Fingerprint patterning of solid nanoparticles embedded in a cholesteric liquidcrystal

Abstract

Metallic nanoparticles dispersed in a cholesteric liquid crystal can order in accordance withthe helical structure of the chiral phase. Since the liquid crystals we used havea glassy state, the nanostructures may be examined by transmission electronmicroscopy. The platinum nanoparticles form periodic ribbons which mimic thewell-known fingerprint cholesteric texture. The particles do not decorate the pristinetexture but create a novel structure with a larger periodicity. The distance betweenthe ribbons is directly correlated to the helical pitch which therefore becomes asimple control parameter to tune the structuring of nanoparticles. Investigations ofcross-sections show how the particles are arranged in the volume; a selective segregationproceeds at the periphery of the film and the particle ordering is localized close tothe film–air interface. On the fingerprint patterning of nanoparticles, we do ananalogy with the positive staining of polymer films with heavy-metal-containingcompounds for transmission electron microscopy investigations and we discuss theaccumulation of particles in the sites with the highest energy of director distortions.