Since the explosion of nanotechnology in the last couple of decades, the terminology used to describe a liquid dispersion has become very confused and contentious. The terms nanodispersion, nanoparticle dispersion, nanosuspension, colloidal dispersion, and colloid suspension are often used interchangeably or limited to rigid definitions, according to personal preference and the field of technology.

Colloidal dispersion

A classical definition of a colloidal dispersion is one where the dispersed particles or droplets have at least one dimension in the range 1nm to 1μm with no restriction of the aspect ratio. Hence, other dimensions may significantly exceed 1μm. Furthermore, the random diffusion of the particles (or droplets) keeps them suspended and are not affected by gravity. This latter constraint is too limiting. After all, would a system not considered a colloidal dispersion because of sedimentation be considered a colloidal dispersion in zero gravity? Yes. Wouldn’t the sediment formed in a sedimenting system of stabilized particles still be a colloid albeit highly concentrated? Highly likely. In an aggregating dispersion, once the aggregates are large enough to be influenced by gravity, is the system no longer a colloid? Of course not.

(Colloidal) suspension

Often, the term suspension is used to differentiate sedimenting and non-sedimenting systems even when the particles are of similar size. This is an arbitrary distinction. Therefore, the terms colloidal dispersion and colloidal suspension can be considered the same as far as applying the principles of colloid science is concerned.

Nanodispersion

By one strict definition, a nanoparticle is a solid or liquid object with at least one dimension in the range 1nm to 100nm, and an aspect ratio no greater than three (thereby excluding needles, plates and rods). Thus a nanodispersion is a fluid dispersion of nanoparticles. This is simply a subset of the classical definition of a colloidal dispersion and the principles of colloid science apply.

Confusion has arisen because of three official, but contradictory, standards each issued by different governing bodies, namely the European Union, ISO, and IUPAC.

Nanosuspension

In the medical field, a nanosuspension is a colloidal dispersion where the maximum dimension of particles is approximately 500nm. This is inconsistent with the strict definition of a nanodispersion and, not surprisingly, a source of confusion. A nanosuspension is simply a specific case of a colloidal dispersion and the principles of colloid science apply.

Liquid dispersion

This term is usually synonymous with colloid dispersion.

Sadly, the past couple of decades have seen a significant reduction in the use of “colloid” in the scientific literature and conference papers even though colloid science is the foundation of the technologies that use the terms above.

But the semantics of nomenclature are not important. The most important consideration is the answer to this question:

Can the fundamental concepts of colloid science be applied to my products to improve their quality and reduce waste?

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