Chemical and Biomolecular Engineering - Research Publications
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ItemNo Preview AvailableInfluence of Surfactant Structure on Polydisperse Formulations of Alkyl Ether Sulfates and Alkyl Amidopropyl Betaines(AMER CHEMICAL SOC, 2023-12-28)Surfactants provide detergency, foaming, and texture in personal care formulations, yet the micellization of typical industrial primary and cosurfactants is not well understood, particularly in light of the polydisperse nature of commercial surfactants. Synergistic interactions are hypothesized to drive the formation of elongated wormlike self-assemblies in these mixed surfactant systems. Small-angle neutron scattering, rheology, and pendant drop tensiometry are used to examine surface adsorption, viscoelasticity, and self-assembly structure for wormlike micellar formulations comprising cocoamidopropyl betaine, and its two major components laurylamidopropyl betaine and oleylamidopropyl betaine, with sodium alkyl ethoxy sulfates. The tail length of sodium alkyl ethoxy sulfates was related to their ability to form wormlike micelles in electrolyte solutions, indicating that a tail length greater than 10 carbons is required to form wormlike micelles in NaCl solutions, with the decyl homologue unable to form elongated micelles and maintaining a low viscosity even at 20 wt % surfactant loading with 4 wt % NaCl present. For these systems, the incorporation of a disperse ethoxylate linker does not enable shorter chain surfactants to elongate into wormlike micelles for single-component systems; however, it could increase the interactions between surfactants in mixed surfactant systems. For synergy in surfactant mixing, the nonideal regular solution theory is used to study the sulfate/betaine mixtures. Tail mismatch appears to drive lower critical micelle concentrations, although tail matching improves synergy with larger relative reductions in critical micelle concentrations and greater micelle elongation, as seen by both tensiometric and scattering measurements.
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ItemNo Preview AvailableCascaded compression of size distribution of nanopores in monolayer graphene(NATURE PORTFOLIO, 2023-11-30)Monolayer graphene with nanometre-scale pores, atomically thin thickness and remarkable mechanical properties provides wide-ranging opportunities for applications in ion and molecular separations1, energy storage2 and electronics3. Because the performance of these applications relies heavily on the size of the nanopores, it is desirable to design and engineer with precision a suitable nanopore size with narrow size distributions. However, conventional top-down processes often yield log-normal distributions with long tails, particularly at the sub-nanometre scale4. Moreover, the size distribution and density of the nanopores are often intrinsically intercorrelated, leading to a trade-off between the two that substantially limits their applications5-9. Here we report a cascaded compression approach to narrowing the size distribution of nanopores with left skewness and ultrasmall tail deviation, while keeping the density of nanopores increasing at each compression cycle. The formation of nanopores is split into many small steps, in each of which the size distribution of all the existing nanopores is compressed by a combination of shrinkage and expansion and, at the same time as expansion, a new batch of nanopores is created, leading to increased nanopore density by each cycle. As a result, high-density nanopores in monolayer graphene with a left-skewed, short-tail size distribution are obtained that show ultrafast and ångström-size-tunable selective transport of ions and molecules, breaking the limitation of the conventional log-normal size distribution9,10. This method allows for independent control of several metrics of the generated nanopores, including the density, mean diameter, standard deviation and skewness of the size distribution, which will lead to the next leap in nanotechnology.
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ItemNo Preview AvailableNucleation Rate of N2 and O2 in Cryogenic H2 and He(AMER CHEMICAL SOC, 2023-11-09)The homogeneous nucleation of N2 and O2 in cryogenic H2 and He is investigated by using classical molecular dynamics (MD) simulations. The nucleation kinetics of N2 and O2 clusters, including nucleation rate, critical cluster size, and cluster energy, are elucidated in H2 and He carrier gas at thermalization temperatures of 30-80 K and initial gas densities of 5.65 × 1024-2 × 1027 m-3. The energy released from the clusters during nucleation increases the system temperature by 77-138%, consistent with N2 nucleation experiments in supersonic nozzles and the mean-field kinetic nucleation theory. The nucleation rate derived by MD, Jsim, spans across 2.14 × 1029-5.25 × 1036 m-3 s-1 for both N2 and O2 under all conditions. The MD-obtained homogeneous nucleation rate is in agreement with predictions from the self-consistent classical nucleation theory (CNT) at low temperature (<70 K) but is 3-7 orders of magnitude faster than the CNT when temperature exceeds 70 K, consistent with the literature. Increasing temperature and decreasing concentration of the nucleating vapors leads to larger critical cluster sizes. The CNT underpredicts the critical cluster size at cryogenic temperatures below 60 K by 200-700%. The present MD methodology can be used for the direct determination of the nucleation rate and critical cluster size of N2 and O2 under cryogenic conditions, circumventing the assumptions inherent in CNT.
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ItemSurface analysis insight note: Differentiation methods applicable to noisy data for determination of sp2-versus sp3-hybridization of carbon allotropes and AES signal strengths(WILEY, 2023-03)The derivatives of the spectra are commonly used for quantification in Auger Electron Spectroscopy (AES) spectra, while the derivative of the KLL C Auger line has proven to be valuable in obtaining a measure of the relative proportions of sp2‐ and sp3‐hybridization using the D‐parameter in both AES and X‐ray Photoelectron Spectroscopy (XPS). Differentiation of X‐ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) spectra by numerical means is presented and illustrated for polymeric, such as PEEK and Nylon, as well as for graphitic materials including highly ordered pyrolytic graphite and graphene oxide. The most commonly available Savitzky–Golay method is explained mathematically and developed through the case of constructing a 5‐point quadratic polynomial convolution kernel suitable for differentiating spectra of adequate signal to noise. The concept of differentiation of spectra where signal to noise is less than adequate is also developed. Two alternative strategies to Savitzky–Golay differentiation are presented, which fit curves to data that allow derivatives to be obtained where Savitzky–Golay would otherwise fail. These alternative methods involve constructing a parametric curve that fits data over the entire energy interval of interest. Derivatives of spectra are then obtained by differentiating these parametric curves directly. A comparison of results for different materials for which specific sp2‐ vs sp3‐hybridized carbon proportions are of interest is used to emphasize the importance of characterizing methods used to differentiate spectra and understanding the characteristics of instrumentation used to measure spectra. The case for using Principal Component Analysis noise reduction with C KLL spectra is made for spectra collected from a heterogeneous graphene oxide sample.
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ItemAtomically Thin Synaptic Devices for Optoelectronic Neuromorphic Vision(Wiley, 2023)Imaging sensors with inbuilt processing capability are expected to form the backbone of low-latency and highly energy efficient artificial vision systems. A range of emerging atomically thin materials provide opportunities to exploit their electrical and optical properties for human vision and brain inspired functions. This work reports atomically thin nanosheets of β-In2S3 which exhibit inherent persistent photoconductivity (PPC) under ultraviolet and visible wavelengths. This PPC effect enables β-In2S3-based optoelectronic devices to optically mimic the dynamics of biological synapses. Based on the material characterizations, the PPC effect is attributed to the intrinsic defects in the synthesized β-In2S3 nanosheet. Furthermore, the feasibility of adopting these atomically thin synaptic devices for optoelectronic neuromorphic hardware is demonstrated by implementing a convolutional neural network for image classification. As such, the demonstrated atomically thin nanosheets and optoelectronic synaptic devices provide a platform for scaling up complex vision-sensory neural networks, which can find many promising applications for multispectral imaging and neuromorphic computation.
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ItemNo Preview AvailableEmerging Strategies for CO2 Photoreduction to CH4: From Experimental to Data-Driven Design (Adv. Energy Mater. 20/2022)(Wiley, 2022-05)Through experimental strategies (human brain) and data-driven strategies (machine brain) that have been reported, high-performance photocatalysts are gradually being explored and developed under the huge data flow (transmitted by neurons). In article number 2200389, Gang Kevin Li, Zongyou Yin, Sibudjing Kawi and co-workers show that the combination of experimentation and data-driven design (brain ensemble) is a powerful solution for the future design of novel catalysts for selective photocatalytic reduction of carbon dioxide to methane.
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ItemNo Preview AvailableLocalized Electron Density Redistribution in Fluorophosphate Cathode: Dangling Anion Regulation and Enhanced Na‐Ion Diffusivity for Sodium‐Ion Batteries (Adv. Funct. Mater. 4/2022)(Wiley, 2022-01)In article number 2109694, Hong Yu, Cheng-Feng Du, Xing-Long Wu, and co-workers develop Cl-doped Na3V2(PO4)2O2F (NVPO2−xClxF) as superior cathode material for sodium-ion batteries. In NVPO2−xClxF, Cl doping tunes the electronic structure and causes the electron redistribution on vanadium center/dangling anions. As a result, a revised redox behavior of vanadium and increased Na+- diffusivity/electrochemical properties are achieved.
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ItemEquilibrium Sorption of Monovalent and Divalent Organic Ions in Anion Exchange Membranes(AMER CHEMICAL SOC, 2023-11-15)Ion transport in ion exchange membranes (IEMs) involving weak electrolytes such as organic acid species can exhibit considerably different behavior compared to the transport of inorganic species, partly due to their pH-dependent dissociation behavior. In this work, the concentration-dependence of the equilibrium sorption of sodium co-ions and organic counterions in a strongly basic anion exchange membrane (AEM) is systematically studied for organic acids with one and two carboxylic acid groups, namely, lactic acid and tartaric acid, with the AEMs being equilibrated in organic salt solutions containing predominantly the highest valency of the organic ions. It is discovered that up to ∼28% of total lactic acid within the membrane phase exists as neutral lactic acid molecules and up to ∼30% of total tartaric acid exists as monovalent bitartrate ions, over the range of external salt concentration investigated (0.1-1 equiv/L). This indicates a shift in the acid dissociation equilibria from the external solution to the membrane phase, which appears to be more significant at higher salt concentrations. Our quantification of organic ion speciation in AEMs will contribute to future fundamental studies of organic ion transport in IEMs, enabling a rational design of polymer chemistry and development of electromembrane processes to maximize separation performance.
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ItemElectrical Conductivity of Pipeline Deposits Under Pressure and Their Impacts on Sales-Gas Pipeline Cathodic Protection Systems(Society of Petroleum Engineers (SPE), 2023-10-11)Natural gas pipelines are critical for safe and efficient energy transport across large distances. To maintain operational safety, pipelines use cathodic protection systems that minimize the rate of external corrosion. This work characterizes the effects of black powder deposits, a widely experienced operational hazard across the natural gas industry, on the failure of pipeline cathodic protection systems due to electrical "shorting"of isolation devices. Black powder sludgy deposits from coal seam gas (CSG) pipelines were analyzed, revealing electrical conductivity values within the range of 580 to 5400 μS/cm when under pipeline pressure. These values were used to calculate the internal resistances of monolithic isolation joints (MIJs), a type of electrical isolation device, to show that electrical shorting (internal resistance of < 100 Ω) can occur for black powder sludgy deposit thicknesses in the range of millimeters. To reduce the frequency of such shorting events, it is recommended that upstream dehydration systems be designed to reduce carry-over of triethylene glycol (TEG), that internal nonconductive coatings be applied to isolation devices, and that these devices are installed in ways that facilitate regular cleaning.