Toward the Elucidation of the Competing Role of Evaporation and Thermal Decomposition in Ionic Liquids: A Multitechnique Study of the Vaporization Behavior of 1-Butyl-3-methylimidazolium Hexafluorophosphate under Effusion Conditions.

The evaporation/decomposition behavior of the imidazolium ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6) was investigated in the overall temperature range 425-551 K by means of the molecular-effusion-based techniques Knudsen effusion mass loss (KEML) and Knudsen effusion mass spectrometry (KEMS), using effusion orifices of different size (from 0.2 to 3 mm in diameter). Specific effusion fluxes measured by KEML were found to depend markedly on the orifice size, suggesting the occurrence of a kinetically delayed evaporation/decomposition process. KEMS experiments revealed that other species are present in the vapor phase besides the intact ion pair BMImPF6(g) produced by the simple evaporation BMImPF6(l) = BMImPF6(g), with relative abundances depending on the orifice size-the larger the orifice, the larger the contribution of the BMImPF6(g) species. By combining KEML and KEMS results, the conclusion is drawn that in the investigated temperature range, when small effusion orifices are used, a significant part of the mass loss/volatility of BMImPF6 is due to molecular products formed by decomposition/dissociation processes rather than to evaporated intact ion pairs. Additional experiments performed by nonisothermal thermogravimetry-differential thermal analysis (TG-DTA) further support the evidence of simultaneous evaporation/decomposition, although the conventional decomposition temperature derived from TG curves is much higher than the temperatures covered in effusion experiments. Partial pressures of the BMImPF6(g) species were derived from KEMS spectra and analyzed by second- and third-law methods giving a value of ΔevapH298K° = 145.3 ± 2.9 kJ·mol-1 for the standard evaporation enthalpy of BMImPF6. A comparison is done with the behavior of the 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide (BMImNTf2) ionic liquid.

Investigation of bioactivity, biocompatibility and thermal behavior of sol-gel silica glass containing a high PEG percentage.

SiO2/PEG organic-inorganic hybrid materials, which contain 60 or 70 weight percentage of PEG, were synthesized by the sol-gel technique. The materials were characterized and subjected to various tests to assess their application in the biomedical field. The evaluation of their morphology by scanning electron microscopy (SEM) confirms the homogeneity of the samples on the nanometer scale. Fourier transform infrared spectroscopy (FT-IR) indicated that the two components of the hybrids (SiO2 and PEG) are linked by hydrogen bonds. This feature makes them class I hybrids. Simultaneous thermogravimetry/differential thermal analysis (TG/DTA) was used to investigate their thermal behavior and to establish the best temperatures for their pre-treatment. The fundamental properties that a material must have to be used in the biomedical field are biocompatibility and bioactivity. The formation of a hydroxyapatite layer was observed on the hybrid surface by SEM/EDX and FTIR after soaking in simulated body fluid. This indicates that the materials are able to bond to bone tissue. Moreover, the biocompatibility of SiO2/PEG hybrids was assessed by performing WST-8 cytotoxicity tests on fibroblast cell NIH 3T3 after 24h of exposure. The cytotoxicity tests highlight that the cell viability is affected by the polymer percentage. The results showed that the synthesized materials were bioactive and biocompatible. Therefore, the results obtained are encouraging for the use of the obtained hybrids in dental or orthopedic applications.