Aggregates - agglomerates

Size Surface area Porosity Aggregates Agglomerates... 

Packing of the primary carbon particle aggregates creates voids. The resulting void volume depends on the size and shape of the aggregates, the aggregate agglomeration, and the porosity of the primary particles. Therefore, the carbon black structure can be considered as the sum of a number of accessible voids by unit weight, namely... 

According to United States Pharmacopeia (USP) <776>, a particle is defined as the smallest discrete unit, and collections of particles can be described by their degree of association such as aggregates, agglomerates, lamellar, conglomerates and spherulites. An aggregate is a mass of adhered panicles, agglomerates are fused or cemented... 

Fig-1 The final NM-induced toxic effect observed in vitro is the result of multiple processes (1) interaction with proteins (formation of the protein corona, activation/inactivation of enzymes) (2) dissolution and release of toxic ions (3) production of ROS at the NMs surface (4) aggregation/agglomeration (5) diffusion and sedimentation that influence NM transport to the cell layer and the final effective concentration (6) interaction with the cell membrane and membrane receptors (activation/inhibition) (7) cell uptake (including receptor-mediated endocytosis and other uptake mechanisms) (8) interaction with intracellular enzymes (activation/inhibition) (9) production of intracellular ROS (10) activation of transcription factors and (11) binding to nucleic acids and genotoxicity, among others. Processes (1)—(5) are closely interconnected. The resulting effect observed is the result of the composite rate of all these different reactions... 

Many nanopartide preparations lack suffident stability (above. Fig. 11.5) to allow the ordered assembly of two-dimensional or three-dimensional materials and structures, in which the particles are dosely packed, without the onset of uncontrolled aggregation (agglomeration). To overcome this problem, the partides must be rendered chemically stable, for example by ligand stabilization, also to avoid degradation processes such as partial oxidation or undesired sintering of particles [11.6]. 

Aggregation, agglomeration and flocculation are structural phenomena ranging from transient rotating doublets observed within dilute region, to a pseudo-solid-like behavior of flocculated suspensions with yield stress. Aggregation can occur... 

Magnesium Oxide In some cases, metal oxides are converted to a more soluble chemical and dissolve more rapidly. For example, magnesium oxide is relatively insoluble in water, but is converted to a more soluble carbonate form by exposure to body fluids whose buffer is bicarbonate (25). This would be expected to enhance the dissolution of magnesium oxide nanoparticles (25). However, titanium dioxide s most soluble form is the acid chloride. If the particles were porous, the porosity (access to the internal surface area) could enhance solubility stiU further for MgO. Empirical evidence suggests that the aggregated-agglomerated metal oxide nanoparticles have minimal reduction of measured surface area, or solubUity properties that parallel such surface areas. 

A powder consists of aggregates/agglomerates of small particles and mechanical work is performed in dispersing particles into a liquid. The forces that exist at the interface determine the ease with which the process can be brought about. Once dispersed, the particles are free to move in their new environment, and any tendency for flocculation is prevented by various chemical and physical mechanisms, all of which relate to the character of the solid/ liquid interface between the dispersed and the continuous phase. It is not surprising therefore that studies of this interface form an essential part of our... 

The GPC/SEC analyses of the resins at different ageing periods indicated that both polymer condensation and aggregation/agglomeration proceed during storage. This technique permits to monitor accurately the ageing of UP resins. 

Sonochemical method is valid for a large number of nanostructured and amorphous metals, alloys and refractory compounds [253-257]. Volatile organometallic compounds decompose inside the collapsing bubbles and the metal atoms are collected in the aggregates, agglomerates and pellets. 

Aggregate dimensions measured by the Feret diameter method can range from as small as 100 nm to a few micrometres (a cluster of physically bound and entangled aggregates). Agglomerates can vary widely in size, from less than a micrometre to a few millimetres in the pallet. Figure 6.11 shows the distinction between a particle and an aggregate in CB. 

Exposure route Particle size, aggregation/agglomeration ... 

Secondary phase physicochemical characterization refers to those nanoscale properties of the material as a wet state. Secondary phase physical and chemical characterization relevant to toxicity testing includes concentration and purity size and size distribution (including aggregation/agglomeration/ coagulation state) surface activity/reactivity and presence of reactive oxygen species in the solution/suspension. 

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