Abstract:The thermodynamic and surface properties of four structurally related thermotropic liquid crystals (LC) were investigated to understand their organization at gas-liquid and gas-solid interfaces. In this study, LC with a benzoyloxy azobenzene mesogenic core substituted with heptyloxy and/or dioxyethylene ether groups were used. The propensity of the LC to form self-assembled multilayers was demonstrated in the films spread at the air/aqueous interface using the Langmuir technique and Brewster angle microscopy a… Show more
“…The reversible formation of well defined single, triple, and even thicker multilayers by compression of monolayers was also reported for amphiphilic liquid crystals with a polar group at only one end, and incorporated rodlike105–110 or disclike anisometric units 111. For these compounds, a predominately vertical or tilted alignment of the rigid cores was observed, whereas bolaamphiphiles with polar groups at both ends adopt the side‐on arrangement in monolayers 112.…”
Section: Self‐assembly Of T‐shaped and X‐shaped Polyphiles At Intesupporting
of the original manuscript:Ungar, G.; Tschierske, C.; Abetz, V.; Holyst, R.; Bates, M.A.; Lui, F.; Prehm, M.; Kieffer, R.; Zeng, X.; Walker, M.; Glettner, B.; Zywocinski, A.: Keywords: columnar liquid crystals, polygonal honeycombs, polyphiles, miktoarm star terpolymers, simulation, Langmuir films, rod-coil molecules, surface alignment Abstract: This article reviews the diversity of phase morphologies observed recently in starbranched liquid crystalline and polymeric compounds containing at least three immiscible segments. Bolaamphiphiles and facial amphiphiles with a rod-like aromatic core, two endgroups and one (T-shape) or two chains (X-shape) attached laterally to the core form numerous honeycomb-like liquid crystal phases, as well as a variety of novel lamellar and 3D-ordered mesophases. Molecular self-organization is described in bulk phases and in thin films on solid and liquid surfaces, as well as in Langmuir-Blodgett films. The remarkably reversible formation of mono-and tri-layer films is highlighted. In the bulk, T-shaped "rod-coil" molecules without the appended end-groups form predominantly lamellar phases if the core is a straight rod, but the bent-core variety forms hexagonal honeycombs. Furthermore, selfassembly of "Janus"-type molecules, such as those with Y-shaped star mesogens bearing different mutually incompatible side-groups, is discussed. Also covered is the diversity of morphologies observed in miktoarm star terpolymers i.e. polymers with three different and 3 incompatible arms of well-defined lengths. A range of bulk phases with 3D or 2D order are observed, combining layers, cylinders and cocontinuous networks. Similarities and differences are highlighted between the liquid crystal morphologies on the 3-15 nm scale and the polymer morphologies on the scale 10-100 nm. A separate section is dedicated to computer simulations of such systems, particularly those using dissipative particle and molecular dynamics. Of special interest are the recently synthesised X-shaped tetraphilic molecules, where two different and incompatible side-chains are attached at opposite sides of the rod-like core. The tendency for their phase separation produces LC honeycombs with cells of different compositions that can be represented as paving a plane with different color tiles.
Self-Assembly at Different Length Scales: Polyphilic StarBranched Liquid Crystals and Miktoarm Star CopolymersThe independent variation of chain length and "color" creates the potential for developing a considerable range of complex new 2d-and 3d soft nanostructures. Analogous X-shaped rodcoil compounds with unequal side groups are also of considerable interest, forming tubular lyotropic structures capable of confining strings of guest molecules.
“…The reversible formation of well defined single, triple, and even thicker multilayers by compression of monolayers was also reported for amphiphilic liquid crystals with a polar group at only one end, and incorporated rodlike105–110 or disclike anisometric units 111. For these compounds, a predominately vertical or tilted alignment of the rigid cores was observed, whereas bolaamphiphiles with polar groups at both ends adopt the side‐on arrangement in monolayers 112.…”
Section: Self‐assembly Of T‐shaped and X‐shaped Polyphiles At Intesupporting
of the original manuscript:Ungar, G.; Tschierske, C.; Abetz, V.; Holyst, R.; Bates, M.A.; Lui, F.; Prehm, M.; Kieffer, R.; Zeng, X.; Walker, M.; Glettner, B.; Zywocinski, A.: Keywords: columnar liquid crystals, polygonal honeycombs, polyphiles, miktoarm star terpolymers, simulation, Langmuir films, rod-coil molecules, surface alignment Abstract: This article reviews the diversity of phase morphologies observed recently in starbranched liquid crystalline and polymeric compounds containing at least three immiscible segments. Bolaamphiphiles and facial amphiphiles with a rod-like aromatic core, two endgroups and one (T-shape) or two chains (X-shape) attached laterally to the core form numerous honeycomb-like liquid crystal phases, as well as a variety of novel lamellar and 3D-ordered mesophases. Molecular self-organization is described in bulk phases and in thin films on solid and liquid surfaces, as well as in Langmuir-Blodgett films. The remarkably reversible formation of mono-and tri-layer films is highlighted. In the bulk, T-shaped "rod-coil" molecules without the appended end-groups form predominantly lamellar phases if the core is a straight rod, but the bent-core variety forms hexagonal honeycombs. Furthermore, selfassembly of "Janus"-type molecules, such as those with Y-shaped star mesogens bearing different mutually incompatible side-groups, is discussed. Also covered is the diversity of morphologies observed in miktoarm star terpolymers i.e. polymers with three different and 3 incompatible arms of well-defined lengths. A range of bulk phases with 3D or 2D order are observed, combining layers, cylinders and cocontinuous networks. Similarities and differences are highlighted between the liquid crystal morphologies on the 3-15 nm scale and the polymer morphologies on the scale 10-100 nm. A separate section is dedicated to computer simulations of such systems, particularly those using dissipative particle and molecular dynamics. Of special interest are the recently synthesised X-shaped tetraphilic molecules, where two different and incompatible side-chains are attached at opposite sides of the rod-like core. The tendency for their phase separation produces LC honeycombs with cells of different compositions that can be represented as paving a plane with different color tiles.
Self-Assembly at Different Length Scales: Polyphilic StarBranched Liquid Crystals and Miktoarm Star CopolymersThe independent variation of chain length and "color" creates the potential for developing a considerable range of complex new 2d-and 3d soft nanostructures. Analogous X-shaped rodcoil compounds with unequal side groups are also of considerable interest, forming tubular lyotropic structures capable of confining strings of guest molecules.
“…Molecular integration using the Langmuir−Blodgett (LB) technique is a powerful tool for preparing organized molecular films with controlled molecular orientations. − Ordered monolayer films obtained by the LB method have been intensively studied for the development of electronic and optical molecular devices, molecular recognition, sensors, and surface-modification agents. , Proper molecular design of amphiphiles spread on water surfaces leads to the formation of a variety of monolayer structures (Figure ). − The monolayer formation of amphiphiles consisting of functional rodlike or disklike cores and aliphatic chains has been reported to give ordered 2D molecular assemblies with different orientations of the cores such as the side-by-side stacking of upright rods and an edge-on or face-on orientation of disks (Figure a). − In those monolayer films, alkyl chains cover the uppermost surfaces, and the functional cores are buried within the films or located in the aqueous phases. 1 Schematic illustration of monolayer structures: (a) monolayers of conventional amphiphiles with rodlike and disklike cores; (b) monolayer behavior of normal bolaamphiphiles; and (c) monolayer behavior expected for a bolaamphiphile used in the present study.…”
We designed and synthesized a new bolaamphiphile consisting of a biphenyl core, flexible trisiloxane spacers, and terminal ammonium groups. The compression of the trisiloxane-containing bolaamphiphile at the air-water interface led to the formation of monolayer films with the hydrophobic rigid core lying flat on the film surface. Such monolayer structures were formed through the compression-induced conformational change of the flexible bolaamphiphile from an extended state to a folded one as confirmed by surface pressure-area isotherm measurements, water contact angle measurements, atomic force microscopy, and UV-vis spectroscopy.
“…In the plateau region no further change of the dipole moment was observed, which supports the proposed model of molecular organization whereby in the plateau region a bilayer of antiparallel‐organized molecules (compensated dipole moments) is formed on top of the monolayer, leading to trilayer formation. For trilayer formation a reversible “rollover” mechanism (Figure 2, process B ) was proposed firstly for rodlike amphiphilic liquid crystals (aromatics perpendicular to or tilted relative to the surface)35–39 and then for T‐shaped facial amphiphiles40 that have an arrangement of rodlike aromatics parallel to the surface as also found for the bolaamphiphiles X1 – X4 . More recently, trilayer formation was also reported for semi‐perfluorinated hydrocarbons,17 amphiphiles with bulky aromatic end groups41 and for mixed monolayers formed by co‐assembly of cationic lipids with anionic porphyrins 42.…”
Synthetic anion transporters (SATs) of the general type (n-C18H37)2N-COCH2OCH2CO-(Gly)3-Pro-(Gly)3-O-n-C7H15, 1, are amphiphilic peptides that form anion-conducting pores in bilayer membranes. To better understand membrane insertion, assembly and aggregation dynamics, and membrane penetration, four novel fluorescent structures were prepared for use in both aqueous buffer and phospholipid bilayers. The fluorescent residues pyrene, indole, dansyl, and NBD were incorporated into 1 to give 2, 3, 4, and 5, respectively. Assembly of peptide amphiphiles in buffer was confirmed by monitoring changes in the pyrene monomer/excimer peaks observed for 2. Solvent-dependent fluorescence changes that were observed for indole (3) and dansyl (4) side-chained SATs in bilayers showed that these residues experienced an environment between epsilon=9 (CH2Cl2) and epsilon=24 (EtOH) in polarity. Fluorescence resonance energy transfer (FRET) between 2 and 3 demonstrated aggregation of SAT monomers within the bilayer. This self-assembly led to pore formation, which was detected as Cl(-) release from the liposomes. The results of acrylamide quenching of fluorescent SATs supported membrane insertion. Studies with NBD-labeled SAT 5 showed that peptide partition into the bilayer is relatively slow. Dithionite quenching of NBD-SATs suggests that the amphiphilic peptides are primarily in the bilayer's outer leaflet. Images obtained by using a fluorescence microscope revealed membrane localization of a fluorescent SAT. Taken together, this study helps define the insertion, membrane localization, and aggregation behavior of this family of synthetic anion transporters in liposomal bilayers.
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