Colloids Flashcards
To remember the basic definitions for understanding colloidal systems.
What is a colloid?
A substance consisting of a material dispersed or suspended in a continuous phase.
What are colloidal suspensions/sols?
Suspensions of solid particles in a liquid, e.g., clay, paint
What is a lyophobic colloid?
A colloid in which dispersed particles don’t “like” suspended medium e.g. emulsion minimises SA-vol. ratio
What is a lyophilic colloid?
A colloid in which dispersed particles “like” suspended medium e.g. particles absorb water in gelatin sol
What is a monodisperse colloid?
A colloid in which the dispersed particles are all the same size.
What is a polydisperse colloid?
A colloid in which there is a distribution of particle sizes.
What is flocculation?
The process by which a loose agglomeration of particles form an open aggregate; a floc.
What is coagulation?
The process by which a strong agglomeration of particles form a dense aggregate; a coagulum.
What is sedimentation?
When colloidal particles form aggregates denser than the solvent.
What is creaming?
When colloidal particles form aggregates less dense than the solvent.
What is thermodynamic stability?
When the system has adopted the state with the absolute minimum Gibbs free energy.
What are dispersion methods?
Methods where particles of colloidal dimensions are formed by breaking down bulk matter.
What are condensation methods?
Methods where particles of colloidal dimensions are formed by the aggregation of molecular units
What is comminution?
The fragmentation of bulk solid material to form small particles, generally achieved by grinding bulk material to form a powder.
What is a side-effect of comminution and why does it happen?
Caking; comminution causes an increase in the surface free energy arising from the interfacial tension between the solid and, say, the air, leading to the tendency of particles in powders to undergo adhesion to one another.
