Thermal conductivity of tunable lamellar aluminum oxide/polymethyl methacrylate hybrid composites
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Michel B. Johnson Institute for Research in Materials, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4R2
Kevin P. Plucknett Institute for Research in Materials, and Department of Process Engineering and Applied Science, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4R2
Mary Anne Whitea) Departments of Chemistry, and Physics and Atmospheric Science, and Institute for Research in Materials, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4R2 (Received 12 January 2012; accepted 14 March 2012)
We prepared hybrid aluminum oxide (Al2O3)/polymethyl methacrylate (PMMA) composites with tunable lamellae, produced through a two-step synthetic method: fabrication of inorganic scaffolds via ice-templating, followed by organic infiltration polymerization as a substitute for the sublimed ice. The final lamellar hybrid products show anisotropic physical properties. The thermal conductivity in both principal directions was determined for three different samples as a function of temperature (;3 K–300 K). Typical room temperature thermal conductivities are in the range of 0.5–2.5 W/(m K), depending on the composition and direction. Across the lamellae, the thermal conductivity is well modeled by a linear series of thermal resistors, and along the lamellae it is well represented by parallel thermal resistors of continuous slabs of PMMA and ;200-lm long slabs of Al2O3, joined by PMMA. From the thermal conductivity perspective, the Al2O3/PMMA composite is a nacre mimic.
I. INTRODUCTION
Hybrid composite materials, formed by combining organic and inorganic materials, can show superior properties compared with their pure components; they have potential applications in medicine,1 optics,2 membrane separations,3 tissue engineering,4 catalysis,5 and electrochemistry.6 Of particular interest are layered organic-inorganic hybrid materials, inspired by natural materials such as bone, wood and nacre. The advantages come from a combination of physical properties such as high toughness and strength, while having a relatively low density.7–9 These materials can, in principle, provide significant information concerning the relationship between structure and properties. Recently methods based on ice-templating have been used to fabricate complex composites.10,11 So called freeze-casting is a simple and environmentally friendly process, offering micrometerlevel control to prepare layered, interconnected scaffolds, into which a second component can be incorporated.12–15 The ultimate challenge is finding a feasible method to tailor the physical properties of organic-inorganic hybrid a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.112 J. Mater. Res., Vol. 27, No. 14, Jul 28, 2012
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materials for specific applications. The aim of the present work is to demonstrate that physical properties of hybrid materials can be tailored by controlling the structure of inorganic-organic hybrids produced by freeze-casting methods. In part
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