The invention provides a method to produce flat, smooth and sizeable nanocellular polymeric foam using constant-pressure, hot-press foaming process. The methods consist of saturation of PMMA sheets with predesigned condition; foaming of the saturated sample using hot-press methods. In this methods, the micro-porous metal plates are used to sandwich the samples during foaming. This makes it possible to produce a flat, smooth surface and scalable nanocellular foam. Cell morphology is controlled by saturation, foaming conditions, and blending PMMAs with different molecular weights. As the results, the flat and smooth surface PMMA nanocell foam with dimensions of 100 × 70 × 6~8 mm3 was obtained. The foam has a cell size of <200 nm and a density of >1014 cells/cm3. The cellular morphology was tuned to be homogenous and bimodal nanocell foam. Relative density ranges from 0.23 to 0.38 for homogeneous nanocell foam and 0.19 to 0.38 for bimodal nanocell foam. Thermal conductivity is measured using a steady-state commercial heat flow meter and is tuned by cell structure. Homogeneous nanocell foam exhibits lower thermal conductivity than bimodal nanocell foam for the same relative density. Microcellular foams exhibit the highest thermal conductivity. The results were affected by the constituting nanocells due to the Knudsen effect.
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