Intermolecular interactions in composites of organically-modified silica aerogels and polymers: A molecular simulation study

Abstract

Two types of ORMOSIL-based composite systems have been studied by all-atom molecular dynamics simulations: (i) tetramethylorthosilicate (TMOS) and vinyltrimethoxysilane (VMTS) with polydimethylsiloxane (PDMS); and (ii) tetraethylorthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES) or TEOS/(3-glycidyloxypropyl)trimethoxysilane (GLYMO) with the polyimides/polyamic acids of 3,3’,4,4’-biphenyltetracarboxylic dianydride – 4,4’-oxydianiline (BPDA-ODA) and pyromellitic dianhydride – 3,5-diaminobenzoic acid (PMDA-DBA). For systems (i) it was concluded that an increase in the % mol of PDMS leads to the formation of smaller aggregates of silica primary particles, which is explained by the reduction in the number of silica–silica H-bonds in favor of silica-PDMS H-bonds; both electrostatic and van der Waals interactions contribute significantly for the overall attractive forces between the two phases. In the case of systems (ii), the silica hydroxyl and amine groups form H-bonds with anhydride, carbonyl, carboxyl and terminal amine groups in the polyimides/polyamic acids, whereas for the TEOS/GLYMO the most prevalent H-bonds are those developed between hydroxyl silica groups and carboxyl or terminal amine groups of the polymer chains; in the latter composite systems, van der Waals forces play a more significant role in the adhesion between silica particles and the polymer.