RESUMO
Biological materials with hierarchically laminated structures usually exhibit a good synergy between strength and fracture toughness. Here, we show that a bio-inspired (polyelectrolyte (PE)/TiO2)4 nanolayered composite with a thickness ratio of TiO2 and amorphous PE layers of about 1.1 has been prepared successfully on Si substrates by layer-by-layer self-assembly and chemical bath deposition methods. Microstructures of the nanolayered composite were investigated by scanning electron microscopy, secondary ion mass spectroscopy, and high-resolution transmission microscopy. Mechanical performance of the composite was characterized by instrumented indentation. The composite consisting of 17.9-nm-thick nanocrystalline TiO2 and 16.4-nm-thick amorphous PE layers has a strength of about 245 MPa, which is close to that of shells, while the fracture toughness of the composite, KIC = 1.62 ± 0.30 MPa · m1/2, is evidently higher than that of the bulk TiO2. A possible strategy to build the composite at nanoscale for high mechanical performance was addressed.
RESUMO
A novel method is suggested for the determination of benzo[a]pyrene in mainstream smoke. Extraction of Cambridge pads was cleaned up with methanol/n-heptane extraction system and silica solid-phase extraction (SPE). The eluted solution containing benzo[a]pyrene was evaporated gently to complete dryness with N2 flow, then reconstituted in 200 microL ethyl acetate for determination with gas chromatography-mass spectrometry selected ion monitoring (SIM). The proposed method had good results and precision for the separation of pyrene in complex matrices.
