Assemblies of Titanium Dioxide-Polystyrene Hybrid Nanoparticles for Dielectric Applications

Abstract

Macroscopic assemblies of hybrid nanoparticles composed of titanium dioxide core surrounded by covalently grafted polystyrene corona have been prepared by a combination of phosphonate coupling and "click" chemistry. The attached polymer chains existed in the brush regime, with grafting density inversely proportional to the degree of polymerization. Solution casting afforded preparation of robust films of the composite material where all the polymer chains were covalently bound to the uniformly distributed inorganic particles. Inorganic content from 60 to 80 wt % (27 to 50 vol %) was obtained by varying the molecular weight of polystyrene as well as by using the mixture of high and low molecular weight polymer for grafting. The TiO 2 grafted with 10 5 g/mol polystyrene had a volume fraction of nanoparticles of 27% and exhibited glass transition at 110 °C and ∼100% extensibility above T g . Thin films of this material had a dielectric constant of 6.4 and a dielectric loss of 0.04 at 1 kHz.

Dielectric performance of high permitivity nanocomposites: impact of polystyrene grafting on BaTiO3 and TiO2

“…All nanocomposites were prepared with polystyrene, a non-polar polymer that exhibits relatively low breakdown strength (measured at 175 V/μm in this study) and relative permittivity (2.4 at 1 kHz), but maintains a low dielectric loss (ε′ = 10 titanate (BaTiO 3 ) nanoparticles, approximately 7.0 ± 1.5 nm in diameter, 23,24 were grafted with polystyrene (102 kg/mol M w ) following a previously reported procedure involving phosphonate coupling and click chemistry 18 ( Fig. 1a-c, see Supporting Information for full details).…”

“…Tchoul et al reported that hairy PS@TiO 2 matrix free assemblies at 27% v/v inorganic loading have a relative dielectric constant of 6.4, compared to 2.4 for neat PS, while maintaining low dielectric loss similar to PS (tan δ = 0.04 at 1 kHz). 18 X-ray scattering demonstrated excellent particle dispersion with no visible clustering; thus, the deleterious effects of percolation that create conduction pathways and increase dielectric loss were avoided. 19 Similarly, Paniagua et al demonstrated that films of PMMA@BaTiO 3 HNPs achieved a maximum extractable energy density of 2 J/cc at intermediate loadings (22% v/v) -a twofold increase over a physically blended nanocomposite at comparable BaTiO 3 loading.…”

Hairy nanoparticle assemblies as one-component functional polymer nanocomposites: opportunities and challenges

“…For lower graft densities, particle-polymer interactions responsible for packing frustrations of freely jointed chains at a curved surface could lead to either an increase or decrease. For example, Tchoul et al [74] showed that the T g of 100 kDa PS tethered (0.03 chains/nm 2 ) to TiO 2 (r = 18 nm, l = 40 nm) decreased by 30°C relative to the bulk, even though TiO 2 is close to a neutral surface to PS. Thermal cleavage of the tethering point restored the T g to that of the bulk, implying the suppression was due to excess free volume arising from frustrated chain packing.…”

“…Initial studies on TiO 2 /polystyrene HNP systems with high dielectric constants show that the concept is workable, but purity of the final material is critical to maintaining high breakdown fields. [74] For batteries and supercapacitors, ionically conductive electrolytes are desired. HNP-based electrolytes for lithium-ion batteries have higher mechanical strength than pure polymer electrolytes and exhibit superionic conductivities.…”

“…These hybrid photonic crystals would have a significant advantage over conventional micron-sized particle superlattice crystals in that they would retain the fracture resistance and processability of the polymer that makes up the brush. Following from the recent studies of the dielectric properties of TiO 2 -PS HNPs, [74] optically transparent films that combine the processability of neat HNPs with high refractive index (n > 3) and low scattering loss (no morphological features less than 1/10th of the wavelength of incident light) are possible. New optical coatings and metamaterials with complex refractive index profiles would then be feasible for use as gradient refractive index (GRIN) lenses and fiber and slab lasing media.…”