Liquid crystal self-assembly of upconversion nanorods enriched by depletion forces for mesostructured material preparation

TL;DR

This paper demonstrates how depletion forces can be used to self-assemble nanorods into liquid crystalline structures with unique optical properties, advancing the design of mesostructured materials.

Contribution

It introduces a novel method of using depletion interactions to organize photon-upconversion nanorods into ordered liquid crystal phases with functional optical properties.

Findings

Depletion forces induce nematic and smectic-like ordering of nanorods.

The resulting composites exhibit polarization-dependent photon upconversion.

The method enables new applications of anisotropic nanoparticles in structured materials.

Abstract

Monodisperse rod-like colloidal particles are known for spontaneously forming both nematic and smectic liquid crystal phases, but their self-assembly was typically exploited from the fundamental soft condensed matter physics perspective. Here we demonstrate that depletion interactions, driven by non-adsorbing polymers like dextran and surfactants, can be used to enrich self-organization of photon-upconversion nanorods into orientationally ordered nematic and smectic-like membrane colloidal superstructures. We study thermodynamic phase diagrams and demonstrate polarization-dependent photon upconversion exhibited by the ensuing composites, which arises from the superposition of unique properties of the solid nanostructures and the long-range ordering enabled by liquid crystalline self-organization. Finally, we discuss how our method of utilizing self-assembly due to the steric and electrostatic interactions, along with attractive depletion forces, can enable technological uses of lyotropic colloidal liquid crystals and mesostructured composite materials enabled by them, even when they are formed by anisotropic nanoparticles with relatively small aspect ratios.