Nanoscale Synthesis and Characterization Laboratory, Lawrence Livermore National Laboratory , 7000 East Avenue, Livermore, California 94550, United States.
Atomic Weapons Establishment , Aldermaston, Reading RG7 4PR, United Kingdom.
ACS Appl Mater Interfaces. 2016 Dec 21;8(50):34706-34714. doi: 10.1021/acsami.6b12320. Epub 2016 Dec 6.
A robust, millimeter-sized low-density Cu foam with ∼90% (v/v) porosity, ∼30 nm thick walls, and ∼1 μm diameter spherical pores is prepared by the slip-casting of metal-coated polymer core-shell particles followed by a thermal removal of the polymer. In this paper, we report our key findings that enable the development of the low-density Cu foams. First, we need to synthesize polystyrene (PS) particles coated with a very thin Cu layer (in the range of tens of nanometers). A simple reduction in the amount of Cu deposited onto the PS was not sufficient to form such a low-density Cu foams due to issues related to foam collapse and densification upon the subsequent polymer removal step. Precise control over the morphology of the Cu coating on the particles is essential for the synthesis of a lower density of foams. Second, improving the dispersion of PS-Cu particles in a suspension used for the casting as well as careful optimization of a baking condition minimize the formation of irregular large voids, leading to Cu foams with a more uniform packing and a better connectivity of neighboring Cu hollow shells. Finally, we analyzed mechanical properties of the Cu foams with a depth-sensing indentation test. The uniform Cu foams show a significant improvement in mechanical properties (∼1.5× modulus and ∼3× hardness) compared to those of uncontrolled foam samples with a similar foam density but irregular large voids. Higher surface areas and a good electric conductivity of the Cu foams present a great potential to future applications.
一种具有约 90%（体积比）孔隙率、约 30nm 厚的壁和约 1μm 直径的球形孔的坚固、毫米级别的低密度 Cu 泡沫是通过金属涂覆的聚合物核壳颗粒的 slip-casting 制备的，然后通过热去除聚合物。在本文中，我们报告了使低密度 Cu 泡沫得以开发的关键发现。首先，我们需要合成涂覆有很薄的 Cu 层（在几十纳米范围内）的聚苯乙烯（PS）颗粒。由于与随后的聚合物去除步骤中泡沫塌陷和致密化有关的问题，仅减少沉积在 PS 上的 Cu 量不足以形成如此低密度的 Cu 泡沫。对颗粒上 Cu 涂层的形态进行精确控制对于合成低密度泡沫至关重要。其次，改善悬浮液中 PS-Cu 颗粒的分散性以及仔细优化烘烤条件，可最大程度地减少不规则大空隙的形成，从而使 Cu 泡沫具有更均匀的堆积和相邻 Cu 空心壳的更好连通性。最后，我们通过深度感应压痕测试分析了 Cu 泡沫的机械性能。与具有类似泡沫密度但具有不规则大空隙的未控制泡沫样品相比，均匀的 Cu 泡沫在机械性能方面（约 1.5×模量和约 3×硬度）有显著提高。Cu 泡沫具有更高的比表面积和良好的导电性，具有很大的应用潜力。
