Study of translational and rotational dynamics of birefringent colloidal particles by depolarized light scattering in the far- and near-field regimes

Abstract

We characterize the translational and rotational dynamics of birefringent spherical colloidal particles by depolarized light scattering in the far- and near-field regimes. For this purpose, we use depolarized dynamic light scattering and propose an extension of dynamic heterodyne near-field light scattering that takes into account the polarization state of the light. Such a combination of methods allows to access colloidal dynamics in an extended q-range and permits to evaluate different modes of particles motion in suspension. Furthermore, we obtain a good agreement between results from the far- and near-field approaches thus validating our proposal and opening the possibility to investigate simultaneously the subtle interplay between translational and rotational motions of anisotropic colloidal particles in length-scales from the order of the particle size to several interparticle distances.

Differential dynamic microscopy microrheology of soft materials: A tracking-free determination of the frequency-dependent loss and storage moduli

“…The tracer used in this study consists of spherical colloidal particles, with a polymerized nematic liquid-crystal core, whose birefringence makes the particles optically anisotropic, with a uniaxial symmetry [18,19,39,40]. The particles were prepared and purified according to the protocols described in detail in Refs.…”

“…In general, the measurement with optical means of the rotational dynamics is technically more challenging than its translational counterpart and usually requires the use of specialized shape [14][15][16] or optically [17][18][19][20] anisotropic tracers. Rotational diffusion microrheology has been initially demonstrated by using a light streak tracking method enabling the time-resolved measurement of the axial orientation of a single, optically trapped microdisk [14].…”

Two-dimensional Brownian motion of anisotropic dimers

“…Furthermore, the translational and rotational motion of colloidal particles that are anisotropic either in shape or optical properties have been quantitatively characterized using depolarized dynamic light scattering (DLS) [31][32][33][34][35][36]. Depolarized DLS has been complemented by near-field depolarized DLS to study translational and rotational dynamics on a larger length scale [37,38]. Combining microscopy and scattering approaches, in movies obtained using a polarization or dark field microscope the temporal correlations of the spatial Fourier modes of the intensity fluctuations can be analyzed.…”

Differential dynamic microscopy to measure the translational diffusion coefficient of nanorods

“…DDM therefore has the possibility to make low angle measurements not possible with standard DLS. DDM has been applied to non-spherical particles, [6,7] and both DDM [8,9] and heterodyne near-field scattering (HNFS) [10] have been applied to optically anisotropic spherical particles. However, the potential for low angle measurements to separate the translational diffusion of nanorods with different aspect ratios has not previously been explored.…”