Structural and dielectrical properties of PMMA/TiO₂ composites in terms of free volume defects probed by positron annihilation lifetime spectroscopy

Abstract

A suspension of ultrasonically agitated Titanium dioxide micrometer-sized powder has been introduced into a poly(methyl methacrylate) (PMMA) matrix by solvent (CHCl3) mixing under slow mechanical stirring, and the resulting suspension was used to cast free-standing PMMA/TiO2 composite films. Filler contents from 0 wt% to 7.5 wt% were selected, since TiO2 particles could not be previously suspended in chloroform at higher concentrations by ultrasonic agitation. Optical and dielectric properties of composites were determined by ultraviolet (UV)-visible and dielectric spectrometry. In the UV region, 450% improvement of UV absorption was achieved in the TiO2/PMMA composite compared with neat PMMA. The structural properties and hole-free volume of the composites were determined by X-ray diffractometry and positron annihilation lifetime spectroscopy, respectively. The particle size and homogeneous dispersion of the particles in the polymer matrix were related to the hole-free volume of the PMMA.

High-Entropy-Alloy Nanocrystal Based Macro- and Mesoporous Materials

“…At 250 °C, the signals corresponding to the fcc phase are detected: this is the onset of metal crystallization. However, at this temperature, another signal can be observed at 15.5°, which can be attributed either to residual chloride precursors (RhCl 3 or RuCl 3 ) , or to the PMMA latex template , (Figure S7A). The SEM characterization confirms that the PMMA latex beads are still present in the samples annealed at 250 °C (Figure S8 A–C).…”