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Anisotropic Solvation of Rod-Shaped Nanostructures in Liquid Crystalline Solvents

Our interest in liquid crystals is centered around the understanding of how nanostructured solutes such as rod-shaped polymers align in an anisotropic medium. We are studying the orientation and degree of alignment of conductive light emitting polymers in thermotropic liquid crystals by using single molecule polarization spectroscopy. Because of the larger size of a polymer solute compared to the liquid crystalline molecules, the solute is aligned to a much greater extent. The aim of this project is to gain a deeper understanding of how molecular solvent-solute interactions govern short and long range orientation, alignment and diffusion of solutes in liquid crystalline solvents. We are examining the anisotropic solvation and diffusion of macro-molecules and nanoparticles as a function of size, shape, liquid crystalline phase, and solvent order. By using a combination of ensemble and single molecule/particle polarization spectroscopy techniques we are able to extract solute order parameters, which give us detailed information about anisotropic solvation in liquid crystals.

The figure above shows a typical fluorescence transient (left) of polymer molecules diffusing in a liquid crystal. Each burst corresponds to a single molecule passing through the laser excitation spot. The fluorescence is split into two orthogonally polarized components (blue and red trace), which allows us to calculate the polarization anisotropy of each molecule and then generate a histogram of polarization anisotropy values (right). Modeling of the polarization anisotropy distribution allows us to extract the degree of orientational alignment of the solute in the liquid crystal.

Publications:

  1. J. Olson, P. Swanglap, W.-S. Chang, S. Khatua, D. Solis, S. Link, Detailed mechanism for the orthogonal polarization switching of gold nanorod plasmons. Phys. Chem. Chem. Phys, ASAP. link
  2. W.-S. Chang, J. B. Lassiter, P. Swanglap, H. Sobhani, S. Khatua, P. Nordlander, N. J. Halas, S. Link, A Plasmonic Fano Switch. Nano Lett. 12, 4977 (2012). link
  3. S. Khatua, W.-S. Chang, P. Swanglap, J. Olson, S. Link, Active Modulation of Nanorod Plasmons. Nano Lett. 11, 3797 (2011). link
  4. S. Khatua, P. Manna, W.-S. Chang, A. Tcherniak, E. Friedlander, E. R. Zubarev, S. Link, Plasmonic Nanoparticles – Liquid Crystal Composites. J. Phys. Chem. C 114 7251 (2010). link
  5. A. Tcherniak, D. Solis, S. Khatua, A. A. Tangonan, T. R. Lee, S. Link, Chain-length dependent nematic ordering of conjugated polymers in a liquid crystal solvent. J. Am. Chem. Soc. 130, 12262 (2008). link