Abstract
The objective of the work reported in this paper is to create multi-scale and hierarchical surface structures using a simple imprinting process. The hierarchical structures can be fabricated with only simple patterned molds by proposed multi-step imprinting process, instead of using a high cost hierarchical-patterned mold. In the proposed process, the starting material is a layered sheet material. The layered sheet is pressed by a mold with a finer pattern, and subsequently pressed by a mold with a rougher pattern. A pure polymer sheet is employed as the upper layer, which will be removed during heating processes as a sacrificed layer, while the lower layer is a compound material of polymer and ceramic powder. After heating process, ceramic compact is sintered and formed a full-dense patterned sheet. By the proposed multi-step imprinting process with a layered material, ceramic sheets with micro hierarchical pattern can be fabricated with low cost. In the present work, poly(vinyl alcohol) (PVA) was prepared as the upper layer, and a compound material of alumina powder and PVA as a lower layer. Molds with finer and rougher patterns were also prepared for multi-step imprinting. As a result, a hierarchical structure on a thin ceramic sheet could be fabricated.
Highlights
Hierarchical surface patterns are found in the natural world, and they show lots of different functions; e.g., surface structures on moth eye eliminate reflection [1]; and lotus leaves have micro-scale hierarchical pattern, which causes super hydrophobicity [2]
Our process is based on nano imprint lithography, which has been proposed by Stephen Chou in 1995; a sub-100 nm patterns were demonstrated by physically deforming a thermoplastic material as a substrate in a temperature and pressure controlled printing process with a fine mold [3]
After the first imprinting with 5 lm depth mold with line & space pattern, interface height H was increased with decrease of the initial thickness of the upper layer
Summary
Hierarchical surface patterns are found in the natural world, and they show lots of different functions; e.g., surface structures on moth eye eliminate reflection [1]; and lotus leaves have micro-scale hierarchical pattern, which causes super hydrophobicity [2]. Nano imprint lithography is considered as one of the efficient methods to fabricate nano-scale patterns on surface of polymer material. It is a high-throughput and low-cost method. Authors proposed a combined process with powder metallurgy as micro powder imprint method [4,5,6,7,8,9]. In this process, a compound material, mixture of ceramic powder and a polymer binder system, is used for a working material. The compound sheet is pressed by a mold with micrometer scale patterns, and subsequently the polymer
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