force in Section III C, and finally we discuss the behaviour of a chucker which sediments against an absorbing or hard-planar surface in Section III D. We begin by investigating the concentration profile of solute particles around the chucker in our MC simulations when R$_{1}$/R$_{2}$ = 10 , for a fixed chucker. Since the solute particles do not interact with each other, we expect the steady-state solute concentration profile to cor- respond to the solution of the diffusion equation (3), using the Green’s function appropriate for a sink at distance L from the chucker. This solution (for the solute concentration c ) is c ( r ) = k c 4 πD 2 ( 1 r − 1 L ) , so that the solute volume fraction φ is given by φ ( r ) = k c R 3 2 3 D 2 ( 1 r − 1 L ) . We note that this is not a true volume fraction, since solute particles do not interact and can overlap in our model (so that φ can be greater than one); but it does give some indication of the density of the solutes, for comparison to real systems. Figure 3 shows a comparison between the radial profiles for φ obtained from our simu- lations with the analytical expression, for L = 4 R$_{1}$ . The simulation data agrees very well with the analytical expression; the small discrepancy close to the boundary ( r/R$_{1}$ = 4 ) occurs because the analytical expression is computed for a spherical boundary whereas the simulation has a cubic boundary. We are also interested in how closely the solute particles are packed around the chucker: if the volume fraction close to the chucker surface is too high then the the Asakura-Oosawa approximation fails to accurately describe a real solute (e.g. polymer coils), since it neglects solute-solute interactions. Figure 4 shows the volume fraction φ of solute particles in spher- ical shells centred on the chucker in our MC simulations, computed for a freely diffusing chucker with R$_{1}$/R$_{2}$ = 10 , over the full range of chucking rates used in our simulations ( 0 < k$_{c}$R 2 $_{2}$/D$_{1}$ ≤ 600 ). The maximum volume fraction obtained close to the chucker is about 0.12, and for most chucking rates it is much lower. This suggests that our neglect of solute-solute interactions is justified over the range of parameters used in this work. 9 A. Solute concentration profiles