Simulation studies of microstructure of colloids in sedimentation

Abstract

Direct numerical simulations are performed to investigate the microstructure of sedimenting particles, using a smoothed profile method. We used pair distribution function to find out particle preference to orient themselves with respect to a test particle. We found that at low Peclet number (Pe), particles show an isotropic microstructure due to strong effects of thermal fluctuations and with increasing Pe at , particles prefer to orient themselves in the horizontal direction due to dominance of hydrodynamic interactions at low volume fraction. This preference decreases with increasing volume fraction and at high volume fraction (), microstructure becomes isotropic due to dominance of many-body interactions. The microstructure analysis at high Reynolds number (Re = 1, 10) revealed the deficiency of the particles in the vicinity of a test particle. This deficiency decreases with the increase of volume fraction and at high volume fraction, we observed an isotropic microstructure due to many-body interactions. Moreover, we also observed that the range of volume fraction affected by this deficiency increases with increasing Re.

Keywords::

• microstructure
• sedimentation
• direct numerical simulations
• smooth profile method

Acknowledgements

This work was supported by KAKENHI 23244087 and the Global COE Program, ‘International Center for Integrated Research and Advanced Education in Materials Science’ from the Ministry of Education, Culture, Sports, Science and Technology of Japan.