Measured correlated diffusion coefficients D ∥ / D s ( n ) (a) and D ⊥ / D s ( n ) (b) as functions of r/(2a) for sample S1 at different particle area fractions n on a log–log plot. The concentration n ranges from 0.007 to 0.20, and the friction coefficient of the particle monolayer ranges from 0.06 cP · μ m to 3.53 cP · μ m . The differently colored symbols represent different values of n and different viscosity coefficients, where the black squares correspond to n ≈ 0.007 and the maroon inverted triangles correspond to n ≈ 0.020 . The dashed lines are guides for the eye, corresponding to ∼ 1 / r in panel (a) and to ∼ 1 / r 2 in panel (b).