Interfacial behavior of silicone oils interacting with nanosilica and silica gels

Abstract

The interfacial behavior of silicone oils Oxane 1000 and Oxane 5700 (polydimethylsiloxanes, PDMS) interacting with dried or hydrated (hydration h=0.005 or 0.1g/g) silica gels Si-60 and Si-100 or nanosilica A-400 was studied using low-temperature 1H NMR spectroscopy over the 210–310K range. Broadening of the melting temperature range toward both sides from the freezing point is observed for silicone oils confined in mesopores (2–15nm in radius) of silica gel particles (0.2–0.5mm in size) or voids (1–100nm) between silica nanoparticles (5–10nm in size) in their aggregates. This effect is a consequence of the phase state heterogeneity, since both liquid and solid-like fractions of adsorbed PDMS are observed over a large temperature range. The adsorbed PDMS heterogeneity depends on the pore size distribution (confined space effect), and it is lower for silica gel Si-100 possessing broader pores than Si-60. An increase in the amounts of adsorbed polymer and water diminishes the effects of confined space on PDMS because a fraction of the polymers is located in broader pores or out of pores (voids). This leads to relative decrease in interactions of PDMS with the silica surface. 1H NMR spectra of PDMS and n-decane bound to silica gels reveal much stronger heterogenization of adsorbed PDMS (depending on the polymer length) than that of the alkane.