Diffusion and surface excess of a confined nanoswimmer dispersion

The diffusivity and surface excess of nanoswimmers which are confined in two plates with the separation H are explored by dissipative particle dynamics. Both mean squared displacement and velocity autocorrelation function methods are used to study the diffusive behavior of nanoswimmers with the Brownian diffusivity D₀ and the results obtained from both methods are consistent. The active diffusivity of confined nanoswimmers (D - D₀) depends on the wall separation, swimming speed ν_a, and run time τ. Our simulation results show that (D - D₀)/ν_a²τ is a function of ν_aτ/H. The reduction in the diffusivity of active colloids is more significant than that of passive particles. The distribution of nanoswimmers between two parallel walls is acquired and two regions can be identified. The accumulation of nanoswimmers near walls is quantitatively described by the surface excess Γ. It is found that Γ grows as the nanoswimmer concentration c_b, swimming speed ν_a, and run time τ are increased. The coupling between the ballistic trajectory of nanoswimmers and the walls results in nanoswimmer accumulation. The simulation outcomes indicate that Γ/Hc_b is a function of H/ν_aτ.