Brian R. Wiesenauer

Scalable fabrication of polymer membranes with vertically aligned 1 nm pores by magnetic field directed self-Assembly

There is long-standing interest in developing membranes possessing uniform pores with dimensions in the range of 1 nm and physical continuity in the macroscopic transport direction to meet the needs of challenging small molecule and ionic separations. Here we report facile, scalabe fabrication of polymer membranes with vertically (i.e., along the through-plane direction) aligned 1 nm pores by magnetic-field alignment and subsequent cross-linking of a liquid crystalline mesophase. We utilize a wedge-shaped amphiphilic species as the building block of a thermotropic columnar mesophase with 1 nm ionic nanochannels, and leverage the magnetic anisotropy of the amphiphile to control the alignment of these pores with a magnetic field. In situ X-ray scattering and subsequent optical microscopy reveal the formation of highly ordered nanostructured mesophases and cross-linked polymer films with orientational order parameters of ca. 0.95. High-resolution transmission electron microscopy (TEM) imaging provides direct visualization of long-range persistence of vertically aligned, hexagonally packed nanopores in unprecedented detail, demonstrating high-fidelity retention of structure and alignment after photo-cross-linking. Ionic conductivity measurements on the aligned membranes show a remarkable 85-fold enhancement of conductivity over nonaligned samples. These results provide a path to achieving the large area control of morphology and related enhancement of properties required for high-performance membranes and other applications.

Thermotropic liquid crystal behaviour of gemini imidazolium-based ionic amphiphiles

Thermotropic ionic liquid crystals (LCs) are useful for a number of applications such as anisotropic ion transport and as organised reaction media/solvents because of their ordered fluid properties and intrinsic charge units. A large number of different ionic LC architectures are known, but only a handful of examples of gemini (i.e. paired or dimeric) ionic LCs have been prepared and studied. In this work, a series of 20 new symmetric, imidazolium-based, gemini cationic LCs containing two bridged imidazolium cations and two pendant alkyl chains was synthesised, and the thermotropic LC behaviours were characterised. The imidazolium unit provides a highly tunable and modular platform for the design and synthesis of gemini cationic LCs which offers excellent structure control. As expected, the thermotropic LC properties of these new amphilphilic, gemini ionic LCs were found to be strongly influenced by the length of the spacer between the imidazolium units, the length of the pendant alkyl tails, and the nature of the anion. Smectic A (SmA) thermotropic LC phases were observed in more than half of the gemini imidazolium LC systems studied.

Thin Polymer Films with Continuous Vertically Aligned 1 nm Pores Fabricated by Soft Confinement

Membrane separations are critically important in areas ranging from health care and analytical chemistry to bioprocessing and water purification. An ideal nanoporous membrane would consist of a thin film with physically continuous and vertically aligned nanopores and would display a narrow distribution of pore sizes. However, the current state of the art departs considerably from this ideal and is beset by intrinsic trade-offs between permeability and selectivity. We demonstrate an effective and scalable method to fabricate polymer films with ideal membrane morphologies consisting of submicron thickness films with physically continuous and vertically aligned 1 nm pores. The approach is based on soft confinement to control the orientation of a cross-linkable mesophase in which the pores are produced by self-assembly. The scalability, exceptional ease of fabrication, and potential to create a new class of nanofiltration membranes stand out as compelling aspects.

New ionic organic compounds containing a linear tris(imidazolium) core and their thermotropic liquid crystal behaviour

Imidazolium-containing thermotropic ionic liquid crystals (TILCs) are of interest because of their structural similarity to imidazolium-based ionic liquids (ILs), allowing them to exhibit some IL-like properties in addition to the LC order. More imidazolium units are important for increasing the IL character; however, the effect of multiple imidazolium units on LC behaviour is not well known. Most reported imidazolium TILCs contain one imidazolium unit; only a handful containing multiple imidazolium units is known. The only examples of TILCs with multiple imidazolium units sequentially linked with a flexible spacer are based on an alkyl- or oligo(ethylene oxide)-bridged bis(imidazolium) core with an n-alkyl tail at each end. Herein, a series of 10 new symmetric compounds containing three hexyl-bridged imidazolium bromide units as the core and two terminal n-alkyl chains was synthesised and analysed. Thermotropic LC phases were generally not observed for homologues with even-numbered tails less than 16 carbons. However, after initial annealing, the homologues containing 16-, 18- and 20-carbon tails, all form a smectic A phase in the 25–137°C range, with the latter two also forming a higher-order smectic phase. This indicates that with sufficiently long n-alkyl tails to counterbalance the poly(ion) core, these tris(imidazolium) salts can exhibit thermotropic mesomorphism.

Design of Functionalized Room-Temperature Ionic Liquid-Based Materials for CO2 Separations and Selective Blocking of Hazardous Chemical Vapors

The design and synthesis of several new types of functionalized room-temperature ionic liquids (RTILs), ionic polymers based on RTILs (i.e., poly(RTIL)s), poly(RTIL)-RTIL solid-liquid composites, and gelled RTIL systems for gas separations and reactive vapor transport applications are presented. The design concepts behind these new RTIL materials are discussed in the context of first, CO2 removal from CH4 and N2 for natural gas purification and greenhouse gas reduction, respectively; and second selective blocking or sorption of chemical warfare agent simulant and toxic industrial compound vapors from water vapor for protection applications. The role of the RTIL components and their unique properties in these two separations areas will be highlighted.