Particle size control and dependence on solution pH of carboxylate±alumoxane nanoparticles Cullen T. Vogelson, Andrew R. Barron * Department of Chemistry, Center for Nanoscale Science and Technology, Rice University, MS-60, 6100 Main Street, Houston, TX 77005, USA Received 5 April 2000; received in revised form 23 November 2000 Abstract A series of water dispersible carboxylate±alumoxane nanoparticles were prepared by the reaction of various carb- oxylic acids with the mineral boehmite. The acids used were: acetic A±H), methoxyacetic MA±H), methoxyethoxy- acetic MEA±H), methoxyethoxyethoxyacetic MEEA±H), and lysine L±H). For each of the derived carboxylate± alumoxanes, particle size measurements were obtained by means of photon correlation spectroscopy PCS) as a function of solution pH. In all cases, at higher pHs, slight increases in solution basicity corresponded to large increases in particle size. At lower pHs, however, changes in solution basicity yielded only slight to moderate increases in particle size. It was also found during these investigations that methoxyacetic±alumoxane MA±A) had a large buering ca- pacity, and that this eect could be explained by correlation with the aluminum:carboxylate group ratio for the various carboxylate±alumoxanes. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction The ability to control particle sizes of compo- nents in a matrix is an important process which hasbeenstudiedextensivelybychemists,physicists and material scientists [1]. Since smaller particles possess larger numbers of reactive sites, they are important for applications ranging from catalysis to optical, mechanical, and electronic devices [2± 4]. In addition, small particles are of great im- portance as ®llers in epoxy resin materials due to their ability to limit crack propagation sites while, at the same time, increasing both the tensile and ¯exural strength of the cured resin [5,6]. For these reasons, among others, the ability to systemati- cally control component particle sizes in various solutions is highly desirable. Speci®c control of particle size is often quite dicult. In chemical polymerization processes, particle size is directed by the careful control of monomer, initiator, and/or solvent concentration [7,8]. In the case of oxide ceramics produced through sol±gel polymerization processes, several additional techniques, both physical and chemical, have been employed. Commonly, the method used in the sol±gel approach involves the careful mon- itoring of temperature, water content, and the presence of reacted products in the sol [2,4]. Other techniques frequently used for ceramic powders include centrifugal processing to induce size se- lectivity [9]. One ®nal means of selecting particle size in both cases involves adjusting the pH of Journal of Non-Crystalline Solids 290 2001) 216±223 www.elsevier.com/locate/jnoncrysol * Corresponding author. Tel.: +1-713 348 5610; fax: +1-713 348 5619. E-mail address: arb@rice.edu A.R. Barron). 0022-3093/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0022-309301)00643-3