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991.
Modification of Polyimide in Barrier Discharge Air-Plasmas: Chemical and Morphological Effects 总被引:4,自引:0,他引:4
Chemical and physical modifications of polyimide (PI) surfaces caused by an air plasma have been studied. The plasma-induced surface changes of PI were investigated by using a local dielectric barrier discharge (DBD) in air at atmospheric pressure and room temperature as a function of the plasma exposure time and plasma power, while the excitation frequency was kept constant at about 130 kHz. The first results obtained in this work suggest that DBDs operating in air at atmospheric pressure can be an efficient alternative plasma source for surface treatment of polymers: a short time air plasma treatment of few seconds leads to chemical and physical changes including the rise of wettability, surface oxidation, and enhancement of surface roughness. Therefore, this simple kind of dry surface treatment seems to be an effective, low cost method for production of well-adhering subsequent layers such as metal films, paints, glues, etc. on DBD pretreated polymers. 相似文献
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995.
Jacob Thorhauge Mogens Johannsen Karl Anker Jrgensen 《Angewandte Chemie (International ed. in English)》1998,37(17):2404-2406
Valuable substrates for the synthesis of natural products , compounds 3 (R1=alkyl, aryl, alkoxy; R2, R3=alkyl) are formed from β,γ-unsaturated α-keto esters 1 and vinyl ethers 2 by the title reaction [Eq. (1)]. Copper(II ) bisoxazolines act as catalysts, and in many cases enantiomeric excesses higher than 99.5 % are achieved. 相似文献
996.
Sulan Yao Mogens Johannsen Rita G. Hazell Karl Anker Jrgensen 《Angewandte Chemie (International ed. in English)》1998,37(22):3121-3124
1 mol% of catalyst is sufficient : The hetero Diels–Alder reaction of α-imino esters 1 with activated conjugated dienes 2 (R=H, Me) needs only 1 mol% of a 2,2′-bis(diarylphosphanyl)-1,1′-binaphthyl (BINAP) copper(I ) complex as the catalyst to generate the adducts 3 in good yields and with enantioselectivities up to 96%. The reaction can also be carried out on gram scale! Tos=H3CC6H4SO2; TMS=Me3Si. 相似文献
997.
F. Lagarde M. B. Amran M. J. F. Leroy C. Demesmay M. Ollé A. Lamotte H. Muntau P. Michel P. Thomas S. Caroli E. Larsen P. Bonner G. Rauret M. Foulkes A. Howard B. Griepink E. A. Maier 《Fresenius' Journal of Analytical Chemistry》1999,363(1):18-22
Tuna fishes were collected in the Straits of Messina (Italy), were dissected and dorsal muscles minced, freeze-dried, ground
and sieved. The obtained powder was stabilised by γ-irradiation and filled into brown glass bottles. The homogeneity and stability
at +20 °C and +40 °C were verified with regards to the total arsenic, dimethylarsinic acid and arsenobetaine contents. Ten
laboratories participated in the certification study. All participants had demonstrated beforehand their ability to produce
accurate results for the As speciation in fish tissue. The certified values are: total arsenic (4.8 ± 0.3) mg/kg, arsenobetaine
(52 ± 3) μmol/kg, dimethylarsinic acid (2.0 ± 0.3) μmol/kg. The material is available from the BCR since early 1998.
Received: 31 March 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998 相似文献
998.
F. Lagarde M. B. Amran M. J. F. Leroy C. Demesmay M. Ollé A. Lamotte H. Muntau P. Michel P. Thomas S. Caroli E. Larsen P. Bonner G. Rauret M. Foulkes A. Howard B. Griepink E. A. Maier 《Fresenius' Journal of Analytical Chemistry》1999,363(1):5-11
Six interlaboratory studies were organised by the Standard, Measurement and Testing Programme of the European Commission on
the determination of arsenic species (arsenobetaine, arsenocholine, monomethylarsonic acid, dimethylarsinic acid, As(III)
and As(V)) in marine matrices and soil. A step-by-step approach was used and a meeting was held at the end of each study to
help the participants to discover errors and to improve their analytical methods. The successive steps investigated the calibration
procedures on various solutions, the separation and derivatisation techniques on solutions and extracts and the extraction
on mussel and fish tissues. All materials used for the study were monitored for their stability. Verified calibration solutions
and compounds were distributed to the participants in each exercise in order to trace calibration problems. The agreement
between the results improved regularly and at the end of the six campaigns allowed the certification of a reference material
of tuna-fish tissue (BCR-CRM 627) for its total arsenic, arsenobetaine and dimethylarsinic acid contents.
Received: 31 March 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998 相似文献
999.
M.C. Larsen P. Hvelplund M.O. Larsson H. Shen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):283-289
The fragmentation of anions and cations resulting from 50 keV collisions with rare gas targets is studied. Positive ion fragment
patterns are recorded, and dramatic changes in these patterns are observed as a function of target atom number. The fragment
pattern dependence on the target atom size is investigated within a simple model, normally used for stopping power calculations.
Fair agreement is obtained between calculated and experimental spectra. From these comparisons we conclude that the range
of the screened atomic potentials, as e.g., the Thomas-Fermi potential, is an essential parameter in the collisional induced fragmentation process.
Received: 13 February 1998 / Revised: 27 October 1998 / Accepted: 29 October 1998 相似文献
1000.
F. Lagarde M. B. Amran M. J. F. Leroy C. Demesmay M. Ollé A. Lamotte H. Muntau P. Michel P. Thomas S. Caroli E. Larsen P. Bonner G. Rauret M. Foulkes A. Howard B. Griepink E. A. Maier 《Analytical and bioanalytical chemistry》1999,363(1):18-22
Tuna fishes were collected in the Straits of Messina (Italy), were dissected and dorsal muscles minced, freeze-dried, ground and sieved. The obtained powder was stabilised by γ-irradiation and filled into brown glass bottles. The homogeneity and stability at +20?°C and +40?°C were verified with regards to the total arsenic, dimethylarsinic acid and arsenobetaine contents. Ten laboratories participated in the certification study. All participants had demonstrated beforehand their ability to produce accurate results for the As speciation in fish tissue. The certified values are: total arsenic (4.8 ± 0.3) mg/kg, arsenobetaine (52 ± 3) μmol/kg, dimethylarsinic acid (2.0 ± 0.3) μmol/kg. The material is available from the BCR since early 1998. 相似文献