4. Nano- and Subnanocomposites with Silica Units Introduced by a Sol–gel Method

The results of physical studies of the hybrid CER-silica composites with 0.01–10 wt.% silica prepared via a sol–gel technology are presented. HAADF-STEM, EDXS, DMA, DSC, and TGA were used for their characterization. It was found that the greatest positive effect of introducing covalently embedded silica units into the matrix is observed at their ultra-low content of 0.02–0.1 wt.%. The possibility of creating subnanometer-sized silica nodes in the matrix network in the absence of clustering was revealed in this case, and the term “subnanocomposites” was introduced into the literature. The effect of the quasi-regular distribution of silica subnanounits or molecularly dispersed nanoparticles in nanovolumes of amorphous matrix was detected. The superiority of the properties of polymer subnanocomposites over those of the corresponding composites with SiO₂ nanoclusters was shown. Certain correlations between the nanostructure, matrix dynamics, and the properties of the investigated composites were traced. Additional calculations based on the obtained structural data were performed, which made it possible to establish the nature of the above effects. It turned out that the dynamics of the matrix as a whole transformed into the state of constrained interfacial dynamics in this case.