Editing DLVO theory (section)

== Overview ==
DLVO theory is a theory of colloidal dispersion stability in which [[zeta potential]] is used to explain that as two particles approach one another their ionic atmospheres begin to overlap and a repulsion force is developed.<ref>{{Cite book | title = Encyclopedic Dictionary of Polymers|url = https://archive.org/details/encyclopedicdict00gooc_001|url-access = limited | last = Jan W. Gooch|year = 2007|isbn = 978-1-4419-6246-1|pages = [https://archive.org/details/encyclopedicdict00gooc_001/page/n348 318]| publisher=Springer }}</ref>  In this theory, two forces are considered to impact on colloidal stability: [[Van der Waals force]]s and [[Double layer (surface science)|electrical double layer]] forces.

The total [[potential energy]] is described as the sum of the attraction potential and the repulsion potential. When two particles approach each other, electrostatic repulsion increases and the interference between their electrical [[Double layer (surface science)|double layers]] increases. However, the [[Van der Waals force|Van der Waals]] attraction also increases as they get closer. At each distance, the net potential energy of the smaller value is subtracted from the larger value.<ref name=":0">{{Cite web|url=http://nptel.ac.in/courses/103103033/module3/lecture5.pdf |archive-url=https://web.archive.org/web/20151208045549/http://nptel.ac.in/courses/103103033/module3/lecture5.pdf |url-status=live |archive-date=December 8, 2015 |title=NPTEL Chemical Engineering Interfacial Engineering }}</ref>

At very close distances, the combination of these forces results in a deep attractive well, which is referred to as the primary minimum. At larger distances, the energy profile goes through a maximum, or [[energy barrier]], and subsequently passes through a shallow minimum, which is referred to as the secondary minimum.<ref name=":1">{{Cite web|url = http://www.zeta-meter.com/5min.pdf|title = The DLVO theory explains the tendency of colloids to agglomerate or remain discrete.}}</ref>

At the maximum of the energy barrier, repulsion is greater than attraction. Particles rebound after interparticle contact, and remain dispersed throughout the medium. The maximum energy needs to be greater than the thermal energy. Otherwise, particles will aggregate due to the attraction potential.<ref name=":1" /> The height of the barrier indicates how stable the system is. Since particles have to overcome this barrier in order to aggregate, two particles on a collision course must have sufficient [[kinetic energy]] due to their velocity and mass.<ref name=":0" /> If the barrier is cleared, then the net interaction is all attractive, and as a result the particles aggregate. This inner region is often referred to as an energy trap since the [[colloid]]s can be considered to be trapped together by [[Van der Waals force]]s.<ref name=":0" />

For a [[colloidal system]], the thermodynamic equilibrium state may be reached when the particles are in deep primary minimum. At primary minimum, attractive forces overpower the repulsive forces at low molecular distances. Particles coagulate and this process is not reversible.<ref>{{Cite web|title = Laboratory of Colloid and Surface Chemistry (LCSC)|url = http://www.colloid.ch/index.php?name=dlvo|website = www.colloid.ch|access-date = 2015-12-04}}</ref> However, when the maximum energy barrier is too high to overcome, the colloid particles may stay in the secondary minimum, where particles are held together but more weakly than in the primary minimum.<ref>{{Cite journal|title = Extended DLVO theory: Electrostatic and non-electrostatic forces in oxide suspensions|author1=Boström, Deniz |author2=Franks, Ninham |journal = Advances in Colloid and Interface Science|date=2006 |issue = 26|volume = 123|pages=5–15 |doi=10.1016/j.cis.2006.05.001 |pmid=16806030 |hdl=1885/25336 |hdl-access=free }}</ref> Particles form weak attractions but are easily redispersed. Thus, the adhesion at secondary minimum can be reversible.<ref>{{Cite web|title = DLVO Theory - folio|url = https://folio.brighton.ac.uk/user/lc355/dlvo-theory|website = folio.brighton.ac.uk|access-date = 2015-12-04|archive-date = 2020-08-13|archive-url = https://web.archive.org/web/20200813084430/https://folio.brighton.ac.uk/user/lc355/dlvo-theory|url-status = dead}}</ref>