Nanoconfinement of guest materials by helical nanofilament networks of bent-core mesogens

Abstract

The helical nanofilament (HNF) liquid crystal phase is a complex, hierarchical self-assembly in which bentcore molecules cooled from the isotropic melt form dense periodic arrays of nanoscale filaments of twisted smectic layers, a structure driven by an inherent tendency of the layers to be locally saddle-splayed. Here we report the results of a study of mixtures of an HNF-forming bent-core liquid crystal with a variety of organic guest molecules, showing that the high temperature, isotropic phase is completely mixed but that upon cooling the filaments form and grow, expelling the guest material from their internal volume. The nanofilaments form a network which acts as a porous nanoconfinement medium of large internal area ($100 m 2 cm À3 ), with the guest material confined to nanoscale interstitial volumes between the filaments. Such helical nanofilament networks represent a robust platform for potential applications in chiral separations, asymmetric synthesis, and photonic metamaterials.

A Dual Modulated Homochiral Helical Nanofilament Phase with Local Columnar Ordering Formed by Bent Core Liquid Crystals: Effects of Molecular Chirality

“…Concerning their practical applications, HNFs are being investigated as potential photovoltaic materials and for chiral recognition due to their capacity to serve as porous nanotemplates with chiral surfaces that can host materials, such as low molecular weight LCs, LC polymers, conducting polymers, and fullerene derivatives such as PCBM (phenyl‐C61‐butyric acid methyl ester, an n‐type semiconductor) . These examples show how the self‐assembled, chirality‐preserving 3D porous network of the HNF phase can be used to organize guest materials, by locally expelling and confining guest molecules.…”

Diastereomeric liquid crystal domains at the mesoscale

“…13, indicate that guest nematic order extends over 475% of the available volume. As the nematic order is filling the guest volume, the distribution of pore sizes P(p) in the HNF network, ranging from HNFs in contact to those spaced by hundreds of nanometres 40 , must be taken into account. Filamentary networks typically have lognormal pore size distributions with extended tails for larger pore sizes 63 , visible up to the micron scale in the FFTEM of mixtures 42 .…”

“…1f) that is completely homochiral, that is, every HNF grown in a given domain has the same handedness 45,46 . In each chiral domain, the guest material is nanoconfined to the pores of the HNF network, which has a large surface-area-to-volume ratio (B100 m 2 cm À 3 , comparable to aerogel) 40,41 . This geometry suggests that HNF networks might be useful in chiral separations or catalysis 47 , if the appropriate chemical distinctions can be exhibited by the HNF surface.…”

Dark conglomerate phases of bent-core liquid crystals

“…Chirality tuning in an achiral system by applying electric field of different strengths and frequencies is important for the applications in chiro-optical and nonlinear optics devices. In addition, the DC phases having the helical nanofilament structures represents interesting materials for a variety of other optoelectronic applications, such as organic semiconductors, thin-film transistors and solar cells [57,58] as thin-film polarizers [59] as nonlinear optical materials [60], for the detection and amplification of chirality [61,62] and for separation of enantiomers and enantioselective synthesis [63].…”