1. . 
A condition in which clays, polymers or other small charged particles become attached and form a fragile structure, a floc. In dispersed clay slurries, flocculation occurs after mechanical agitation ceases and the dispersed clay platelets spontaneously form flocs because of attractions between negative face charges and positive edge charges.
2. . 
The aggregation of small particles into larger particles. In the context of heavy oil, asphaltenes are known to flocculate at the molecular level (before precipitation) and in the precipitated state. The extent of asphaltene flocculation changes with fluid composition, temperature and pressure. For precipitated asphaltenes, flocculation is also affected by the shear environment.
See: heavy oil