Preparation of Ni micropillar arrays with high aspect ratios using anodic porous alumina template and their application to molds for imprinting

Preparation of Alumina Membrane Filters with Framework Structures by Al Anodization

Alumina membrane filters consisting of a thin filter layer (200-700 nm in thickness) supported by a framework (30-100 μm in thickness) were fabricated on the basis of the anodization of an Al substrate. The solution permeability of alumina membrane filters with tubular pores of uniform size and shape varies with membrane thickness; therefore, membrane filters with a filter layer thickness of less than 1 μm showed high solution permeability. Although the filter layer is thin, it is reinforced by a thick framework, enabling the fabrication of large freestanding membrane filters (2.5 × 2 cm2 in size). The pore size of the anodic porous alumina formed by the anodization of Al can be controlled in the range from 10 nm to ca. 2 μm by varying the preparation conditions. The alumina membrane obtained by this method is therefore useful as a membrane filter that can efficiently separate particles of various sizes, including microplastics, viruses, and bacteria. This method enables the fabrication of membrane filters with uniform pore size, high solution permeability, and sufficient mechanical strength for handling as freestanding membranes, which have been difficult to achieve with the reported preparation processes for membrane filters. The obtained membrane filters with frameworks can be applied to efficient microfiltration.

Micro-nano hierarchical pillar array structures prepared on curved surfaces by nanoimprinting using flexible molds from anodic porous alumina and their application to superhydrophobic surfaces

Flexible molds with micro-nano hierarchical structures on the surface were fabricated by a two-step template process using anodic porous alumina as a starting material. The obtained flexible molds could be used to form micro-nano hierarchical pillar arrays on the surface of glass tubes and convex lenses by photo-nanoimprinting. The contact angle characteristics of the surfaces with hierarchical pillar arrays were measured, and it was confirmed that they exhibit superhydrophobic properties with a water-droplet contact angle exceeding 150°. The flexible molds obtained in this study can be used repeatedly and efficiently to form micro-nano hierarchical surfaces with superhydrophobic properties on the surfaces of substrates with various curvatures.