Gravity and Patch Coverage Impact on Patchy Colloidal Gel Collapse

Patchy colloidal gels with strong directional interactions exhibit a rich range of phase behavior and serve as a robust model system for protein and other gels. Equilibrium and non-equilibrium states (e.g., gels and glasses) are influenced by the number and size of patches on particle surfaces. While the morphology and compactness of these systems are predominantly determined by the strength of inter-particle potential, gravity plays a role in shaping the number and size of clusters. Moreover, the extent of patch coverage dictates when gravitational effects come into play. Previous investigations into the collapse of colloidal gels under gravity have identified three distinct phases: slow compaction, transition to rapid collapse, and long-term densification, indicating that the primary mechanism driving gel collapse is non-equilibrium phase separation. In this work, we examine how the interplay between gravitational force and patch coverage affects the collapse of colloidal gels. We characterize microscopic changes in the gel structure by tracking particle positions, coordination numbers, and bond dynamics. Osmotic pressure helps distinguish between phase-separation-driven condensation and compaction due to gravity. Besides monitoring the gravitational collapse, we construct a comprehensive phase diagram encompassing equilibrium and non-equilibrium phases.