Biomedical Engineering Reference
In-Depth Information
sonication, could also have an impact on particle size. Thus, sample preparation is
widely recognized as one of the most critical steps toward a successful characteriza-
tion of nanomaterial size and size distribution.
1.3 AGGREGATION AND AGGLOMERATION STATE
According to ISO/TS 27687:2008, aggregates are strongly bonded or fused
particles for which the resulting external surface area may be significantly smaller
than the sum of calculated surface areas of the individual components. The forces
holding an aggregate together are strong forces, for example, covalent bondings.
Agglomerates, however, are weakly or loosely bonded particles or aggregates
or mixtures of the two, and the forces holding the agglomerates together are
weak forces, for example, van der Waals forces. Aggregates and agglomerates
are also termed “secondary particles” and single particles are termed “primary
particles.” The state of aggregation/agglomeration refers to the number of second-
ary particles in comparison to the total number of primary particles in the sus-
pending medium, as well as the number of primary particles in the agglomerate/
aggregate.
Whether a particle remains as a single-dispersed particle or forms an aggregate/
agglomerate is mainly dependent on the probability of nanoparticle-nanoparticle
collisions and the relative mechanical or thermal energy possessed by the particles
when the interaction occurs. Dispersion of nano-objects is controlled by not only the
distance between the particles but also the balance between the particles and their
surroundings. Thus, slight perturbations in the properties of the dispersing medium,
such as temperature, pH, ionic strength, or the presence of biological molecules, can
significantly modify the whole system. Therefore, conditions applied during sample
preparation are crucial to obtain reliable results.
Methods used to determine the state of agglomeration and aggregation are mainly
the techniques used for measurement of primary particles size (see Particle size/size
200
FIGURE 1.5
Aggregates of silver nanoparticles (NanoGEM.Ag_50.EO).
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