Hunaid B. Nulwala

A Simple and Universal Gel Permeation Chromatography Technique for Precise Molecular Weight Characterization of Well-Defined Poly(ionic liquid)s

Poly(ionic liquid)s (PILs) are an important class of technologically relevant materials. However, characterization of well-defined polyionic materials remains a challenge. Herein, we have developed a simple and versatile gel permeation chromatography (GPC) methodology for molecular weight (MW) characterization of PILs with a variety of anions. PILs with narrow MW distributions were synthesized via atom transfer radical polymerization, and the MWs obtained from GPC were further confirmed via nuclear magnetic resonance end group analysis.

Fabrication of MMMs with improved gas separation properties using externally-functionalized MOF particles

Mixed matrix membranes (MMM) have the potential to overcome the limitations of traditional polymeric membranes for gas separation by improving both the permeability and selectivity. The most difficult challenge is accessing defect free and optimized MMM membranes. Defects are generally due to incompatible interfaces between the polymer and the filler particle. Herein, we present a new approach to modify and optimize the surface of UiO-66-NH2 based MOF particles to improve its interaction with Matrimid® polymer. A series of surface modified UiO-66-NH2 particles were synthesized and characterized using 1H NMR spectroscopy, mass spectrometry, XPS, and powder X-ray diffraction. MMMs containing surface optimized MOF particles exhibit improved thermal and mechanical properties. Most importantly, the MMMs show significantly enhanced gas separation properties; CO2 permeability was increased by ∼200% and CO2/N2 ideal selectivity was increased by ∼25%. These results confirm the success of the proposed technique to mitigate defective MOF/Matrimid® interfaces.

Copolymer-templated nitrogen-enriched porous nanocarbons for CO2 capture

Nitrogen-enriched porous carbon materials made via the carbonization of polyacrylonitrile containing block copolymer act as efficient and highly selective CO(2) sorbents. Nitrogen content and surface area, which are both influenced by pyrolysis temperature and atmosphere, are crucial for CO(2) adsorption performance.

Modular polymerized ionic liquid block copolymer membranes for CO2/N2 separation

The continuing discovery of broad classes of materials, such as ionic liquids, zeolites, metal–organic frameworks, and block copolymers, presents an enormous opportunity in developing materials for new applications. Polymerized ionic liquid block copolymers (PIL-BCPs) fall at the union of two already large sets of materials, and are an emerging class of materials useful in gas separation membranes, ion and electron conducting materials, and as mechanical actuators. A wide range of ionic liquid moieties can be used as pendant groups along the polymer backbone, potentially allowing for a wide variation in the resulting material properties; however in practice the range of ionic liquids explored is hindered by the need to optimize polymerization conditions for each new monomer. Here, we present a modular approach to PIL-BCP synthesis where a variety of olefin bearing cations are readily conjugated to polymers using thiol-Michael click chemistry. This approach allowed for the rapid development of a diverse material library including phase separated thin films, ion-gels, and liquid PIL-BCPs, with a reduced investment in synthetic time. Finally, we demonstrate that this approach identified PIL-BCPs with increased CO2 permeability relative to PILs, which could find use in carbon capture from flue gas.

Contribution of the Acetate Anion to CO2 Solubility in Ionic Liquids: Theoretical Method Development and Experimental Study

A new theoretical method was developed to compute the Henrys law constant for gas absorption in a solvent through strong nonphysical interactions. The new method was created by expanding the test particle insertion method typically applied to physisorbing systems to account for the strong intermolecular interactions present in chemisorbing systems. By using an ab initio (AI)-based Boltzmann-averaged potential to model the interaction between CO2 and the tetra-n-butylphosphonium acetate ([P4444][CH3COO]) ionic liquid, the total Henryss law constant at 298 K was computed to be 0.011 to 0.039 bar, reasonably comparable to the experimental value of 0.18 bar measured in this work. Three different AI potentials were used to verify the applicability of this approach. In contrast, when a classical force field (FF) was used to describe the interaction between CO2 and [P4444][CH3COO], the Henrys law constant was computed to be 27 bar, significantly larger than the experimental value. The classical FF underestimates the CO2-[P4444][CH3COO] interaction compared with the AI calculations, which in turn leads to the smaller simulated CO2 solubility. Simulations further indicate that the CO2 interaction with the [CH3COO](-) anion is much stronger than with the [P4444](+) cation. This result strongly suggests that the large CO2 solubility in [P4444][CH3COO] is due to the strong CO2-[CH3COO](-) interaction.

Nuclear Spin Relaxation and Molecular Interactions of a Novel Triazolium-Based Ionic Liquid

Nuclear spin relaxation, small-angle X-ray scattering (SAXS), and electrospray ionization mass spectrometry (ESI-MS) techniques are used to determine supramolecular arrangement of 3-methyl-1-octyl-4-phenyl-1H-triazol-1,2,3-ium bis(trifluoromethanesulfonyl)imide [OMPhTz][Tf2N], an example of a triazolium-based ionic liquid. The results obtained showed first-order thermodynamic dependence for nuclear spin relaxation of the anion. First-order relaxation dependence is interpreted as through-bond dipolar relaxation. Greater than first-order dependence was found in the aliphatic protons, aromatic carbons (including nearest neighbors), and carbons at the end of the aliphatic tail. Greater than first order thermodynamic dependence of spin relaxation rates is interpreted as relaxation resulting from at least one mechanism additional to through-bond dipolar relaxation. In rigid portions of the cation, an additional spin relaxation mechanism is attributed to anisotropic effects, while greater than first order thermodynamic dependence of the octyl side chains spin relaxation rates is attributed to cation-cation interactions. Little interaction between the anion and the cation was observed by spin relaxation studies or by ESI-MS. No extended supramolecular structure was observed in this study, which was further supported by MS and SAXS. nuclear Overhauser enhancement (NOE) factors are used in conjunction with spin-lattice relaxation time (T1) measurements to calculate rotational correlation times for C-H bonds (the time it takes for the vector represented by the bond between the two atoms to rotate by one radian). The rotational correlation times are used to represent segmental reorientation dynamics of the cation. A combination of techniques is used to determine the segmental interactions and dynamics of this example of a triazolium-based ionic liquid.

Probing the effect of electron donation on CO2 absorbing 1,2,3-triazolide ionic liquids

Development of the next generation materials for effective separation of gases is required to address various issues in energy and environmental applications. Ionic liquids (ILs) are among the most promising material types. To overcome the many hurdles in making a new class of materials technologically applicable, it is necessary to identify, access, and scale up a range of representative substances. In this work, CO2 reactive triazolide ILs were synthesized and characterized with the aim of developing a deeper understanding of how structural changes affect the overall properties of these substances. It was found that substituents on the anion play a crucial role in dictating the physical properties for CO2 capture. Depending upon the anion substituent, CO2 capacities between 0.07 and 0.4 mol CO2 per mol IL were observed. It was found that less sterically-hindered anions and anions containing electron donating groups were more reactive towards CO2. Detailed spectroscopic, CO2 absorption, rheological, and simulation studies were carried out to understand the nature and influence of these substituents. The effect of water content was also evaluated, and it was found that water had an unexpected impact on the properties of these materials, resulting in an increased viscosity, but little change in the CO2 reactivity.

Multifunctional photo-crosslinked polymeric ionic hydrogel films

A facile approach was developed to prepare crosslinked ionic polymer hydrogel films by photo-crosslinking utilizing p-vinylbenzyl trimethylammonium chloride (VBTMACl) or p-vinylbenzyl trimethylammonium hydroxide (VBTMAOH) as the monomer and poly(ethylene oxide) dimethacrylate (PEODMA, Mn = 750) as the crosslinker. The films with different crosslinking degrees (20%, 40%, 60%, 80%, and 100%) were prepared and characterized by swelling measurements, scanning electron microscopy (SEM), UV-visible spectroscopy, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and small-angle X-ray scattering (SAXS). It was found that the mechanical and thermal properties of the films were largely influenced by the contents of the crosslinker in the films. By ion-exchange of the anions in the films with various other anions, the hydrophobicity/hydrophilicity of the films was changed. In addition, fluorescent films were prepared by treatment with fluorescein, and paramagnetic films with FeCl4− as a counter anion showed catalytic activity for Friedel–Crafts alkylation. The ionic films with quaternary ammonium chloride groups displayed antimicrobial activity against Escherichia coli (E. coli) with almost 100% killing efficiency. Multifunctional films with various tunable properties have significant potential for a wide range of applications.

Toward a Materials Genome Approach for Ionic Liquids: Synthesis Guided by Ab Initio Property Maps

The Materials Genome Approach (MGA) aims to accelerate development of new materials by incorporating computational and data-driven approaches to reduce the cost of identification of optimal structures for a given application. Here, we use the MGA to guide the synthesis of triazolium-based ionic liquids (ILs). Our approach involves an IL property-mapping tool, which merges combinatorial structure enumeration, descriptor-based structure representation and sampling, and property prediction using molecular simulations. The simulated properties such as density, diffusivity, and gas solubility obtained for a selected set of representative ILs were used to build neural network models and map properties for all enumerated species. Herein, a family of ILs based on ca. 200,000 triazolium-based cations paired with the bis(trifluoromethanesulfonyl)amide anion was investigated using our MGA. Fourteen representative ILs spreading the entire range of predicted properties were subsequently synthesized and then characterized confirming the predicted density, diffusivity, and CO2 Henrys Law coefficient. Moreover, the property (CO2, CH4, and N2 solubility) trends associated with exchange of the bis(trifluoromethanesulfonyl)amide anion with one of 32 other anions were explored and quantified.

Cubosomes from hierarchical self-assembly of poly(ionic liquid) block copolymers.

Cubosomes are micro- and nanoparticles with a bicontinuous cubic two-phase structure, reported for the self-assembly of low molecular weight surfactants, for example, lipids, but rarely formed by polymers. These objects are characterized by a maximum continuous interface and high interface to volume ratio, which makes them promising candidates for efficient adsorbents and host-guest applications. Here we demonstrate self-assembly to nanoscale cuboidal particles with a bicontinuous cubic structure by amphiphilic poly(ionic liquid) diblock copolymers, poly(acrylic acid)-block-poly(4-vinylbenzyl)-3-butyl imidazolium bis(trifluoromethylsulfonyl)imide, in a mixture of tetrahydrofuran and water under optimized conditions. Structure determining parameters include polymer composition and concentration, temperature, and the variation of the solvent mixture. The formation of the cubosomes can be explained by the hierarchical interactions of the constituent components. The lattice structure of the block copolymers can be transferred to the shape of the particle as it is common for atomic and molecular faceted crystals.