Observation of the Dynamic Colloidal Interaction Forces between Casein-Coated Latex Particles

We describe a refined version of the particle scattering apparatus due to van de Ven (Langmuir 1994, 10, 3046) for measuring the dynamic interactions between colloidal particles in a flow field. Polystyrene latex particles (diameter 5.1 μm) were studied, stabilized by β-casein and α s1 -casein, at pH 7 and ionic strengths of 0.1 and 0.01 mol dm -3 , The β-casein system exhibited stronger interparticle repulsion and less tendency for particle flocculation at the lower ionic strength. At ionic strength = 0.1 mol dm -3 the α s1 -casein system exhibited stronger interparticle repulsion than the β-casein system. This behavior is consistent with other measurements on the properties of casein-coated particles.