Freezing a water droplet on an aligned Si nanorod array substrate

Abstract

When a water droplet is dried on a vertically aligned Si nanorod array surface, thenanorods are bundled together. To understand how bundles are formed, a water droplet isfrozen rapidly on a Si nanorod array surface observed under a cryo-SEM (scanning electronmicroscope). The nanorods in the precursor film form similar bundles as those dried in air.But the nanorods under the apparent frozen water droplet are only slightly deformed. Wepropose that the bundling of nanorods is caused by non-uniform water–nanorodinteraction, which could happen either during the water spreading or drying process.Therefore, controlling the liquid–nanostructure interaction could minimize the bundling.In addition, the rapid freezing process does not preserve the water inside thenanochannels, and almost all the water forms ice on top of the nanorod surface, eitheras a planar interface or as particles, depending on the locations. The separatedice–nanorod interface will have potential applications in chemical separation and crystalgrowth.