Surface 3D Micro Free Forms: Multifunctional Microstructured Mesoporous α-Alumina by in Situ Slip Casting Using Excimer Laser Ablated Polycarbonate Molds

Abstract

Ceramic surface microstructuring is a rapidly growing field with a variety of applications in tribology, wetting, biology, and so on. However, there are limitations to large-area microstructuring and fabrication of three-dimensional (3D) micro free forms. Here, we present a route to obtain intricate surface structures through in situ slip casting using polydimethylsiloxane (PDMS) negative molds which are replicated from excimer laser ablated polycarbonate (PC) master molds. PC sheets are ablated with a nanosecond KrF (λ = 248 nm) excimer laser mask projection system to obtain micron-scale 3D surface features over a large area of up to 3 m(2). Complex surface structures that include 3D free forms such as 3D topography of Switzerland, shallow structures such as diffractive optical elements (60 nm step) and conical micropillars have been obtained. The samples are defect-free produced with thicknesses of up to 10 mm and 120 mm diameter. The drying process of the slip cast alumina slurry takes place as a one-dimensional process, through surface evaporation and water permeation through the PDMS membrane. This allows homogeneous one-dimensional shrinkage during the drying process, independent of the sample's lateral dimensions. A linear mass diffusion model has been proposed to predict and explain the drying process of these ceramic colloidal suspensions. The calculated drying time is linearly proportional to the height of the slurry and the thickness of the negatively structured PDMS and is validated by the experimental results. An experimentally observed optimum Sylgard PDMS thickness range of ∼400 μm to 1 mm has achieved the best quality microstructured green compacts. Further, the model predicts that the drying time is independent of the microstructured areas and was validated using experimental observations carried out with microstructured areas of 300 mm(2), 1200 mm(2), and 120 cm(2). Therefore, in principle, the structures can be further replicated in areas up to 3 m(2) with the same drying time for the same slurry height. The surface-structured ceramics display interesting wetting properties, for example, eicosane-coated mesoporous microstructured alumina shows superhydrophobic behavior. Additionally, ceramic bulk samples could be further used as second-generation very hard and low-wear molds for further microfabrication.

Flexural strength evaluations and fractography analyses of slip cast mesoporous submicron alumina

“…% of particles have diameters ≤ 150 nm). The particles have a narrow particle size distribution, and majority of the grain diameters lay between 90 nm and 220 nm as published earlier [22].…”

“…Slip casting is often used and a cost effective technique to obtain bulk porous ceramics as well as surface hierarchical micro and nano scale porosities [22], [23].This technique can be combined with replication techniques to obtain surface, micro/nano features such as hierarchical porosities, pillars, tear cavities, which can find applications in the field of tribology and wetting [22][23][24].…”

Perfluoropolyether-Impregnated Mesoporous Alumina Composites Overcome the Dewetting–Tribological Properties Trade-Off

“…Sample Preparation and Microstructural Chracterizations: Mesoporous α─Al 2 O 3 green compacts were synthesized by employing slip casting process 23,27,28 . Both cuboidal and cylindrical shaped green compacts were manufactured to utilize them as a tribo pair.…”

Abrasion‐Resistant, Hot Water‐Repellent and Self‐Cleaning Superhydrophobic Surfaces Fabricated by Electrophoresis of Nanoparticles in Electrodeposited Sol–Gel Films

“…However, consideration still should be taken like the wear resistant ability and thermal stability of the polymer, the compatibility between NPs and polymeric matrix, and the adhesion strength of the polymer to the substrate . Another strategy is to create microscopic roughness from the bulk matrix materials themselves at the surfaces like chemical etching, plasma texturing, laser ablating on metal and its alloy. The comprising part of matrix materials to create the required micro/nanostructure is destructive to the substrates and the required special and expensive equipment also limits their use.…”