Smectic Liquid Crystalline Titanium Dioxide Nanorods: Reducing Attractions by Optimizing Ligand Density

Abstract

Crystalline titanium dioxide (TiO 2) semiconductor nanorods (NRs) feature several optical properties, such as birefringence combined with high refractive indexes and a wide bandgap precluding optical absorption in visible-light spectrum, making them attractive for many applications such as optoelectronics. Dispersing these NRs in suitable solvents creates inorganic liquid crystals (LCs) offering enhanced collective and orientation-dependent properties, which can additionally be utilized to manipulate optical behavior. Herein, a synthetic procedure from literature is scaled up and coupled with an important post-synthesis-treatment step such that self-assembled NRs dried onto a liquid interface and in bulk can be investigated. Comprehensive characterizations confirm the vital role of surface ligand density of the NRs in reducing the effects of attractions between them and thus increasing the range of volume fractions in which these dispersions can be exploited. Various symmetries (hexagonal or tetragonal) can be achieved in the smectic layers of NRs by tuning the aspect ratios of the NRs from 4.8 to 8.5. Experiments show that external fields such as shear flow or electric fields can easily either induce a reversible nematic order in isotropic dispersions or order existing LC phases over much longer regions, opening many opportunities to manipulate light for optical applications.

Heating-Induced Transformation of Anatase TiO2 Nanorods into Rock-Salt TiO Nanoparticles: Implications for Photocatalytic and Gas-Sensing Applications

“…3 corresponds to a lattice spacing of 2.90 Å, corresponding to the (211)-reflection of brookite. The DP of the specimens at 950 °C was also compared to the as-synthesized brookite NRs at 20 °C (synthesized with the same method as the previous work 27 ). From the comparison (shown in Figure S6 ), most of the rings in the DP of the specimen at 950 °C could be related to the corresponding rings in the DP of brookite, except for rings no.…”

“… 26 The anatase NRs investigated in this study are also proper candidates for serving as building blocks for liquid crystals due to their shape and orientation-dependent collective properties, which has been demonstrated already for brookite NRs. 27 The morphology, size, and crystal structure of the particles are directly related to their functional properties such as catalytic and (opto)electrical properties, determining the range of applicable operation temperatures. For applications in gas sensors and antibacterial coatings, the desired operation temperatures can be very high.…”

“… 39 , 40 Moreover, the shape of the particles could be also manipulated during synthesis. 18 , 27 , 41 It is also possible to enhance the adsorption properties of the nanocrystals (NCs) by exposing different facets. 34 , 42 The shape of the NC is therefore important to take into consideration during investigation of the phase stability of TiO 2 NCs.…”

Synthesis and Characterization of Anatase TiO2 Nanorods: Insights from Nanorods’ Formation and Self-Assembly

“…The TEM grids were further dried in a vacuum chamber to remove residuals and used for microscopy analysis. To examine liquid crystalline structures of self-assembled domains in bulk, a sedimentation experiment was performed as previously reported elsewhere [18,39]. Briefly, a glass capillary (0.1 × 1.0 × 60.0 mm 3 , Vitrocom) was filled with ligand-capped titania NRs dispersion with an initial volume fraction of 29.8 vol.%, effective length L = 27.6 nm, diameter D = 6.6 nm, and an aspect ratio of 4.18, in which the ligand length of 1.5 nm was taken into account.…”

“…We are interested in the unique intrinsic properties of crystalline titania NPs, such as high refractive indexes, wide bandgap, and strong UV absorption with no light absorption in the visible part of the spectrum. Additionally, we want to benefit from the shape and orientation-dependent collective properties of these inorganic NPs in liquid crystalline states for optical applications, as such nanorod (NR) liquid crystal phases can be switched at lower field strengths than molecular counterparts [18,19]. Thus, we focused on titania NRs as colloidal anisotropic building blocks to not only benefit from their spontaneous liquid crystal (LC) formation but also to gain other advantages over spherical titania counterparts in terms of high surface-to-volume ratio, improved number of delocalized carriers, and enhanced charge transport provided by their anisotropic geometry for relevant research in optoelectronics and photocatalysis [20,21].…”