We use fluorescence microscopy to study the dynamics of a Brownian probe particle driven by a constant external force through dilute colloidal suspensions with hard-sphere interparticle potential.  As the probe particle moves through the colloidal suspension it collides with colloidal particles deforming the equilibrium suspension microstructure.  The shape and the range of this distortion is determined by the volume fraction of the colloidal suspension and by the relative strength of the external force with respect to the entropic restoring force of the colloidal particles.  We find that the average velocity of the probe particle is linear with the external force and it decreases with increasing volume fraction.  Moreover, there is an increasing anisotropy with increasing forcing between the velocity fluctuations of the probe particle oriented parallel vs. transverse to the imposed force.  At high forcing, there is an increased probability of collisions on the front of the probe particle, and although these will partially contribute to transverse velocity fluctuations, they mainly contribute to parallel velocity fluctuations causing pronounced anisotropy.  We compare our results with force-induced diffusion measured by Brownian dynamics simulations.  Future studies will include studying probe particle dynamics in colloidal suspensions with a range of interparticle attractive strengths.

Single particle motion in dilute colloidal suspensions

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.