Anisotropic dynamics and kinetic arrest of dense colloidal ellipsoids in the presence of an external field studied by differential dynamic microscopy

Abstract

Anisotropic dynamics on the colloidal length scale is ubiquitous in nature. Of particular interest is the dynamics of systems approaching a kinetically arrested state. The failure of classical techniques for investigating the dynamics of highly turbid suspensions has contributed toward the limited experimental information available up until now. Exploiting the recent developments in the technique of differential dynamic microscopy (DDM), we report the first experimental study of the anisotropic collective dynamics of colloidal ellipsoids with a magnetic hematite core over a wide concentration range approaching kinetic arrest. In addition, we have investigated the effect of an external magnetic field on the resulting anisotropic collective diffusion. We combine DDM with small-angle x-ray scattering and rheological measurements to locate the glass transition and to relate the collective short- and long-time diffusion coefficients to the structural correlations and the evolution of the zero shear viscosity as the system approaches an arrested state.

Particle sizing for flowing colloidal suspensions using flow-differential dynamic microscopy

“…We refer to a simple diffusive fit to g ⊥ as "anisotropic-DDM", a technique which has been used for particles influenced by a magnetic field. 22,25 A combination of a finite field of view and flow will also cause decorrelation due to particles leaving the image (and being replaced by on average uncorrelated particles). 28 This introduces a finite-size term into the total ISF, which for flow along the x direction takes the form…”

“…DDM has been used to characterise the micro-rheological properties of fluids; [14][15][16] to enable high-throughput measurements of micro-organism motility; [17][18][19] and to measure particle diffusion in complex environments, 20,21 under external fields, 22 and even in dense or turbid systems. [23][24][25] However, for flowing suspensions the fluid's velocity can impact many particle-sizing techniques, causing an apparent increase in diffusion and an underestimation of particle size. 7,26 Therefore, for reliable particle sizing microscopic diffusive motion must be disentangled from the impact of bulk flow.…”

Preparation, properties, and applications of magnetic hematite microparticles

“…109 Again it is noteworthy that for the hematite spindles the influence of magnetic fields on the phase behaviour and particle alignment for different composite systems and at high concentrations has been explored in detail by several groups. [130][131][132][133][134][135][136][137]…”

Potential and limits of a colloid approach to protein solutions

“…While there are some simulation as well as experimental studies focusing on various aspects of the dynamics of ellipsoids at high concentrations, most of the experimental work is on (quasi-) 2D systems, with only a few notable exceptions on 3D bulk behavior. [73][74][75][76][77][78][79] Progress on the experimental side is primarily hindered by the fact that most existing model systems for such ellipsoidal particles are highly turbid at high concentrations, thus making an investigation of dynamic properties such as the collective or self diffusion coefficient or the particle mean square displacement very difficult or impossible with standard optical tools. It is only through the use of recently introduced techniques such as differential dynamic microscopy or X-ray photon correlation spectroscopy that these properties have become accessible at high concentrations close to the glass transition for these model ellipsoids also.…”

“…It is only through the use of recently introduced techniques such as differential dynamic microscopy or X-ray photon correlation spectroscopy that these properties have become accessible at high concentrations close to the glass transition for these model ellipsoids also. 63,79 During the last 2 decades, enormous experimental and theoretical effort has also been devoted to the design and synthesis and to the understanding of the phase behaviour of so-called patchy colloidal particles, i.e. particles with site-specifically engineered surfaces (see Fig.…”