Reversible switching of structural and plasmonic properties of liquid-crystalline gold nanoparticle assemblies

Abstract

Hybrid materials built of spherical gold nanoparticles with three different sizes covered with (pro)mesogenic molecules have been prepared. Small-angle X-ray diffraction studies showed that after thermal annealing most of the obtained materials formed long-range ordered assemblies. Variation of the (pro)mesogenic ligand architecture enabled us to achieve a switchable material, which could be reversibly reconfigured between 3D long-range ordered structures with tetragonal and face centred cubic symmetries. This structural reconfiguration induces changes to the plasmonic response of the material. This work demonstrates that it is possible to use LC-based self-assembling phenomena to prepare dynamic materials with structural properties important for the development of active plasmonic metamaterials.

Size-Dependent Thermo- and Photoresponsive Plasmonic Properties of Liquid Crystalline Gold Nanoparticles

“…[39]), and 5 nm diameter Au nanocrystal cores, various phases and phase transition temperatures are observed. The overall tendency is that the larger the nanocrystal core, the higher temperatures are required to observe reconfiguration of anisotropic aggregates of NPs into short-range or close-packed structures, in analogy to some of the previously reported LC NP systems [43,50]. These observations are consistent with the fact that increasing the size of nanocrystals translates to a larger volume fraction of Au; this, in turn, increases van der Waals interactions between nanocrystals and density of the material.…”

“…As expected from XRD results, there was almost no shift observed for nanoparticles at 25 • C after UV irradiation, as no clear structural changes occur under these conditions. Based on our previous work, we know that if a sample of liquid-crystal-like ligand coated nanoparticles exhibits reversible switching of the structure, the reversible switching of the plasmonic band maxima is also observed [39,43,51].…”

“…It is crucial given that the deformation of the nanoparticles' shape is required for anisotropic self-assembly. In this regard, it should be mentioned, that most of the up-to-date reports on liquid-crystalline phases made of nanoparticles require narrowing the size distribution of nanoparticles (often below 10%) through size-exclusive purification methods [36,39,42,43]. Consequently, the final synthetic yields are relatively low.…”

Gold Nanoparticles Thin Films with Thermo‐ and Photoresponsive Plasmonic Properties Realized with Liquid‐Crystalline Ligands

“…Covering the surface of nanoparticles with properly designed LC ligands yields systems able to form nematic, smectic, and complex 3D structures. [23][24][25][26][27] It was shown that the melting of LC affects the plasmonic properties of the material (i.e., causes the shift of SPR wavelength), therefore significant effort was directed at controlling the organization of nanoparticles by temperature. [18] However, obtaining fast-reacting or remotely controlled materials require use of stimuli other than temperature.…”

Liquid‐Crystalline Elastomers with Gold Nanoparticle Cross‐Linkers

“…[10] The NPs vibrate in an oscillating magnetic field, and dissipation of thermal energy causes heat-inducedi sotropization of the hybrid LCE. [18] The future photonic applications of these systemsr equirem echanical stability andr etention of liquid-crystalline behavior, so the introduction of this type of nanoparticles to polymers exhibitingaliquid-crystal state is crucial toa chieving this goal. As imilar method has been presented by Schmidt, Finkelmann et al [11] In most cases the hybrid materials are obtained by incorporating NPs into the oligomerm ixture before the polymerization step or by swelling of LCE with as olution of nanoparticles.…”