# Particle Drag in colloids

How does one evaluate the drag force on a particle moving through a colloid? And how does this depend on the size of the particle compared to the constituents making up the collloid?

For particles much larger than the constituents I can imagine one can just do the same as for a normal fluid and use the various correlations that exist. If the rheology of the colloid is non-Newtonian I can imagine you evaluate the viscosity for a shear, characteristic to the moving particle. But I can also imagine the particle size matters. I would say for particle sizes much smaller than the colloid constituents, the viscous drag experienced by the particle is that of the liquid phase, the interaction with the constituents playing little role. Is that correct?

If so, how does the viscosity in the drag force expressions change with particle size relative to the colloid constituents?

Any experience, refererences, thoughts, comments are welcome!