactive methacryloyl group have been used as reagents for the chemical modification of synthetic Laponite clay platelets in toluene. Qualitative evidence of the presence of chemically attached silane molecules was provided by Fourier transform infrared and 29 Si and 13 C solid-state NMR spectroscopies. Quantitative data (grafted amount and grafting yield) were also obtained by means of elemental and thermogravimetric analysis. While the trifunctional coupling agent was grafted on the clay edges in the form of oligomers pillaring the clay stacks, the monofunctional derivative selectively attached to the individual clay sheets as confirmed by X-ray diffraction and Brunauer-Emmett-Teller measurements. In agreement with these findings, only the clay stacks grafted using the monofunctional coupling agent could be satisfactorily redispersed into water. The aqueous suspensions of the grafted colloidal disks were characterized by small-angle X-ray scattering, dynamic light scattering, and cryogenic transmission electron microscopy. Emulsion copolymer latexes, the surface of which was decorated by individual Laponite platelets, were finally produced using the grafted clay particles as seeds. This new method provides an efficient way for constructing water-based polymer/exfoliated clay nanocomposites. I. Introduction During the past 50 years, there has been an increased interest in the synthesis of nanocomposite materials by embedding nanosized inorganic particles into polymers. 1,2 Since the optical, thermal, rheological, or mechanical properties of these materials strongly depend on the techniques used for their elaboration, a variety of synthesis strategies have been reported worldwide with the aim to control the dispersion of the inorganic component within the polymer matrix at the nanoscale. Among the wide range of nanostructured materials, effort has more recently focused on the elaboration of polymer/layered silicate nanocomposites using natural and synthetic clay minerals. 3-5 Clays exhibit many interesting structural features: active sites such as hydroxyl groups, Lewis and Bro ¨ nsted acidity, and exchangeable interlayer cations. 6,7 In addition, the high aspect ratio of clay minerals and the small dimensions of the individual layers render them particularly attractive in several areas of material science. Although there has been much work in the field of polymer/layered silicate nanocomposites since the 1980s, surprisingly only few studies report on the elaboration of exfoliated clay/polymer nanostructures through emulsion polymerization. 5,8-11 Emulsion polymers, however, are widely used in industry and can find applications in a variety of domains including water-borne adhesives, paints, and coating formulations. In addition, the latex route obviously offers interesting perspectives to produce homogeneous dispersions of clay minerals into polymer matrixes by taking advantage of the naturally occurring swelling behavior of clay platelets in water. Among the various swelling clay materials, Laponite, a synthetic hectorite made of discoid platelets with a thickness of about 1 nm, a diameter of about 25 nm, and a negative surface charge density of 0.014 e - /Å, is of particular interest because of its high purity and lateral crystal size of the order of magnitude of latex particle diameter. 12 However, as far as is known, no study has been performed on the incorporation of Laponite platelets into polymer latexes through in situ emulsion polymer- ization, although Laponite has gained importance in numerous fields of applications. 13 * To whom correspondence should be addressed. † Laboratoire de Chimie et Proce ´de ´s de Polyme ´risation - UMR 140 CNRS/CPE. ‡ Laboratoire des Multimate ´riaux et Interfaces - UMR CNRS 5615 - Universite ´ Claude Bernard Lyon 1. § Centre de Recherches sur les Macromole ´cules Ve ´ge ´ tales - UPR 5301 CNRS. | Laboratoire des Mate ´riaux Polyme ` res et Biomate ´ riaux - UMR CNRS 5627 IMP, Universite ´ Claude Bernard Lyon 1. (1) Kickelbick, G.; Schubert, U. In Synthesis, Functionalization and Surface Treatment of Nanoparticles; Baraton, M.-I., Ed.; American Scientific Publishers: Stevenson Ranch, CA, 2002; Chapter 6, p 1. (2) Bourgeat-Lami, E. J. Nanosci. Nanotechnol. 2002, 2, 1. (3) For a review, see: Alexandre, M.; Dubois, P. Mater. Sci. Eng. 2001, 28, 1. (4) Messersmith, P. B.; Giannelis, E. P. Chem. Mater. 1993, 5, 1064. (5) Wang, D.; Zu, J.; Yao, Q.; Wilkie, C. A. Chem. Mater. 2002, 14, 3837. (6) van Olphen, H. An Introduction to Clay Colloid Chemistry; Wiley: New York, 1997. (7) Lee, D. C.; Jang, L. W. J. Appl. Polym. Sci. 1996, 61, 1117. (8) Noh, M. W.; Lee, D. C. Polym. Bull. 1999, 42, 619. (9) Noh, M. W.; Jang, L. W.; Lee, D. C. J. Appl. Polym. Sci. 1999, 74, 179. (10) Noh, M. W.; Lee, D. C. J. Appl. Polym. Sci. 1999, 74, 2811. (11) Kim, Y. K.; Choi, Y. S.; Wang, K. H.; Chung, I. J. Chem. Mater. 2002, 14, 4990. (12) Laponite Technical Bulletin L104/90/A; Laporte Industries Ltd.: 1990; p 1. 1564 Langmuir 2004, 20, 1564-1571 10.1021/la0349267 CCC: $27.50 © 2004 American Chemical Society Published on Web 02/04/2004