Bms1027 Emulsions And Dispersions

Front 1

Dispersion types

Back 1

- true solution, disperse phase 1nm (monophase)
- colloidal dispersion, 1nm - 0.5um (diphase)
- coarse dispersion, >0.5um (diphase)

Front 2

Rheology

Back 2

the science of deformation and flow behaviour of matter

Front 3

Viscosity

Back 3

resistance to flow
= shear stress/ shear rate
(shear stress = force/area and shear rate = velocity/clearance(film thickness))

Front 4

Newtonian flow

Back 4

when shear stress is proportional to rate of sheer
- linear positive correlation on graph

Front 5

pseudoplastic flow

Back 5

shear thinning (viscosity decreases with shear)
- positive curve with decreaseing gradient with rate

Front 6

Dilatant flow

Back 6

shear thickening (viscosity increases with shear)
- Positive curve with increasing gradient with rate

Front 7

Bingham plastic

Back 7

Yield stress has to be overcome before the material starts to flow
- positive linear correlation at non 0 value

Front 8

Gels

Back 8

a continuous phase of interconnected particles or molecules mixed with a continuous liquid phase (can set on heating/cooling)

Front 9

Protein gels - Reversible

Back 9

gels cross linked by non-covalent bonds which can be broken and remade

Front 10

Protein gels - Non reversible

Back 10

Fixed with covalent bonds so cant be reformed (aggregated particles)

Front 11

Polysaccharide gels - Thermoreversible

Back 11

gels melt of heating and set on cooling (<1% gelatine)

Front 12

Polysaccharide gels - Carrageenan gels

Back 12

double helix of sugar produces a gel which aggregate in coils to form turbid gel (soluble if in coils)

Front 13

Factors that affect gel formation

Back 13

- temp
- chemical alteration
- reduction in polarity (ph)
- addition of water competitive compounds (sugar)

Front 14

Emulsion

Back 14

when an immiscible liquid is dispersed in small droplets (dispersed phase) in another immiscible liquid (continuous phase)

Front 15

Oil in water emulsion

Back 15

oil droplets dispersed in a continuose phase of water

Front 16

water in oil emulsion

Back 16

water droplets dispersed in a continuous phase of oil

Front 17

How to make an emulsion

Back 17

1) mix oil and water with homogenise at hight speed
2) add biopolymer to create secondary emulsion (bilayer)

Front 18

Emulsifying agents

Back 18

- eg proteins, phospholipids, sterols, gms, fatty acids, carboxymethyl cellulose
- needs to be amphipathic (hydrophilic and phobic end) so can be absorbed at interface to form mono/multilayer
- must lower surface tension

Front 19

Emulsifying capacity

Back 19

- rate of emulsion
- contact angle (to favour which type of dispersion)
- lower surface tension to reduce energy use

Front 20

Emulsion stability

Back 20

depends on van der waals forces and electrostatic repulsions between electrical double layers of identical charge
- needs to encourage repulsion between droplets to over come attractive VDW's

Front 21

Methods of assessing stability

Back 21

1) measure change in dispersion (droplet size under microscope)
2) measure charge on the droplet by electrophoresis
3) application of stress centrifugation or heating

Front 22

Foams

Back 22

dispersion of gas bubbles in a liquid, spearated by liquid walls called lamellae (elastic to withstand pressure/force)
- same principles as emulsion stability/capacity