Squeeze flow between plane and spherical surfaces

Experiments are described in which a constant force F squeezed a fluid, eit her between two parallel circular plates, or between a plate and convex sph erical lens. Newtonian fluids obeyed the relation of Stefan (1874) for plat es, and the relation of Adams et al. (1994) for plate and lens. The non-New tonian yield stress fluids Brylcreem, Laponite and Sephadex were squeezed b etween plates of various diameter D to attain a stationary separation h. On ly for separations greater than h* (which depended on the fluid) did Brylcr eem and Laponite obey the relation F/D-3 proportional to h(-1) of Scott (19 31) and give a yield stress in agreement with the vane method. For Sephadex the dependence of F/D-3 on h disagreed with Scott's relation, but varied a s h(-5/2) for h > 0.6 mm and h(-3/2) for h < 0.6 mm. On rotating one plate in its plane the yield stress fluids at a fixed F suffered a marked decreas e of h. This, and the existence of h*, are discussed in terms of the soft g lassy material model of Sollich et al. (1997) and Sollich (1998). Brylcreem and Laponite were squeezed between a plate and lenses of various curvature and their yield stress obtained using the relation of Adams et al. (1994) was compared with measurements by plate-plate squeeze-flow and vane methods .