Self-assembled nanoparticle micro-shells templated by liquid crystal sorting

Abstract

A current goal in nanotechnology focuses on the assembly of different nanoparticle types into 3D organized structures. In this paper we report the use of a liquid crystal host phase in a new process for the generation of micron-scale vesicle-like nanoparticle shells stabilized by ligand-ligand interactions. The constructs formed consist of a robust, thin spherical layer, composed of closely packed quantum dots (QDs) and stabilized by local crystallization of the mesogenic ligands. Ligand structure can be tuned to vary QD packing within the shell and made UV cross-linkable to allow for intact shell extraction into toluene. The assembly method we describe could be extended to other nanoparticle types (metallic, magnetic etc.), where hollow shell formation is controlled by thermally sorting mesogen-functionalized nanoparticles in a liquid crystalline host material at the isotropic to nematic transition. This process represents a versatile method for making non-planar 3D nano-assemblies.

Quantum Dot/Liquid Crystal Nanocomposites in Photonic Devices

“…One of the most apparent differences here seen in the optical microscopy is that at this concentration (0.1 wt%), the ODA-QD mixture exhibits much larger aggregates in the cholesteric liquid crystal (CLC) whereas the LC-QDs produce small but also distinct aggregates. This result is consistent with prior results [13,14] in which the nematic phase transition acts to assemble the included nanoparticles into templated structures at the phase transition. At 0.1 wt% and above, we expect aggregate formation for both of these particle types [18].…”

“…The mesogenic ligands may act to stabilize these structures (Figure 4) providing a mechanism to create hierarchical composite materials. Recently, our group developed a new methodology to assemble large-scale QD structures using the particles' spatial distribution across the nematic to isotopic phase transition [13,14]. Figure 4a,b shows a fluorescence image of QD "vesicles" or micro-shells stabilized by this process in which the particles are densely packed with an average separation of ~11 nm [14].…”

“…Recently, our group developed a new methodology to assemble large-scale QD structures using the particles' spatial distribution across the nematic to isotopic phase transition [13,14]. Figure 4a,b shows a fluorescence image of QD "vesicles" or micro-shells stabilized by this process in which the particles are densely packed with an average separation of ~11 nm [14]. Quantum dot membranes an also be prepared by a similar process (Figure 4c) in which the nanoparticles are stabilized in an interfacially templated assembly.…”

“…Such results support recent observations of lasing in a Transmission similar device with very high QD content (up to 8 wt%) [21] in which aggregation and non-uniform QD distribution is likely. We propose that controllably assembled QD aggregates such as the QD shells [14] and membranes shown in Figure 3 may find application in photonic devices, provided the host phase alignment is not significantly disrupted by the embedded emitting structures.…”

“…We will discuss our approaches to producing liquid crystal-based materials with defined nanoparticle distributions, focusing specifically on quantum dots owing to their unique size-tunable luminescent properties. Nanoparticle ligands can be designed to respond to the ordered molecular environment of a liquid crystal phase, inducing dispersion [12], clustering [13] or assembly at the interface of a liquid crystal phase transition [14]. These techniques can provide easily scalable methods for producing a rich variety of quantum dot and nanoparticles assemblies.…”