Editing Colloid (section)

===Monitoring stability===
[[File:MLS scan.gif|thumb|Measurement principle of multiple light scattering coupled with vertical scanning]]

The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple [[light scattering]] coupled with vertical scanning.<ref>{{cite journal|doi=10.1016/S0378-5173(03)00364-8|title=Systematic characterisation of oil-in-water emulsions for formulation design|year=2003|last1=Roland|first1=I|journal=International Journal of Pharmaceutics|volume=263|pages=85–94|pmid=12954183|last2=Piel|first2=G|last3=Delattre|first3=L|last4=Evrard|first4=B|issue=1–2}}</ref><ref>{{cite journal|doi=10.1023/A:1025017502379|year=2003|last1=Lemarchand|first1=Caroline|last2=Couvreur|first2=Patrick|last3=Besnard|first3=Madeleine|last4=Costantini|first4=Dominique|last5=Gref|first5=Ruxandra|s2cid=24157992|journal=Pharmaceutical Research|volume=20|pages=1284–92|pmid=12948027|title=Novel polyester-polysaccharide nanoparticles|issue=8}}</ref><ref>{{cite journal|doi=10.1016/S0927-7757(98)00680-3|title=Characterisation of instability of concentrated dispersions by a new optical analyser: the TURBISCAN MA 1000|year=1999|last1=Mengual|first1=O|journal=Colloids and Surfaces A: Physicochemical and Engineering Aspects|volume=152|issue=1–2|pages=111–123 }}</ref><ref>{{cite book|author=Bru, P. |title= Particle sizing and characterisation|editor1=T. Provder |editor2=J. Texter |year=2004|display-authors=etal}}</ref> This method, known as [[turbidimetry]], is based on measuring the fraction of light that, after being sent through the sample, it backscattered by the colloidal particles. The backscattering intensity is directly proportional to the average particle size and volume fraction of the dispersed phase. Therefore, local changes in concentration caused by sedimentation or creaming, and clumping together of particles caused by aggregation, are detected and monitored.<ref>{{Cite journal|last1=Matusiak|first1=Jakub|last2=Grządka|first2=Elżbieta|date=2017-12-08|title=Stability of colloidal systems - a review of the stability measurements methods|url=https://journals.umcs.pl/aa/article/view/4877|journal=Annales Universitatis Mariae Curie-Sklodowska, sectio AA – Chemia|volume=72|issue=1|pages=33|doi=10.17951/aa.2017.72.1.33|doi-access=free}}</ref> These phenomena are associated with unstable colloids.

[[Dynamic light scattering]] can be used to detect the size of a colloidal particle by measuring how fast they diffuse. This method involves directing laser light towards a colloid. The scattered light will form an interference pattern, and the fluctuation in light intensity in this pattern is caused by the Brownian motion of the particles. If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion. This technique can confirm that aggregation has occurred if the apparent particle size is determined to be beyond the typical size range for colloidal particles.<ref name="Everett-1988" />