Growth of TiO 2 Particles within a Polymeric Matrix
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GROWTH OF TiO 2 PARTICLES WITHIN A POLYMERIC MATRIX J.W. BURDON and PAUL CALVERT, Arizona Materials Laboratory, 4715 East Fort Lowell Road, Tucson, Arizona 85712 USA. ABSTRACT As a simple model for biomineralization we are investigating the deposition of oxide particles into polymers by the in situ hydrolysis of oxides. By light scattering and electron microscopy we have observed the development of titania in polyvinylchloride. Hydrolysis is due to exposure to atmospheric moisture after film formation under very dry conditions. We believe that 6--
of alkoxide initially phase separate and then are hydrolysed. Using a strongly Aolymer as a matrix for silica formation we present evidence for catalysis of particle
-tby the matrix. aODUCTION Synthetic ceramics and composites are usually produced by first preparing filler particles 1 fibers, which are then processed and packed into the required shape.
The structural
mplexity of these man-made materials is often limited. Nature however provides a wealth i structurally complex biological composites, such as bones, teeth, and shell. Typically, these aaterials contain fine arrays of ordered, or aligned particles, with high packing density. The important difference which separates biological composites from synthetic ones is that the inorganic filler particles are grown in-situ in a pre-formed organic polymer matrix [1]. In setting out to mimic and enhance the materials produced biologically, the initial problem is that of finding a suitable chemistry that is able to precipitate inorganics within an organic matrix.
For this we took advantage of the already broad knowledge of alkoxide
chemistry, which is used extensively to produce ceramics, glass systems, and monosized particles [2,3]. Most kinetic work has revolved around the hydrolysis of alkoxides in solution [4,5]. In our system however, hydrolysis is occurring in a solid polymer matrix, and so we would not expect to be able to apply solution kinetics. We would eventually like to show that the organic polymer phase has a direct affect on nucleation, growth, and particle orientation. PRECIPITATION OF TITANIA IN POLYVINYLCHLORIDE Many metal alkoxides are quite compatible with polymers so that single phase mixtures can be formed and precipitation induced by treatment of the polymer-alkoxide film with water, base or water vapor [12,13, 14]. In our past studies we have found that the particles which form are typically 0.5 pm diameter and appear to be agglomerates of smaller particles. We have recently been using light scattering to follow growth of these particles as the alkoxide Mat. Res. Soc. Symp. Proc. Vol. 218. @1991 Materials Research Society
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hydrolyses in polymers under carefully controlled conditions. Materials and Sample Preparation Poly(vinyl chloride) (PVC) was dried by placing in a vacuum oven overnight at 30 °C. Titanium (IV) tetraisopropoxide, Titanium (IV) tetrabutoxide, and Titanium (IV) 2-ethylhexoxide, were used as received. Tetrahydrofuran (THF), was dried by distillation over sodium metal. All
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