Impedance spectroscopy studies of surface engineered TiO2 nanoparticles using slurry technique

Abstract

Dielectric analysis of nanometre range size ceramic particles like TiO 2 is very important in the understanding of the performance and design of their polymer nanocomposites for energy storage and other applications. In recent times, impedance spectroscopy is shown to be a very powerful tool to investigate the dielectric characteristics of not only sintered and/or pelleted ceramic materials but also particulates/powders (both micron-sized and nano-sized) using the slurry technique. In the present work, impedance spectroscopy employing slurry methodology was extended to study the influence of various chemical groups on the nano-TiO 2 surface on the electrical resistivity and the dielectric permittivity of nanoparticles. In this regard, different organophosphate ligands with linear, aromatic and extended aromatic nature of organic groups were employed to remediate the surface effects of nanoTiO 2. It was observed that the type of chemical nature of surface engineered nanoparticles' surface played significant role in controlling the surface electrical resistivity of nanoparticles. Surface passivated nanoTiO 2 yielded dielectric permittivity of about 70-80, respectively.

Dielectric properties study of surface engineered nano $$\hbox {TiO}_{2}$$ TiO 2 /epoxy composites

“…TGA measurements of MDDP and PP-treated TiO 2 nanoparticles showed surface group density of about one organophosphate molecule per nm 2 area of nanoTiO 2 , which is about one-fourth that of the theoretical surface group density of organophosphonate groups per nm 2 for highly ordered self-assembled monolayers [18]. A polycrystalline nature of TiO 2 nanoparticles surface and the possible multidentate bonding of the surface modifiers on nanoparticles surface are held responsible for relatively less order or less surface group density compared to theoretical assumption [15,16]. Organic weight loss of NP-treated TiO 2 nanoparticles resulted in the surface group density of only about half an organophosphate molecule per nm 2 , which is attributed mainly to the pronounced steric effect offered by the aryl groups (naphthyl) of NP surface modifier.…”

“…MDDP-treated nanoTiO 2 was observed to result in 50% reduction in the electrical resistivity, whereas PP-and NP-treated nanoTiO 2 were observed to result in about 100 and 150% increase in the electrical resistivity as compared to untreated nanoTiO 2 . Improvement in the electrical resistivity of particle resistivity was observed to be in the order of MDDP < PP < NP [16]. This difference in the electrical resistivity is attributed to the difference in the chemical nature of ligands present on the nanoTiO 2 surface.…”

“…At above 200 • C, a significant weight loss was observed (refer to figure 2) for the organophosphate modified nanoTiO 2 . This weight loss was attributed mainly to the thermal decomposition and volatilization of organic residues from the organic groups present on the surface of TiO 2 as a result of surface modification [15,16]. Based on the organic weight loss, surface group density of the surface modifier present on the nanoparticles surface was then calculated using the particle surface area and mass of TiO 2 and the organic molecular weight of the surface modifier using similar method that was reported earlier for surface modified metal oxide particles [17].…”

“…XPS measurements indicate the introduction of phosphorus groups on the surfacemodified nanoTiO 2 samples. The surface-modified powders mainly showed bridged phosphate oxygen corresponding to the phosphonyloxygen (P=O), phosphoryl oxygen (P-O) and R-O-P bonds, where R is alkyl or aryl (phenyl, naphthyl) carbon of the organophosphate ligands at the regions ranging from 532 to 534 eV [16].…”

“…The powders, modified and unmodified, were analysed by a thermogravimetric analyser (TGA), X-ray photoelectron spectroscopy (XPS) and impedance spectroscopy through powder slurry technique in Maxwell liquid as described elsewhere [16]. Nanodielectric films were made by first dispersing surface-treated TiO 2 nanoparticles into epoxy resin (DER 332) via a planetary ball mill (Retsch, PM 100 Model, Germany) for ∼15 h. BYK-w-9010 was added to unmodified TiO 2 nanoparticle dispersion into epoxy as an experimental control to compare a dispersed particle composite against a self-dispersing (surface modified) particle, wherein the particle uses the bound surface groups to aid its dispersion.…”