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- 2010 (13) (entfernen)
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- Zeitschriftenartikel (5)
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- Posterpräsentation (2)
Schlagworte
- Adhesion-promoting layers (1)
- Chemical derivatisation (1)
- DNA hybridization (1)
- DNA immobilization (1)
- Depth profiling (1)
- Derivatisation (1)
- Dielectric barrier discharge (1)
- ESCA/XPS (1)
- Electrospray deposition (1)
- Ellipsometry (1)
Eingeladener Vortrag
- nein (4)
The potential of spectrofluorometry and fluorescence microscopy for the characterization and quantification of different functionalities like OH and NH2 groups at plasma-chemically modified polymer surfaces is assessed using traditional reactive dyes such as dansyl derivatives and a sophisticated VIS-excitable chromogenic and fluorogenic pyrylium label showing binding-induced spectral and intensity changes in absorption and emission. Aiming at an improved fluorometric surface analysis, based upon these measurements, several sources of uncertainty inherent to fluorescence measurements are illustrated ranging from environment-dependent dye absorption and emission features over spectral correction and nonspecific adsorption to the critical influence of label choice on the measured background. Solutions to these drawbacks are given thereby underlining the potential of fluorometry for surface analysis.
A first inter-laboratory comparison was conducted to demonstrate and document the capability of interested laboratories to measure the fraction of C—OH species on a plasma oxidised poly(propylene) sample by using a chemical derivatisation XPS approach. This report presents the results from that inter-laboratory comparison and includes the data received for the measured values and their associated standard deviations of laboratory means, at a 95% confidence level. The measurements were guided by a protocol developed within the group before and summarised shortly in the paper. Standard deviations that may characterise the state-of-the-art for the nominally simple and rather often practised case of TFAA chemical derivatisation XPS of C—OH species on a plasma oxidised polyolefin surface are calculated following ISO 5725-2:1994. The main conclusion is that the associated degree of equivalence reached by the participating laboratories in this comparison is still low. Further research to improve chemical derivatisation XPS protocols is mandatory.
Aerosol-based DBD - a simple way to provide polymers with functional groups for adhesion promotion
(2010)
In this paper the preparation of silicon and titanium oxide thin films using an atmospheric pressure plasma process will be reported. To obtain these oxide films hexamethyldisiloxane and titanium tetraisopropoxide were used as precursor materials. Based on the different chemical reaction mechanisms the film deposition processes were carried out in the direct as well as in the remote PACVD mode. The deposition parameters were varied and the influence on different film properties was studied. The deposited oxide films were characterised by profilometry, ellipsometry, SEM, UV-VIS-NIR-transmission measurements. FT-IR spectroscopy and contact angle measurements. Additionally, first results will be presented concerning the creation of composite films using a combination of plasma and liquid dye nebulization technique.
Plasma-chemical bromination has been shown to be well-suited for highly selective and efficient C–Br-functionalization of polyolefin surfaces and has now been applied to graphitic materials, including highly oriented pyrolytic graphite (HOPG), natural graphite, carbon nanotubes, and graphitized carbon fibres. In contrast to the radical substitution of hydrogen by bromine at hydrogen-terminated sp3-hybridized carbon, bromination of all-carbon bound sp2-hybridized carbon in graphene requires addition to aromatic double bonds. The related change of sp2 to sp3 hybridization of the carbon atoms involved helps to explain experimental results of a loss in surface planarity on brominated HOPG. Bromine concentrations of up to 50 bromine atoms per 100 C-atoms were achieved in elemental bromine vapour under low-pressure plasma conditions using low-energetic inductively coupled radio-frequency plasma excitation. The time scale of the bromination progress was found to increase with the specific surface area of the material. The results of plasma-chemical bromination are compared to that of wet-chemical electrophilic addition reactions, which achieved 28 Br per 100 C for MWCNT. The resulting C–Br bonds from plasma-chemical processing of graphitic materials were shown to be well-suited for hydroxyl functionalization and for grafting of organic molecules by nucleophilic substitution with 1,6-diaminohexane and (3-aminopropyl)triethoxysilane.
Immobilization of silanized DNA on glass: influence of the silane tether on the DNA hybridization
(2010)
Two trifunctional (trimethoxy and triethoxy) and one difunctional (methyldimethoxy) 3-mercaptopropyl-alkoxysilanes were covalently tethered to thiolated DNA oligonucleotides in solution. After deposition as microarrays onto glass, the immobilized DNA probes were tested for hybridization ability by a florescence-based method. The results demonstrate a large enhancement in the fluorescence signal when the functionality of the silane tether is reduced from three to two. An XPS analyses revealed that this is not due to a higher DNA surface density. FTIR spectra of the spin-coated silanes showed that the trifunctional silanes form branched and cyclic siloxane moieties, whereas the difunctional silane generates predominantly short straight siloxane chains. Therefore, the propensity of trifunctional silanes to form more complex networks leads to conformations of the bound DNA which are less favorable for the specific interaction with the complementary strand. The data implicate that further significant improvements in the DNA hybridization ability are possible by adroit choice of the silane system.
Polyolefins are chemically inert and do not adhere well to metals, polymers or inorganics. To overcome this problem, polyolefin surfaces were modified thermally, plasmachemically, or by flame treatment with different oxygen-containing groups, however, unfortunately, such treatments were accompanied by undesired, adhesion lowering polymer degradation. To solve this dilemma, solutions of synthetic polymers and copolymers were prepared, sprayed into the barrier discharge or electrosprayed without discharge and deposited as thin adhesion-promoting layers. The deposited polymer layers from poly(vinylamine), poly(ethylene glycol)-poly(vinyl alcohol) copolymers and poly(acrylic acid) were endowed with monotype functional groups. Using the aerosol - dielectric barrier discharge only a fraction of functional groups survived the deposition process in contrast to the electrospray in which all functional groups were retained.