Measurement of the stiffness of hard-sphere colloidal crystal-liquid interfaces

We investigated the stiffness of the interfaces between hard-sphere colloidal face-centered cubic crystals sedimented onto (100), (110), and (111) oriented templates and their equilibrium liquid with special attention to the in-plane anisotropy. The stiffness was determined from thermal fluctuations in the interface position imaged by confocal microscopy. The colloidal particles of diameter σ are nearly density-matched with the suspending fluid so that the amount of liquid above the interface was much greater than in an earlier similar hard-sphere colloid experiment. We find stiffness values of 0.47k_BT/σ² for the (100) interface 0.53k_BT/σ² for the (110) interface and 0.41k_BT/σ² for the (111) interface. These values are generally closer to those found in computer simulations than to the earlier colloid results. No evidence was found however for the expected in-plane anisotropy of the (110) interface. This surprising finding confirms that of the earlier colloid work.