Silicone elastomers filled with rare earth oxides

Mihail Iacob,Mihai Asandulesa,Anton Airinei,Maria Cazacu,Leonor Hernandez,Mihaela Dascalu,Nita Tudorachi

doi:10.1088/2053-1591/ab7a5e

Abstract

Silicones which possess, amongst others, remarkable mechanical properties, thermal stability over a wide range of temperatures and processability, and rare earth oxides (REO), known for their unique optic, magnetic and catalytic properties can be coupled into multifunctional composite materials (S-REOs). In addition, the intrinsic hydrophobicity of REO and polysiloxanes makes them easily compatible without the need for surface treatments of the former. Thus, europium oxide (Eu2O3), gadolinium oxide (Gd2O3) and dysprosium oxide (Dy2O3) in amounts of 20 pph are incorporated as fillers into silicone matrices, followed by processing mixture as thin films and crosslinking at room temperature. The analysis of the obtained films reveals the changes induced by these fillers in the thermal, mechanical, dielectric and optical properties, as well as the hydrophobicity of the silicones. The luminescence properties of S-REO composites were investigated by fluorescence spectra and lifetime - resolved measurements with a multiemission peaks from blue to greenish register. The thermogravimetrical analysis indicates an increasing of thermal stability of the composites that contain REO, compared to pure silicone. As expected, the dielectric permittivity significantly increased due to nature of the fillers, while the dielectric loss values are relatively low for all samples, indicating a minimal conversion of electrical energy in the form of heat within bulk composites. The presence of rare earth oxides into the silicone matrix facilitates the motions of long-range charge carriers through the network resulting in higher values of conductivity of the composite films. The stress-strain measurements revealed the reinforcing effect of the rare earth metal oxides on a silicone matrix, leading to a significant increase of Young modulus. The known hydrophobicity of silicones is further enhanced by the presence of REO.

Highlights

The scientific and technological interest of rare earths is based on their special physical or chemical properties that are caused by their particular electronic structure (4f orbitals with parallel-spin unpaired electrons, being paramagnetic) [1, 2]
A series of silicone-rare earth oxide (S-rare earth oxides (REO)) composites were prepared by physical mixing in bulk and stabilized by room temperature vulcanization
In order to avoid the migration of siloxane polymer chains to the surface of composite material, the samples were frozen in liquid nitrogen and immediately fractured before analysing

Summary

Introduction

The scientific and technological interest of rare earths is based on their special physical (optical, electrical, magnetic) or chemical (e.g., catalytic, anti-corrosive) properties that are caused by their particular electronic structure (4f orbitals with parallel-spin unpaired electrons, being paramagnetic) [1, 2]. The optical materials doped with rare earths are of interest for light sources in optoelectronics, for optical amplification and other elements of photonics [3]. Rare earths can extend the life of the free radicals, by rapidly catching electrons on orbital 4f [3]. X-ray shielding studies at different tube voltages, with polymer composites of different thicknesses, especially based on natural rubber incorporating varying amounts of modified rare earth oxides (REO), indicate the latter as promising materials for medical imaging [4]. REO are capable of absorbing strongly in the near-UV spectrum (300 nm), being useful in coating technologies as UV absorbers [6]

Methods

Results

Conclusion