Open Access Publications

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Open access publications by faculty, postdocs, and graduate students in the Department of Chemical and Biomolecular Engineering


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Now showing 1 - 20 of 133
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    A novel digital lifecycle for Material-Process-Microstructure-Performance relationships of thermoplastic olefins foams manufactured via supercritical fluid assisted foam injection molding
    (Polymer Engineering and Science, 2024-03-15) Pradeep, Sai Aditya; Deshpande, Amit M.; Lavertu, Pierre‐Yves; Zheng, Ting; Yerra, Veera Aditya; Shimabukuro, Yiro; Li, Gang; Pilla, Srikanth
    This research significantly enhances the applicability of thermoplastic olefins (TPOs) in the automotive industry using supercritical N2 as a physical foaming agent, effectively addressing the limitations of traditional chemical agents. It merges experimental results with simulations to establish detailed material-process-microstructure-performance (MP2) relationships, targeting 5–20% weight reductions. This innovative approach labeled digital lifecycle (DLC) helps accurately predict tensile, flexural, and impact properties based on the foam microstructure, along with experimentally demonstrating improved paintability. The study combines process simulations with finite element models to develop a comprehensive digital model for accurately predicting mechanical properties. Our findings demonstrate a strong correlation between simulated and experimental data, with about a 5% error across various weight reduction targets, marking significant improvements over existing analytical models. This research highlights the efficacy of physical foaming agents in TPO enhancement and emphasizes the importance of integrating experimental and simulation methods to capture the underlying foaming mechanism to establish material-process-microstructure-performance (MP2) relationships. Highlights - Establishes a material-process-microstructure-performance (MP2) for TPO foams - Sustainably produces TPO foams using supercritical (ScF) N2 with 20% lightweighting - Shows enhanced paintability for TPO foam improved surface aesthetics - Digital lifecycle (DLC) that predicts both foam microstructure and properties - DLC maps process effects & microstructure onto FEA mesh for precise prediction
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    Modeling scalability of impurity precipitation in downstream biomanufacturing
    (Biotechnology Progress, 2024-03-27) Guo, Jing; Traylor, Steven J.; Agoub, Mohamed; Jin, Weixin; Hua, Helen; Diemer, R. Bertrum; Xu, Xuankuo; Ghose, Sanchayita; Li, Zheng Jian; Lenhoff, Abraham M.
    Precipitation during the viral inactivation, neutralization and depth filtration step of a monoclonal antibody (mAb) purification process can provide quantifiable and potentially significant impurity reduction. However, robust commercial implementation of this unit operation is limited due to the lack of a representative scale-down model to characterize the removal of impurities. The objective of this work is to compare isoelectric impurity precipitation behavior for a monoclonal antibody product across scales, from benchtop to pilot manufacturing. Scaling parameters such as agitation and vessel geometry were investigated, with the precipitate amount and particle size distribution (PSD) characterized via turbidity and flow imaging microscopy. Qualitative analysis of the data shows that maintaining a consistent energy dissipation rate (EDR) could be used for approximate scaling of vessel geometry and agitator speeds in the absence of more detailed simulation. For a more rigorous approach, however, agitation was simulated via computational fluid dynamics (CFD) and these results were applied alongside a population balance model to simulate the trajectory of the size distribution of precipitate. CFD results were analyzed within a framework of a two-compartment mixing model comprising regions of high- and low-energy agitation, with material exchange between the two. Rate terms accounting for particle formation, growth and breakage within each region were defined, accounting for dependence on turbulence. This bifurcated model was successful in capturing the variability in particle sizes over time across scales. Such an approach enhances the mechanistic understanding of impurity precipitation and provides additional tools for model-assisted prediction for process scaling.
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    Factors affecting product association as a mechanism of host-cell protein persistence in bioprocessing
    (Biotechnology and Bioengineering, 2024-01-19) Oh, Young Hoon; Becker, Matthew L.; Mendola, Kerri M.; Choe, Leila H.; Min, Lie; Lee, Kelvin H.; Yigzaw, Yinges; Seay, Alexander; Bill, Jerome; Li, Xuanwen; Roush, David J.; Cramer, Steven M.; Menegatti, Stefano; Lenhoff, Abraham M.
    Product association of host-cell proteins (HCPs) to monoclonal antibodies (mAbs) is widely regarded as a mechanism that can enable HCP persistence through multiple purification steps and even into the final drug substance. Discussion of this mechanism often implies that the existence or extent of persistence is directly related to the strength of binding but actual measurements of the binding affinity of such interactions remain sparse. Two separate avenues of investigation of HCP-mAb binding are reported here. One is the measurement of the affinity of binding of individual, commonly persistent Chinese hamster ovary (CHO) HCPs to each of a set of mAbs, and the other uses quantitative proteomic measurements to assess binding of HCPs in a null CHO harvested cell culture fluid (HCCF) to mAbs produced in the same cell line. The individual HCP measurements show that the binding affinities of individual HCPs to different mAbs can vary appreciably but are rarely very high, with only weak pH dependence. The measurements on the null HCCF allow estimation of individual HCP-mAb affinities; these are typically weaker than those seen in affinity measurements on isolated HCPs. Instead, the extent of binding appears correlated with the initial abundance of individual HCPs in the HCCF and the forms of the HCPs in the solution, i.e., whether HCPs are present as free molecules or as parts of large aggregates. Separate protein A chromatography experiments performed by feeding different fractions of a mAb-containing HCCF obtained by size-exclusion chromatography (SEC) showed clear differences in the number and identity of HCPs found in the protein A eluate. These results indicate a significant role for HCP-mAb association in determining HCP persistence through protein A chromatography, presumably through binding of HCP-mAb complexes to the resin. Overall, the results illustrate the importance of considering more fully the biophysical context of HCP-product association in assessing the factors that may affect the phenomenon and determine its implications. Knowledge of the abundances and the forms of individual or aggregated HCPs in HCCF are particularly significant, emphasizing the integration of upstream and downstream bioprocessing and the importance of understanding the collective properties of HCPs in addition to just the biophysical properties of individual HCPs.
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    Dissipation in nonequilibrium thermodynamics and its connection to the Rayleighian functional
    (Physics of Fluids, 2024-01-04) Beris, Antony N.; Edwards, Brian J.
    We examine quantitatively the role of dissipation in nonequilibrium thermodynamics and its connection to variational principles and the Rayleighian functional. The extremum of the Rayleighian is sometimes used to describe the inertialess (dissipation-dominated) dynamics of continuum systems, and it has been applied recently for the modeling of soft matter dynamics. We discuss how dissipation is considered within one of the modern complete descriptions of nonequilibrium thermodynamics, namely the single generator bracket formalism. Within this formalism, dissipation is introduced through the use of the dissipation bracket, describing irreversible dynamics, which is added to a Poisson bracket that describes the reversible dynamics of the system. A possible connection with the Rayleighian functional is then demonstrated that in all cases considered herein, the Rayleighian is equal to minus one half of the effective dissipation rate of the Lagrangian functional. The effective dissipation rate is obtained starting with an inertial (i.e., flux-based or velocity-based) system description, involving the Poisson bracket and the primitive part (i.e., without the entropy correction term) of the dissipative bracket. Several examples are discussed in detail, ranging from an algebraic model (damped oscillator) to continuum ones: modeling of fluid flow in porous particle media, viscous Newtonian compressible and incompressible fluid flows, and more interestingly, flow of a nematic liquid-crystalline material.
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    Ethylene production: process design, techno-economic and life-cycle assessments
    (Green Chemistry, 2024-01-29) Chen, Yuqiu; Kuo, Mi Jen; Lobo, Raul; Ierapetritou, Marianthi
    Replacing the steam cracking process with oxidative dehydrogenation for ethylene production offers potential energy and environmental benefits. To evaluate these possibilities, a study combining conceptual process design, techno-economic analysis, and life cycle assessments of the oxidative dehydrogenation of ethane (ODHE) for producing ethylene at an industrial scale is performed. For comparison, the conventional steam cracking process of ethane is also simulated and optimized. The techno-economic analysis results for ODHE with a boron-containing zeolite chabazite (B-CHA) catalyst, as developed in our group, demonstrate that it is economically competitive ($790 per t ethylene production) compared to the steam cracking process ($832 per t ethylene production). However, a “cradle-to-gate” life-cycle assessment shows that the ODHE process emits more greenhouse gases (2.42 kg CO2 equiv. per kg ethylene) compared to the steam cracking counterpart (1.34 kg CO2 equiv. per kg ethylene). The discrepancy between the initial hypothesis and the results arises from the significant refrigerant input required by the ODHE process to recover ethylene from byproducts such as CO, CH4, and unreacted oxygen and ethane. Further scenario analysis reveals that plausible improvements in the C2H6 conversion per pass, the selectivity to ethylene and the ratio of ethane to oxygen in the current ODHE process could render it both economically and environmentally viable as a replacement for the steam cracking process.
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    Neutron Scattering Analysis of Cryptococcus neoformans Polysaccharide Reveals Solution Rigidity and Repeating Fractal-like Structural Patterns
    (Biomacromolecules, 2024-02-12) Wang, Ziwei; Teixeira, Susana C. M.; Strother, Camilla; Bowen, Anthony; Casadevall, Arturo; Cordero, Radamés J. B.
    Cryptococcus neoformans is a fungal pathogen that can cause life-threatening brain infections in immunocompromised individuals. Unlike other fungal pathogens, it possesses a protective polysaccharide capsule that is crucial for its virulence. During infections, Cryptococcus cells release copious amounts of extracellular polysaccharides (exo-PS) that interfere with host immune responses. Both exo-PS and capsular-PS play pivotal roles in Cryptococcus infections and serve as essential targets for disease diagnosis and vaccine development strategies. However, understanding their structure is complicated by their polydispersity, complexity, sensitivity to sample isolation and processing, and scarcity of methods capable of isolating and analyzing them while preserving their native structure. In this study, we employ small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) for the first time to investigate both fungal cell suspensions and extracellular polysaccharides in solution. Our data suggests that exo-PS in solution exhibits collapsed chain-like behavior and demonstrates mass fractal properties that indicate a relatively condensed pore structure in aqueous environments. This observation is also supported by scanning electron microscopy (SEM). The local structure of the polysaccharide is characterized as a rigid rod, with a length scale corresponding to 3–4 repeating units. This research not only unveils insights into exo-PS and capsular-PS structures but also demonstrates the potential of USANS for studying changes in cell dimensions and the promise of contrast variation in future neutron scattering studies. Graphical abstract available at:
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    Combined Effects of Pressure and Ionic Strength on Protein–Protein Interactions: An Empirical Approach
    (Biomacromolecules, 2024-01-08) Paul, Brian; Furst, Eric M.; Lenhoff, Abraham M.; Wagner, Norman J.; Teixeira, Susana C. M.
    Proteins are exposed to hydrostatic pressure (HP) in a variety of ecosystems as well as in processing steps such as freeze–thaw, cell disruption, sterilization, and homogenization, yet pressure effects on protein–protein interactions (PPIs) remain underexplored. With the goal of contributing toward the expanded use of HP as a fundamental control parameter in protein research, processing, and engineering, small-angle X-ray scattering was used to examine the effects of HP and ionic strength on ovalbumin, a model protein. Based on an extensive data set, we develop an empirical method for scaling PPIs to a master curve by combining HP and osmotic effects. We define an effective pressure parameter that has been shown to successfully apply to other model protein data available in the literature, with deviations evident for proteins that do not follow the apparent Hofmeister series. The limitations of the empirical scaling are discussed in the context of the hypothesized underlying mechanisms. Graphical abstract available at:
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    Surface-mediated spontaneous emulsification of the acylated peptide semaglutide
    (Proceedings of the National Academy of Sciences, 2024-01-16) Li, Qi; Tangry, Vasudev; Allen, David P.; Seibert, Kevin D.; Qian, Ken K.; Wagner, Norman J.
    Significance We identify the fundamental mechanisms of an undesired instability known as “ouzo” formation in a class of therapeutics used for treating type 2 diabetes and obesity. Spontaneous emulsification in solutions of acylated peptides in the presence of hydrophobic surfaces is elucidated as a function of physico-chemical conditions and surface hydrophobicity as characterized by Hansen solubility parameters. Quantitative prediction of the colloidal size is demonstrated using the classical Rayleigh theory, while formation rates reduce to a master curve dependent on the surface hydrophobicity and stirring rate. We demonstrate that colloidal physics and molecular thermodynamics provide quantitative predictions of the colloidal droplet size and qualitatively rank formation rates, thereby improving our understanding of this important class of therapeutic molecules. Abstract Acylated peptides composed of glucagon-like peptide-1 receptor agonists modified with a fatty acid side chain are an important class of therapeutics for type 2 diabetes and obesity but are susceptible to an unusual physical instability in the presence of hydrophobic surfaces, i.e., spontaneous emulsification, also known as ouzo formation in practice. In this work, light scattering, small-angle X-ray scattering, and circular dichroism measurements are used to characterize the physical properties of the semaglutide colloidal phase, including size distribution, shape, secondary structure, internal structure, and internal composition, as a function of solution physico-chemical conditions. The existence and size of the colloids formed are successfully predicted by a classical Rayleigh model, which identifies the parameters controlling their size and formation. Colloid formation is found to be catalyzed by hydrophobic surfaces, and formation rates are modeled as an autocatalytic reaction, enabling the formation of a master curve for various surfaces that elucidates the mechanism. Surfaces differ due to differences in surface wettability, which can be correlated with Hansen solubility parameters. This work provides insights into this unusual colloidal phenomenon and guides the peptide synthesis process and drug product formulation in the pharmaceutical industry.
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    DNA transfer between two different species mediated by heterologous cell fusion in Clostridium coculture
    (mBio, 2024-01-12) Charubin, Kamil; Hill, John D.; Papoutsakis, Eleftherios Terry
    Prokaryotic evolution is driven by random mutations and horizontal gene transfer (HGT). HGT occurs via transformation, transduction, or conjugation. We have previously shown that in syntrophic cocultures of Clostridium acetobutylicum and Clostridium ljungdahlii, heterologous cell fusion leads to a large-scale exchange of proteins and RNA between the two organisms. Here, we present evidence that heterologous cell fusion facilitates the exchange of DNA between the two organisms. Using selective subculturing, we isolated C. acetobutylicum cells which acquired and integrated into their genome portions of plasmid DNA from a plasmid-carrying C. ljungdahlii strain. Limiting-dilution plating and DNA methylation data based on PacBio Single-Molecule Real Time (SMRT) sequencing support the existence of hybrid C. acetobutylicum/C. ljungdahlii cells. These findings expand our understanding of multi-species microbiomes, their survival strategies, and evolution. IMPORTANCE Investigations of natural multispecies microbiomes and synthetic microbial cocultures are attracting renewed interest for their potential application in biotechnology, ecology, and medical fields. Previously, we have shown the syntrophic coculture of C. acetobutylicum and C. ljungdahlii undergoes heterologous cell-to-cell fusion, which facilitates the exchange of cytoplasmic protein and RNA between the two organisms. We now show that heterologous cell fusion between the two Clostridium organisms can facilitate the exchange of DNA. By applying selective pressures to this coculture system, we isolated clones of wild-type C. acetobutylicum which acquired the erythromycin resistance (erm) gene from the C. ljungdahlii strain carrying a plasmid with the erm gene. Single-molecule real-time sequencing revealed that the erm gene was integrated into the genome in a mosaic fashion. Our data also support the persistence of hybrid C. acetobutylicum/C. ljungdahlii cells displaying hybrid DNA-methylation patterns.
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    Conformations of polyolefins on platinum catalysts control product distribution in plastics recycling
    (Chemical Science, 2023-01-03) Zare, Mehdi; Kots, Pavel A.; Caratzoulas, Stavros; Vlachos, Dionisios G.
    The design of catalysts for the chemical recycling of plastic waste will benefit greatly from an intimate knowledge of the interfacial polymer–catalyst interactions that determine reactant and product distributions. Here, we investigate backbone chain length, side chain length, and concentration effects on the density and conformation of polyethylene surrogates at the interface with Pt(111) and relate them to experimental product distributions resulting from carbon–carbon bond cleavage. Using replica-exchange molecular dynamics simulations, we characterize the polymer conformations at the interface by the distributions of trains, loops, and tails and their first moments. We find that the preponderance of short chains, in the range of 20 carbon atoms, lies entirely on the Pt surface, whereas longer chains exhibit much broader distributions of conformational features. Remarkably, the average length of trains is independent of the chain length but can be tuned via the polymer–surface interaction. Branching profoundly impacts the conformations of long chains at the interface as the distributions of trains become less dispersed and more structured, localized around short trains, with the immediate implication of a wider carbon product distribution upon C–C bond cleavage. The degree of localization increases with the number and size of the side chains. Long chains can adsorb from the melt onto the Pt surface even in melt mixtures containing shorter polymer chains at high concentrations. We confirm experimentally key computational findings and demonstrate that blends may provide a strategy to reduce the selectivity for undesired light gases.
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    A polydisperse model for thixotropic elasto-viscoplastic suspensions of aggregating particles using population balances
    (AIChE Journal, 2023-09-18) Jariwala, Soham; Song, Rong; Hipp, Julie B.; Diemer, R. Bertrum; Wagner, Norman J.; Beris, Antony N.
    An improved population balance-based rheological constitutive framework for polydisperse aggregating suspensions is derived by incorporating detailed models for orthokinetic and perikinetic aggregation and shear breakage processes. The framework accounts for critical properties such as dynamic arrest, viscoelasticity, kinematic hardening, thixotropy, and yield stress to generate a full range of thixotropic elasto-viscoplastic (TEVP) response. Additionally, the model is thermodynamically consistent because the dynamics and timescales are completely determined by internal structural and kinetic variables. The model connects the rheological response to the structural descriptors such as the size distribution of agglomerates, mean sizes, fractal dimension, and agglomerate volume fraction. Predictions are compared against a wide range of shear rheology measurements data for model thixotropic suspensions of fumed silica and carbon black, including large amplitude oscillatory shear (LAOS), as well as ultra-small angle neutron scattering under steady shear (Rheo-uSANS).
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    Polysiloxane Inks for Multimaterial 3d Printing of High-Permittivity Dielectric Elastomers
    (Advanced Functional Materials, 2023-12-27) Danner, Patrick M.; Pleij, Tazio; Siqueira, Gilberto; Bayles, Alexandra V.; Venkatesan, Thulasinath Raman; Vermant, Jan; Opris, Dorina M.
    Dielectric elastomer transducers (DET) are promising candidates for electrically-driven soft robotics. However, the high viscosity and low yield stress of DET formulations prohibit 3D printing, the most common manufacturing method for designer soft actuators. DET inks optimized for direct ink writing (DIW) produce elastomers with high stiffness and mechanical losses, diminishing the utility of DET actuators. To address the antagonistic nature of processing and performance constraints, principles of capillary suspensions are used to engineer DIW DET inks. By blending two immiscible polysiloxane liquids with a filler, a capillary ink suspension is obtained, in which the ink rheology can be tuned independently of the elastomer electromechanical properties. Rheometry is performed to measure and optimize processibility as a function of filler and secondary liquid fraction. Including polar polysiloxanes as the secondary liquid produces a printed elastomer exhibiting a four-fold permittivity increase over commercial polydimethylsiloxane. The characterization and multimaterial printing into layered DET devices demonstrates that the immiscible capillary suspension improves the processability of the inks and enhances the properties of the elastomers, enabling actuation of the devices at comparatively low voltages. It is anticipated that this formulation approach will allow soft robotics to harness the full potential of DETs.
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    Growth factors and growth factor gene therapies for treating chronic wounds
    (Bioengineering and Translational Medicine, 2023-12-28) Mullin, James A.; Rahmani, Erfan; Kiick, Kristi L.; Sullivan, Millicent O.
    Chronic wounds are an unmet clinical need affecting millions of patients globally, and current standards of care fail to consistently promote complete wound closure and prevent recurrence. Disruptions in growth factor signaling, a hallmark of chronic wounds, have led researchers to pursue growth factor therapies as potential supplements to standards of care. Initial studies delivering growth factors in protein form showed promise, with a few formulations reaching clinical trials and one obtaining clinical approval. However, protein-form growth factors are limited by instability and off-target effects. Gene therapy offers an alternative approach to deliver growth factors to the chronic wound environment, but safety concerns surrounding gene therapy as well as efficacy challenges in the gene delivery process have prevented clinical translation. Current growth factor delivery and gene therapy approaches have primarily used single growth factor formulations, but recent efforts have aimed to develop multi-growth factor approaches that are better suited to address growth factor insufficiencies in the chronic wound environment, and these strategies have demonstrated improved efficacy in preclinical studies. This review provides an overview of chronic wound healing, emphasizing the need and potential for growth factor therapies. It includes a summary of current standards of care, recent advances in growth factor, cell-based, and gene therapy approaches, and future perspectives for multi-growth factor therapeutics. Translational Impact Statement Chronic wounds persist as a healthcare challenge despite extensive research on various treatments, including growth factors and gene therapies. Progress in translating these therapeutics to clinical use has been slow, with many growth factor approaches demonstrating promise in preclinical studies but providing limited benefits in clinical trials or clinical application. This review presents recent advances in growth factor therapies and growth factor gene therapies, discusses obstacles to regulatory approval, and offers perspectives on potential innovations for successful clinical translation.
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    Nitro Biosciences: Enhancing immune response via an expanded genetic code
    (Delaware Journal of Public Health, 2023-11-30) Butler, Neil; Kunjapur, Aditya
    Novel modalities of vaccine will be required to address the current and future public health concerns we face. Many infectious diseases lack clinically approved vaccines causing immense burden to the health care system both domestically and abroad. More concerningly, the prevalence of antimicrobial resistance (AMR) is anticipated to rise over the coming decades and limit our tools to treat these infections. There is thus an urgent need to develop vaccinations to overcome these rising gaps in treatment and prevent infections moving forward. At Nitro Biosciences, we are developing a platform to create next-generation vaccines for diseases currently lacking clinically approved products. By harnessing an expanded genetic code, we can precisely modify antigens to enhance their immunogenicity, enabling a broadening of the scope of antigens to target in vaccine development and enhancing the potential to create efficacious vaccines where other efforts have failed.
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    Unlocking Circularity Through the Chemical Recycling and Upcycling of Lignin-Derivable Polymethacrylates
    (Macromolecules, 2023-11-22) Christoff-Tempesta, Ty; O’Dea, Robert M.; Epps, Thomas H. III
    The synthesis of polymers from lignin-derivable compounds can replace petrochemical building blocks with a renewable feedstock. However, the end-of-life management of bioderivable, nonbiodegradable polymers remains an outstanding challenge. Herein, the chemical recycling and upcycling of two higher-glass-transition temperature (>100 °C), lignin-derivable polymethacrylates, poly(syringyl methacrylate) (PSM) and poly(guaiacyl methacrylate) (PGM), is reported. Neat PSM and PGM were thermally depolymerized to quantitative conversions, producing their constituent monomers at high yields and purity. The deconstruction atmosphere influenced the depolymerization reaction order, and depolymerization was thermodynamically favored in air over N2. Further, monomer bulkiness and volatility impacted depolymerization activation energies. Notably, bulk depolymerization of PSM and PGM was performed without solvent or catalyst to high polymer conversions (89–90 wt %) and monomer yields (86–90 mol %) without byproduct formation. The resultant monomers were then upcycled to narrow-dispersity polymers and phase-separated block polymers. The findings herein offer a pathway to material circularity for higher-performance, lignin-derivable polymethacrylates.
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    Plasma-Enabled Ligand Removal for Improved Catalysis: Furfural Conversion on Pd/SiO2
    (ACS Nano, 2023-11-14) Nguyen, Darien K.; Vargheese,Vibin; Liao, Vinson; Dimitrakellis, Panagiotis; Sourav, Sagar; Zheng, Weiqing; Vlachos, Dionisios G.
    A nonthermal, atmospheric He/O2 plasma (NTAP) successfully removed polyvinylpyrrolidone (PVP) from Pd cubic nanoparticles supported on SiO2 quickly and controllably. Transmission electron microscopy (TEM) revealed that the shape and size of Pd nanoparticles remain intact during plasma treatment, unlike mild calcination, which causes sintering and polycrystallinity. Using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS), we demonstrate the quantitative estimation of the PVP plasma removal rate and control of the nanoparticle synthesis. First-principles calculations of the XPS and CO FTIR spectra elucidate electron transfer from the ligand to the metal and allow for estimates of ligand coverages. Reactivity testing indicated that PVP surface crowding inhibits furfural conversion but does not alter furfural selectivity. Overall, the data demonstrate NTAP as a more efficient method than traditional calcination for organic ligand removal in nanoparticle synthesis.
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    Soft matter roadmap
    (Journal of Physics: Materials, 2023-12-12) Barrat, Jean-Louis; Del Gado, Emanuela; Egelhaaf, Stefan U.; Mao, Xiaoming; Dijkstra, Marjolein; Pine, David J Pine; Kumar, Sanat K.; Bishop, Kyle; Gang, Oleg; Obermeyer, Allie
    Soft materials are usually defined as materials made of mesoscopic entities, often self-organised, sensitive to thermal fluctuations and to weak perturbations. Archetypal examples are colloids, polymers, amphiphiles, liquid crystals, foams. The importance of soft materials in everyday commodity products, as well as in technological applications, is enormous, and controlling or improving their properties is the focus of many efforts. From a fundamental perspective, the possibility of manipulating soft material properties, by tuning interactions between constituents and by applying external perturbations, gives rise to an almost unlimited variety in physical properties. Together with the relative ease to observe and characterise them, this renders soft matter systems powerful model systems to investigate statistical physics phenomena, many of them relevant as well to hard condensed matter systems. Understanding the emerging properties from mesoscale constituents still poses enormous challenges, which have stimulated a wealth of new experimental approaches, including the synthesis of new systems with, e.g. tailored self-assembling properties, or novel experimental techniques in imaging, scattering or rheology. Theoretical and numerical methods, and coarse-grained models, have become central to predict physical properties of soft materials, while computational approaches that also use machine learning tools are playing a progressively major role in many investigations. This Roadmap intends to give a broad overview of recent and possible future activities in the field of soft materials, with experts covering various developments and challenges in material synthesis and characterisation, instrumental, simulation and theoretical methods as well as general concepts.
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    Ab Initio Molecular Dynamics Study of Pt Clustering on γ-Al2O3 and Sn-Modified γ-Al2O3
    (Journal of Physical Chemistry C, 2023-10-05) Chen, Tso-Hsuan; Vlachos, Dionisios G.; Caratzoulas, Stavros
    We have conducted AIMD free energy simulations to examine the dynamics of Pt atoms and Ptn (n = 2–3) species on dry γ-Al2O3(100), dry γ-Al2O3(110), and wet γ-Al2O3(110) surfaces, with OH coverages corresponding to 500 K (11.8 OH/nm2) and 800 K (5.9 OH/nm2), while varying the Pt and Sn loading. Under the same dry conditions and temperature, comparing the (100) and (110) surface terminations revealed that the interactions between Pt and the surface play a crucial role in determining whether the potential of mean force between reduced Pt atoms is repulsive, as observed on the (100) surface, or if it can support a bound Pt–Pt state, as observed on the (110) surface. The hydration of the (110) surface had a significant impact. At a Pt loading of 0.75 Pt/nm2, with hydration of 5.9 OH/nm2, the energy of the potential of mean force increases. Although a Pt–Pt bound state is still supported, it becomes kinetically less accessible from the dispersed state. At an even higher water loading of 11.8 OH/nm2, the Pt–Pt potential of mean force becomes predominantly repulsive and can no longer sustain the Pt–Pt bound state. Higher Pt loadings of 1.12 Pt atoms/nm2 promote the aggregation of Pt into progressively larger clusters, but high levels of hydration can kinetically impede particle growth. On Sn-modified γ-Al2O3(110), Pt tends to associate with Sn, except at high levels of surface hydration where the potential of mean force between Pt and Sn atoms becomes repulsive. The presence of Sn inhibits the aggregation of Pt particles, and the Pt–Pt potential of mean force becomes increasingly repulsive with higher Sn loading.
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    Microflow chemistry and its electrification for sustainable chemical manufacturing
    (Chemical Science, 2022-08-06) Chen, Tai-Ying; Wei Hsiao, Yung; Baker-Fales, Montgomery; Cameli, Fabio; Dimitrakellis, Panagiotis; Vlachos, Dionisios G.
    Sustainability is vital in solving global societal problems. Still, it requires a holistic view by considering renewable energy and carbon sources, recycling waste streams, environmentally friendly resource extraction and handling, and green manufacturing. Flow chemistry at the microscale can enable continuous sustainable manufacturing by opening up new operating windows, precise residence time control, enhanced mixing and transport, improved yield and productivity, and inherent safety. Furthermore, integrating microfluidic systems with alternative energy sources, such as microwaves and plasmas, offers tremendous promise for electrifying and intensifying modular and distributed chemical processing. This review provides an overview of microflow chemistry, electrification, their integration toward sustainable manufacturing, and their application to biomass upgrade (a select number of other processes are also touched upon). Finally, we identify critical areas for future research, such as matching technology to the scale of the application, techno-economic analysis, and life cycle assessment.
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    Direct Integration of Strained-Pt Catalysts into Proton-Exchange-Membrane Fuel Cells with Atomic Layer Deposition
    (Advanced Materials, 2021-07-28) Xu, Shicheng; Wang, Zhaoxuan; Dull, Sam; Liu, Yunzhi; Lee, Dong Un; Pacheco, Juan S. Lezama; Orazov, Marat; Vullum, Per Erik; Dadlani, Anup Lal; Vinogradova, Olga; Schindler, Peter; Tam, Qizhan; Schladt, Thomas D.; Mueller, Jonathan E.; Kirsch, Sebastian; Huebner, Gerold; Higgins, Drew; Torgersen, Jan; Viswanathan, Venkatasubramanian; Jaramillo, Thomas Francisco; Prinz, Fritz B.
    The design and fabrication of lattice-strained platinum catalysts achieved by removing a soluble core from a platinum shell synthesized via atomic layer deposition, is reported. The remarkable catalytic performance for the oxygen reduction reaction (ORR), measured in both half-cell and full-cell configurations, is attributed to the observed lattice strain. By further optimizing the nanoparticle geometry and ionomer/carbon interactions, mass activity close to 0.8 A mgPt−1 @0.9 V iR-free is achievable in the membrane electrode assembly. Nevertheless, active catalysts with high ORR activity do not necessarily lead to high performance in the high-current-density (HCD) region. More attention shall be directed toward HCD performance for enabling high-power-density hydrogen fuel cells.
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