Effects of confined geometry on phase-separated dextran/gelatine mixtures exposed to shear

The effect of shear on aqueous phase-separated dextran/fish gelatine mixtures with a total concentration of 5 and 10% was studied in a confined geometry. It was measured as a function of composition, strain rate and gap size. This was done by using both small-angle light scattering and a shear cell combined with a confocal laser scanning microscope. At a total polymer concentration of 5%, small-angle light scattering results showed that up to 100 s(-1) the deformation of the domains increases with the strain rate. At strain rates less than 100 s(-1), the response of the system to strain is dominated by strain rate-dependent deformation. At a higher strain rate there might be balance between break-up and re-coalescence. At a total concentration of 10%, small effects of the gap size were found. In confined geometry, the coalescence rate was faster than expected from viscous hydrodynamic growth. The microscope images showed that the gelatine-enriched phase forms a wetting layer on the surface of the glass wall. The degree of wetting appears to increase with increasing the strain rate up to 60 s(-1) and decreases again at higher strain rates.