3D interconnected ionic nano-channels formed in polymer films: self-organization and polymerization of thermotropic bicontinuous cubic liquid crystals

Humidity-modulated phase control and nanoscopic transport in supramolecular assemblies

Supramolecular assembly allows for enhanced control of bulk material properties through the fine modulation of intermolecular interactions. We present a comprehensive study of a cross-linkable amphiphilic wedge molecule based on a sulfonated trialkoxybenzene with a sodium counterion that forms liquid crystalline (LC) phases with ionic nanochannel structures. This compound exhibits drastic structural changes as a function of relative humidity (RH). Our combined structural, dynamical, and transport studies reveal deep and novel information on the coupling of water and wedge molecule transport to structural motifs, including the significant influence of domain boundaries within the material. Over a range of RH values, we employ (23)Na solid-state NMR on the counterions to complement detailed structural studies by grazing-incidence small-angle X-ray scattering. RH-dependent pulsed-field-gradient (PFG) NMR diffusion studies on both water and the wedge amphiphiles show multiple components, corresponding to species diffusing within LC domains as well as in the domain boundaries that compose 10% of the material. The rich transport and dynamical behaviors described here represent an important window into the world of supramolecular soft materials, carrying implications for optimization of these materials in many venues. Cubic phases present at high RH show fast transport of water (2 × 10(-10) m(2)/s), competitive with that observed in benchmark polymeric ion conductors. Understanding the self-assembly of these supramolecular building blocks shows promise for generating cross-linked membranes with fast ion conduction for applications such as next-generation batteries.

3D Anhydrous proton-transporting nanochannels formed by self-assembly of liquid crystals composed of a sulfobetaine and a sulfonic acid

Herein we describe anhydrous proton transportation through 3D interconnected pathways formed by self-assembled molecular complexes. A thermotropic bicontinuous cubic (Cub(bi)) phase has been successfully obtained by mixing a wedge-shaped sulfobetaine with benzenesulfonic acid in different ratios. These ionic complexes exhibit the Cub(bi) phase in a wide range of temperatures, while the single zwitterionic compound shows only a columnar hexagonal phase, and benzenesulfonic acid is nonmesomorphic. Anhydrous proton conduction on the order of 10(-4) S cm(-1) has been achieved for the mixture in the Cub(bi) phase over 100 °C, which can be useful for the development of new electrolytes for the next generation of fuel cells.

Cation modules as building blocks forming supramolecular assemblies with planar receptor-anion complexes

Ion-based materials were fabricated through ion pairing of planar receptor-anion complexes and cation modules as negatively and positively charged building blocks, respectively. Anion receptors that could not form soft materials by themselves provided mesophases upon anion binding and subsequent ion pairing with aliphatic cation modules. The mesogenic behaviors were affected by structural modification of both the cation module and the anion receptor. Synchrotron X-ray diffraction measurements suggested the formation of columnar mesophases with contributions from charge-by-charge and charge-segregated arrangements. Flash-photolysis time-resolved microwave conductivity measurements further revealed a higher charge-carrier mobility in the assembly with a large contribution from the charge-segregated arrangement than in the charge-by-charge-based assembly.

Structural transitions of CTAB micelles in a protic ionic liquid

Micellar solutions of hexadecyltrimethylammonium bromide (CTAB) in a protic ionic liquid, ethylammonium nitrate (EAN), are studied by shear rheology, polarizing optical microscopy (POM), conductivity measurements, and small angle neutron scattering (SANS). Three concentration regimes are examined: A dilute regime (with concentrations [CTAB] < 5 wt %) consisting of noninteracting spherical micelles, a semidilute regime (5 wt % ≤ [CTAB] ≤ 45 wt %) where micelles interact via electrostatic repulsions, and a concentrated regime (45 wt % < [CTAB] ≤ 62 wt %) where a reversible, temperature-dependent isotropic (L(1)) to hexatic (Hex) phase transition is observed. The L(1)-Hex transition, which has been predicted but not previously observed, is characterized by (1) a sharp increase in the shear viscosity, (2) the formation of focal conical birefringence textures (observed by POM), and (3) enhancement of the crystalline order, evidenced by the appearance of Bragg reflections in the SANS profiles. Ionic conductivity is not sensitive to the L(1)-Hex transition, which corroborates the absence of topological transitions.

Self-organized liquid-crystalline nanostructured membranes for water treatment: selective permeation of ions

A membrane with ordered 3D ionic nanochannels constructed by in situ photopolymerization of a thermotropic liquid-crystalline monomer shows high filtration performance and ion selectivity. The nanostructured membrane exhibits water-treatment performance superior to that of an amorphous membrane prepared from the isotropic melt of the monomer. Self-organized nanostructured membranes have great potential for supplying high-quality water.