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.
What is caking?
The process of particles clumping together to form larger, cohesive masses.
What is emulsification?
The process by which two or more immiscible liquids are mixed to form an emulsion - the liquid-phase analogue of comminution
What are emulsifying agents?
Molecules that lower the interfacial tension between two immiscible liquids => Are adsorbed preferentially at the interfaces => stabilisation of droplets
What is a bicontinuous phase?
When both phases form a continuous network that is interconnected throughout the system w/out clear boundaries.
What is a Pickering emulsion?
An emulsion in which a solid emulsifying agent is used to stabilise it i.e. colloidal silica.
What are suspension methods?
Methods that involve forming a liquid emulsion but then initiating a chemical reaction within the droplets to form a solid.
What is the excluded volume effect?
In the hard-spheres model, steric repulsion prevents particles from overlapping.
What is configurational entropy?
The degree of disorder or randomness in the arrangement of particles.
What are ferrofluids?
Colloids composed of ferro/ferrimagnetic nanoparticles in a carrier fluid.
