Dynamics of ordered colloidal particle monolayers at nematic liquid crystal interfaces.
We prepare two-dimensional crystalline packings of colloidal particles on surfaces of the nematic liquid crystal (NLC) 5CB, and we investigate the diffusion and vibrational phonon modes of these particles using video microscopy. Short-time particle diffusion at the air-NLC interface is well described by a Stokes-Einstein model with viscosity similar to that of 5CB. Crystal phonon modes, measured by particle displacement covariance techniques, are demonstrated to depend on the elastic constants of 5CB through interparticle forces produced by LC defects that extend from the interface into the underlying bulk material. The displacement correlations permit characterization of transverse and longitudinal sound velocities of the crystal packings, as well as the particle interactions produced by the LC defects. All behaviors are studied in the nematic phase as a function of increasing temperature up to the nematic-isotropic transition.
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. weiwe@sas.upenn.edu.
Wei-Shao
WS
Wei
Department of Physics, McGill University, Montreal, Quebec, Canada and Department of Chemistry, McGill University, Montreal, Quebec, Canada.
Mohamed Amine
MA
Gharbi
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. weiwe@sas.upenn.edu.
Matthew A
MA
Lohr
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. weiwe@sas.upenn.edu.
Tim
T
Still
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. weiwe@sas.upenn.edu.
Matthew D
MD
Gratale
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. weiwe@sas.upenn.edu.
T C
TC
Lubensky
Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Kathleen J
KJ
Stebe
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. weiwe@sas.upenn.edu.
A G
AG
Yodh