Behaviour of droplets in simple shear flow in the presence of a protein emulsifier

doi:10.1016/S0927-7757(96)03972-6

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Volume 125, Issues 2–3, 2 June 1997, Pages 189-200

https://doi.org/10.1016/S0927-7757(96)03972-6 Get rights and content

Abstract

The effect of two structurally diverse protein emulsifiers, β-lactoglobulin and β-casein, upon the break-up behaviour of a single aqueous droplet in a Couette flow field has been studied over a wide range of protein concentrations for bulk viscosity ratios between 8 × 10⁻⁵ and 0.05.

It has been found that β-casein and low concentrations (⩽10⁻² g l⁻¹) of β-lactoglobulin cause the droplets to be at least as stable as expected from conventional theories on the basis of their equilibrium interfacial tension. In such cases the presence of the emulsifier at the deforming interface is thought to enhance the interfacial elasticity. This effect can be characterized by an effective interfacial tension, which is higher than the equilibrium value.

High concentrations of β-lactoglobulin (⩾ 10⁻¹ g l⁻¹), on the other hand, have been shown to cause droplets to be less stable than would have been predicted from the equilibrium interfacial tension. It is thought that an interfacial protein network is formed, which limits the droplet deformation and makes the droplet interface rigid with respect to tangential stresses. As a result, the critical deformation and capillary number are found to be essentially independent of the viscosity ratio.

It is proposed that the interfacial structure may be probed using a combination of interfacial shear and dilational rheological measurements. From this type of analysis it may be possible to predict the break-up stability of droplets.

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¹: Present address: Unilever Research, Colworth House, Sharnbrook, Bedford MK44 1LQ, UK.

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Behaviour of droplets in simple shear flow in the presence of a protein emulsifier

Abstract

Physica A

Colloids Surfaces

J. Non-Newtonian Fluid Mech.

Colloids Surfaces

J. Colloid Interface Sci.

Colloids Surf.

J. Colloid Sci.

Ann. Rev. Fluid Mech.