Emulsions/suspensions Flashcards
Emulsions and suspensions
Liquid or solid phase in external liquid phase
Disperse phase=the phase that is split up
Continuous phase=the phase in which the disperse phase is split into
Why do emulsions/suspensions require stabilisers?
They are inherently unstable systems therefore to give an acceptable shelf life stabilisers are necessary
Emulsions attain equilibrium when…
When internal droplet join up to form one micro phase with the smallest possible surface area
3 ways in which particles encounter one another in suspension
Brownian movement
Creaming/sedimentation
Convection
Sedimentation rate (Vsed) is affected by…
Particle diameter= increase cause increase in Vsed
Particle density= increase causes increase in Vsed
Viscousity= increase cause decreases in Vsed
Vtotal=Va+Vr
Explain this equation
Calculates total energy of interaction
Va=attractive potential energy
Vr=electrostatic repulsive energy
Where do different forces dominate?
Primary minimum-At v.short distances attraction dominates causing particles to agglomerate
Primary Maximum-At medium distance repulsive forces dominate and particles remain in suspension
Secondary minimum-At larger distances repulsive force lessens and particles have weak attraction
Effect of electrolytes on stability
Low conc gives a larger primary maximum but no 2ndry minimum
Moderate conc gives a 2ndry min allowing flocculation to occur as well as a primary max. preventing coagulation
High conc. gives no primary max or min
Flocculation
Forms loose aggregates preventing caking
Held together with weak interparticulate forces forming a lattice type structure.
How does caking occur?
Where particles are deflocculated they aren’t associated and so settle on top of one another
The pressure from the particles on top pushes to the bottom particle into the primary minimum
This irreversibly binds the particles
Microemulsions
Homogenous, transparent and low viscosity
Low interfacial tension but v. high interfacial area
Lots of surfactant necessary (surfactant+2nd cosurfactant usually)
Semi-solid emulsions
Stable o/w cream with: dispersed oil phase crystalline gel phase crystalline hydrate phase bulk phase containing dilute surfactant solution
