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1. An automated flow chemistry platform to decouple mixing and reaction times

   https://doi.org/10.1039/D0RE00129E  

   Epps, Robert W. ; Volk, Amanda A. ; Abdel-Latif, Kameel ; Abolhasani, Milad ( January 2020 , Reaction Chemistry & Engineering)

   Although a vital parameter in many colloidal nanomaterial syntheses, precursor mixing rates are typically inconsistent in batch processes and difficult to separate from reaction time in continuous flow systems. Here, we present a flow chemistry platform that decouples early-stage precursor mixing rates from reaction time (residence time) using solely off-the-shelf, commercially available, and standard dimension components. We then utilize the developed flow chemistry platform towards time- and material-efficient studies of the mass transfer-controlled synthesis of cesium lead bromide perovskite quantum dots.
2. Continuous production of ultrathin organic–inorganic Ruddlesden–Popper perovskite nanoplatelets via a flow reactor

   https://doi.org/10.1039/d1nr03239a  

   Biesold, Gill M. ; Liang, Shuang ; Wagner, Brent K. ; Kang, Zhitao ; Lin, Zhiqun ( August 2021 , Nanoscale)

   Because of their enhanced quantum confinement, colloidal two-dimensional Ruddlesden–Popper (RP) perovskite nanosheets with a general formula L 2 [ABX 3 ] n −1 BX 4 stand as a promising narrow-wavelength blue-emitting nanomaterial. Despite ample studies on batch synthesis, for RP perovskites to be broadly applied, continuous synthetic routes are needed. Herein, we design and optimize a flow reactor to continuously produce high-quality n = 1 RP perovskite nanoplatelets. The effects of antisolvent composition, reactor tube length, precursor solution injection rate, and antisolvent injection rate on the morphology and optical properties of the nanoplatelets are systematically examined. Our investigation suggests that flow reactors can be employed to synthesize high-quality L 2 PbX 4 perovskite nanoplatelets ( i.e. , n = 1) at rates greater than 8 times that of batch synthesis. Mass-produced perovskite nanoplatelets promise a variety of potential applications in optoelectronics, including light emitting diodes, photodetectors, and solar cells.
3. Stochastic Lagrangian dynamics of vorticity. Part 1. General theory for viscous, incompressible fluids

   https://doi.org/10.1017/jfm.2020.491  

   Eyink, Gregory L. ; Gupta, Akshat ; Zaki, Tamer A. ( October 2020 , Journal of Fluid Mechanics)

   Prior mathematical work of Constantin & Iyer ( Commun. Pure Appl. Maths , vol. 61, 2008, pp. 330–345; Ann. Appl. Probab. , vol. 21, 2011, pp. 1466–1492) has shown that incompressible Navier–Stokes solutions possess infinitely many stochastic Lagrangian conservation laws for vorticity, backward in time, which generalize the invariants of Cauchy ( Sciences mathématiques et physique , vol. I, 1815, pp. 33–73) for smooth Euler solutions. We reformulate this theory for the case of wall-bounded flows by appealing to the Kuz'min ( Phys. Lett. A , vol. 96, 1983, pp. 88–90)–Oseledets ( Russ. Math. Surv. , vol. 44, 1989, p. 210) representation of Navier–Stokes dynamics, in terms of the vortex-momentum density associated to a continuous distribution of infinitesimal vortex rings. The Constantin–Iyer theory provides an exact representation for vorticity at any interior point as an average over stochastic vorticity contributions transported from the wall. We point out relations of this Lagrangian formulation with the Eulerian theory of Lighthill (Boundary layer theory. In Laminar Boundary Layers (ed. L. Rosenhead), 1963, pp. 46–113)–Morton ( Geophys. Astrophys. Fluid Dyn. , vol. 28, 1984, pp. 277–308) for vorticity generation at solid walls, and also with a statistical result of Taylor ( Proc. R. Soc.more »Lond. A , vol. 135, 1932, pp. 685–702)–Huggins ( J. Low Temp. Phys. , vol. 96, 1994, pp. 317–346), which connects dissipative drag with organized cross-stream motion of vorticity and which is closely analogous to the ‘Josephson–Anderson relation’ for quantum superfluids. We elaborate a Monte Carlo numerical Lagrangian scheme to calculate the stochastic Cauchy invariants and their statistics, given the Eulerian space–time velocity field. The method is validated using an online database of a turbulent channel-flow simulation (Graham et al. , J. Turbul. , vol. 17, 2016, pp. 181–215), where conservation of the mean Cauchy invariant is verified for two selected buffer-layer events corresponding to an ‘ejection’ and a ‘sweep’. The variances of the stochastic Cauchy invariants grow exponentially backward in time, however, revealing Lagrangian chaos of the stochastic trajectories undergoing both fluid advection and viscous diffusion.« less
4. Evaluation of ambient ammonia measurements from a research aircraft using a closed-path QC-TILDAS operated with active continuous passivation

   https://doi.org/10.5194/amt-12-3717-2019  

   Pollack, Ilana B. ; Lindaas, Jakob ; Roscioli, J. Robert ; Agnese, Michael ; Permar, Wade ; Hu, Lu ; Fischer, Emily V. ( January 2019 , Atmospheric Measurement Techniques)

   Abstract. A closed-path quantum-cascade tunable infrared laserdirect absorption spectrometer (QC-TILDAS) was outfitted with an inertialinlet for filter-less separation of particles and several custom-designedcomponents including an aircraft inlet, a vibration isolation mountingplate, and a system for optionally adding active continuous passivation forgas-phase measurements of ammonia (NH3) from a research aircraft. Theinstrument was then deployed on the NSF/NCAR C-130 aircraft during researchflights and test flights associated with the Western wildfire Experiment forCloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) field campaign.The instrument was configured to measure large, rapid gradients in gas-phaseNH3, over a range of altitudes, in smoke (e.g., ash and particles), inthe boundary layer (e.g., during turbulence and turns), in clouds, and in ahot aircraft cabin (e.g., average aircraft cabin temperatures expected toexceed 30 ∘C during summer deployments). Important designgoals were to minimize motion sensitivity, maintain a reasonable detectionlimit, and minimize NH3 “stickiness” on sampling surfaces to maintainfast time response in flight. The observations indicate that adding ahigh-frequency vibration to the laser objective in the QC-TILDAS andmounting the QC-TILDAS on a custom-designed vibration isolation plate weresuccessful in minimizing motion sensitivity of the instrument during flight.Allan variance analyses indicate that the in-flight precision of theinstrument is 60 ppt at 1 Hz corresponding to a 3σ detectionmore »limitof 180 ppt. Zero signals span ±200, or 400 pptv total, withcabin pressure and temperature and altitude in flight. The option for activecontinuous passivation of the sample flow path with1H,1H-perfluorooctylamine, a strong perfluorinated base, preventedadsorption of both water and basic species to instrument sampling surfaces.Characterization of the time response in flight and on the ground showedthat adding passivant to a “clean” instrument system had little impact onthe time response. In contrast, passivant addition greatly improved the timeresponse when sampling surfaces became contaminated prior to a test flight.The observations further show that passivant addition can be used tomaintain a rapid response for in situ NH3 measurements over the duration of anairborne field campaign (e.g., ∼2 months) since passivantaddition also helps to prevent future buildup of water and basic species oninstrument sampling surfaces. Therefore, we recommend the use of activecontinuous passivation with closed-path NH3 instruments when rapid(>1 Hz) collection of NH3 is important for the scientificobjective of a field campaign (e.g., sampling from aircraft or anothermobile research platform). Passivant addition can be useful for maintainingoptimum operation and data collection in NH3-rich and humid environments orwhen contamination of sampling surfaces is likely, yet frequent cleaning isnot possible. Passivant addition may not be necessary for fast operation,even in polluted environments, if sampling surfaces can be cleaned when thetime response has degraded.« less
5. Microfluidic Synthesis of Elastomeric Microparticles: A Case Study in Catalysis of Palladium-Mediated Cross-Coupling

   Bennett, Jeffrey A ; Genzer, Jan ; Abolhasani, Milad ( October 2018 , 2018 AIChE Annual Meeting)

   Metal-mediated cross-coupling reactions offer organic chemists a wide array of stereo- and chemically-selective reactions with broad applications in fine chemical and pharmaceutical synthesis.1 Current batch-based synthesis methods are beginning to be replaced with flow chemistry strategies to take advantage of the improved consistency and process control methods offered by continuous flow systems.2,3 Most cross-coupling chemistries still encounter several issues in flow using homogeneous catalysis, including expensive catalyst recovery and air sensitivity due to the chemical nature of the catalyst ligands.1 To mitigate some of these issues, a ligand-free heterogeneous catalysis reaction was developed using palladium (Pd) loaded into a polymeric network of a silicone elastomer, poly(hydromethylsiloxane) (PHMS), that is not air sensitive and can be used with mild reaction solvents (ethanol and water).4 In this work we present a novel method of producing soft catalytic microparticles using a multiphase flow-focusing microreactor and demonstrate their application for continuous Suzuki-Miyaura cross-coupling reactions. The catalytic microparticles are produced in a coaxial glass capillary-based 3D flow-focusing microreactor. The microreactor consists of two precursors, a cross-linking catalyst in toluene and a mixture of the PHMS polymer and a divinyl cross-linker. The dispersed phase containing the polymer, cross-linker, and cross-linking catalyst is continuously mixed and thenmore »formed into microdroplets by the continuous phase of water and surfactant (sodium dodecyl sulfate) introduced in a counter-flow configuration. Elastomeric microdroplets with a diameter ranging between 50 to 300 micron are produced at 25 to 250 Hz with a size polydispersity less than 3% in single stream production. The physicochemical properties of the elastomeric microparticles such as particle swelling/softness can be tuned using the ratio of cross-linker to polymer as well as the ratio of polymer mixture to solvent during the particle formation. Swelling in toluene can be tuned up to 400% of the initial particle volume by reducing the concentration of cross-linker in the mixture and increasing the ratio of polymer to solvent during production.5 After the particles are produced and collected, they are transferred into toluene containing palladium acetate, allowing the particles to incorporate the palladium into the polymer network and then reduce the palladium to Pd0 with the Si-H functionality present on the PHMS backbones. After the reduction, the Pd-loaded particles can be washed and dried for storage or switched into an ethanol/water solution for loading into a micro-packed bed reactor (µ-PBR) for continuous organic synthesis. The in-situ reduction of Pd within the PHMS microparticles was confirmed using energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and focused ion beam-SEM, and TEM techniques. In the next step, we used the developed µ-PBR to conduct continuous organic synthesis of 4-phenyltoluene by Suzuki-Miyaura cross-coupling of 4-iodotoluene and phenylboronic acid using potassium carbonate as the base. Catalyst leaching was determined to only occur at sub ppm concentrations even at high solvent flow rates after 24 h of continuous run using inductively coupled plasma mass spectrometry (ICP-MS). The developed µ-PBR using the elastomeric microparticles is an important initial step towards the development of highly-efficient and green continuous manufacturing technologies in the pharma industry. In addition, the developed elastomeric microparticle synthesis technique can be utilized for the development of a library of other chemically cross-linkable polymer/cross-linker pairs for applications in organic synthesis, targeted drug delivery, cell encapsulation, or biomedical imaging. References 1. Ruiz-Castillo P, Buchwald SL. Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions. Chem Rev. 2016;116(19):12564-12649. 2. Adamo A, Beingessner RL, Behnam M, et al. On-demand continuous-flow production of pharmaceuticals in a compact, reconfigurable system. Science. 2016;352(6281):61 LP-67. 3. Jensen KF. Flow Chemistry — Microreaction Technology Comes of Age. 2017;63(3). 4. Stibingerova I, Voltrova S, Kocova S, Lindale M, Srogl J. Modular Approach to Heterogenous Catalysis. Manipulation of Cross-Coupling Catalyst Activity. Org Lett. 2016;18(2):312-315. 5. Bennett JA, Kristof AJ, Vasudevan V, Genzer J, Srogl J, Abolhasani M. Microfluidic synthesis of elastomeric microparticles: A case study in catalysis of palladium-mediated cross-coupling. AIChE J. 2018;0(0):1-10.« less