Fraunhofer Research Institution for Polymeric Materials and Composites PYCO

Teltow, Germany

Fraunhofer Research Institution for Polymeric Materials and Composites PYCO

Teltow, Germany
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PubMed | Fraunhofer Research Institution for Polymeric Materials and Composites PYCO, ETH Zurich, Paul Scherrer Institute and Empa - Swiss Federal Laboratories for Materials Science and Technology
Type: Journal Article | Journal: Langmuir : the ACS journal of surfaces and colloids | Year: 2015

Thin plasma polymer films were deposited in hexamethyldisiloxane (HMDSO) and HMDSO/O2 low-pressure discharges and their chemical structures analyzed using infrared (IR) spectroscopy and neutron reflectometry (NR). The (plasma-polymerized) ppHMDSO film exhibits hydrophobic, poly(dimethylsiloxane)-like properties, while the retention of carbon groups is reduced by O2 addition, yielding a more inorganic, hydrophilic ppSiOx film. Both films show a minor (vertical) density gradient perpendicular to the substrate, where the exposed film surface seems to be more oxidized, indicating oxidative aging reactions upon contact with air. The hydration and water uptake abilities of the films in aqueous environments were investigated in humid environments using ellipsometry, NR in D2O, and multiple transmission-reflection IR measurements after equilibration of the films in water.


Bauer M.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Hartmann L.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Kuschel F.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Seiler B.,Chemnitz Materials Mechanics Ltd. | Noack E.,Chemnitz Materials Mechanics Ltd.
Journal of Applied Polymer Science | Year: 2010

The liquid crystal display (LCD) technology is confronted with the task to substitute rigid glass plates enclosing the electro-optically active liquid crystal (LC) material by plastic substrates. In particular, the commercialization of flexible displays requires a sufficient stabilization against external mechanical distortions. To achieve LC layer stabilization, several procedures have been suggested. In this work, the thermal-induced phase separation (TIPS) technique has been applied to generate composite films consisting of LC compartments which are encased by coherent polymer walls after binodal phase separation. Composite films were prepared from a series of poly(methacrylates) and various commercial nematic LC mixtures. Furthermore, the use of copolymers as well as binary blends from ''hard'' and ''soft'' poly(methacrylates) broadens the possibilities to control the film morphology. To compare different polymer/LC composite films regarding their stability under compression load, the samples were investigated by indentation tests using an inverse reflected-light microscope combined with a digital image acquisition technique. The deformation of the compositelayers was evaluated by the uniDAC image analysis which relies on the more general method of Digital Image Correlation (DIC). Some of the fabricated composites show a remarkably high indentation resistance, especially such prepared from poly(1-tetralyl methacrylate) and poly(4-tert-butylcyclohexyl methacrylate). The results facilitate the selection of suitable composite systems for the fabrication of mechanically stabilized flexible LC displays. © 2010 Wiley Periodicals, Inc.


PubMed | Fraunhofer Research Institution for Polymeric Materials and Composites PYCO and CNR Institute for Macromolecular Studies
Type: | Journal: Journal of colloid and interface science | Year: 2016

We propose a novel fabrication method for realizing robust and solvent resistant honeycomb films by combining parylene deposition with the polymer auto-organization phenomenon leading to breath figures. Parylene CVD process is suitable for producing a conformal protective layer on the honeycomb surface, reinforcing and stabilizing this structure. We demonstrate that the stabilized porous films can be filled with chloroform solution of fluorescent materials, without losing the integrity of their microstructure. In addition, liquid crystals can be encapsulated inside the patterned surface between two layers of parylene, showing interesting organization features dictated by the spatial constrains. This is the first reported application of breath figures with liquid crystals, suggesting a new approach for the development of honeycomb-based liquid crystal cells for flexible displays.


Galeotti F.,CNR Institute for Macromolecular Studies | Hartmann L.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Botta C.,CNR Institute for Macromolecular Studies
Journal of Colloid and Interface Science | Year: 2016

We propose a novel fabrication method for realizing robust and solvent resistant honeycomb films by combining parylene deposition with the polymer auto-organization phenomenon leading to breath figures. Parylene CVD process is suitable for producing a conformal protective layer on the honeycomb surface, reinforcing and stabilizing this structure. We demonstrate that the stabilized porous films can be filled with chloroform solution of fluorescent materials, without losing the integrity of their microstructure. In addition, liquid crystals can be encapsulated inside the patterned surface between two layers of parylene, showing interesting organization features dictated by the spatial constrains. This is the first reported application of breath figures with liquid crystals, suggesting a new approach for the development of honeycomb-based liquid crystal cells for flexible displays. © 2015 Elsevier Inc..


Kuschel F.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Hartmann L.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Bauer M.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Weissflog W.,Martin Luther University of Halle Wittenberg
Molecular Crystals and Liquid Crystals | Year: 2014

New chiral additives derived from 1-phenyl-2-aminoalcohols have been prepared and tested. Especially ephedrine and pseudoephedrine as chiral auxiliaries with two asymmetric C atoms offer functional groups of divergent reactivity. Dopants prepared by acylation with promesogenic agents can be used in various electro-optic devices. A specific utilization concerns bistable cholesteric liquid crystal displays with stacked double layer construction in order to enhance the luminance of reflected light. Further, the solubility in nematic mixtures, the long term phase behavior, the dopant's impact on textures and phase behavior, the electro-optic response and the photostability of cholesteric mixtures have been investigated. © 2014 Taylor and Francis Group, LLC.


Hartmann L.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Kuschel F.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Bauer M.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO
SID Conference Record of the International Display Research Conference | Year: 2011

Double-layer test devices filled with cholesteric liquid crystals of opposed handedness have been constructed in order to improve brightness and contrast ratio of bistable cholesteric displays. The contrast ratio of these devices is 1,5 times higher than that of single cells; the use of cells with pretreated surfaces is not necessary.


Kenfack F.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Bauer M.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Bauer M.,TU Brandenburg
Energy Procedia | Year: 2014

A new Phase Change Material (PCM) based on a salt hydrate which can be incorporated in latent heat storage systems for efficient handling of thermal energy around 100°C has been prepared. Compared with the pure salt hydrate, the results showed that the newly developed salt hydrate PYCO-PCM-1 is of high thermal stability. The storage capacity of 83.33 kWh m-3 for a temperature range ΔT = 20 K, corresponds to about four times the energy which can be stored with the same volume of water. Expanded graphite has been proven as a promising additive for improving the conductivity of PYCO-PCM-1. © 2014 The Authors.


Kuschel F.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Hartmann L.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Bauer M.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO
Journal of Applied Polymer Science | Year: 2010

Depending on the processing conditions in liquid crystal (LC) display manufacturing, LC/polymer composite films may exhibit unusual properties with respect to the compositional and phase behavior of the LC constituents. In particular, we have observed extraordinary large shifts of phase transition temperatures in LC/polymer composites, which can not be explained by preferential solvation or adsorption. Therefore, the influence of real manufacturing conditions such as thermal stress, storage in vacuum, and UV irradiation on the nematic-isotropic (n-i) transition temperatures of commercial nematic mixtures was investigated. Shifts of the clearing temperature of up to 88 K, presumably due to partial evaporation or UV degradation, were observed. Furthermore, we found that annealing may lead to the replacement of the nematic phase by the smectic A phase at room temperature in both LC/polymer composites and pure LC samples. Among the tested commercial LC blends, the mixtures E7, MLC-6650, and L101 showed the smallest stress effects. Practical consequences of our results are discussed. © 2010 Wiley Periodicals, Inc.


Kuschel F.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Hartmann L.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Bauer M.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO
Liquid Crystals | Year: 2011

Stabilisation of functional layers in flexible liquid crystal displays (LCDs) is essential if they are to find use in advanced applications. Among the various methods for encapsulation of liquid crystals (LCs) by spatially controlled polymer wall formation within LCD cells, we have devoted particular attention to thermally induced phase separation (TIPS) in LC/polymer systems. A drawback of the standard TIPS procedure is the requirement to fill cells with the isotropic LC/polymer mixture at elevated temperatures. We have demonstrated that compartmentalization can be simplified by precoating the substrate with an appropriate thermoplastic matrix polymer, for example poly(1-tetralyl methacrylate) (PTMA), before assembling and filling the cell with polymer-free LC at ambient temperature. The insular morphology originating from subsequent TIPS in different types of display cells prepared with nematic or chiral nematic mixtures has been examined by polarising microscopy and scanning electron microscopy. The electro-optical characteristics of test devices based on polymer-free LC films or on LC/polymer composites, prepared by both standard TIPS and our novel technique, are compared. © 2011 Taylor & Francis.


Steffen S.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Bauer M.,Fraunhofer Research Institution for Polymeric Materials and Composites PYCO | Decker D.,Clariant | Richter F.,Clariant
Journal of Applied Polymer Science | Year: 2014

This introduces an organic-inorganic thermosetting hybrid resin system based on unsaturated polyester and polysilazanes. It shows the chemical modification of unsaturated polyester structures by end capping to enable the combination of both components. In general, halogen-free unsaturated polyesters are not fire-retardant and have to be equipped with additives. Fillers and intumescent additives are preponderantly used in today's fire-retardant formulations. In contrast to these fire-retardants, polysilazanes act as ceramizing agents. Polysilazanes are suitable fire-retardants for resin transfer molding due to their low viscosity. Both burning behavior and glass transition temperature (Tg) are investigated as important application properties. In contrast to state-of-the-art fire-retardant formulations polysilazane-based thermosetting hybrid resins burn with high intensity and fast extinction. Therefore, total heat and smoke emission is decreased. The formation of ceramic structures during burning results in high residual mechanical properties and a low mass loss. © 2014 Wiley Periodicals, Inc.

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