Nanoparticles, a particle with a diameter that is much smaller than one millionth of a meter, are widely used in everyday products such as cosmetics, and sun and personal care items.
“It is important to be able to determine their size, shape and surface area, in order to be able to improve their properties within various areas of application," said Ann-Cathrin Johnsson of the department of chemistry at the University of Gothenburg, Sweden.
Nanoparticles of a substance can be counted and the size distribution can be determined by dispersing the nanoparticles into a gas. But some nanoparticles tend to aggregate when the surrounding conditions change. New research from scientists at the University of Gothenburg, showed it’s possible to sort and count the particles, even when they have formed aggregates.
Such small particles, such as nanoparticles, are not influenced by gravity, and thus, they do not fall to the bottom of a liquid or gas, and instead spread out throughout the container. Their area of contact with the surrounding medium is very large due to their small size; as a result, many interesting properties arise. Nanoparticles of a substance behave, quite simply, differently than large particles of the same substance.
Certain types of nanoparticles can start to aggregate in special conditions, and sometimes a so-called gel may form. The process is similar to boiling an egg: the proteins in the egg white aggregate and form the solid-like structure that we recognize as boiled egg.
Johnsson's thesis work has studied one of these aggregating systems, colloidal silica. The gel that forms when salt is added to colloidal silica can be used, for example, to seal rock and to stabilize soil.
"I started with a method that had been used only for analyzing nanoparticles that had not aggregated, and developed it further. Nanoparticles that have aggregated can be analyzed individually if a colloidal silica gel, which contains these aggregated nanoparticles, is first diluted and then dispersed into the gas phase. If the samples are analyzed immediately after being diluted, this method gives an accurate picture of the gelated system."