From SiO1.5CH3 to vitreous SiO2: A structural evolution study

The conversion of SiO1.5CH3 into SiO2 glass by pyrolysis in air has been studied by combining density measurements, vibrational spectroscopy, positron annihilation spectroscopy, and nuclear magnetic resonance. The results show that a critical transition takes place between 400 and 500 degrees C and at 600 degrees C the organic features are completely removed. The conversion of the hybrid structure into a fully inorganic network takes place through the formation of metastable 3-membered rings that progressively evolve into more stable 5+ rings as the pyrolysis temperature increases. The evolution of the organic moieties is coupled with the formation of Si-OH and molecular water trapped in the network which are well visible between 500 and 800 degrees C. In such temperature regions, a clear evolution of the network density can be detected, though the amount of free volume is nearly constant (due to the presence of trapped H2O). Only at 1250 degrees C, the network is comparable with a melt-derived glass

Al2O3 Decorated with Zn Single Sites: A Multifunctional Filler for Upgrading the Properties of XNBR Composites

A multifunctional alumina-based filler, AlO@APTES-Zn, has been synthesized by functionalizing AlO nanoparticles with aminopropyl triethoxysilane (APTES) and subsequently anchoring Zn centers. This multifunctional nanofiller acts simultaneously as a reinforcing agent, cross-linking promoter, and thermal conductivity enhancer in carboxylated nitrile rubber (XNBR) composites. The anchored Zn(II) sites also provide ionic interactions with XNBR terminations, enabling dynamic reversible bonds for self-healing properties. The comprehensive characterization of XNBR/AlO@APTES-Zn composites unveils enhanced cross-linking, improved tensile strength and strain at break (up to 17 MPa and 1416% at 24 phr filler), increased thermal conductivity (+11.4% compared to neat AlO at the same loading), and superior self-repairing efficiency (up to 120%). These results demonstrate that the tailored surface and interfacial properties of AlO@APTES-Zn represent a promising benchmark for resilient and sustainable composites in applications, such as hoses, seals, gaskets, and automotive components.The authors thank Itziar Mas Giner from ICTP-CSIC for her contribution to the experimental work related to the realization and characterization of polymer composites