la8b02498_si_001.pdf (163.22 kB)
Tumbling of Quantum Dots: Rheo-Optics
journal contribution
posted on 2018-11-04, 00:00 authored by Run Li, Marisol Ripoll, Naveen Reddy, Jan K.G. Dhont, Ruben Dierick, Zeger Hens, Christian ClasenLinear
flow dichroism is shown to be a powerful tool to characterize
the hydrodynamic dimensions of extremely small nonspherical colloids
in solution. Dispersions of prolate and oblate quantum dots (QDs)
are employed to investigate the validity of flow dichroism as a characterization
tool. Shape-anisotropic QDs are important from an application perspective,
where it is necessary to have a good knowledge of their hydrodynamic
dimensions to predict and control their orientation during solution
processing. Flow dichroism quantifies the tumbling motion of QDs in
shear flow by optical means, which provides a characteristic signature
of the particle shape, hydrodynamic friction, and size distribution.
The effects of particle size and shape, size polydispersity, and shear
rate on the temporal evolution of the flow-induced alignment are discussed
in detail on the basis of numerical solutions of the Smoluchowski
equation that describes the motion for the probability of the orientation
of colloids in shear flow. It is shown that the combination of flow-dichroism
experiments and the theoretical approach on the basis of the Smoluchowski
equation provides a means to measure hydrodynamic aspect ratios and
polydispersity, which for such small particles is not feasible with
standard methods similar to light scattering. Flow dichroism will
be useful not only for shape-anisotropic colloidal QDs, but also for
other nanoscale systems.