Langmuir 2000, 16, 9031-9034
9031
Encapsulation of Nanosized Silica by in Situ Polymerization of tert-Butyl Acrylate Monomer† Ivan Sondi,‡ Theodore H. Fedynyshyn,§ Roger Sinta,§ and Egon Matijevic´*,‡ Center for Advanced Materials Processing, Clarkson University, Box 5814, Potsdam, New York 13699-5814, and Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420-9108 Received April 27, 2000. In Final Form: July 12, 2000 Stable dispersions of nanosilica ranging in size between 8 and 11 nm were coated with tert-butyl acrylate polymer by in situ polymerization of monomer adsorbed on the particles in 2-propanol. The system was developed for use in the encapsulated inorganic resist technology. To achieve a high coating efficiency, silica was first modified with the 3-(trimethoxysilyl)propylmethacrylate (MPS) coupling agent at two different degrees of grafting. The presence of the bound MPS agent and of the polymer at the silica surface was determined by the attenuated total reflection infrared spectroscopy, while the amounts bound were assessed by the thermogravimetric analysis. Under studied conditions, the encapsulation efficiency was governed by the degree of MPS grafting and by the initial concentration of the monomer. Finally, the dissolution rate of these particles in aqueous base, a key parameter in photoresist application, was drastically reduced with increasing amount of grafted tert-butyl acrylate polymer at the silica surface.
Introduction The encapsulation of inorganic particles with polymers is desirable in many applications in order to alter the surface characteristics of the cores, to enhance the stability of the dispersions, and to improve the dispersibility in organic media.1-3 In principle, the most direct approach to coat the particles is to adsorb preformed polymers, which under certain conditions may yield a uniform shell.4-6 When dealing with nanosized dispersions, the encapsulation of nonaggregated particles is a challenging task. A more promising approach to achieve organic shells is to interact the inorganic cores with monomers and to polymerize the latter in situ. According to Luzinov and co-workers,7 this procedure is more favorable for obtaining a uniform coating of each particle, because of the substantially higher accessibility of the active surface of cores for molecules of a monomer rather than for the corresponding macromolecules. Indeed, colloidal particles have been successfully encapsulated by dispersion polymerization.1,8,9 Owing to many uses of silica, different methods for the encapsulation of such particles have been reported.10-14 † Part of the Special Issue “Colloid Science Matured, Four Colloid Scientists Turn 60 at the Millennum”. ‡ Clarkson University. § Massachusetts Institute of Technology.
(1) van Herk, A. M. In Polymeric Dispersions: Principles and Applications; Asua, J. M., Ed.; Kluwer Academic Publishers: Dordrecht, 1997; pp 435-450. (2) Pu, J.-L.; Hanna, J. I.; Kokado, H. J. Imaging Sci. 1988, 32, 129. (3) Sato, T.; Ruch, R. Stabilization of Colloidal Dispersions by Polymer Adsorption; Marcel Dekker: New York, 1980; p 155. (4) King, S. M.; Cosgrove, T.; Eaglesham, A. Colloids Surf. 1996, 108, 159. (5) Bijsterbosch, H. D.; Cohen Stuart, M. A.; Fleer, G. J. J. Colloid Interface Sci. 1999, 210, 37. (6) Dijt, J. C.; Cohen Stuart, M. A.; Fleer, G. J. Macromolecules 1994, 27, 3207. (7) Luzinov, I.; Evchuk, I.; Minko, S.; Voronov, S. J. Appl. Polym. Sci. 1998, 67, 229. (8) Oyama, H. T.; Sprycha, R.; Xie, Y.; Partch, R. E.; Matijevic´, E. J. Colloid Interface Sci. 1993, 160, 298. (9) Huang, C.-L.; Partch, R. E.; Matijevic´, E. J. Colloid Interface Sci. 1995, 170, 275. (10) Tsubokawa, N.; Kimoto, T.; Koyama, K. Colloid Polym. Sci. 1993, 271, 940.
Recently, the preparation of structurally well-defined silica-polystyrene composites was achieved by dispersion polymerization in polar media.15,16 It appears, however, that the formation of an organic shell on extremely small silica nanoparticles (
