Andreas Janke

Melt mixing of polycarbonate/multi-wall carbon nanotube composites

—Composites of polycarbonate (PC) with multi-wall carbon nanotubes (MWNT) of different concentrations are prepared by diluting a PC based masterbatch containing 15 wt% MWNT using melt mixing in a DACA-Micro Compounder (4 g scale). Electrical resistivity measurements indicate that the percolation of MWNT is reached between 1 and 1.5 wt%. In addition, melt rheology was applied as another sensitive method to detect the percolation of the nanotubes. Atomic Force Microscopy and visual observations of the composite dispersions in a PC-solvent were used to characterise the state of MWNT dispersion. Differential Scanning Calorimetry and Dynamic Mechanical Analysis were applied to detect changes in the glass transition temperature of PC as a result of processing and of MWNT interactions with the PC matrix including the state of dispersion. In addition, DMA confirmed the reinforcement effect of the nanotubes. The results show that the nanotube incorporation also influences the processing behaviour. Due to the enhancement in melt viscosity by adding nanotubes and the enhanced shear forces, the molecular weight of the PC in the composites is reduced as compared to PC extruded under the same conditions. This effect leads to changes in the glass transition temperature and modulus which counteracts the effects originating from the nanotube-polymer interaction.

Electrical properties and stability of polypyrrole containing conducting polymer composites

Abstract Conducting polymer composites of polyethylene and polypyrrole (PE/PPy), polypropylene and polypyrrole (PP/PPy), and poly (methyl methacrylate) and polypyrrole (PMMA/PPy) were prepared by means of a chemical modification method, resulting in a network-like structure of polypyrrole embedded in the insulating polymer matrix. The content of polypyrrole determined by elemental analysis varied from 0.25 to 17 wt.%. Electrical conductivity of compression-moulded samples depends on the concentration of polypyrrole and reached values from 1 × 10 −11 to 1 S/cm. The morphology of the composites was investigated by low-voltage scanning electron microscopy (LVSEM). Potential contrast measurements as a function of the acceleration voltage were used to prove the perfection of the PPy network structure. The electrical transport mechanism in PP/PPy composite was studied. The data of the temperature dependence of conductivity were fitted following the function for a charge-energy-limited tunnelling (CELT) model. There is only a small drop in conductivity caused by annealing of PP/ PPy composites in air at temperatures up to 80 °C. A stabilizing effect of PPy on thermal stability of polypropylene is shown by thermogravimetric analysis. The antistatic properties of PE/PPy and PMMA/PPy composites were demonstrated.

Melt Mixing as Method to Disperse Carbon Nanotubes into Thermoplastic Polymers

Abstract This paper presents melt mixed composites where two ways of introducing nanotubes in polymer matrices were used. In the first case, commercially available masterbatches of nanotube/polymer composites are used as the starting materials that are diluted by the pure polymer in a subsequent melt mixing process (masterbatch dilution method) while in the other case nanotubes are directly incorporated into the polymer matrix. As an example of the masterbatch dilution method, composites of polycarbonate with MWNT are presented which are produced using a Brabender PL‐19 single screw extruder. In this system, electrical percolation was found at about 0.5 wt% MWNT. The nanotube dispersion as observed by TEM investigations is quite homogeneous. The direct incorporation method is discussed in composites of polycarbonate with MWNT and SWNT. For commercial MWNT percolation was found between 1.0 and 3.0 wt% depending on the aspect ratio and purity of the materials. For HiPCO‐SWNT from CNI percolation occurred between 0.25 wt% and 0.5 wt% SWNT. The incorporation of nanotubes significantly changes the stress‐strain behavior of the composites: modulus and stress are enhanced; however, the elongation at break is reduced especially above the percolation concentration.

Liquid-fluid contact angle measurements on hydrophilic cellulosic materials

Abstract Contact angle measurements with captive bubbles have been used to quantify the wettability of different cellulosic materials in contact with pure water or aqueous protein solutions. The application of a new contact angle technique (axisymmetric drop shape analysis) in combination with atomic force microscopy permits new insights into the wetting behaviour of these hydrophilic surfaces. It was found that the unmodified cellulose membrane has a very smooth and homogeneous surface in the water-swollen state. There is almost no hysteresis between the advancing and receding water contact angles. The chemical modification of the cellulose with diethylaminoethyl groups results in a smooth but heterogeneous water-swollen membrane surface with fewer hydrophilic properties. A water-swollen cellulose acetate film was used as a model surface for wetting measurements with buffered protein solutions. It was found that different proteins (human serum albumin, fibrinogen) yielded different contact angles in their adsorbed state; after the adsorption of fibrinogen the contact angle of the pure aqueous buffer solution on the cellulose acetate was lower than the contact angle measured after the adsorption of human serum albumin.

Characterization of ion-beam modified polyimide layers

Thin chemically modified polyimide films are widely used as functional layers for new microelectronic sensors. Modification of the chemistry of these polymers can lead to different mechanical, optical and electrical properties. Ion implantation is a preferred method to modify polyimide structures. In this work the ion-induced changes of chemical structures of three polyimides were analyzed by attenuated total reflection. Fourier transform infrared spectroscopy (ATR-FTIR); X-ray photoelectron spectroscopy (XPS); Raman spectroscopy; and spectroscopic ellipsometry and atomic force microscopy (AFM). The results indicate that during the implantation process the imide structures were partly destroyed. Carbon-rich, graphite-similar and amorphous structures were formed in the surface-near area of the polyimide layers. The changes in molecular structures especially depend on the dose of implanted boron ions.

Temperature dependent physicochemical properties of poly(N-isopropylacrylamide-co-N-(1-phenylethyl) acrylamide) thin films

The physicochemical properties of thermo-responsive polymer films are dynamically altered upon changes in environmental conditions. We report on the design and detailed characterization of a novel thermo-responsive polymer film with a temperature transition tuned to fit applications related to the control of marine biofouling. A copolymer consisting of poly(N-isopropylacrylamide) (PNIPAAm) and N-(1-phenylethyl) acrylamide (PEAAm) was synthesized and immobilized as a thin film onto Teflon AF surfaces using a low pressure argon plasma treatment. The temperature dependent physicochemical properties of the thermo-responsive film were thoroughly characterized and the impact of sea water on the film properties was investigated. The immobilized thermo-responsive film exhibits a reversible swelling/deswelling with temperature. Atomic force microscopy showed no morphological changes with varying temperature. Streaming current measurements performed above and below the transition temperature of the thermo-responsive hydrogel indicated that the charging of the polymer/aqueous solution interface is mainly determined by the preferential water ion adsorption at the Teflon AF surface. Inverse contact angles measured using captive air bubbles and analysed by axisymmetric drop shape analysis (ADSA) supported the intrinsic properties of the thermo-responsive film, as surface hydrophilicity decreased with increasing temperature. The advancing water contact angle decreased with increasing temperature, which may be explained by the different molecular mobility at different temperatures, allowing or hampering the re-orientation of hydrophobic segments at the solid–liquid and solid–fluid interfaces. These new films will allow investigations on the interaction of microorganisms with environmentally sensitive surfaces.

pH-triggered aggregate shape of different generations lysine-dendronized maleimide copolymers with maltose shell.

Glycopolymers are promising materials in the field of biomedical applications and in the fabrication of supramolecular structures with specific functions. For tunable design of supramolecular structures, glycopolymer architectures with specific properties (e.g., controlled self-assembly) are needed. Using the concept of dendronized polymers, a series of H-bond active giant glycomacromolecules with maleimide backbone and lysine dendrons of different generations were synthesized. They possess different macromolecular size and functionality along the backbone. Their peripheral maltose units lead to solubility under physiological conditions and controlled aggregation behavior. The aggregation behavior was investigated depending on generation number, pH value, and concentration. A portfolio of complementary analytical tools give an insight into the influence of the different parameters in shaping a rod-, coil-, and worm-like molecular structure and their controlled aggregate formation. MD simulation helped us to understand the complex aggregation behavior of the linear polymer chain without dendritic units.

Surface structure of fluorinated polymers and block copolymers

SummariesThe self-organisation of semifluorinated segments was used to create polymers and block copolymers with ultra-low surface free energy. The aromatic polyester poly(p-phenylene oxydecyl-perfluorodecyl-isophthalate) showed an extremely low value ofγsv of 9mN/m. It was proven that this low value was caused by an ordered surface structure. Introduction of these semifluorinated polyester segments into block copolymers with a basic structure (A–B)n resulted in a combination of good film-forming properties of polysulfone with the low surface free energy of the semifluorinated polyester. Thus, materials were obtained having both good mechanical performance as well as anti-adhesion properties. The block copolymers can be used to prepare blends with the respective homopolymers with different degrees of phase separation.The polymers and block copolymers can form a self-cleaning surface when coated on roughened aluminium substrates. It was shown that the adsorption of proteins, such as human serum albumin and fibrinogen from buffer solutions, significantly decreased on such polymer surfaces.RésuméL’autoorganisation des segments semi-fluorés a été utilisée pour créer des polymères et des bloc copolymères avec une énergie surfacique libre ultrabasse. Le polyester poly(p-phenylène oxydécylperfluorodécyl-isophthalate) aromatique a montré une très basse valeur deγsv de 9mN/m. Il a été prouvé que cette basse valeur était causée par une structure surfacique ordonnée. L’introduction de ces segments de polyester semi-fluorés dans des bloc copolymères ayant une structure fondamentale (A–B)n a ajouté les bonnes qualités du polysulphone vis à vis de la formation du feuil à la basse énergie surfacique libre du polyester semi-fluoré. Donc on a obtenu des matériaux qui démontraient une bonne performance mécanique aussi bien que des propriétés d’anti-adhésion. Les bloc polymères peuvent être utilisés avec les homopolymères respectifs pour préparer des mélanges ayant de différents degrés de séparation de phase.Les polymères et les bloc polymères peuvent former une surface autonettoyante quand ils revêtissent un substrat d’aluminium rendu rugeux. On a montré que l’adsorption des protéines telles que le sérum humain, albumine et le fibrinogène des solutions tampon diminue sur de telles surfaces polymériques.ZusammenfassungDie Selbstausrichtung von semifluorinierten Segmenten wurde verwendet, um Polymere und Block-Copolymere mit extrem niedriger freier Oberflächenenergie herzustellen. Das aromatische Polyester Poly(p-phenylen oxydecyl-perfluorodecyl-isophthalat) zeigte einen extrem niedrigen gsv-Wert von 9mN/m. Es wurde gezeigt, daß dieser niedrige Wert auf eine gut geordnete Oberflächenstruktur zurückgeführt werden konnte.Die Hinzufügung von semifluorinierten Polyestersegmenten zu Block-Copolymeren mit einer Struktur von (A–B)n ergab eine Kombination von den guten filmbildenden Eigenschaften von Polysulfon mit der niedrigen freien Oberflächenenergie von semifluoriniertem Polyester — in anderen Worten, ein Material das gute mechanische Eigenschaften mit einer niederen Adhäsionskraft vereinbarte. Durch die Verwendung von Block-Copolymeren lassen sich Mischungen mit den respektiven Homopolymeren mit verschiedenen Graded der Phasentrennung herstellen.Die Polymere und Block-Copolymere können auf aufgerauhte Aluminiumoberflächen aufgetragen werden, wo sie eine selbstreinigende Oberfläche bilden. Es wurde ausserdem gezeigt, daß die Adsorption von Proteinen wie Serum Albumin oder Fibrinogen von Pufferlösungen auf so beschichteten Oberflächen deutlich zurückging.

A novel tyrosine-modified low molecular weight polyethylenimine (P10Y) for efficient siRNA delivery in vitro and in vivo

The delivery of nucleic acids, particularly of small RNA molecules like siRNAs for the induction of RNA interference (RNAi), still represents a major hurdle with regard to their application in vivo. Possible therapeutic applications thus rely on the development of efficient non-viral gene delivery vectors. While low molecular weight polyethylenimines (PEIs) have been successfully explored, the introduction of chemical modifications offers an avenue towards the development of more efficient vectors. In this paper, we describe the synthesis of a novel tyrosine-modified low-molecular weight polyethylenimine (P10Y) for efficient siRNA complexation and delivery. The comparison with the respective parent PEI reveals that knockdown efficacies are considerably enhanced by the tyrosine modification, as determined in different reporter cell lines, without appreciable cytotoxicity. We furthermore identify optimal conditions for complex preparation as well as for storing or lyophilization of the complexes without loss of biological activity. Beyond reporter cell lines, P10Y/siRNA complexes mediate the efficient knockdown of endogenous target genes and, upon knockdown of the anti-apoptotic oncogene survivin, tumor cell inhibitory effects in different carcinoma cell lines. Pushing the system further towards its therapeutic in vivo application, we demonstrate in mice the delivery of intact siRNAs and distinct biodistribution profiles upon systemic (intravenous or intraperitoneal) injection. No adverse effects (hepatotoxicity, immunostimulation/alterations in immunophenotype, weight loss) are observed. More importantly, profound tumor-inhibitory effects in a melanoma xenograft mouse model are observed upon systemic application of P10Y/siRNA complexes for survivin knockdown, indicating the therapeutic efficacy of P10Y/siRNA complexes. Taken together, we (i) establish tyrosine-modified PEI (P10Y) as efficient platform for siRNA delivery in vitro and in vivo, (ii) identify optimal preparation and storage conditions as well as (iii) physicochemical and biological properties of P10Y complexes, and (iv) demonstrate their applicability as siRNA therapeutic in vivo (v) in the absence of adverse effects.

LC multiblock copolymers containing polysulfone segments. I. Synthesis and morphology

Multiblock copolymers offer the possibility to combine the properties of different polymers. Thus, new materials with tailor-made unique properties are available by coupling of different suitable polymeric segments. The goal of the work discussed in this paper was to combine advantageous properties of liquid-crystalline polymers (LCP) with those of polysulfone (PSU). Therefore, liquid crystalline poly(ethylene terephthalate-co-1,4-oxybenzoates) were connected with PSU oligomers. Chemically homogeneous multiblock copolymers with high molecular weight were obtained by a melt transesterification procedure. It was demonstrated by wide angle x-ray scattering (WAXS), polarizing microscopy, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) that the properties of the multiblock copolymers (solid phase structure, phase behavior, morphology, glass transition, and melting behavior) can be balanced by the segment length of the incorporated blocks. The investigations clearly reveal the existence of a two-phase structure. However, a change of properties compared to the corresponding homopolymers refers to certain interactions between the phase due to the chemical connection of the LCP and PSU segments.