Influence of Surface Forces on Suspension Flow

Note that for hard spheres, surprisingly there is no influence of the particle size on the viscosity. The only concern about particle size in hard sphere suspensions is that if the particles are too big they will settle out. If the particles are neutrally buoyant sedimentation issues are not significant. 

The second factor to influence fine particle and colloidal suspension rheology is the interaction force between the particles. (The first factor being the volume fraction of particles.) The sense (attractive or repulsive), range and magnitude of the surface forces all influence the suspension rheological behaviour. 

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