Project B8

Phase Transitions of Confined Nanorods in Electric Fields

Project leaders

Summary

We propose to make monodisperse droplets of (mixed) nanorod liquid crystal (LC) phases and manipulate the director field and defect patterns of the confined LC phase and possibly the droplet shape with an external electric field. We will also try to manipulate the droplet shape and defect patterns by changing the surface coating of the nanorods, the size of the droplets and concentration of the nanorods in the droplets by evaporation. The LC phases will consist of metal (Au) and semiconductor (CdSe) nanorods and mixtures thereof. The individual nanorods have strong aspect ratio dependent optical resonances of the conduction electrons called plasmons (Au) and demonstrate strong photoluminescence linearly polarized along their long axis (CdSe). In a mixture the local fields of the Au-rods can enhance the luminescence of the CdSerods possibly to even non-linear effects such as 2-photon excitation, the properties of which in a collective nematic LC phase can be strongly influenced by an electric field. Such an electric field and field gradients can moreover be used to guide a second self organization step in which the nanorod LC droplets will be arranged into 1D strings, 2D sheets and 3D colloidal crystal phases as we already demonstrated for 'simpler' dielectric spheres. The arrangement of the switchable LC metamaterials on lattice spacings commensurate with the wavelength of light will further enable tenability for opto-electronic applications. Our proposal combines experience in opto-electronic characterization of nanoparticles, the manipulation of the self-organization of colloids with external fields and a theoretical and computer simulation approach to describe, guide and study these phenomena.