Surface Properties and Porosity of Silica Particles Studied by Wide-Angle Soft X-ray Scattering

Abstract

Wide-angle soft X-ray scattering on free silica particles of different porosity prepared in a beam is reported. The explored q region is mostly dominated by features due to surface roughness and bulk porosity. A comprehensive experimental and theoretical analysis of silica particles of different porosity is presented for various incident photon energies. A correlation analysis, based on the theory of Porod, is used to test the validity of exact Mie theory in different pore density limits. The ability of the discrete dipole scattering model (DDSCAT) to resolve local effects, caused by various pore distributions, is discussed. Characteristic differences between the soft X-ray scattering patterns of the particle samples of different surface properties and porosity are detected. For all mentioned cases, it was confirmed that the effective radius concept of the Guinier model can be successfully extended to Mie theory and DDSCAT in describing the additive contributions of the primary particles, including a thin inhomogeneous solvent-rich surface shell and empty bulk pores. Close agreement, within ±15%, between the calculated and observed pore sizes and porosity values is reached. The influence of pores is alternatively described either in terms of secondary Mie scattering, which is modulated by the local internal electrical field within the particles, or by an independent Mie scattering process induced by the incident field on isolated pores. It is found that for the typical pore/particle size ratios the latter approach presents the best choice.

Effect of different silica coatings on the toxicity of upconversion nanoparticles on RAW 264.7 macrophage cells

“…According to MTT assays and, more specifically, cell cycle analysis, the UCNPs did not exhibit a biocompatibility level similar to that of silica particles without a lanthanide core. It has to be considered that amorphous silica obtained from a Stöber-like growth process is an inherently porous material with a pore size of 1–4 nm [ 35 – 36 ]. Thus, it contains pores that are larger than water molecules, as well as lanthanide and other ions (e.g., Na + and F − ) that are contained in UCNPs.…”

“…However, amorphous silica is a porous material. A typical Stöber silica has a pore size of around 1–4 nm [ 35 – 36 ]; therefore, a thin silica coating shell cannot completely inhibit the dissolution of UCNPs [ 37 ]. The thickness of silica shells on UCNPs can be easily adjusted over a wide range [ 38 ].…”

Effect of Different Silica Coatings on the Toxicity of upconversion nanoparticles on RAW 264.7 macrophage cells

“…It has to be considered that amorphous silica from a Stöber-like growth process is an inherently porous material with a pore size of 1-4 nm. [36,37] Thus, it contains pores far larger than water molecules as well as lanthanide and other ions (Na + and F -) contained in UCNP. An increase in the silica shell will likely further reduce the ions release.…”

“…In contrast to more complex polymeric coating, silica surfaces can be easily functionalized by a wide range of coupling agents and biomolecules, and the interior of the silica shell can be modified by integrating e. g. dye molecules. However, amorphous silica is a porous material, typical Stöber silica has a pore size around 1-4 nm, [36,37] so that a thin silica coating cannot completely inhibit the dissolution of UCNP. [38] Though, the thickness of silica shells on UCNP can be easily adjusted over a wide range.…”

Inelastic mean-free path and mean escape depth of 10–140 eV electrons in SiO2 nanoparticles determined by Si 2p photoelectron yields

“…34 The porous surface layer of the isolated silica nanoparticles may contain solvent residues to a maximum depth of a few nanometers. 33 However, supplementary photoemission studies in the O 1s regime indicate that the solvent cannot be probed. 35 This implies along with the known absorption cross section of ethanol in the energy regime under study ( cf.…”