Microscale Titania Shapes Grown Within Swollen PDMS
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Microscale Titania Shapes Grown Within Swollen PDMS Daniel P. Brennan, Arthur D. Dobley and Scott R. J. Oliver Department of Chemistry, State University of New York at Binghamton Binghamton, NY 13902-6016, U.S.A. ABSTRACT A variety of titania microstructures have been synthesized using a swollen polymer matrix of polydimethylsiloxane (PDMS). The shapes and structures grown to date include spheres, ‘bowls’, ‘nets’ and ‘brain coral’ matrices. The PDMS polymer network can be swollen by one of a variety of organic solvents. These solvents create internal voids or spaces within the PDMS, of particular volume. These spaces can then be filled with metal alkoxide liquid. The metal alkoxide is then polymerized to form metal oxides, in a shape templated by the swollen PDMS polymer. The resultant product is a composite of metal oxide within a polymer. Some of the shapes can be removed mechanically or chemically. Methods of characterization include scanning electron microscopy (SEM) and optical microscopy. Potential applications of the shaped titania include catalysts, fillers, capsules, and chemical separators. The synthesis and characterization of these compounds will be discussed.
INTRODUCTION There is currently a great deal of interest in the synthesis of microscale and nanoscale structures for use in catalysis, chemical separation, and for application as cosmetic and pharmaceutical capsules [1]. Previous work by others with polymeric materials as supports has focused on the growth of inorganic particles or continuous materials [2-5]. One of the most famous examples is the recent work on inverse opals [6-8]. The technique involves the use of tightly packed assemblies of monodisperse microspheres composed of SiO2, polymethylmethacrylate or polystyrene as supports. Carbon, silicon or titania networks can then be synthesized in the opal void space. The support is then either selectively dissolved or calcined away, leaving intact the macroporous inverse replica of the packed spheres. Typically, the technique involves repeated deposition of precursor to achieve complete, free-standing titania replicas. In contrast to this costly and comparatively complicated technique, our work reported here centers on the void space present within a swollen polymer network as a template for the growth of various titania morphologies. Although swelling must be carried out under moisture-free conditions, the liquid precursors infiltrate the polymer matrix at room temperature and complete filling is accomplished in a single step. By varying the metal of the alkoxide precursor, we can select the composition of the morphology that will form in the polymer template. Condensation polymerization of precursor can be carried out by one of several methods, such as exposure to atmospheric moisture under ambient conditions. Our method has the benefits of low cost and tunable morphology, controllable through choice of swelling solvent, metal oxide precursor and swelling time.
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EXPERIMENTAL DETAILS PDMS was synthesized using the Sylgard 18
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