RESUMEN
Uniformly distributed silica/epoxy nanocomposites (2 and 6 wt.% silica content) were obtained through a "solvent-free one-pot" process. The inorganic phases were obtained through "in situ" sol-gel chemistry from two precursors, tetraethyl orthosilicate (TEOS) and (3-aminopropyl)-triethoxysilane (APTES). APTES acts as a coupling agent. Surprisingly when changing TEOS/APTES molar ratio (from 2.32 to 1.25), two opposite trends of glass transformation temperature (Tg) were observed for silica loading, i.e., at lower content, a decreased Tg (for 2 wt.% silica) and at higher content an increased Tg (for 6 wt.% silica) was observed. High-Resolution Transmission Electron Microscopy (HRTEM) showed the formation of multi-sheet silica-based nanoparticles with decreasing size at a lower TEOS/APTES molar ratio. Based on a recently proposed mechanism, the experimental results can be explained by the formation of a co-continuous hybrid network due to reorganization of the epoxy matrix around two different "in situ" sol-gel derived silicatic phases, i.e., micelles formed mainly by APTES and multi-sheet silica nanoparticles. Moreover, the concentration of APTES affected the size distribution of the multi-sheet silica-based nanoparticles, leading to the formation of structures that became smaller at a higher content. Flammability and forced-combustion tests proved that the nanocomposites exhibited excellent fire retardancy.
RESUMEN
Lithium metal oxide nanoparticles were synthesized by induction thermal plasma. Four different systems-Li-Mn, Li-Cr, Li-Co, and Li-Ni-were compared to understand formation mechanism of Li-Me oxide nanoparticles in thermal plasma process. Analyses of X-ray diffractometry and electron microscopy showed that Li-Me oxide nanoparticles were successfully synthesized in Li-Mn, Li-Cr, and Li-Co systems. Spinel structured LiMn2O4 with truncated octahedral shape was formed. Layer structured LiCrO2 or LiCoO2 nanoparticles with polyhedral shapes were also synthesized in Li-Cr or Li-Co systems. By contrast, Li-Ni oxide nanoparticles were not synthesized in the Li-Ni system. Nucleation temperatures of each metal in the considered system were evaluated. The relationship between the nucleation temperature and melting and boiling points suggests that the melting points of metal oxides have a strong influence on the formation of lithium metal oxide nanoparticles. A lower melting temperature leads to a longer reaction time, resulting in a higher fraction of the lithium metal oxide nanoparticles in the prepared nanoparticles.
RESUMEN
Soy protein isolate (SPI) nanoparticles (28-179 nm) were prepared by employing a cold gelation method with a slight modification. The obtained nanoparticles exhibited uniform size distribution and spherical shape with a unique honeycomb-like core structure. Nanoparticle characteristics including size, surface charge and hydrophobicity could be adjustable by changing calcium concentration and environmental pH. Generally, higher calcium concentration and lower pH led to formation of nanoparticles with larger size, lower surface charge and hydrophobicity. Both protein conformation and nanoparticle dissociation studies indicated that calcium likely shielded negative charges on the SPI polypeptide chains, and functioned as a salt-bridge to permit polypeptide chains to approach one another. In this process, calcium favoured the development of ß-sheet structures to form SPI aggregates stabilised by hydrogen bonding. These aggregates were then associated to build SPI nano-networks through hydrophobic interactions. In vitro study indicated that the SPI nanoparticles were non-toxic and mainly located in the cytoplasm when uptaken into Caco-2 cells.