Synthesis, Structure and Mechanics of Nano-Particulate Aggregates

Abstract

In the most industrial processes nano-sized particles aggregate during their synthesis and the subsequent drying step forming aggregates with sizes in the order of several micrometers. The properties of these aggregates for application or further processing are specified by particle characteristics such as morphology, size, size distribution, bonding mechanism and structure of primary and secondary particles. In this study, the effect of the process parameters during particle synthesis and the following drying step on the structure formation and the resultant product and processing characteristics of precipitated nano-structured silica aggregates were investigated. For this purpose, the educts concentrations, stabilizing additives, mechanical energy input, pH-value and precipitation temperatures were varied during the precipitation process. In addition to the structure formation during precipitation, the resultant micromechanical aggregate properties of spherical silica model aggregates with a well-defined aggregate structure were characterized via nanoindentation and related to the aggregate structure and the interparticulate interaction forces. The micromechanical properties of these model aggregates were modelled depending on their structure using a modified form of the elementary breaking stress model of Rumpf. Since the characterization of particle-particle interactions in the nanometer size range is hardly possible, this effect on the aggregate fracture and deformation behavior was investigated by simulating the nanoindentation measurement of single aggregates using the "discrete element method".

Structure and Biocompatibility of Bioabsorbable Nanocomposites of Aliphatic-Aromatic Copolyester and Cellulose Nanocrystals

“…The percolation threshold of the overlapping spheres with random packing arrangement occurs at the volume fraction of 0.32. Thus, the volume fraction of CNC within each sphere can be written as According to the Rumpf’s theory of strength of granular materials and aggregates, the strength of an aggregate can be written as where the ε is the porosity of the spherical units (= 1 – φ/0.32), A H is the Hamaker constant, z 0 is the cutoff distance, and d is the effective agglomerate diameter. The Hamaker constant is calculated by A H = 2π z 0 2 γ, where γ is the surface energy of the cellulose nanocrystals taken as 18.6 mJ/m 2 .…”

“…4 /3 P 3 (7) According to the Rumpf's theory of strength of granular materials and aggregates, 51 the strength of an aggregate can be written as…”