Lecture 7 - Emulsions and Suspensions Flashcards
What does flocculation do?
Prevents rigid cohesion by forming loose aggregates (flocculates)
Held together with weak intern-particulate forces
Reduces caking
Define oil-in-water emulsions
Oil disperse phase
water continuous phase
Define water-in-oil emulsions
water disperse phase
oil continuous phase
Define dispersed phase
phase that is sub-divided
Define continuous phase
Phase in which disperse phase is distributed
Define liquid or solid phase
dispersed in an external
Are emulsions and suspensions one or two phase systems
2 phase systems
thermodynamically unstable
they only attain equilibrium when internal droplets coalesce to form one ‘macro-phase’ - SA minimised
How do suspensions achieve a low SA?
Flocculating and aggregating - no coalescence
How can colloids be stabilised?
by repulsive forces due to the adsorption of macromolecules or surfactants to their surfaces
adsorbed molecules are hydrated and these chains get in the way of each other - prevents the particles from aggregating - form lose aggregates
If suspending agents are added does viscosity increase or decrease?
Increase
If we increase the sedimentation rate what happens to the viscosity?
decreases
At shorter-inter particle distances what forces dominate?
Attractive forces
As the inter-particle distance increases what force predominates?
Repulsive forces
As the inter-particle distance increases further and further what force predominates?
Repulsive force decrease and the particles are weak attracted
What is a disadvantage of a multiple emulsion?
High viscosity due to oil in continuous phase
Physical degradation of w/o/w possible via
coalescence of internal water droplets
coalescence of oil droplets surrounding them
rupture of oil film separating aqueous phases
osmotic flux of water to/ from internal droplets
How is caking avoided?
Flocculating agent
What benefits does a surfactant monolayer provide?
Decreases potential for collisions
Define HLB
The balance between hydrophobic and hydrophilic components of a surfactant
What do mixtures of surfactants improve stability?
yes more so than the use of single surfactants
What are micro emulsions and how are they formed?
low-viscosity colloidal systems
form spontaneously when correctly formulated
