Abstract
Most materials expand when heated, which can lead to thermal stress and even failure. Whereas thermomiotic materials exhibit negative thermal expansion, the creation of materials with near-zero thermal expansion presents an ongoing challenge due to the need to optimize thermal and mechanical properties simultaneously. The present work describes the preparation and properties of polymer–ceramic composites with low thermal expansion. Ceramic scaffolds, prepared by freeze-casting of low-thermal-expansion Al2W3O12, were impregnated with poly(methylmethacrylate) (PMMA). The resulting composites can have a coefficient of thermal expansion as low as 2 × 10−6 K−1, and hardness values of 4.0 ± 0.3 HV/5 (39 ± 3 MPa) and 16 ± 3 HV/5 (160 ± 30 MPa) parallel and perpendicular to the ice growth, respectively. The higher hardness perpendicular to the ice growth direction indicates that the PMMA is acting to improve the mechanical properties of the composite.
Highlights
Most materials experience a substantial change in volume with change in temperature
We describe combining a near-zero thermal expansion material (Al2 W3 O12 ) with a polymer (polymethylmethacrylate (PMMA)) to produce composites with 98–34 vol % Al2 W3 O12 prepared via unidirectional freeze-casting (Figure 1) and subsequent in situ polymerization
Larger agglomerates are detrimental to ice growth, as it is more difficult for the growing ice crystals to push such large particles aside [33,37]
Summary
Thermal expansion can lead to thermal stress and, damage and fracture, limiting the usable temperature range of materials [1]. Thermomiotic materials, i.e., materials with negative coefficients of thermal expansion (NTE) [1], offer the potential to create novel near-zero thermal expansion materials by use in combination with positive thermal expansion (PTE) materials in composites [1,2,3]. Such an approach potentially allows precise tailoring of the bulk coefficient of thermal expansion (CTE) in conjunction with other physical properties. The characteristically low stiffness and large CTE of polymers make them attractive targets for combination with thermomiotics
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