Experimental Assessment of Suspension Stability

Compared to emulsions and foams discussed earlier, assessment of the stability of suspensions is relatively straightforward in most cases. Bottle or centrifuge tests are commonly used. Samples of the suspension components, and the suspension stabilizer or destabilizer to be tested, if any, are mixed in bottles or centrifuge tubes in a specified way, then let stand or centrifuged at a specified -force level. After a defined period of time, the suspensions are examined. For this, a timescale appropriate to the process under consideration has to be set. 

Historically, gravitational methods have often been used for the collection of aerosol particles or droplets, but such methods tend to be highly biased towards 

For liquid aerosols, the droplets can be collected on specially prepared slides or on a continuous tape moving behind a sampling slit (the Formvar  

Some common size range descriptions for atmospheric aerosol particles and droplets are shown in Tables 1.5 and 1.6. These ranges and descriptions are based mostly on the techniques used to determine the sizes [122,124,125]. Aitken particles and droplets (diameters less than 0.2 pm) are typically detected using an Aitken nucleus counter (also called a Nolan-Pollak counter or a Poliak counter). Here, the aerosol is introduced into a chamber containing vapour-saturated gas. Rapid volume expansion and adiabatic cooling are used to induce supersaturation in the gas, which in turn causes condensation on the original particles, which act as nuclei [122, 125]. This makes the original, small particles or droplets easy to observe and count with a microscope. (The principle just described is somewhat similar to the operation of a Wilson cloud chamber (see Section 7.1.4).) 

Nanoparticle aerosols (also referred to as atmospheric ultrafine particles, UFPs), having diameters from less than 1 to about 100 nm, are formed from gases by gas-to-particle conversion processes. The mass concentration of nanoparticle aerosols is typically small, but they may contain the highest number concentration of particles and a significant fraction of the total exposed surface area. As a result, these particles are very important in atmospheric chemistry and environmental health. 

---