Depletion Interactions Effected by Different Variants of fd Virus

Abstract

The depletion interaction between a probe sphere and a flat wall induced by fd-virus is investigated by means of total internal reflection microscopy (TIRM). The viruses serve as a model system for mono-disperse, rod-like colloids. We find that the experimental potentials are well described by the first-order density approximation up to an fd-content of several overlap concentrations. This is in accordance with higher order density theory as confirmed by numerical calculations. Since the first order analytical description still holds for all measurements, this exemplifies that higher order terms of the theory are unimportant for our system.Comparing the potentials induced by wild-type fd to those induced by a more rigid fd variant, it can be shown that the influence of the virus stiffness is beyond our experimental resolution and plays only a negligible role for the measured depletion potentials.

Phase stability of colloidal mixtures of spheres and rods

“…Asakura and Oosawa already predicted in the 1950s 11,16 that for this reason, rod-like particles should be very efficient depletants. This efficiency has been confirmed experimentally with direct depletion potential measurements [17][18][19][20][21] . Moreover, due to the shape anisotropy of rods, rod/sphere mixtures have a very rich phase behaviour.…”

“…The viruses have an aspect ratio ≈ 130 and are charge stabilized at values of pH > 4.2 due to the negative surface charge of the coat proteins 37 . In several studies, fd-virus has been used to mediate an attraction between single spherical particles and a fixed wall and to determine the corresponding depletion potential 17,[19][20][21] . The equilibrium phase behaviour of mixtures of fd-virus and polystyrene spheres has been investigated by Adams et al 6 for size ratios ξ ranging from 6 − 80, obtained by using polystyrene spheres with different radii.…”

Near wall dynamics of a spherical particle in crowded suspensions of colloidal rods – dynamic information from TIRM revisited

“…Particle mean displacements and mean squared displacements were calculated as a function of time and starting position according to eqn (22) and (23). Some representative examples for the time dependence of MDs and MSDs are shown in Fig.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16] Total internal reflection microscopy (TIRM) 17 has proven to be an ideal method for the measurement of depletion interactions between a probe sphere and a flat glass wall. 6,7,[18][19][20][21][22][23][24] In our previous contribution 16 we used TIRM to show that depletion potentials induced by the rod-like fd-virus follow the classical Asakura-Oosawa (AO) predictions at depletant concentrations and size ratios at which this theory is expected to fail. Further, at high concentrations, we observed deviations from the ideal gas behavior, which are much more pronounced than theoretically predicted by Mao et al 8 In the present study we discuss experiments on the statics, providing additional experimental data, as well as the dynamics of probe spheres of various sizes relative to the depletant size, and extend earlier approaches to resolve the dynamics as a function of the starting position of the probe sphere.…”

DataSheet1.pdf

“…Slender rods are far more effective depletant than the commonly used polymers, as also the orientational entropy is strongly reduced when rods are confined between two cells [37][38][39]. As such the rod-like virus is a pure depletant that induces long-ranged attraction at very low volume fractions, inducing a depletion force that can be tuned by varying the concentration of these rods [40][41][42][43][44].…”