| Nanoconfinement has profound implications for system behavior. Salient features such as melting point depression and influence on structure are important in fields ranging from aerosols to drug discovery. Here we introduce a two-dimensional colloidal model system of nearly hard discs in soft confinement. A ring of colloidal particles is defined using holographic optical tweezers and the interior of this ring is populated with similar particles. Confinement in the third dimension is achieved by gravitational sedimentation. The structure of this system differs from similar systems with hard walls in that at sufficient density, local hexagonal ordering is observed to compete with the concentrically layered structure, leading to melting point depression and anisotropic dynamics. Additionally, through comparing the behaviour of the soft wall for populated and unpopulated confining rings, the radial pressure is found as a function of area fraction, leading to a direct measurement of the equation of state. Rotating the trapped particles leads to a novel model geometry to explore phenomena such as shear banding at the single-particle level. |
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