Disperse Systems: Suspensions and Emulsions

Vocabulary flashcards covering core terms related to colloids, emulsions, suspensions, sedimentation, rheology, and stabilization strategies as presented in the lecture notes.

Colloid

A disperse system in which one phase exists as tiny particles or droplets within another continuous phase.

Emulsion

A liquid medicine where one insoluble liquid is dispersed as microscopic droplets in another immiscible liquid, usually oil and water.

Suspension

A liquid medicine in which insoluble solid particles (often drug) are dispersed in a liquid vehicle.

Disperse Phase

The suspended particles or droplets within an emulsion or suspension.

Vehicle

The continuous liquid phase in which particles are suspended in a suspension.

Emulsifier

A molecule that forms a stabilizing film at the oil–water interface, preventing droplet coalescence in emulsions.

Homogenization

Energy-intensive process used to reduce droplet size and produce stable emulsions.

Oil-in-Water (O/W) Emulsion

System where oil droplets are dispersed in a continuous water phase.

Water-in-Oil (W/O) Emulsion

System where water droplets are dispersed in a continuous oil phase.

Multiple Emulsion

Complex emulsion such as W/O/W or O/W/O in which droplets contain smaller dispersed droplets of the opposite phase.

Physical Instability

Observable separation phenomena in suspensions, including sedimentation and caking.

Sedimentation

Settling of dispersed particles under gravity, described by Stokes’ law.

Stokes’ Law

Equation giving sedimentation velocity: v = (2a²g(σ−ρ))/9η, influenced by particle size, density difference, and vehicle viscosity.

Caking

Formation of a dense, hard sediment that is difficult to redisperse after particles settle and pack tightly.

Thickening Agent

Substance added to increase vehicle viscosity and slow sedimentation of particles.

Xanthan Gum

Natural polysaccharide thickener obtained from bacteria that entangles to raise suspension viscosity.

Cellulose Ethers

Modified cellulose polymers (e.g., HPMC) used to thicken suspension vehicles by chain entanglement.

Carbomer

Synthetic polymer that thickens by charge dispersion; particles repel, increasing resistance to flow.

Bentonite

Clay mineral of tiny plate-like particles that increase viscosity through charge dispersion.

Flocculation

Intentional formation of loose, weakly bonded particle aggregates (flocs) to prevent hard caking and allow easy redispersion.

Flocs

Porous, weak particle clusters that break apart on shaking and reform on standing.

Deflocculated Suspension

System where particles remain separate, leading to dense caking over time.

Shear Thinning (Pseudoplasticity)

Rheological behavior where apparent viscosity decreases as shear rate increases, aiding flow when shaking a suspension.

Non-Newtonian Fluid

Liquid whose viscosity changes with applied shear rate, typical of polymer-thickened suspensions.

Ostwald Ripening

Process where small particles dissolve and redeposit on larger ones, leading to growth of large particles over time.

Charge Dispersal

Mechanism by which charged colloidal particles repel each other, increasing viscosity and stability.

Surfactant Adsorption

Attachment of surfactant molecules to particle surfaces, imparting charge or steric hindrance for stabilization or floc formation.

Density Matching

Formulation strategy of adjusting vehicle density closer to particle density to reduce sedimentation rate.

Rheology

Science of flow and deformation of suspensions; crucial for understanding viscosity and shear behavior.

Sedimentation Velocity

Rate at which particles settle; slowed by reducing size, increasing viscosity, or minimizing density differences.

Particle Size Reduction

Decreasing particle diameter to slow sedimentation; nanometre-scale needed for multi-year suspension stability.

Viscosity

Resistance of a liquid to flow; increasing it retards particle settling.

Plastic Flow

Rheological behavior where material behaves as a solid until a yield stress is exceeded, then flows.

Newtonian Flow

Flow with constant viscosity regardless of shear rate; contrast with non-Newtonian polymer solutions.