Aqueous suspensions of poly(ethylene glycol)/pyrocarbon/fumed silica

Aqueous suspensions of fumed silica and pyrocarbon/silica (CS) in the prese nce of dissolved poly(ethylene glycol) (PEG) were studied using H-1 NMR spe ctroscopy with freezing-out of bulk water and quantum chemical computations of the chemical shifts. The freezing effect for PEG/water is akin to that for low-molecular organics, as formation of solid phases of water (ice) and PEG occurs, and their mixture forms at the eutectic temperature. In the aq ueous suspensions of fumed silica or CS, PEG molecules are localized at the solid-liquid interfaces and do not form the bulk solution even at large co ncentrations; however, the amount of bulk undisturbed water rises due to fo rmation of the immobilized PEG layer. For such suspensions of silica or CS at a low amount of pyrocarbon (C-C = 4 wt%), there is a portion of the grap h of the surface free energy (gamma (s)) increasing nearly linearly with th e PEG concentration (C-PEG); however, in the case of large C-C = 40 wt% in CS, a similar effect is not observed, as gamma (s) is maximal at low C-PEG = 0.1 wt%. (C) 2001 Academic Press.