Text of Properties of Emulsions and Foams FDSC400. Goals Properties of emulsions –Type –Size –Volume...
Properties of Emulsions and Foams FDSC400
Goals Properties of emulsions Type Size Volume fraction Destabilization of emulsions Creaming Flocculation Coalescence Foams
Emulsion A fine dispersion of one liquid in a second, largely immiscible liquid. In foods the liquids are inevitably oil and an aqueous solution.
Types of Emulsion Oil-in-water emulsion Water-in-oil emulsion Water Oil mm
Multiple Emulsions Water-in-oil-in-water emulsionOil-in-water-in-oil emulsion Water Oil mm
Emulsion Size < 0.5 m 0.5-1.5 m 1.5-3 m >3 m
Number Distributions < 0.5 m 0.5-1.5 m 1.5-3 m >3 m Number Very few large droplets contain most of the oil
Median Polydispersity Large droplets often contribute most to instability (Volume in class Total volume measured) Note log scale
Volume Fraction =Total volume of the dispersed phase Total volume of the system Close packing, max Monodisperse Ideal ~0.69 Random ~0.5 Polydisperse Much greater
Viscosity Viscosity is the force required to achieve unit flow rate Force /N Distance/ m No slip at the wall Maximum induced flow rate /ms -1 Shear rate /s -1 Force per unit area /Nm -2 Slope viscosity /Nm -2 s
Emulsion Viscosity Emulsion droplets disrupt streamlines and require more effort to get the same flow rate Viscosity of emulsion Continuous phase viscosity Dispersed phase volume fraction
Chemical Composition Interfacial layer. Essential to stabilizing the emulsion Oil Phase. Limited effects on the properties of the emulsion Aqueous Phase. Aqueous chemical reactions affect the interface and hence emulsion stability