The interaction of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with Au or Ag nanospheres, Au nanostars, and Ag nanoprisms was investigated using surface-enhanced Raman scattering (SERS). The SERS investigation showed that adsorption of MEH-PPV strongly depends on the nature of the nanoparticle surface. On gold nanostars that present a thick layer of capping polymer, SERS spectrum is only observed in relatively concentrated MEH-PPV solution (1 mmol L −1 ). On the other hand, Au and Ag nanospheres present SERS spectra down to 10 −6 mol L −1 and no chemical interaction of MEH-PPV and metal surface is observed. The spectra of MEH-PPV on Ag nanoprisms with PVP as stabilizing agent suggest that the capping polymer induces a planar conformation of MEH-PPV and consequently an increase of conjugation length. These results give support for the application of MEH-PPV on optoelectronics in which interfacial effects are critical in the device efficiency and stability.
This article tells the story of the proof known as reductio ad absurdum, through the biographies of Heraclitus, Parmenides and his disciple Zeno. Emphasis is placed on Zeno’s paradoxes and some classic demonstrations of modern mathematics, in which proof by reductio ad absurdum is used widely. In other words, we intend to discuss the logical-mathematical history of reductio ad absurdum, from the birth of logic in Heraclitus, Parmenides and Zeno and ipso facto to establish a relationship between Heraclitus, Parmenides and Zeno and modern mathematical logic. The method used was the bibliographic, referring mainly to secondary sources due to the strictly theoretical nature of the subject.
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