ABSTRACT
The structural (volume and enthalpy) relaxation of polymers during physical aging has a great relevance in materials science and engineering as it significantly changes the long-term material performance. In this article, we propose a methodological approach of (cryo-)atomic force microscopy (AFM) monitoring of macromolecular rearrangements which accompany structural relaxation within bulk of the polymer during physical aging. In contrast to conventional spectroscopic, scattering and thermal analysis techniques, high resolution topographical/phase imaging of the bulk cross-section over a large period of time and within a wide range of temperatures (-120 °C to +20 °C) yields unique information about the evolution of the polymer ultrastructure as a function of time and temperature in situ.
ABSTRACT
Here we report on the fabrication and characterization of ultra-thin nanocomposite layers used as gate dielectric in low-voltage and high-performance flexible organic thin film transistors (oTFTs). Reactive sputtered zirconia layers were deposited with low thermal exposure of the substrate and the resulting porous oxide films with high leakage currents were spin-coated with an additional layer of poly-alpha-methylstyrene (P alphaMS). After this treatment a strong improvement of the oTFT performance could be observed; leakage currents could be eliminated almost completely. In ellipsometric studies a higher refractive index of the ZrO(2)/P alphaMS layers compared to the "as sputtered" zirconia films could be detected without a significant enhancement of the film thickness. Atomic force microscopy (AFM) measurements of the surface topography clearly showed a surface smoothing after the P alphaMS coating. Further studies with X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) also indicated that the polymer definitely did not form an extra layer. The polymer chains rather (self-)assemble in the nano-scaled interspaces of the porous oxide film giving an oxide-polymer "nanocomposite" with a high oxide filling grade resulting in high dielectric constants larger than 15. The dielectric strength of more than 1 MV cm(-1) is in good accordance with the polymer-filled interspaces.
ABSTRACT
Comparative analysis of DNA packing density in Phi KZ and T4 bacteriophages was carried out by atomic force microscopy. Irrespective of the support (mica or highly ordered pyrrolytic graphite), Phi KZ bacteriophage was compressed stronger than T4. The most probable causes of this difference are analyzed.
Subject(s)
Bacteriophage T4/genetics , DNA, Viral/chemistry , Bacteriophage T4/chemistry , Bacteriophages/chemistry , Bacteriophages/genetics , Microscopy, Atomic Force , Nucleic Acid ConformationABSTRACT
DNA packing of bacteriophage phikz (Pseudomonas aeruginosa) was studied by electron microscopy after gentle destruction of the capsid with powerful laser impulse in aqueous virus suspension in the presence organic dye. Suspension of destroyed phage heads contained complexes of genomic DNA with endogenous capsid proteins characterized by pronounced regular structure. The type of these structures corresponds to one the main model of phage DNA packing, the so-called coil packing.