Complex Fluids

Fluctuations and defects in quasi 2D smectic phases

We found a surface freezing transition in a mixture of colloidal liquid crystals and non-adsorbing polymers. In the surface induced phase, smectic layers wet the isotropic-nematic interface with rods lying in the place of the interface. Using optical microscopy we can directly visualize the quasi-2D smectic phase and quantify its fluctuations. Surprisingly we find that by changing the conditions it is possible to continuously swell the surface induced smectic phase to the point where individual smectic layers are observed.

Movie: 2D smectic with splay. [MOV - 2mb]

Fluctuations of the surface induced smectic phase are shown in the above movie. A dense nematic phase is below the image plane while a polymer rich isotropic phase is above the image plane. The thickness of the surface-induced smectic phase is about 100 nm while the diameter of an individual fd rod is about 10 nm. There is a strong coupling between the surface smectic layer and the background nematic phase which results in novel fluctuation spectrum.

An isotropic-nematic surface which is partially covered by smectic layers. A bacterium often gets trapped at the interface and swims along the nematic director. The flagella of the bacterium can easily distort the smectic layers as is visible in the movie. Alternatively it is possible to scan a laser tweezer along the interface and create novel defects.

Movie: Bacteria on surface. [MOV - 2mb] Movie: Dislocation. [MOV - 2mb]

A low volume fraction of rods is fluorescently labeled and fluorescent image is overlaid over DIC image. We hope to simultaneously study the dynamics of individual rods using fluorescence microscopy and long wavelength fluctuations using DIC microscopy.