Water-associated dielectric relaxation in oxide nanoparticles

Abstract

Audio frequency dielectric relaxation studies were carried out over the temperature range 120 to 390 K on nanoscale mesoporous silica coated with polystyrene and nanoscale γ alumina. Two features are observed, both of which are attributed to water. A relaxation is observed at about 150 K and 1000 Hz that is thermally activated. The activation enthalpy is relatively high and the pre-exponential appears to be unusually low and to depend upon the water concentration. A model is presented that accounts for the apparently anomalous behaviour. This relaxation is attributed to water molecules bound at surface hydroxyl groups. A feature is found in the vicinity of 250 K and 1000 Hz that is associated with conductivity that varies as ωn. This response is attributed to hopping conductivity in loosely bound surface water.

Calorimetric and Dielectric Study of Renewable Poly(hexylene 2,5-furan-dicarboxylate)-Based Nanocomposites In Situ Filled with Small Amounts of Graphene Platelets and Silica Nanoparticles

“…The time scale as well as the E act (~0.5 eV) of S process (α HN~0 .2, β HN = 1) correlates quite well with similar relaxations recorded in the past in initial silica nanoparticles with moderate amounts of hydration water (dashed/dotted lines in Figure 10) [63][64][65]. S relaxation, therein, was considered to arise from the surface hydroxyls of silica, most probably, with attached water molecules (-Si-OH•••H 2 O) [66]. Therefore, we conclude to the similar origin of S in P10S here.…”

Interfacial dynamics of polydimethylsiloxane adsorbed on fumed metal oxide particles of a wide range of specific surface area

“…(2), f 0 is a characteristic frequency related to the frequency of maximum dielectric loss, and a HN and b HN are the shape parameters of the relaxation. One HN term of the type (2) for each of the relaxations (namely a bulk , a int , and S OH , the local relaxation of the eOH groups on the surface of the particles [23]) was fitted to the experimental data at each temperature and the fitting parameters were determined, compare Refs. [2,11] for details.…”

Filler's impact on structure and physical properties in polyester resin–oxide nanocomposites

“…Despite of the filling oxides had been annealed before preparing the samples and the samples themselves underwent the heat treatment before measuring the permittivity, the trace water molecules still remain in the nanocomposites. The water-related relaxation known as S -relaxation have recently been observed at mesoporous silica–polystyrene interface in the frequency region of 1–10 5 Hz (Fontanella et al., 2009) and at TiO 2 –polydimethylsiloxane interfaces in the kHz-frequency region (Klonos et al., 2016). This relaxation is attributed to water molecules bound at surface hydroxyl groups.…”

“…An independence of " 1 (C f,m ) on frequency evidences on the physical mechanism that makes the permittivity of the nanocomposites vary with loading remains the same both in the high-frequency region where the dielectric response is caused by vibration of light molecular fragments of the polyester chains and styrene cross-links and in the lowfrequency region (f 10 3 Hz) where the response is related to vibration of heavy molecular moieties of polymer chains and styrene molecules. The water molecules, if any, should be considered to be active contributors in " 1 over the whole frequency region studied (Fontanella et al, 2009). Figure 6.…”