Where does coagulation collide?

In colloid chemistry, coagulation is the loss of stability of a dispersion: particles that normally stay apart because their electrical double layers repel one another begin to stick on contact once that repulsive barrier is lowered, for instance by adding electrolyte, so they aggregate and eventually settle. Derjaguin and Landau (1941) and Verwey and Overbeek's Theory of the stability of lyophobic colloids framed this as a balance between van der Waals attraction and double-layer repulsion, the account now called DLVO theory. The referent is the rate and extent of particle aggregation in a sol, with nothing in common with a blood clot or a cheese curd beyond the shared idea of a dispersed system turning solid.[1][2]

Unit

The rate and extent of particle aggregation in a dispersion

Recovery means

Sometimes reversible by peptization, which re-disperses loosely aggregated particles; strongly coalesced aggregates do not redisperse

Measured by

Tracked by the stability ratio, the critical coagulation concentration of added electrolyte, and the zeta potential of the particles

In physiology, coagulation is the clotting of blood: a chain of inactive plasma proteins activate one another in sequence until thrombin converts soluble fibrinogen into insoluble fibrin, which with platelets forms a clot that seals an injured vessel. Davie and Ratnoff (1964) and Macfarlane (1964) independently described this as a cascade or waterfall in which each activated factor switches on the next, amplifying a small trigger into a decisive response. The referent is the regulated biochemical conversion of flowing blood into a gel, measured in clotting times, and it is a distinct construct from colloidal aggregation or dairy curd despite the common word.[3][4]

Unit

The time and strength of clot formation from flowing blood

Recovery means

Fibrinolysis dissolves the fibrin clot once the vessel is repaired, returning blood to a flowing state

Measured by

Assessed by prothrombin time, activated partial thromboplastin time, and assays of individual clotting factors

In dairy science, coagulation is the gelling of milk: the casein micelles that keep milk fluid are destabilised, either enzymatically when rennet cleaves the stabilising kappa-casein layer or by acid as the pH falls toward the casein isoelectric point, and the freed micelles aggregate into a continuous curd. Lucey's (2002) review of milk protein gels sets out how this network forms and how its firmness develops, the foundation of cheese and yogurt making. The referent is the onset and firming of a milk-protein gel, measured as curd firmness and set time, and it is its own construct distinct from a clotting cascade or a flocculating sol.[5]

Unit

The set time and firmness of the milk-protein curd

Recovery means

Not applicable

Measured by

Gauged by rennet coagulation time, dynamic rheology of the forming gel, and curd firmness at cutting