Physical boundaries within aggregates – differences between amorphous, para‐crystalline, and crystalline Structures

Abstract

SEM images of isolated aggregates of silica and titania show structural similarities at the several hundred nanometer scale (red). However, high resolution TEM reveals distinct differences of the interior structure down to the nanoscale. Pyrogenic titania entities are formed by intergrown crystallites (blue). Grain or solid phase boundaries are detected. Synthetic silicas of different production technology are completely amorphous (green) and, thus, the aggregate is the constituent particle. This conclusion is confirmed by 3D‐TEM investigations. (Picture: P. Albers et al., pp. 846–865, in this issue)

Structure and Bottom-up Formation Mechanism of Multisheet Silica-Based Nanoparticles Formed in an Epoxy Matrix through an In Situ Process

“…Figure 2 b and Figure S3 show that, at higher magnification, the nanoparticles appear to be consisting of equally spaced sheets, similar to the nanocrystalline structures observed through HRTEM by other researchers. 39 The sheet thickness determined by a method described in the literature 39 shown in Figure S3 is 0.34 nm, which is quite close to the lower value given by SAXS investigation (i.e., 0.485 nm, Figure 1 b). Some particles have a different aspect ( Figure 2 c).…”

“…A simple hypothesis about the nature of the “smaller structural units“ on the basis of the growth process and a more detailed mechanism of the formation of nanoparticles of Figure 2 a is proposed in the following, where the terms nanomaterial, aggregate, and agglomerate will be used according to the “EU recommendation 696/201″ (ISO 26824, ISO TS 27687): 39 , 45 nanomaterial is “a minute piece of matter with defined physical boundaries”; an aggregate is “a particle comprising of strongly bound and fused particles”; an agglomerate is “a collection of weakly bound particles or aggregates where the resulting external surface area is similar to the sum of the surface areas of the individual components”. At first, it is worth reminding that, according to the above described procedure, during the first synthesis step, APTES is left to react with the DGEBA resin at 80 °C for 2 h in a molar ratio of DGEBA/APTES of 0.294 mol of DGEBA to 0.0226 mol of APTES (see the Experimental Section), yielding a molar ratio of epoxy/NH 2 of 26.…”

Effects of Sample Preparation on Particle Size Distributions of Different Types of Silica in Suspensions

“…Figure 1 a–c show SEM (JEOL Ltd, Tokyo, Japan) images of typical aggregates of FS, PS and SG [ 50 ]. In contrast, CS ( Figure 1 d) contains isolated spherical nanoparticles, which have gathered into an agglomerate-like structure upon drying on the TEM grid.…”

“…SAS products are nanostructured NMs [ 46 ] as they consist of aggregates and agglomerates of nanosized constituent particles (FS, PS and SG, cf. [ 50 ]) or well-dispersed nano-objects (CS). Accordingly, the preparation of suspensions of FS, PS and SG requires defined dispersion procedures for their use, e.g., in toxicity studies, and characterization, whereas this is not really necessary for colloidal silica [ 19 , 20 ].…”

Overview of Multiscale Molecular Modeling and Simulation of Silica Aerogels

“…The model was further benchmarked by simulating water permeation through a cylindrical pore. 56 This FF has been employed, for example, in MD simulations of the interactions of silica surfaces with lipid bilayers, 133,134 graphene, 135,136 salt solutions, 137 and insulin. 138 Besides unmodified silica aerogel surfaces, some computational studies regarding other chemical functionalizations have been reported.…”