Hydrodynamically Coupled Colloidal Motors

Description

A detailed unterstanding of the interplay between rotational and translational degrees of freedom, as well as the effect of rotational diffusion on hydrodynamic interactions is not available at the time; this is mainly due to the fact that the available data from dynamic light scattering are not easily separable into translational and rotational contributions when the concentration is so high that particles can no longer be expected to rotate independently of each other. Furthermore, the calculation of observable transport quantities such as the self or collective diffusion constant becomes more and more involved with increasing particle density, partly due to the ensemble averaging required, but also due to the increasing importance of many-body effects in hydrodynamic interactions.


In a joined experimental and theoretical project, we thus propose an alternative route to study the effect of rotational motion on hydrodynamic interactions under controlled conditions. As a key element of our investigation we us colloid motors, i.e., birefrigent colloidal particles which can be set in rotation by circularly polarized laser light. On the experimental side, we plan to develop a polarization-modulated tweezer array to manipulate and control both the position and orientation of several colloidal motors which will then be recorded by real space imaging. On the thereotical side, we use Brownian and Stokesion dynamics to analyze the experimental system by both analytical and numerical means. By these methods we will address two complementary situations: the cross-correlations in the thermal position and orientation fluctuations of a pair of trapped particles, isolated or surrounded by further particles, and the response of clusters of particles of different size and shape when one or several particles experience an external torque. From our experimental and theoretical approach we expect new and direct information on the propagation of angular momentum in colloidal suspensions and on many-body effects in hydrodynamic interactions associated with rotational motion.

A detailed unterstanding of the interplay between rotational and translational degrees of freedom, as well as the effect of rotational diffusion on hydrodynamic interactions is not available at the time; this is mainly due to the fact that the available data from dynamic light scattering are not easily separable into translational and rotational contributions when the concentration is so high that particles can no longer be expected to rotate independently of each other. Furthermore, the calculation of observable transport quantities such as the self or collective diffusion constant becomes more and more involved with increasing particle density, partly due to the ensemble averaging required, but also due to the increasing importance of many-body effects in hydrodynamic interactions.


In a joined experimental and theoretical project, we thus propose an alternative route to study the effect of rotational motion on hydrodynamic interactions under controlled conditions. As a key element of our investigation we us colloid motors, i.e., birefrigent colloidal particles which can be set in rotation by circularly polarized laser light. On the experimental side, we plan to develop a polarization-modulated tweezer array to manipulate and control both the position and orientation of several colloidal motors which will then be recorded by real space imaging. On the thereotical side, we use Brownian and Stokesion dynamics to analyze the experimental system by both analytical and numerical means. By these methods we will address two complementary situations: the cross-correlations in the thermal position and orientation fluctuations of a pair of trapped particles, isolated or surrounded by further particles, and the response of clusters of particles of different size and shape when one or several particles experience an external torque. From our experimental and theoretical approach we expect new and direct information on the propagation of angular momentum in colloidal suspensions and on many-body effects in hydrodynamic interactions associated with rotational motion.

Institutions
  • FB Physik
Funding sources
NameProject no.DescriptionPeriod
Deutsche Forschungsgemeinschaft609/02no information
Further information
Period: 01.07.2002 – 30.06.2005