Simultaneous characterization of rotational and translational diffusion of optically anisotropic particles by optical microscopy.
We probe the roto-translational Brownian motion of optically anisotropic particles suspended in water with a simple and straightforward optical microscopy experiment that does not require positional or rotational particle tracking. We acquire a movie of the suspension placed between two polarizing elements and we extract the translational diffusion coefficient D T and the rotational diffusion coefficient D R from the analysis of the temporal correlation properties of the spatial Fourier modes of the intensity fluctuations in the movie. Our method is successfully tested with a dilute suspension of birefringent spherical colloidal particles obtained by polymerizing an emulsion of droplets of liquid crystal in a nematic phase, whose roto-translational dynamics is found to be well described by theory. The simplicity of our approach makes our method a viable alternative to particle tracking and depolarized dynamic light scattering.
Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università degli Studi di Milano, via F.lli Cervi 93, 20090 Segrate, Italy.
Fabio
F
Giavazzi
Catalina
C
Haro-Pérez
Roberto
R
Cerbino