We report on efforts to mimic the wetting behaviour of surfaces or leaves of certain plants, which are rendered ultrahydrophobic through a dense layer of hairs grown on top of the leaf. We use a simple moulding approach to obtain elastic hydrophilic hydrogel networks with pillar structures that may serve as model systems for such hairy surfaces. In order to generate such structures, we first generate either a steel master or directly use a lady's mantle leaf. Second, the master is moulded against a silicone to yield an elastomer, which is a negative of the hairy surface. A subsequent radical polymerization in the negative leads to the formation of an elastic hydrogel even for the very high aspect ratios characteristic of the natural system. The results of some preliminary contact angle measurements on the obtained structures are discussed.

Abstract. We consider stochastic elliptic variational inequalities of the second kind involving a bilinear form with stochastic diffusion coefficient. We prove existence and uniqueness of weak solutions, propose a stochastic Galerkin approximation of an equivalent parametric reformulation, and show equivalence to a related collocation method. Numerical experiments illustrate the efficiency of our approach and suggest similar error estimates as for linear elliptic problems.

Components for microsystems are basically produced using processes from the semiconductor technology or by LIGA. Silicon serves as basic material for this components. The material properties of silicon often don't achieve the demands of for example: micro-surgery, biotechnology, fluidics or high temperature environments. High volume production by replication techniques also needs tool materials with more adapted properties and high lifetime. Therefore materials such as polymers, metals, composits and ceramics becoming more and more important in MST and there is an increasing requirement of suitable manufacturing techniques and processes for this materials. For complex-shapes electro-dischargemachining (EDM) can be applied. Wire EDM (WEDM) is usefull for cutting shapes in materials with an minimum conductivity of about 0,01 s/cm. In our department we use wire diameters down to 20 lm. We will show the newest application from our department made by very fine wires on an universal WEDM machine. IntroductionIn MST there are only few technologies and processes for threedimensional structuring of complex shapes with good surface quality in a variety of materials. One of the most important is wire EDM (WEDM). WEDM is useful for cutting complex 3D shapes in materials with an minimum conductivity of about 0.01 s/cm [1][2][3][4][5][6][7]. In the middle of the ninety, first groups start also using electro-discharge-diesinking to produce microstructures in very robust materials, useful for microreactors [6]. This groups adopt LIGA electrodes for EDM structuring of high aspect ratio structures in different metals. So the electroplating materials of LIGA can be expanded. Tools for replication techniques are complex and therefore there are different processes to make them.The department of process technology-IMTEK of the university of freiburg apply ultra precision milling/turning/planing/drilling and UV-LIGA for electrode making and WEDM and ECM for injection moulding and embossing tools. Together with the metrology and design tools, the complete process chain is available for prototyping and upscaling to medium and high volume production. Especially WEDM and ECM is appropriate for economic prototyping and production of microparts in high stressed materials. Microparts made by WEDM in metalsAim by this application was the developing of polymer micro-structures with hydrophilic materials and no dewetting of the surface, like for the nature example lady's mantle (Alechemilla vulgaris). The hair geometry for the example are: diameter 20 lm, height 1 mm and average distance 500 lm. SEM Fig. 1 shows the first results for the mould tool in steel.In Fig. 2 are the moulded and demoulded structure shown. The material was an DMMA Monomer polymerised by 45°C with an 1.2% EGDM Crosslinker and AIBN used as initiator.For gears in an lot of micromotors applications, to reduce the rotation speed and increase the torque, ductile high tensile materials are necessary. Threedimensional tooth shapes with freeform surfaces reduce the abrasion of the...

The most used processes for production of microsytem components are basically from the semiconductor technology. The material properties of used silicon often don't achieve the demands of for example: microsurgery, biotechnology life science, fluidics or high temperature environment. For microstructuring of highly stressed metals, like stainless and heat resisting steels, cold work tool steels, hot work tool steels and nickel-base-alloys and a variety of metals there is no manufacturingprocess. An interesting possibility for structuring this type of materials are the electrochemical machining processes (ECM). Some new developed ECM-sinking-processes are working with oscillating tool-electrode, to improve shape accuracy. IntroductionIn microsystem technology there are only few technologies and processes for structuring of complex shapes in highly stressed metalls, steel and alloys. An interesting possibility for structuring this type of materials are the processes of electrochemical machining. Electro-chemical-machining (ECM) is the anodic electro-chemical dissolution of metallic materials in an electrolytic medium. Figure 1 shows the principle of electro-chemical dissolution process. The ECM-Process is a well established process in the aviation industry for the production of turbine blades and for placement of cooling air bore holes. These bore holes have diameters between 0.5 and 3.0 mm and an aspect ratio of up to 300:1. Other wellknown applications for the ECM are the EC-deburring-processes, the EC-etching processes and a wide variety of EC-hybrid processes like EC-grinding [1][2][3]7].The process of ECM enables the machining of metallic materials independent of their mechanical properties. This process achieves high material removal rates. In opposite to the Electro-discharge-machining (EDM) process the tool-electrode wear is extremely low and the sub-surface is not damaged. Other advantages of ECM are: -no mechanical contact between tool electrode and workpiece -no burr at the shape -no finishing process -smooth surface -batch processing possibleThe traditionally ECM-processes are working with constant feed rate and constant voltage. Using vibrating tool-electrodes, the ECM-process can be under control. The department of process technology -IMTEK of the University of Freiburg investigates applications and possibilities of ECM die-sinking process with oscillating toolelectrode for microstructuring of highly stressed materials [4]. So we will present some results of our ECM work. ECM die-sinking with vibrating tool-electrodeFor our research we are using a machine-prototype PEM 1360, wich is shown in Fig. 2, of the company PEM, Technologiegesellschaft für elektrochemische Bearbeitung, Dillingen/Saar, Germany. This machine works with vibrating tool-electrode with non-varying frequency of 50 Hz and steady amplitude of 200 lm.The process works in the following principle. The toolelectrode moves in direction of the workpiece superimposed by oscillations. As the tool-electrode and the workpiece approaches, the elect...

While the focus of our preceding investigations, presented on the last HARMST 2001 in Baden Baden, was the miniaturization of fuel cells in order to increase their power density, the current activities at the IMTEK concentrate on the identification of processes that have the potential to lower the production costs of those miniaturised fuel cells. As a novel approach, we replaced the commonly used backing layer and flow fields made from graphite or steel by a flow field with micro channels structured in carbon paper. A micrograph of these structures is shown in Figure 1. For the first time, such structures were produced using Wire Electro Discharge Machining (WEDM). With our proven cell setup [1], we reach energy densities comparable to the system we presented at the last HARMST 2001, while being able to produce the cells at considerably lower costs. Another major advantage of the use of graphitic materials is that the cell is no longer prone to corrosion.