Yi Yang’s research while affiliated with Arizona State University and other places

Water reclamation in spaceflight applications, such as those encountered on the International Space Station (ISS), requires complex engineering solutions to ensure maximum water recovery. Current vapor compression distillation (VCD) technologies are effective but produce highly concentrated brines and often cause scaling within a separation system. This work evaluates initial steps toward integrating pervaporation, a membrane separation process, as a brine management strategy for ISS wastewaters. Pervaporation performs separations driven by a chemical potential difference across the membrane created by either a sweep gas or a vacuum pull. Pervaporation membranes, as with most membrane processes, can be subject to scaling. Therefore, this work studies the anti-scaling properties of zwitterions (polymeric molecules with covalently tethered positive and negative ions) coated onto sulfonated pentablock terpolymer block polymer (Nexar) pervaporation membrane surfaces. We report a method for applying zwitterions to the surface of pervaporation membranes and the effect on performance parameters such as flux and scaling resistance. Membranes with zwitterions had up to 53% reduction in permeance but reduced scaling. The highest amount of scaling occurred in the samples exposed to calcium chloride, and uncoated membranes had weight percent increases as high as 1617 ± 241%, whereas zwitterion-coated membranes experienced only about 317 ± 87% weight increase in the presence of the same scalant.

Charge-containing polymeric materials have been widely studied for a range of applications. The fundamental relationships between the charge species, charge density, and the microscale morphology of charge-containing polymers are critical for defining the application in which they may be used. In this work, a series of thermoplastic poly(arylene ether sulfone) (PAES) copolymers with controllable sulfobetaine charge contents (0–100 mol%) and high molecular weights (Mw ∼ 65 kDa) were prepared. All the zwitterionic PAESs synthesized showed thermal stability up to 250 °C. DSC and tensile tests showed a decreased Tg and mechanical strength with the incorporation of increasing charge density, which suggests a plasticization effect by the charged group. Electron microscopy and X-ray scattering data confirmed the absence of microphase separation in the ion-containing random copolymer system, which corroborated with the observation of a single Tg for all zwitterionic copolymers studied. Furthermore, the relative hydrophilicity of the samples was evaluated by water uptake measurements, which revealed that the water uptake of the zwitterionic PAESs can reach up to 64% for the 72 mol% zwitterion copolymer while the free-standing film in the wet state still maintains a Young's modulus of 185 MPa. The thermoplastic charge-containing copolymers in this work demonstrated potential for applications such as coatings or water purification membranes, in which balancing hydrophilicity, processibility, and thermomechanical performance are important.

Aryl chlorides (ArCl) or aryl fluorides (ArF) were used in polycondensation reactions to form poly(arylene ether sulfone)s (PAES). Interestingly, the kinetics of the ArF reaction fit a third-order rate law, which is attributed to the activation of the carbon-fluorine bond by two potassium cations (at least one bound to phenolate), which form a three-body complex. The ArCl monomer follows a second-order rate law, where a two-body complex forms at the initial state of the aromatic nucleophilic substitution (SNAr) pathway. These metal cation-activated complexes act as intermediates during the attack by the nucleophile. This finding was reproduced with either the potassium or the sodium counterion (introduced via potassium carbonate or sodium carbonate). Through a combination of experimental analysis of reaction kinetics and computational calculations with density functional theory (DFT) methods, the present work extends the fundamental understanding of pol-ycondensation mechanisms for two aryl halides and highlights the importance of the CX–metal interac-tion(s) in the SNAr reaction, which is translational to other ion-activated substitution reactions.

Pervaporation desalination has several advantages over competing desalination technologies, most notably an ability to select for or against volatile organic compounds and the ability to process high salinity feeds at a low transmembrane pressure. Pervaporation has not been commercialized for desalination applications because of its energy intensity. However, emerging processes such as hydraulic fracturing produce high total dissolved solids (>30–45 g/L) byproduct streams that exceed the operational limits of traditional reverse osmosis and could be treated by pervaporation. Here, we demonstrate free-standing pervaporation membranes with excellent permeance and high salt removal based on a partially sulfonated pentablock terpolymer with the tradename Nexar™. Pervaporation membranes were easily cast from this material with desalination performances comparable or superior to commercially available membranes. We found that the polymer degree of sulfonation and casting solvent polarity had a significant impact on the membranes’ water uptake but only a modest impact on the pervaporation desalination performance. Membranes with a degree of sulfonation of 52% (2.0 meq/g IEC) and a casting solution composed of 50 wt% n-propanol and 50 wt% toluene achieved a water flux of 3.32 kg m⁻² h⁻¹ (permeance 135 kg m⁻² h⁻¹ bar⁻¹) with 99.5% salt removal in pervaporation from a 32 g/L sodium chloride feed solution at room temperature. We demonstrated that dense, non-porous Nexar™ pervaporation membrane permeance and salt separation performance were superior to commercial pervaporation membranes and equivalent to commercial membrane distillation membranes, which have much larger pores. This study demonstrates that commercially available sulfonated pentablock terpolymers are excellent membranes for pervaporation desalination because of their ease of casting and excellent performance.

Metabolites control immune cell functions, and delivery of these metabolites in a sustained manner may be able to modulate function of the immune cells . In this study, alpha-ketoglutarate (aKG) and diol based polymeric-microparticles (termed paKG MPs) were synthesized to provide sustained release of aKG and promote an immunosuppressive cellular phenotype. Notably, after association with dendritic cells (DCs), paKG MPs modulated the intracellular metabolic-profile/pathways, and decreased glycolysis and mitochondrial respiration in vitro. These metabolic changes resulted in modulation of MHC-II, CD86 expression in DCs, and altered the frequency of regulatory T cells (Tregs), and T-helper type-1/2/17 cells in vitro. This unique strategy of intracellular delivery of key-metabolites in a sustaine manner provide a paradigm-shift in the immunometabolism field-based immunotherapy with applications in different diseases associated with immune disorders.

Photo-curable nanocomposites have tremendous potential in tissue engineering, advanced manufacturing, and structural, multifunctional materials. This project investigates the effect of silica (SiO2) nanoparticle loading content on the thermal, mechanical, physical, and morphological characteristics of the nanocomposite. An increased concentration of SiO2 nanoparticles causes a decrease in the gel fraction of the nanocomposite, which at low nanoparticle loading degrades the thermal and mechanical properties. However, further addition (>3.8 wt%) causes an increase in Tg, Young’s modulus, and ultimate compressive strength. The addition of the nanoparticles had no significant effect on the hydrophilicity according to water uptake experiments. Small-angle X-ray scattering experiments, in conjunction with SEM and TEM indicated a multimodal particle size distribution and the presence of large-scale aggregates.

Zwitterionic polymers have drawn significant attention for membrane-based separations due to their impressive hydrophilicity and antifouling properties. Here we demonstrated a novel synthesis method to prepare an amphiphilic copolymer poly(arylene ether sulfone-co-sulfobetaine arylene ether sulfone) (PAES-co-SBAES), which was blended with native polysulfone (PSf) to prepare free standing membranes. The polymer chemical structures were analyzed by ¹H NMR spectroscopy and the molecular weight of polymers was identified by size exclusion chromatography (SEC). The PSf/PAES-co-SBAES blend membranes with various zwitterionic SBAES segment contents were fabricated via the non-solvent induced phase separation (NIPS) process. The membrane composition, surface morphology (roughness), and surface hydrophilicity were determined by fourier transform infrared (FT-IR) spectrum, atomic force microscopy (AFM), and water contact angle measurements, respectively. The cross-section morphology and surface hydrophilicity of the as-made membranes was analyzed by scanning electron microscopy (SEM) and water contact angle measurements, respectively. The results indicated that both the porosity of the support layer and surface hydrophilicity increased drastically due to the incorporation of hydrophilic SBAES segments. The water permeance and antifouling ability of the PSf/PAES-co-SBAES blend membranes were both remarkably improved to 2.5 L m⁻² h⁻¹ bar⁻¹ and 94% of flux recovery ratio, respectively, while salt rejection remained at a high level (98%) even under the high exposure to chlorine. This work provided a valuable and scalable strategy to fabricate desalination membranes via the introduction of zwitterionic segments in a rigid polysulfone matrix, and we predict that additional polymer optimization will drive the performance even higher.

Poly(vinyl chloride) (PVC) is one of the most common polymers used in the water treatment industry due to outstanding hydrophobicity and mechanical strength. Generating eco-friendly membranes derived from natural polymers has gained attention, particularly for water purification and producing potable water. In this study, nonwoven mats were prepared by electrospinning polymer solutions. Mats with a tailorable hydrophilicity were prepared by electrospinning solution mixtures containing PVC and an eco-friendly, hydrophilic natural polymer: soy protein. As the viscosity of the solution decreased, the average fiber diameter and average pore surface area reduced. However, when the PVC concentration remained constant and the soy protein concentration increased, the viscosity decreased and average fiber diameter became reduced, while the average pore diameter remained relatively constant. The mats with volumetric ratios of PVC:soy protein of 85:15 and 80:20 displayed optimal characteristics suitable for mat fabrication based on the fiber diameter and average pore surface area. This article is protected by copyright. All rights reserved.

Membranes prepared by electrospinning nonwoven mats have been receiving an increasing amount of interest recently with potential applications as water filtration membranes, drug delivery mats, and environmental sensors. Innovations in membrane processing and characteristics enabled by electrospinning could impact the industry. In this investigation, we demonstrate the effects of changing the chain length of an α,ω-bis(2-carboxymethyl)poly(ethylene glycol) (PEG diacid) crosslinker on the physical properties of electrospun poly(vinyl alcohol) (PVA) nanofibrous mats. Analysis of as-spun PVA mats showed average fiber diameters of 0.13 ± 0.02 μm with average pore areas of 1.67 ± 0.51 μm². Average fiber diameters for mats crosslinked with a shorter PEG diacid (Mn = 250) were 0.20 ± 0.04 μm with average pore areas of 0.64 ± 0.18 μm². Similarly, mats crosslinked with a longer PEG diacid (Mn = 600) had average fiber diameters of 0.22 ± 0.04 μm with average pore areas of 0.44 ± 0.23 μm². Further studies on the durability of the mats showed dramatic improvements in the Young's modulus, the stress at break, and the strain at break that increased with the length of the crosslinker. Developing further knowledge regarding the enhancement and control of electrospun membranes can help improve the field of electrospun membrane with great potential for water purification and can reveal new opportunities for existing technologies moving forward.