Why is Particle Size Important?

Particle size influences many properties of particulate materials and is
a valuable indicator of quality and performance. This is true for powders,
suspensions, emulsions, and aerosols. The size and shape of powders influences
flow and compaction properties. Larger, more spherical particles will typically flow
more easily than smaller or high aspect ratio particles. Smaller particles dissolve
more quickly and lead to higher suspension viscosities than larger ones. Smaller
droplet sizes and higher surface charge (zeta potential) will typically improve
suspension and emulsion stability. Powder or droplets in the range of 2-5μm
aerosolize better and will penetrate into lungs deeper than larger sizes. For these
and many other reasons it is important to measure and control the particle size
distribution of many products.
Measurements in the laboratory are often made to support unit operations taking
place in a process environment. The most obvious example is milling (or size
reduction by another technology) where the goal of the operation is to reduce
particle size to a desired specification. Many other size reduction operations and
technologies also require lab measurements to track changes in particle size
including crushing, homogenization, emulsification, microfluidization, and others.
Separation steps such as screening, filtering, cyclones, etc. may be monitored by
measuring particle size before and after the process. Particle size growth may be
monitored during operations such as granulation or crystallization. Determining the
particle size of powders requiring mixing is common since materials with similar
and narrower distributions are less prone to segregation.
There are also industry/application specific reasons why controlling and
measuring particle size is important. In the paint and pigment industries particle
size influences appearance properties including gloss and tinctorial strength.
Particle size of the cocoa powder used in chocolate affects color and flavor.
The size and shape of the glass beads used in highway paint impacts reflectivity.
Cement particle size influences hydration rate & strength. The size and shape
distribution of the metal particles impacts powder behavior during die filling,
compaction, and sintering, and therefore influences the physical properties of
the parts created. In the pharmaceutical industry the size of active ingredients
influences critical characteristics including content uniformity, dissolution and
absorption rates. Other industries where particle size plays an important role
include nanotechnology, proteins, cosmetics, polymers, soils, abrasives,
fertilizers, and many more.

This is taken from the first page of the new HORIBA Particle Size Analysis Guidebook. The complete guide can be found here.