Dielectric and thermal studies of segmental dynamics in silica/PDMS and silica/titania/PDMS nanocomposites

Abstract

Effects of silica and silica/titania nanoparticles on glass transition and segmental dynamics of poly(dimethylsiloxane) (PDMS) were studied for composites of a core–shell type using differential scanning calorimetry, thermally stimulated depolarization current, and dielectric relaxation spectroscopy techniques. Strong interactions between the filler and the polymer suppress crystallinity (Tc, Xc) and affect significantly the evolution of the glass transition in the nanocomposites. The segmental relaxation associated with the glass transition consists of three contributions, arising, in the order of decreasing mobility, from the bulk (unaffected) amorphous polymer fraction (α relaxation), from polymer chains restricted between condensed crystal regions (αc relaxation), and from the semi‐bound polymers in an interfacial layer with strongly reduced mobility due to interactions with surface hydroxyls of silica and silica/titania nanoparticles (α′ relaxation). The evolution of surface affected CH3 groups, as well as the degree of interaction of PDMS molecules with surface hydroxyl groups as a function of treatment temperature, was assessed by Fourier transform infrared spectroscopy, thermogravimetry and differential thermal analysis. The effectiveness of silica/PDMS and silica/titania/PDMS nanocomposites as hydrophobic coatings was investigated by static contact angle measurements. It was shown that the presence of titania nanoparticles and adsorbed PDMS promotes the hydrophobic properties of the PDMS coating after treatment in the 80–650°C range. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41154.

Interfacial phenomena in core–shell nanocomposites of PDMS adsorbed onto low specific surface area fumed silica nanooxides: Effects of surface modification

“…The results suggest that silica particles do not act as crystallization nuclei [33]). Results are similar to those presented here have been obtained in previous work on silica/PDMS NCs [32,34,35], as well as on polymers confined between solid surfaces [24].…”

DSC study of silicas with immobilized polysiloxane layer of different architecture

“…The appearance, though only slightly, of the cold crystallization exothermic peak indicates the formation of isotactic macromolecular chains. The appearance of the cold crystallization for dispersed silicas modified by adsorption with PMS1000 with the same polymer content (40 mass%) was noted by the authors [17,26], with high concentration of active sites on the surface of pristine nanoparticles (before modification). This provides evidence for the theory presented above about the formation of additional active sites during firststage modification (lowering of structure-related complications of adsorption/chemisorption).…”

Effect of Confinement Geometry on Out-of-Equilibrium Glassy Dynamics

“…In terms of surface/volume ratio, this corresponds to a 30 nm thick films. The main relaxation peak in BDS was also employed to characterize the rate of spontaneous fluctuations in polymer nanocomposites with weak interaction polymer/filler [9,12,14,15,22,164]. 12.2 where the loss part of the dielectric permittivity (ɛ′′), taken from ref.…”