Physics – Condensed Matter – Soft Condensed Matter
Scientific paper
2004-11-09
Physics
Condensed Matter
Soft Condensed Matter
Scientific paper
10.1088/0953-8984/17/15/005
We have measured equilibrium sedimentation profiles in a colloidal model system with confocal microscopy. By tuning the interactions, we have determined the gravitational length in the limit of hard-sphere-like interactions, and using the same particles, tested a recent theory [R.van Roij, J. Phys. Cond. Mat. 15, S3569, (2003)], which predicts a significantly extended sedimentation profile in the case of charged colloids with long-ranged repulsions, due to a spontaneously formed macroscopic electric field. For the hard-sphere-like system we find that the gravitational length matches that expected. By tuning the buoyancy of the colloidal particles we have shown that a mean field hydrostatic equilibrium description even appears to hold in the case that the colloid volume fraction changes significantly on the length scale of the particle size. The extended sedimentation profiles of the colloids with long-ranged repulsions are well-described by theory. Surprisingly, the theory even seems to hold at concentrations where interactions between the colloids, which are not modeled explicitly, play a considerable role.
Blaaderen Alfons van
Roij René van
Royall Patrick C.
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