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Papers by Hans-Georg Braun

Research paper thumbnail of Patterned Polypeptoid Brushes

Macromolecular Bioscience, 2015

Patterned polypeptoid brushes on gold and oxide substrates are synthesized by surface-initiated p... more Patterned polypeptoid brushes on gold and oxide substrates are synthesized by surface-initiated polymerization of N-substituted glycine N-carboxyanhydrides. Their biofouling resistance is shown by protein and cell adhesion experiments. The accessibility of the system to common patterning protocols is demonstrated by UV-lithography and a mCP approach. Moreover, the terminal secondary amine group of the polypeptoid brushes is functionalized with different fluorescent dyes to demonstrate their chemical accessibility.

Research paper thumbnail of Polycarbonat (PC) und seine Blends

Research paper thumbnail of Methode zur Herstellung eines portablen, hierarchisch strukturierten und multifunktionalen Mikropartikelarrays

Research paper thumbnail of Micro- and nanomanipulation inside the SEM

Journal of Physics: Conference Series, 2008

... Page 2. Micro-and nanomanipulation inside the SEM Evelyn Meyer, Hans-Georg Braun Leibniz Inst... more ... Page 2. Micro-and nanomanipulation inside the SEM Evelyn Meyer, Hans-Georg Braun Leibniz Institute of Polymer Research Dresden, Max-Bergmann Center of Biomaterials, D-01069 Dresden, Hohe Strasse 6, Germany E-mail: Meyer@IPFDD.DE Abstract. ...

Research paper thumbnail of Polythiophene Grafted on Polyethylene Film

MRS Proceedings, 1999

We have successfully grafted polythiophene on polyethylene (PE) film with a three reactions step:... more We have successfully grafted polythiophene on polyethylene (PE) film with a three reactions step: gas phase bromination on PE, yielding PE-Br; substitution reaction of PE-Br with 2-thiophene thiolate anion, following by chemical oxidative polymerization. The polymerization was carried out in a suspension solution of anhydrous FeCI3 in CHCI 3 , yielding a reddish PE-PT film after dedoping with ethanol. ATR-FTIR shows that the polythiophene (PT) was grafted on PE in the 2,5-position; on the other hand, PT homopolymer shows a small amount of 2,4 coupling. XPS reveals higher intensity of the S2p, including neutral and positive sulfur. SEM image reveals the island of PT on the PE film. AFM analysis found the thickness of the island is in the range of 120-145 nm. The conductivity of these thin films is in the range of 10-6 S/cm.

Research paper thumbnail of Dendritic crystallization in ultrathin micro- structured poly(ethylene oxide) (PEO) films

... techniques as micro-contact printing [1] appropriate molecular units or by electron beam lith... more ... techniques as micro-contact printing [1] appropriate molecular units or by electron beam lithography of self-assembled monolayers [2]. Besides dewetting crystallization in ultrathin films (thickness <i10inm) determines the morphological features of these films [5-7]. Compared to ...

Research paper thumbnail of Nanomanipulation Techniques Inside the Sem First Attempts to Integrate Microfabrication Into a Sem

Research paper thumbnail of μ-Structured Polymers as Components of Chemical Microreactors

Micro Total Analysis Systems ’98, 1998

Research paper thumbnail of Directed assembly of nanoparticles to isolated diatom valves using the non-wetting characteristics after pyrolysis

Nanoscale, Jan 21, 2014

A novel strategy for a directed nanoparticle coupling to isolated Stephanopyxis turris valves is ... more A novel strategy for a directed nanoparticle coupling to isolated Stephanopyxis turris valves is presented. After pyrolysis, the valves exhibit incomplete wetting due to their characteristic T-shaped profiles as a prerequisite for a regioselective coupling reaction. A micromanipulation system allows for precise handling and their immobilization onto an adhesive substrate and manipulation into arrays.

Research paper thumbnail of Structure Formation of Ultrathin PEO Films at Solid Interfaces—Complex Pattern Formation by Dewetting and Crystallization

International journal of molecular sciences, 2013

The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupt... more The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupture caused by dewetting. With crystallisable polymers such as polyethyleneoxide (PEO), molecular self-assembly into partial ordered lamella structures is studied as an additional source of pattern formation. Morphological features in ultrathin PEO films (thickness < 10 nm) result from an interplay between dewetting patterns and diffusion limited growth pattern of ordered lamella growing within the dewetting areas. Besides structure formation of hydrophilic PEO molecules, n-alkylterminated (hydrophobic) PEO oligomers are investigated with respect to self-organization in ultrathin films. Morphological features characteristic for pure PEO are not changed by the presence of the n-alkylgroups.

Research paper thumbnail of New Experiments Concerning the Mechanism of the Solid State Photopolymerization of Di-Styrylpyrazine

Research paper thumbnail of New experiments concerning the mechanism of solid-state photopolymerization of 2,5-distyrylpyrazine

ABSTRACT The photoinduced formation of oligomers in single crystals of 2,5-distyrylpyrazine (DSP)... more ABSTRACT The photoinduced formation of oligomers in single crystals of 2,5-distyrylpyrazine (DSP) was investigated by X-ray and electron diffraction techniques and also by gel permeation chromatography (GPC). The DSP crystals were characterized for the presence and nature of dislocations by dark-field images and etch-pit studies. Small angle grain boundaries were identified to be the prominent feature, but in general the crystals were highly perfect. A correlation between the sites of the defects and the formation of the photoproduct could not be detected. The oligomers formed in a solid-solution under appropriate irradiation conditions. Thus, DSP oligomer of number average degree of polymerization P̄n = 3,2 in macroscopic single crystal texture was obtained for the first time using a laser light source at 478 nm. Deterioration of the single crystal texture of DSP usually observed during photopolymerization is explained as being caused by inhomogeneous light distribution which in turn causes an inhomogeneous product distribution with accumulation of large strain fields. These can be made visible by the multiplication of etch pits. Phase separation between oligomer and polymer is observed on further irradiation of the oligomer single crystals. The oligomer phase seems to play the role of an intermediate in the photopolymerization of DSP at wavelengths λ &lt; 400 nm. The molecular weight distribution of the oligomers was studied by GPC. The data are only compatible with the assumption that the rate constant of dimerization is higher than that for the addition of a monomer to an already existing oligomer.

Research paper thumbnail of Diffusion controlled crystallisation on microstructured surfaces

Research paper thumbnail of Structure formation in micropatterned liquid phases

Research paper thumbnail of Thermoplastic Polypropylene Polyamide Compounds, Process for Their Manufacture and Their Use

Research paper thumbnail of Impact-Resistant Modified Thermoplastic Polyurethane Moulding Compositions, Process for Their Preparation and Their Use

Research paper thumbnail of Cold Impact-Resistant Thermoplastic Polyester Moulding Compositions

Research paper thumbnail of Polymer Blends of Propylene Copolymers and Polyethylene

Research paper thumbnail of Control of Morphological Features in Micropatterned Ultrathin Films

Crystallization in ultrathin films obeys diffusion controlled growth processes (DLA) which result... more Crystallization in ultrathin films obeys diffusion controlled growth processes (DLA) which result in branched growth morphologies. For the first time different morphological features related to diffusion limited aggregation could be created on request by controlled initiation of crystallization processes in ultrathin polymer films (polyethylene oxide). Prerequisite for the controlled initiation is the generation of amorphous-with respect to crystallization -metastable films which can be realized by film formation on micrometer-sized isles surrounded from nonwetting barriers. Inside of this isolated amorphous microareas heterogeneous nucleation can be initiated by contact with an AFM-tip. Morphological features of the DLA-structures such as tipradius, branch widths and correlation lengths are varied in dependence of the growth kinetic which is influenced by temperature, surface properties or other parameters. In addition influences of limited material reservoirs in confined areas on film morphology are discussed.

Research paper thumbnail of 10 Some New Application Aspects of Scanning Electron Microscopy

Research paper thumbnail of Patterned Polypeptoid Brushes

Macromolecular Bioscience, 2015

Patterned polypeptoid brushes on gold and oxide substrates are synthesized by surface-initiated p... more Patterned polypeptoid brushes on gold and oxide substrates are synthesized by surface-initiated polymerization of N-substituted glycine N-carboxyanhydrides. Their biofouling resistance is shown by protein and cell adhesion experiments. The accessibility of the system to common patterning protocols is demonstrated by UV-lithography and a mCP approach. Moreover, the terminal secondary amine group of the polypeptoid brushes is functionalized with different fluorescent dyes to demonstrate their chemical accessibility.

Research paper thumbnail of Polycarbonat (PC) und seine Blends

Research paper thumbnail of Methode zur Herstellung eines portablen, hierarchisch strukturierten und multifunktionalen Mikropartikelarrays

Research paper thumbnail of Micro- and nanomanipulation inside the SEM

Journal of Physics: Conference Series, 2008

... Page 2. Micro-and nanomanipulation inside the SEM Evelyn Meyer, Hans-Georg Braun Leibniz Inst... more ... Page 2. Micro-and nanomanipulation inside the SEM Evelyn Meyer, Hans-Georg Braun Leibniz Institute of Polymer Research Dresden, Max-Bergmann Center of Biomaterials, D-01069 Dresden, Hohe Strasse 6, Germany E-mail: Meyer@IPFDD.DE Abstract. ...

Research paper thumbnail of Polythiophene Grafted on Polyethylene Film

MRS Proceedings, 1999

We have successfully grafted polythiophene on polyethylene (PE) film with a three reactions step:... more We have successfully grafted polythiophene on polyethylene (PE) film with a three reactions step: gas phase bromination on PE, yielding PE-Br; substitution reaction of PE-Br with 2-thiophene thiolate anion, following by chemical oxidative polymerization. The polymerization was carried out in a suspension solution of anhydrous FeCI3 in CHCI 3 , yielding a reddish PE-PT film after dedoping with ethanol. ATR-FTIR shows that the polythiophene (PT) was grafted on PE in the 2,5-position; on the other hand, PT homopolymer shows a small amount of 2,4 coupling. XPS reveals higher intensity of the S2p, including neutral and positive sulfur. SEM image reveals the island of PT on the PE film. AFM analysis found the thickness of the island is in the range of 120-145 nm. The conductivity of these thin films is in the range of 10-6 S/cm.

Research paper thumbnail of Dendritic crystallization in ultrathin micro- structured poly(ethylene oxide) (PEO) films

... techniques as micro-contact printing [1] appropriate molecular units or by electron beam lith... more ... techniques as micro-contact printing [1] appropriate molecular units or by electron beam lithography of self-assembled monolayers [2]. Besides dewetting crystallization in ultrathin films (thickness <i10inm) determines the morphological features of these films [5-7]. Compared to ...

Research paper thumbnail of Nanomanipulation Techniques Inside the Sem First Attempts to Integrate Microfabrication Into a Sem

Research paper thumbnail of μ-Structured Polymers as Components of Chemical Microreactors

Micro Total Analysis Systems ’98, 1998

Research paper thumbnail of Directed assembly of nanoparticles to isolated diatom valves using the non-wetting characteristics after pyrolysis

Nanoscale, Jan 21, 2014

A novel strategy for a directed nanoparticle coupling to isolated Stephanopyxis turris valves is ... more A novel strategy for a directed nanoparticle coupling to isolated Stephanopyxis turris valves is presented. After pyrolysis, the valves exhibit incomplete wetting due to their characteristic T-shaped profiles as a prerequisite for a regioselective coupling reaction. A micromanipulation system allows for precise handling and their immobilization onto an adhesive substrate and manipulation into arrays.

Research paper thumbnail of Structure Formation of Ultrathin PEO Films at Solid Interfaces—Complex Pattern Formation by Dewetting and Crystallization

International journal of molecular sciences, 2013

The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupt... more The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupture caused by dewetting. With crystallisable polymers such as polyethyleneoxide (PEO), molecular self-assembly into partial ordered lamella structures is studied as an additional source of pattern formation. Morphological features in ultrathin PEO films (thickness < 10 nm) result from an interplay between dewetting patterns and diffusion limited growth pattern of ordered lamella growing within the dewetting areas. Besides structure formation of hydrophilic PEO molecules, n-alkylterminated (hydrophobic) PEO oligomers are investigated with respect to self-organization in ultrathin films. Morphological features characteristic for pure PEO are not changed by the presence of the n-alkylgroups.

Research paper thumbnail of New Experiments Concerning the Mechanism of the Solid State Photopolymerization of Di-Styrylpyrazine

Research paper thumbnail of New experiments concerning the mechanism of solid-state photopolymerization of 2,5-distyrylpyrazine

ABSTRACT The photoinduced formation of oligomers in single crystals of 2,5-distyrylpyrazine (DSP)... more ABSTRACT The photoinduced formation of oligomers in single crystals of 2,5-distyrylpyrazine (DSP) was investigated by X-ray and electron diffraction techniques and also by gel permeation chromatography (GPC). The DSP crystals were characterized for the presence and nature of dislocations by dark-field images and etch-pit studies. Small angle grain boundaries were identified to be the prominent feature, but in general the crystals were highly perfect. A correlation between the sites of the defects and the formation of the photoproduct could not be detected. The oligomers formed in a solid-solution under appropriate irradiation conditions. Thus, DSP oligomer of number average degree of polymerization P̄n = 3,2 in macroscopic single crystal texture was obtained for the first time using a laser light source at 478 nm. Deterioration of the single crystal texture of DSP usually observed during photopolymerization is explained as being caused by inhomogeneous light distribution which in turn causes an inhomogeneous product distribution with accumulation of large strain fields. These can be made visible by the multiplication of etch pits. Phase separation between oligomer and polymer is observed on further irradiation of the oligomer single crystals. The oligomer phase seems to play the role of an intermediate in the photopolymerization of DSP at wavelengths λ &lt; 400 nm. The molecular weight distribution of the oligomers was studied by GPC. The data are only compatible with the assumption that the rate constant of dimerization is higher than that for the addition of a monomer to an already existing oligomer.

Research paper thumbnail of Diffusion controlled crystallisation on microstructured surfaces

Research paper thumbnail of Structure formation in micropatterned liquid phases

Research paper thumbnail of Thermoplastic Polypropylene Polyamide Compounds, Process for Their Manufacture and Their Use

Research paper thumbnail of Impact-Resistant Modified Thermoplastic Polyurethane Moulding Compositions, Process for Their Preparation and Their Use

Research paper thumbnail of Cold Impact-Resistant Thermoplastic Polyester Moulding Compositions

Research paper thumbnail of Polymer Blends of Propylene Copolymers and Polyethylene

Research paper thumbnail of Control of Morphological Features in Micropatterned Ultrathin Films

Crystallization in ultrathin films obeys diffusion controlled growth processes (DLA) which result... more Crystallization in ultrathin films obeys diffusion controlled growth processes (DLA) which result in branched growth morphologies. For the first time different morphological features related to diffusion limited aggregation could be created on request by controlled initiation of crystallization processes in ultrathin polymer films (polyethylene oxide). Prerequisite for the controlled initiation is the generation of amorphous-with respect to crystallization -metastable films which can be realized by film formation on micrometer-sized isles surrounded from nonwetting barriers. Inside of this isolated amorphous microareas heterogeneous nucleation can be initiated by contact with an AFM-tip. Morphological features of the DLA-structures such as tipradius, branch widths and correlation lengths are varied in dependence of the growth kinetic which is influenced by temperature, surface properties or other parameters. In addition influences of limited material reservoirs in confined areas on film morphology are discussed.

Research paper thumbnail of 10 Some New Application Aspects of Scanning Electron Microscopy