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- Copper (1)
- DMA (1)
- DNA hybridization (1)
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- Flame retarded polymers (1)
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Stiffness variation in the interphase of amine-cured epoxy adjacent to copper microstructures
(2007)
In an effort to expand the understanding of the mechanical properties of the polymeric interphase on a metal surface, a composite consisting of epoxy and copper was prepared and analyzed. Scanning force microscopy-based force modulation microscopy (SFM-FMM) was employed along with dynamic mechanical analysis (DMA) and energy dispersive X-ray analysis (EDX). Diglycidyl ether of bisphenol A (DGEBA)-based epoxy resins were applied with amine curing agents. The samples were made taking advantage of electron beam lithography (EBL) in order to produce sharp edges of copper structures and a flat surface suitable for the SFM-FMM analysis, which was able to depict the stiffness within the interphase. It is considered significant information because the mechanical characteristic within the narrow interphase was revealed. Comparing with DMA and EDX, the stiffness information of SFM-FMM demonstrated a matching correlation and agreement in terms of preferential adsorption of the curing agent in the vicinity of the interface. The stiffness profiles of the two epoxy systems turned out to be different, and it shows the material dependence of the interphase characteristics.
Low-energy secondary electrons are the most abundant radiolysis species which are thought to be able to attach to and damage DNA via formation and decay of localized molecular resonances involving DNA components. In this study, we analyze the consequences of low-energy electron impact on the ability of DNA to hybridize (i.e., to form the duplex). Specifically, single-stranded thymine DNA oligomers tethered to a gold surface are irradiated with very low-energy electrons (E = 3 eV, which is below the 7.5 eV ionization threshold of DNA) and subsequently exposed to a dye-marked complementary strand to quantify by a fluorescence method the electron induced damage. The damage to (dT)25 oligomers is detected at quite low electron doses with only about 300 electrons per oligomer being sufficient to completely preclude its hybridization. In the microarray format, the method can be used for a rapid screening of the sequence dependence of the DNA-electron interaction. We also show for the first time that the DNA reactions at surfaces can be imaged by secondary electron (SE) emission with both high analytical and spatial sensitivity. The SE micrographs indicate that strand breaks induced by the electrons play a significant role in the reaction mechanism.
Thermal, thermo-oxidative and fire residues of high impact polystyrene/magnesium hydroxide/red phosphorus (HIPS/Mg(OH)2/Pr) are investigated by solid-state NMR and compared with the results for the binary subsystem Mg(OH)2/Pr. The influences of oxygen, nitrogen and temperature are discussed. For a thermal decomposition and pyrolysis during combustion, the main pyrolysis of HIPS takes place while the remaining residue is a rather intact polymer, with a major share of the embedded Pr still present. Subsequently, mainly amorphous phosphates and a slight amount of crystalline Mg3(PO4)2 and Mg2P2O7 are formed at the highest temperatures. Only with increasing mass loss does the remaining polystyrene structure decompose and graphitic structures occur. The influence of oxygen on the decomposition mechanism is most obvious for the binary system Mg(OH)2/Pr. Pr vanishes more rapidly and crystalline, oxygen-rich magnesium phosphates are formed. In HIPS/Mg(OH)2/Pr systems the polymer acts as a barrier to reaction by the embedded particles, so that major characteristics of an anaerobic decomposition are found. Significant amounts of phosphorus are retained in the condensed phase through a reaction of Pr with Mg(OH)2 to mostly amorphous phosphates. This formation of amorphous inorganic magnesium phosphates can act as an additional physical barrier. This study outlines some advanced approaches for controlling the condensed-phase mechanisms of phosphorus and underlines that solid-state NMR is a most powerful tool for investigating the organic and inorganic residues.