Thomas Hanemann

Polymer-nanoparticle composites: From synthesis to modern applications

The addition of inorganic spherical nanoparticles to polymers allows the modification of the polymers physical properties as well as the implementation of new features in the polymer matrix. This review article covers considerations on special features of inorganic nanoparticles, the most important synthesis methods for ceramic nanoparticles and nanocomposites, nanoparticle surface modification, and composite formation, including drawbacks. Classical nanocomposite properties, as thermomechanical, dielectric, conductive, magnetic, as well as optical properties, will be summarized. Finally, typical existing and potential applications will be shown with the focus on new and innovative applications, like in energy storage systems.

Innovations in molding technologies for microfabrication

Micromolding is a key technology for the economic production of components for microsystems. It is applied in several manufacturing techniques including the LIGA process. Especially MicroInjection Molding allows cost-effective large-scale production of components for many applications to be used in microsystems technology. Using special molding machines, lateral dimensions in the micrometer range, structural details down to 200nm and maximum aspect ratios of more than 20 are achieved. Examples for applications are PSU-made housings for microfluidic systems or microcomponents made of PMMA for cardiac catheters. PC or LCP are appropriate materials for interconnection devices in microoptics and electronics. Other examples are injection molded lost plastic molds for electroforming or electroless plating of metal microstructures. An important economic factor is the optimization of the molding process and tool using different simulation techniques. Recently, novel techniques for manufacturing metal or ceramic microstructures were developed by adapting Powder Injection Molding to microtechnologies. Using commercially available feedstocks, microstructures were made of metals or ceramics. Rapid manufacturing of microcomponents is achieved by the so-called Photomolding process using reactive polymer resins as photocurable material and e.g. mold inserts fabricated by laser ablation. The addition of micro- or nanosized ceramics to the resin allows the molding of filled composite with enhanced mechanical properties. Subsequent debindering and sintering steps yield the pure ceramic microcomponents.

Electrolyte Mixtures Based on Ethylene Carbonate and Dimethyl Sulfone for Li-Ion Batteries with Improved Safety Characteristics

In this study, novel electrolyte mixtures for Li-ion cells are presented with highly improved safety features. The electrolyte formulations are composed of ethylene carbonate/dimethyl sulfone (80:20 wt/wt) as the solvent mixture and LiBF4 , lithium bis(trifluoromethanesulfonyl)azanide, and lithium bis(oxalato)borate as the conducting salts. Initially, the electrolytes are characterized with regard to their physical properties, their lithium transport properties, and their electrochemical stability. The key advantages of the electrolytes are high flash points of >140 °C, which enhance significantly the intrinsic safety of Li-ion cells containing these electrolytes. This has been quantified by measurements in an accelerating rate calorimeter. By using the newly developed electrolytes, which are liquid down to T=-10 °C, it is possible to achieve C-rates of up to 1.5 C with >80 % of the initial specific capacity. During 100 cycles in cell tests (graphite||LiNi1/3 Co1/3 Mn1/3 O2 ), it is proven that the retention of the specific capacity is >98 % of the third discharge cycle with dependence on the conducting salt. The best electrolyte mixture yields a capacity retention of >96 % after 200 cycles in coin cells.

Hot Embossing and Injection Molding for Microoptical Components

After the successful development of micro-optical components today the first commercial applications are arising. This induces the necessity of adapted production technologies. Hot embossing and injection molding are two techniques to fabricate micro-optical components characterized by lateral structure details below 1 micrometers , structure heights up to one millimeter and aspect ratios between 20 and 100. Injection molding is famous for its short cycle times which makes this method well suited for mass production.Very delicate microstructures and multilayer components can be fabricated e.g. within the framework of the LIGA-process by hot embossing. Examples for micro-optical components fabricate by molding as well as process equipment will be discussed.

Direct laser-assisted processing of polymers for microfluidic and micro-optical applications

In the microscopic world the need of functional prototypes increases, e.g. as a precondition for a mould insert fabrication for micro-injection moulding. In this work the direct fabrication of prototypes made from polymers with an accuracy down to the micrometer range will be presented. For this purpose the direct patterning or modification of polymers with UV-laser radiation is performed for applications in fluidic and micro-optics. Different UV laser sources such as excimer and frequency-multiplied Nd:YAG were used. In the case of complex designs for fluidic applications it is powerful to use Nd:YAG laser radiation as patterning tool because of their high laser repetition rates: CAD data from complex fluidic designs were transmitted directly via CAM module into the polymeric surface. Because of the very small laser pulse duration of about 400-500 ps the thermal-induced damage during ablation decreases significantly. Process parameters, ablation rates and attainable surface qualities for capillary-electrophoreses chips will be presented. With the aid of a motorised aperture or a rotating mask system, excimer laser radiation is used to enable a well defined patterning of grooves with sharp edges and smooth sidewalls. The direct ablation of polymethylmethacrylate (PMMA), as well as the laser induced modification of the polymeric chemistry is used for the preparation of passive integrated-optical waveguides. Two types of concepts of waveguides are discussed: 1. Laser patterned grooves are filled with index matched materials which leads either to an increase or a decrease of the refractive index relative to pure PMMA. 2. Localised laser-induced polymer modification leads immediately to an integrated waveguide with higher refractive index. Both types of waveguides-concepts are characterised by their optical properties, which will be discussed in detail.

Laser micromachining of mold inserts for replication techniques: state of the art and applications

The rapid fabrication of microcomponents made from polymers will be presented. The whole fabrication process is divided into three main steps: First, direct patterning of polymers with excimer laser radiation enables the fabrication of first prototypes. Second, laser assisted micromachining using Nd:YAG and KrF-Excimer laser allows a rapid manufacturing of microstructured mold inserts. Third, the application of light induced reaction injection molding (UV-RIM) gives the access to the replication of the previously fabricated mold insert. The fabrication of prototypes made of polymer is carried out highly precisely with excimer laser radiation. With the aid of a motorised aperture mask, CAD data are transmitted directly into the polymeric surface. With an appropriate pretreatment of the polymer surface the debris formation can be drastically reduced. A promising method of micropatterning of mold inserts made of steel is called laser microcaving. This processing technique enables a clean patterning process with only a small amount of debris and melt. The etch rate and surface quality strongly depend on the chemical composition of the steel and the process parameters. Surface qualities with a roughness of about 300 nm can be achieved. Microstructures composed of polymers or ceramic-composites are successfully demolded by using the UV-RIM technique with aspect ratios up to 10. Capillary Electrophoresis-Chips made of PMMA are fabricated, and the functionality of the CE-Chips is demonstrated.

Innovative molding technologies for the fabrication of components for microsystems

Economic success of microsystems technology requires a wide range of materials as well as the related manufacturing processes. A suitable technology for medium/large scale production is micro injection molding which actually allows the manufacturing of plastic microstructures with 20 microns minimum thickness, structural details of approximately 0.2 microns or maximum aspect ratios of more than 20. These microstructures are, for example, applied as components in micro optics, micro fluidics or minimally invasive surgery. This is demonstrated by microparts that are currently available or will be available soon. For higher economic efficiency and cost reduction, fully electrical injection modeling machines of higher accuracy have been applied. Also, micro insert injection molding reduces mounting costs. Manufacturing of metal or ceramic microparts by powder injection modeling allows large-scale production of complex shaped microstructures with a wide range of materials. Typical examples are sintered structured like stepped LIGA- gear wheels with minimal dimensions of 50 microns in different metal and ceramic materials. Micro Precision Casting originating from conventional investment casting is a suitable process for small/medium-scale production. Examples are microturbine housings made of precious metal alloys. An approach similar to rapid prototyping applies photocurable reactive resins. Photoinduced molding of low viscous resins under ambient conditions leads to significantly reduced cycle times. Additionally, rapid testing of new composite materials can be performed easily. Microcomponents molded from polymers and different composites like dyes with nonlinear optical properties and nanosized ceramic powders will be presented.

Investigation of Binary Mixtures Containing 1-Ethyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)azanide and Ethylene Carbonate

Temperature dependent viscosity, conductivity, and density data of binary mixtures containing ethylene carbonate (EC) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)azanide (EMIM-TFSA) were determined at atmospheric pressure in a wide temperature range of (20 to 120) °C. Additionally, differential scanning calorimetry (DSC) measurements were performed from (−120 to +100) °C to characterize phase behavior of the mixtures. On the basis of the experimental data it is demonstrated that the lattice hole theory can be applied excellently to the conductivity data of the binary mixture EMIM-TFSA/EC. The viscosity data were fitted according to the Vogel–Fulcher–Tammann–Hesse (VFTH) equation and analyzed with the help of the fractional Walden rule. It is concluded that the mixtures can be classified as fragile according to ionicity. The aim of the study is to present fundamental physicochemical data about the mixtures as a basis for structure–property relationship-calculations of solvent mixtures or u...

Cladded self-written multimode step-index waveguides using a one-polymer approach.

Low-loss optical-coupling structures are highly relevant for applications in fields as diverse as information and communication technologies, integrated circuits, or flexible and highly-functional polymer sensor networks. For this suitable and reliable production methods are crucial. Self-written waveguides are an interesting solution. In this work, we present a simple and efficient one-polymer approach for self-written optical connections between light-guiding structures such as single-mode and multi-mode optical fibers or waveguides that relies on self focusing of the light inside a photopolymerizing mixture. The optical connections are produced in a two-step process by writing into monomer resin using cw laser light in the blue wavelength range and subsequent UV curing. Since only one photopolymerizing resin is required, we reduced the fabrication complexity compared to previous approaches to obtain a waveguide embedded in a rigid cladding material. We discuss the production method, the results obtained as function of relevant process parameters such as writing speed or curing time, and evaluate optical properties and coupling efficiencies.

Micromolding of polymer waveguides

In microsystem technology the fabrication of either passive or active micro optical components made from polymers becomes more and more evident with respect to the intense expanding application possibilities e.g. in telecommunication. Actually, the LIGA process developed at the FZK, Germany allows the direct fabrication of microcomponents with lateral dimensions in the micrometer range, structural details in the submicrometer range, high aspect ratios of up to several hundreds and a final average surface roughness of less than 50 nm in small up to large scales. The molding of polymer components for microoptical applications, especially in the singlemode range, is determined by the achievable maximum accuracy of the molding technique itself and of the acceptable tolerances for low damping and coupling losses. Following the LIGA and related technique e.g. mechanical microengineering we want to present in this work the fabrication of polymer singlemode waveguides using a combination of micromolding and light- curing steps.