1 research outputs found
Surface 3D Micro Free Forms: Multifunctional Microstructured Mesoporous α‑Alumina by in Situ Slip Casting Using Excimer Laser Ablated Polycarbonate Molds
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<sup>2</sup>. 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<sup>2</sup>, 1200 mm<sup>2</sup>, and 120 cm<sup>2</sup>. Therefore, in principle, the structures
can be further replicated in areas up to 3 m<sup>2</sup> 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