Pairwise Interactions of Colloids in Two-dimensional Geometric Confinement

Bum Jun Park, Bomsock Lee and Taekyung Yu

We present the pairwise interaction behaviour of colloids confined in two-dimensional (2D) colloidal cages using optical laser tweezers. A single probe particle inside the hexagonal cage particles at a planar oil-water interface is allowed to diffuse freely and the spring constant is extracted from its trajectories. To evaluate the effect of multibody interactions, the pair interactions between the probe particle and each cage particle are directly measured by using optical tweezers. Based on pairwise additivity, Monte Carlo simulations are used to compare the values of the spring constant obtained from experiments and simulations. We find that the multibody interactions negligibly occur, and thus the particle interactions confined in such colloidal cages are highly pairwise. This work demonstrates that the use of the pairwise assumption in numerical simulations is rational when interparticle repulsive interactions are sufficiently strong, such as the particle interactions at fluid-fluid interfaces.

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