The nature of the exceptional impact of ultra-low silica contents on the properties of cyanate ester resin-based nano- and subnanocomposites

Our study clarifies the nature of the exceptional impact of the ultra-low content of silica (SiO2) units on the properties of the heterocyclic cyanate ester resin (CER) network matrix in the subnano- or nanocomposites. To this effect, we have performed a series of calculations of average distances between SiO2 units and the interfacial area values in the composites as functions of the content and size of SiO2 units. The estimates were made for the CER composites with SiO2 and POSS additives, based on these calculations and the composites' previously measured structural characteristics. It was found that the aforementioned unusual effect was controlled by the constrained interfacial matrix dynamics in the composites. Thus, when (a) the SiO2 content was 0.03-0.1 wt%, (b) SiO2 units and the matrix network had covalent bonding, and (c) SiO2 units had quasi-regular distribution in the amorphous matrix (as found for the subnanocomposites), we found that distances between SiO2 units equaled 6 and 10 nm, that is, these distances were commensurable with the lengths of Kuhn segments in heterocyclic macromolecules.