skip to main content

Title: An automated flow chemistry platform to decouple mixing and reaction times
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.
Authors:
; ; ;
Award ID(s):
1902702
Publication Date:
NSF-PAR ID:
10165733
Journal Name:
Reaction Chemistry & Engineering
ISSN:
2058-9883
Sponsoring Org:
National Science Foundation
More Like this
  1. Whether reagents and samples need to be combined to achieve a desired reaction, or precise concentrations of solutions need to be mixed and delivered downstream, thorough mixing remains a critical step in many microfluidics-based biological and chemical assays and analyses. To achieve complete mixing of fluids in microfluidic devices, researchers have utilized novel channel designs or active intervention to facilitate mass transport and exchange of fluids. However, many of these solutions have a major limitation: their design inherently limits their operational throughput; that is, different designs work at specific flow rates, whether that be low or high ranges, but have difficulties outside of their tailored design regimes. In this work, we present an acoustofluidic mixer that is capable of achieving efficient, thorough mixing across a broad range of flow rates (20–2000 μL min −1 ) using a single device. Our mixer combines active acoustofluidic mixing, which is responsible for mixing fluids at lower flow rates, with passive hydrodynamic mixing, which accounts for mixing fluids at higher flow rates. The mechanism, functionality, and performance of our acoustofluidic device are both numerically and experimentally validated. Additionally, the real-world potential of our device is demonstrated by synthesizing polymeric nanoparticles with comparable sizes overmore »a two-order-of-magnitude wide range of flow rates. This device can be valuable in many biochemical, biological, and biomedical applications. For example, using our platform, one may synthesize nanoparticles/nanomaterials at lower flow rates to first identify optimal synthesis conditions without having to waste significant amounts of reagents, and then increase the flow rate to perform high-throughput synthesis using the optimal conditions, all using the same single device and maintaining performance.« less
  2. Abstract

    Microreactor-Assisted Nanomaterial Deposition (MAND) process offers unique capabilities in achieving large size and shape control levels while providing a more rapid path for scaling via process intensification for nanomaterial production. This review highlights the application of continuous flow microreactors to synthesize, assemble, transform, and deposit nanostructured materials for Solar Photovoltaics, the capabilities of MAND in the field, and the potential outlook of MAND.

    Microreactor-Assisted Nanomaterial Deposition (MAND) is a promising technology that synthesizes reactive fluxes and nanomaterials to deposit nanostructured materials at the point of use. MAND offers precise control over reaction, organization, and transformation processes to manufacture nanostructured materials with distinct morphologies, structures, and properties. In synthesis, microreactor technology offers large surface-area-to-volume ratios within microchannel structures to accelerate heat and mass transport. This accelerated transport allows for rapid changes in reaction temperatures and concentrations, leading to more uniform heating and mixing in the deposition process. The possibility of synthesizing nanomaterials in the required volumes at the point of application eliminates the need to store and transport potentially hazardous materials. Further, MAND provides new opportunities for tailoring novel nanostructures and nano-shaped features, opening the opportunity to assemble unique nanostructures and nanostructured thin films. MAND processes control the heat transfer,more »mass transfer, and reaction kinetics using well-defined microstructures of the active unit reactor cell that can be replicated at larger scales to produce higher chemical production volumes. This critical feature opens a promising avenue in developing scalable nanomanufacturing. This paper reviews advances in microreactor-assisted nanomaterial deposition of nanostructured materials for solar photovoltaics. The discussions review the use of microreactors to tailor the reacting flux, transporting to substrate surfaces via controlling process parameters such as flow rates, pH of the precursor solutions, and seed layers on the formation and/or transformation of intermediary reactive molecules, nanoclusters, nanoparticles, and structured assemblies. In the end, the review discusses the use of an industrial scale MAND to apply anti-reflective and anti-soiling coatings on the solar modules in the field and details future outlooks of MAND reactors.

    Graphical abstract

    « less
  3. The design and optimization of highly nonlinear and complex processes like plasma etching is challenging and timeconsuming. Significant effort has been devoted to creating plasma profile simulators to facilitate the development of etch recipes. Nevertheless, these simulators are often difficult to use in practice due to the large number of unknown parameters in the plasma discharge and surface kinetics of the etch material, the dependency of the etch rate on the evolving front profile, and the disparate length scales of the system. Here, we expand on the development of a previously published, data informed, Bayesian approach embodied in the platform RODEo (Recipe Optimization for Deposition and Etching). RODEo is used to predict etch rates and etch profiles over a range of powers, pressures, gas flow rates, and gas mixing ratios of an CF4/Ar gas chemistry. Three examples are shown: (1) etch rate predictions of an unknown material “X” using simulated experiments for a CF4/Ar chemistry, (2) etch rate predictions of SiO2 in a Plasma-Therm 790 RIE reactor for a CF4/Ar chemistry, and (3) profile prediction using level set methods.
  4. Knowledge of the viscosity of particles containing secondary organic material (SOM) is useful for predicting reaction rates and diffusion in SOM particles. In this study we investigate the viscosity of SOM particles as a function of relative humidity and SOM particle mass concentration, during SOM synthesis. The SOM was generated via the ozonolysis of α-pinene at < 5 % relative humidity (RH). Experiments were carried out using the poke-and-flow technique, which measures the experimental flow time (τexp, flow) of SOM after poking the material with a needle. In the first set of experiments, we show that τexp, flow increased by a factor of 3600 as the RH increased from < 0.5 RH to 50 % RH, for SOM with a production mass concentration of 121 µg m−3. Based on simulations, the viscosities of the particles were between 6  ×  105 and 5  ×  107 Pa s at < 0.5 % RH and between 3  ×  102 and 9  ×  103 Pa s at 50 % RH. In the second set of experiments we show that under dry conditions τexp, flow decreased by a factor of 45 as the production mass concentration increased from 121 to 14 000 µg m−3. From simulations of the poke-and-flow experiments, the viscosity of SOM with a production mass concentration of 14 000 µg m−3 was determined to be between 4  ×  104 and 1.5  ×  106 Pa smore »compared to between 6  ×  105 and 5  ×  107 Pa s for SOM with a production mass concentration of 121 µg m−3. The results can be rationalized by a dependence of the chemical composition of SOM on production conditions. These results emphasize the shifting characteristics of SOM, not just with RH and precursor type, but also with the production conditions, and suggest that production mass concentration and the RH at which the viscosity was determined should be considered both when comparing laboratory results and when extrapolating these results to the atmosphere.« less
  5. The synthesis of metal–organic frameworks (MOFs) by using traditional wet-chemistry methods generally requires very long durations and still suffers from non-uniform heat and mass transfer within the bulk precursor solutions. Towards addressing these issues, a microdroplet-based spray method has been developed. In a typical spray process, an MOF's precursor solution is first atomized into microdroplets. These droplets serve as microreactors to ensure homogeneous mixing, fast evaporation, and rapid nucleation and crystal growth to form MOF particles. However, the fundamental MOF formation mechanisms by using this strategy have not been fully understood. In this work, the role of the operating pressure in the synthesis of a representative MOF ( i.e. , Cu(TPA)·(DMF); TPA: terephthalic acid, DMF: dimethylformamide) was systematically investigated. Detailed characterization showed that the pressure variations significantly affected both the morphologies and crystalline structures of Cu(TPA)·(DMF). Numerical simulations revealed that the morphology changes are mainly attributed to the variations in supersaturation ratios, which are caused by different microdroplet evaporation rates due to the regulation of operating pressure, while the crystalline structure variations are closely related to the dissociation of DMF molecules at lower operating pressures. Besides, the dissociation of DMF molecules decreased the surface area of the MOF crystals, butmore »gave rise to massive coordinatively unsaturated metal sites, which greatly enhanced the interaction of CO 2 with the MOF crystal and thus led to improved CO 2 adsorption capacity and selectivity. The outcome of this work would contribute to the fundamental understanding of MOF synthesis using the microdroplet-based spray method.« less