Fluorinated Liquid Crystals: Design of Soft Nanostructures and Increased Complexity of Self-Assembly by Perfluorinated Segments

Abstract

The effects of perfluorinated and semiperfluorinated hydrocarbon units on the self-assembly of rod-like, disc-like, polycatenar, taper- and star-shaped, dendritic, and bent-core liquid crystalline (LC) materials is reviewed. The influence of fluorinated segments is analyzed on the basis of their contributions to the cohesive energy density, molecular shape, conformational flexibility, micro-segregation, space filling, and interface curvature. Though the focus is on recent progress in the last decade, previous main contributions, general aspects of perfluorinated organic molecules, and the basics of LC self-assembly are also briefly discussed to provide a complete overall picture. The main focus is on structure-property-relations and the use of micro-segregation to tailor mesophase morphologies. Especially polyphilic molecules with perfluorinated segments provide new modes of LC self-assembly, leading to ordered fluids with periodic multi-compartment structures and enhanced complexity compared to previously known systems.

Selected physicochemical aspects of poly- and perfluoroalkylated substances relevant to performance, environment and sustainability—Part one

“…The unique combination of high polarity, low polarisability, and steric and conformational effects of F-chains allows formation of liquid crystal phases with unique characteristic (Kirsch, 2006;Hird, 2007;Tschierske, 2012). F-alkyl segments stabilize all positionally ordered liquid-crystal phases, owing to reduced cohesive energy density, as compared to hydrocarbon segments.…”

“…F-chains provide insulating layers for separating charge carrier pathways, thus enhancing the efficiency of devices based on ion conduction or electron/hole transportation. Rod-like mesogens with short F-chains lead to de Vries phases and to 90°-tilted antiferroelectric smectic chiral phases that have potential for orthoconic switching in display applications (Tschierske, 2012). Fluorination also leads to enhanced polarisation in ferroelectric and antiferroelectric liquid-crystal phases.…”

“…Vesicles with bilayer membranes made from fluorinated phospholipids can resist sterilization, be less permeant, resist enzymatic hydrolysis and be less easily phagocytized then those made of hydrogenated analogues (Riess, 1994(Riess, , 1995Krafft, 2012a). Mesogens containing fluorinated chains form a wide range of liquid crystals (Kirsch, 2006;Krafft and Riess, 2009;Tschierske, 2012). Templates tailored from fluorosurfactants (Giulieri and Krafft, 1994).…”

“…F-alkyl segments stabilize all positionally ordered liquid-crystal phases, owing to reduced cohesive energy density, as compared to hydrocarbon segments. Polyphilic molecules with fluorinated segments form multilayered, coreshell structures and new types of liquid-crystals (Tschierske, 2012). F-chains provide insulating layers for separating charge carrier pathways, thus enhancing the efficiency of devices based on ion conduction or electron/hole transportation.…”

Effects of Lateral and Terminal Chains of X-Shaped Bolapolyphiles with Oligo(phenylene ethynylene) Cores on Self-Assembly Behaviour. Part 1: Transition between Amphiphilic and Polyphilic Self-Assembly in the Bulk

“…Enhanced mesophase stability is attributed to the segregation of the fluorinated segments from the non-fluorinated parts (RF), known to stabilize LC self-assembly [104][105][106]. This stronger segregation of RF compared to RH inhibits the mixing between lateral chains and the OPE rods, thus leaving only the possibility of lateral staggering of the OPE cores in the cylinder walls for reduction of the space in the triangular honeycombs (Figure 7c).…”