Depletion induced clustering in mixtures of colloidal spheres andfd-virus

Abstract

We determined the phase boundary of an ideal rod-sphere mixture consisting of fd-virus, which is an established model system for mono-disperse colloidal rods, and density matched mono-disperse polystyrene beads employing diffuse wave spectroscopy. The low volume fraction of fd needed to induce a phase separation at relatively low ionic strength exemplifies the fact that slender rods are very effective depletion agents. Confocal microscopy showed that stable clusters are formed during phase separation. Relaxation after shear deformation of these clusters showed that the phase separation is gas-liquid-like and that the interfacial tension involved is very low as in colloid-polymer mixtures.

Phase stability of colloidal mixtures of spheres and rods

“…Thus, the phase transition point lies between these two rod concentrations. All the experimental phase transitions measured here are liquid-liquid like, as determined with confocal laser scanning microscopy in a similar fashion as discussed in a previous paper 38 .…”

“…The rod concentrations were much lower than in the experiments of Adams et al and the size ratio used was ξ = 3.5. Guu et al observed a transition from isotropic to an isostructural fluid/fluid coexistence upon increasing rod concentration, as predicted by FVT calculations 38 . However, there was a big discrepancy between the onset of phase separation predicted by FVT and the experimental results.…”

“…where V free is the ensemble averaged free volume. In previous FVT studies on mixtures of rods and spheres, the rods were treated as infinitely thin 25 or the chemical potential of the rods was assumed to be ideal and the volume that is excluded by the rod depletants themselves is neglected in the free volume expressions for both the reservoir and the system 27,28,38 .…”

“…Also in these experiments, the rod concentrations used were either close to the I − N coexistence regime or were already at relatively high rod volume fractions where the rods self-assemble into highly ordered phases and no fluid/fluid demixing was observed. Guu et al 38 studied the effect of the rod thickness D on the phase behaviour of fd-virus and polystyrene spheres by varying the effective rod thickness through changing the ionic strength. The rod concentrations were much lower than in the experiments of Adams et al and the size ratio used was ξ = 3.5.…”

Direct calculation of distortion energies in colloidal liquid crystals from single-particle data

“…These rod-shaped viruses, with a length of 880 nm and a width of 6 nm, form a cholesteric phase in bulk and are often used as a model system for liquid crystals [15][16][17][18][19][20][21][22].…”