Interfacial phenomena and molecular dynamics in core-shell-type nanocomposites based on polydimethylsiloxane and fumed silica: Comparison between impregnation and the new mechano-sorption modification as preparation methods

In this study, we investigate interfacial phenomena in nanocomposites of the ‘core-shell’ type based on fumed silica nanoparticles (core) and linear polydimethylsiloxane, PDMS, (shell) of low molecular weight (~3 kg/mol). In particular, we study the interfacial polymer in terms of the amount and dynamics and compare between two methods of nanocomposite preparation, the simple impregnation (liquid phase method) and the relatively new and environmentally more friendly mechano-sorption modification, MSM (gas phase method). To that aim, we employ differential scanning calorimetry, DSC, and broadband dielectric spectroscopy, BDS, as the main investigation tools, supplemented by scanning electron microscopy, SEM, and Fourier transform infrared spectroscopy, FTIR. The silica-PDMS interactions result in constraints on the polymer diffusion/mobility and, subsequently, on the formation of an interfacial polymer fraction being rigid in DSC or exhibiting retarded dynamics in BDS. In qualitative agreement between the two techniques, the amount of interfacial polymer was found systematically larger for MSM as compared to impregnation, confirming actually the scope of employing MSM. The latter is shown here for the first time in silica nanocomposites employing the said experimental methodology. From the basic research point of view, the bulk-like dynamics (glass transition and α/αc relaxations) is mainly similar between the nanocomposites and neat PDMS, with the larger interfacial amounts imposing a slight increase of the Tg. Owing to the high resolving power of BDS, the interfacial polymer dynamics is recorded individually via the αint relaxation next to the bulk-like α/αc in the nanocomposites. αint exhibits a non-cooperative character and relatively high strength, which, comparing to previous work on similar and systems, suggests the existence of many PDMS tails distributed on the silica surfaces, with the interfacial chains packing being possibly more dense in the case of MSM as compared to impregnation. [Display omitted] •Silica-PDMS core-shell nanocomposites synthesized by a new Mechano-Sorption Modification (MSM).•Investigation employing structural (SEM, FTIR), thermal (DSC) and dielectric (BDS, TSDC) methods.•MSM was found to produce larger interfacial polymer fraction, as compared to conventional impregnation.•The interfacial polymer dynamics was recorded individually (αint process, BDS) from the bulk-like one (α).•Results suggest the existence of many PDMS tail