Engineering topics
Gin, Douglas L.
Publications and source records attributed to Gin, Douglas L..
110th Anniversary: The Dehydration and Loss of Ionic Conductivity in Anion Exchange Membranes Due to FeCl 4 – Ion Exchange and the Role of Membrane Microstructure
Anion-exchange membranes (AEMs) often dehydrate and lose ionic conductivity in ferric chloride solutions used in all-iron or iron–chromium redox flow batteries (RFB). In this work, the change in material and ionic transport properties of three AEMs with similar concentrations of ion exchange sites and hydration numbers (mol H 2 O/mol ion exchange site) upon exposure to ferric chloride/hydrochloric acid solutions were studied. Raman spectroscopy and iron sorption measurements show that FeCl 4 – occupies a fraction of the AEM ion exchange sites that depends on the ferric chloride concentration in the external solution. The AEM hydration number is linearly proportional to the amount of iron sorbed in the AEMs, suggesting that the displacement of the original hydrated Cl – counterions for unhydrated FeCl 4 – is the dominant mechanism for membrane dehydration. The ionic resistivity of the AEMs containing FeCl 4 – increased by as much as 4 orders of magnitude due to dehydration and, at high FeC l3 solution concentrations (≥1.4M), also due to nonideal solution effects. Although the three AEMs have similar ion exchange site concentrations, the AEM with the closer local spacing of ion exchange sites exhibits higher FeCl 4 – sorption, and a correspondingly greater dehydration and resistivity increase in dilute FeCl 3 solutions.
Thermoplastic elastomer hydrogels
Provided herein is a block copolymer hydrogel, comprising a glass formed from a dry blend of polystyrene-poly(ethylene oxide) diblock copolymer (SO) and polystyrene-poly(ethylene oxide)-polystyrene triblock copolymer (SOS) in a molar ratio from between 95:5 and 1:99 SO/SOS and a liquid medium at a concentration between about 32:1 and about 2:1 liquid medium/SO—SOS by weight. The block copolymer hydrogel has a fatigue resistance to at least 500,000 compression cycles. Also provided are methods for forming the hydrogel.
Evaluation of a nanoporous lyotropic liquid crystal polymer membrane for the treatment of hydraulic fracturing produced water via cross-flow filtration
Current commercial nanofiltration and reverse osmosis membranes are limited in scope and performance due to their physicochemical properties. Desalination of hydraulic fracturing wastewater poses a particular challenge to membrane filtration given the high concentrations of both organic compounds and salts present in these waters. The recently-developed nanoporous, bicontinuous cubic, lyotropic liquid crystal, thin-film-composite polymer membrane (TFC Q I membrane), having unique physicochemical properties, enables an alternative treatment of hydraulic fracturing wastewater. Specifically, the TFC Q I membrane recovers the organic compounds from this high-salinity wastewater, enabling biodegradation to occur after desalination. However, other performance criteria must be demonstrated for a membrane to reach application. The work presented herein demonstrates the stable performance of the TFC Q I membrane during 66 h of cross-flow filtration of hydraulic fracturing produced water. Compared to the commercial NF90 membrane, the TFC Q I membrane recovered a larger portion of the organic compounds, had a higher thickness-normalized water flux, and fouled less. Finally, the combination of the TFC Q I membrane's selectivity with its reduced fouling propensity makes possible a treatment for hydraulic fracturing wastewater and other complex aqueous streams inaccessible by most commercial membranes, motivating the further study and development of the TFC Q I membrane.
Self-assembly of highly asymmetric, poly(ionic liquid)-rich diblock copolymers and the effects of simple structural modification on phase behaviour
A series of thermally processable, phase-separating diblock copolymers made via sequential ATRP of styrene and styrenic ionic liquid (IL) monomers with various alkyl imidazolium substituents were synthesized to cover a wide range of volume fractions, most notably those on the IL-rich side of the phase diagram. Small-angle X-ray scattering (SAXS) analysis was used to confirm melt-state (and glassy state) phase behavior in which all four classic equilibrium diblock copolymer morphologies – body-centered cubic spheres (S BCC ), hexagonally packed cylinders (Hex), lamellae (Lam), and notably, bicontinuous gyroid (Gyr) – were observed. These PS-PIL diblock copolymers were found to have a high degree of conformational asymmetry and/or electrostatic cohesion within the PIL block, highlighted by the shift of the Lam phase window with boundaries falling between f PIL = 0.31 and 0.55. Finally, variation of the alkyl group appeared to influence the strength of the Flory-like interaction parameter of the system, χ PS/PIL , such that simple substitution of methyl by n-butyl on the imidazolium IL substituent resulted in the emergence of the (notoriously segregation-sensitive) Gyr phase, superseding the persistent coexistence of Lam and Hex in the methyl-substituted imidazolium diblock copolymer phase diagram.
Metal-containing ionic liquid-based, uncharged–charged diblock copolymers that form ordered, phase-separated microstructures and reversibly coordinate small protic molecules
A metal-containing ionic liquid-based, uncharged-charged block copolymer (BCP) system made via RAFT polymerization is presented. Small-angle X-ray scattering studies show these Co(II) bis(salicylate) anion-containing BCPs can form ordered microstructures (including a gyroid phase) in their neat states. Additionally, these BCPs can reversibly coordinate H 2 O or small alcohols with a noticeable color change.
Elastic free-standing RTIL composite membranes for CO2/N2 separation based on sphere-forming triblock/diblock copolymer blends
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