Sediment of Soft Spheres Arranged by Effective Density
Open Access
- Author:
- Gonzalez Serrano, Cesar
- Graduate Program:
- Chemical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 17, 2010
- Committee Members:
- Darrell Velegol, Thesis Advisor/Co-Advisor
Darrell Velegol, Thesis Advisor/Co-Advisor - Keywords:
- Colloids
Packing
Bidisperse
Gravity - Abstract:
- Colloidal suspensions often contain mixtures of particles that must be sorted by size or density. One route to sorting gram-size quantities of particles is sedimentation, which has been studied for decades from both dynamic and thermodynamic perspectives. However, an important question remains unanswered: What sediment structure results when bi-disperse or poly-disperse particles settle rapidly, but remain non-glassy in the final dense sediment? This document shows that bi-disperse colloids having soft-sphere interactions spontaneously arrange into two macroscopic layers after a sedimentation process at Peclet number greater than unity. The layering can be explained without appealing to complex hydrodynamic or thermodynamic arguments; rather, the layering is readily explained simply by minimizing the free energy of the system, which is primarily the gravitational energy. The contribution of entropy and interparticle forces to the total energy of the system is negligible. When minimizing the gravitational energy, it has been found that the way that particles pack is a key parameter. However, the particles may start to aggregate under high centrifugal force or great sediment height. This can be a limitation to the particle reordering. The results presented here may lead to designs for preventing de-mixing of colloidal products during shipment, for improving sorting or size-refinement operations for colloidal particles of different size or density, for sorting mixtures of biological components, or for purifying mixtures of colloidal assemblies.