Emulsion 2 Flashcards
how are emulsifications formed?
homogenising the two phases
-think about farm style milk
how does shear force affect particle size
reduces it
what is required to make an emulision
energy
emulsifier
what is laplace pressure
pressure difference between the inside and outside of a curved surface
-force holding the bubble out
how are droplets broken down into smaller droplets
applying energy greater than laplace energy
how is the energy provided
vigorous agitation
how are food oil-in-water emulsions usually produced?
colloid mills or high-pressure homogenizers
how many homogenisation categories are there and name them
2
primary
secondary
what is primary homogenisation
conversion of bulk liquid into emulsion
-quick whisk creates course emulsion
what is secondary homogenisation
reducing droplet size in existing emulsion
-add course emulsion to blender
-smaller more stable emulsion is produced
what is often used in the food industry to directly homogenise oil and aqueous phases
high speed mixers
what can be used to produce emulsions with fine droplets
high-pressure valve homogenisers
how does a high pressure valve homogeniser work
a coarse emulsion is pushed through a valve which creates pressure and shear turning it into a fine emulsion
describe how a microfluidiser works
under high pressure (6 atmos) two streams (1 aqueous, 1 oil) are brought together at the ‘impact zone’ which creates an emulsion
-can be used for secondary but it usually makes primary
factors that influence the efficacy of the creation of an emulsion
pressure
time between collisions
concentration of emulsifier
solubility of emulsifier
HLB number
propensity for adsorption of emulsifier to surface
other factors effecting emulsification efficiacy
time for migration of the emulsifier to interface
flexibility fo the emulsifier on the surface after adsorbtion
solution conditions such as pH and ionic strength
temperature
fat or oil content
why is time important
rapid adsorbtion results in less coaslecnece, finer droplets and better emulsification
types of physcial instability
creaming
sedimentation
coalscence
flocculation
ostwald
ripening
breaking (phase seperation)
what is creaming
emulsion particles rise due to lower density
what is sedimentation
particles settle at bottom due to higher density
what is coalscence
particles merge to form larger particles
average droplet size increases over time
what is flocculation
particles aggregate without coalensnce due to attractive forces
what is ostwald ripening
growth of larger particles at the expense of smaller ones
what is breaking
complete seperation of phases
what is stokes law
used to describe the velocity of seperation
what is the driving force of seperation
gravity
stokes law equation, write it down
V= 2gr^2 (p2-p1)/9n
what is r
radius of particle
what is p2
density of continous phase
what is p1
density of dispersed phase
what is n
viscosity of continuous phase
what is the driving force for emulsion coalscence
thinning and disruption of the liquid film
how can coalescence be avoided?
having a stable interfacial layer
