Scalable Fabrication of Anisotropic Nanocellular Foam by Hot-Press Foaming

Nanocellular foam has raised much interest because its physical and mechanical properties are superior to those of microcellular foams. The hot-bath foaming method has been common on a laboratory scale due to its faster heat transfer rate. However, because of the nature of the free foaming process, the hot-bath foaming method may not be capable of making large, flat samples. This study uses the hot-press process to produce nanocellular foam. The results of hot-bath and hot-press foaming methods were compared with theoretical simulations. Both processes were able to produce cell sizes lower than 40 nm. The hot-press foamed samples exhibited larger cell size, higher expansion ratio, and higher aspect ratio (AR) than the hot-bath foamed samples. The hot-press foaming process demonstrated that it has the potential to create sizable and flat nanocellular samples. The AR of cells foamed in the hot-press method was as high as 1.93, creating a new manufacturing method for anisotropic nanocellular foam with a cell size of less than 100 nm.