*Special Seminar*:"Control of Nanoparticle Self-assemblies using Distorted Liquid Crystals”

Fri, 01/15/2016 - 14:00
Emmanuelle Lacaze (Institut de Nano-Sciences de Paris, Université Pierre et Marie Curie)

Directed assembly of nanoparticles is a promising alternative for original nanoparticle organizations. New kinds of optical properties are expected when semi-conductive or metallic nanoparticles are concerned.  Using liquid crystal matrices oriented by their interfaces, it is possible to induce anisotropic nanoparticle organizations. We can then investigate the influence of these matrices on the optical properties of the nanoparticles. Concerning the liquid crystal matrix, we focus here on arrays of  topological defects  in thin  smectic  films  and  o  elastically  distorted  cholesteric  films;  concerning nanoparticles,  we  focus  on  fluorescent  semi-conducting  nanorods, which  behave  like single photon emitters and gold nanoparticles for their plasmon resonance properties.

I will show how  to  create  hierarchical  arrays  of  oriented  topological  defects  in  thin smectic  films  that  act  as  efficient  traps  for  a  specific  localization  and  orientation  of nanoparticles  and  may  allow  for  specific  nanoparticle  assemblies  depending  on  the nanoparticle size. For trapped fluorescent nanorods, a fine control of the polarization of the single photons is obtained.  Similarly the orientation of gold nanorods leads to the control of their luminescence as well as of their plasmon resonance by light polarization. I will show that,  when  the  nanoparticle  concentration  is  increased,  single  chains  are formed, and can lead to a strong electromagnetic coupling between the particles. We are not only capable of linearly confined the particles, but also of varying the inter-particle interactions and thus modify their optical properties which are sensitive to the inter-particle distance. I will compare nanospheres chains formed in smectic arrays of topological defects to nanosphere ribbons formed in elastically distorted cholesteric films in order to discuss the influence of the liquid crystal matrix on the induced electromagnetic coupling between nanoparticles.

LRSM, Reading Room