In Search of Colloidal Hard Spheres

Abstract

We recently reviewed the experimental determination of the volume fraction, $\varphi$, of hard-sphere colloids, and concluded that the absolute value of $\varphi$ was unlikely to be known to better than $\pm 3$-6%. Here, in a second part to that review, we survey effects due to softness in the interparticle potential, which necessitates the use of an {\em effective} volume fraction. We review current experimental systems, and conclude that the one that most closely approximates hard spheres remains polymethylmethacrylate spheres sterically stabilised by polyhydroxystearic acid `hairs'. For these particles their effective hard sphere diameter is around 1-10% larger than the core diameter, depending on the particle size. We argue that for larger colloids suitable for confocal microscopy, the effect of electrostatic charge cannot be neglected, so that mapping to hard spheres must be treated with caution.

11 pages

References in corpus (3)

• Crystallization of hard-sphere glasses
• Viscoelasticity and shear flow of concentrated, non-crystallizing colloidal suspensions: Comparison with Mode-Coupling Theory
• Local structure and dynamics in colloidal fluids and gels

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• Non-classical pathways of crystallization in colloidal systems
• Free Energy Barriers for Crystal Nucleation from Fluid Phases
• Local elastic response measured near the colloidal glass transition
• Low-density crystals in charged colloids : Comparison with Yukawa theory
• Relating Microstructure and Particle-level Stress in Colloidal Crystals Under Increased Confinement