Coaxial microreactor for particle synthesis
Inventors
Bartsch, Michael • Kanouff, Michael P. • Ferko, Scott M. • Crocker, Robert W. • Wally, Karl
Assignees
National Technology and Engineering Solutions of Sandia LLC • Sandia National Laboratories
Publication Number
US-8563325-B1
Publication Date
2013-10-22
Expiration Date
2030-09-29
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Abstract
A coaxial fluid flow microreactor system disposed on a microfluidic chip utilizing laminar flow for synthesizing particles from solution. Flow geometries produced by the mixing system make use of hydrodynamic focusing to confine a core flow to a small axially-symmetric, centrally positioned and spatially well-defined portion of a flow channel cross-section to provide highly uniform diffusional mixing between a reactant core and sheath flow streams. The microreactor is fabricated in such a way that a substantially planar two-dimensional arrangement of microfluidic channels will produce a three-dimensional core/sheath flow geometry. The microreactor system can comprise one or more coaxial mixing stages that can be arranged singly, in series, in parallel or nested concentrically in parallel.
Core Innovation
The invention is a coaxial fluid flow microreactor system disposed on a microfluidic chip that utilizes laminar flow to synthesize particles from solution. It employs flow geometries based on hydrodynamic focusing to confine a core flow into a small, axially-symmetric, centrally positioned, and spatially well-defined portion of a flow channel cross-section. This configuration promotes highly uniform diffusional mixing between a reactant core and sheath flow streams. The microreactor is designed so that a substantially planar two-dimensional arrangement of microfluidic channels produces a three-dimensional core/sheath flow geometry.
The microreactor system can comprise one or more coaxial mixing stages arranged singly, in series, in parallel, or nested concentrically in parallel. The fabrication involves undercutting the core channel by the sheath channels to allow sheath fluid to merge substantially above, below, and upstream of the core flow orifice, thereby enabling true three-dimensional hydrodynamic focusing in a chip-based device. This coaxial, highly symmetrical, consistent, and uniform core/sheath interface facilitates the production of particles with homogeneous properties and narrow size distributions.
The problem solved by the invention arises from deficiencies in prior art microreactors and mixing schemes for particle generation, especially larger particles. Prior solutions often rely on external coaxial capillary arrangements or irregular flow patterns that produce non-uniform reacting interfaces and surface nucleation leading to clogging and broad particle size distributions. Two-dimensional focusing causes contact with channel walls resulting in non-uniformity and clogging, and typical parabolic flow velocity profiles cause uneven residence times altering particle growth. The new invention overcomes these limitations by fabricating a device capable of true three-dimensional coaxial focusing on-chip, improving mixing uniformity, reducing clogging, and enabling scale-up for larger particles.
Claims Coverage
The patent includes several independent claims, which mainly cover a fluid flow mixer device, methods of particle synthesis using the mixer, and serial arrangements of such mixers. Five main inventive features are detailed below.
Coaxial fluid flow mixer with symmetrical structure halves
The mixer comprises first and second structure halves joined symmetrically at a common surface, each half having a core channel flanked symmetrically by two sheath flow channels, forming a fluidic junction where the core and sheath channels merge into downstream outlet channel(s). The sheath channels have cross-sections substantially larger than the core channel outlet and are separated from the core by flanking walls.
Undercut flanking walls enabling three-dimensional flow mixing
The flanking walls on either side of the sheath channels are undercut laterally to allow sheath fluid to flow past the core channel before entering the fluidic junction. This configuration helps provide true three-dimensional core/sheath flow and improves fluid detachment from the core channel face. The sheath channels or flanking walls may be tapered to minimize core face area at the core outlet, with the undercut extending at least one-quarter of the core channel face width.
Methods of particle synthesis and control using hydrodynamic focusing
Particles are synthesized by flowing a first reagent in the core channel and a second reagent in the sheath channels, with lateral extent of the reaction interface controlled by hydrodynamic focusing of the core flow. The sheath to core flow rate ratio typically ranges from about 1:10 to 100:1 for effective focusing and reaction control.
Serial arrangement of fluid mixers enabling staged coaxial reactions
Multiple fluid mixers as described are arranged in serial fluid communication so that output flow of one mixer becomes the core flow input of the next. This serial arrangement allows for sequential coaxial reactions, staged introduction of reactants, and layered coaxial flow streams, enabling control over nucleation, growth, and particle functionalization stages.
Integration of particle or fluid diagnostic means
The fluid mixer and serial arrangements include means for particle or fluid diagnostics such as various light scattering techniques, spectroscopy techniques (including Raman, fluorescence, and nuclear magnetic resonance), microscopic imaging, electric and magnetic property measurements, and thermal and chemical concentration sensing to monitor and control particle generation processes.
The independent claims cover the design of a symmetrical coaxial fluid flow mixer with undercut flanking walls for three-dimensional hydrodynamic focusing, methods for particle synthesis using controlled flow focusing, serial fluid mixer arrangements for staged reactions, and incorporation of comprehensive diagnostic means to monitor the fluidic and particle characteristics.
Stated Advantages
The invention enables highly uniform diffusional mixing with a symmetrical and consistent core/sheath interface, producing particles with homogeneous properties and very narrow size distributions.
The design minimizes clogging and surface nucleation by avoiding contact between the reactive interface and channel walls.
Fabrication on-chip allows scalability with advantages in dimensional consistency, integration of multiple functionalities, minimized dead volumes, reduced sample dispersion, and improved durability compared to prior PDMS-based and capillary systems.
Three-dimensional hydrodynamic focusing permits operation at higher Reynolds numbers without flow instability, enabling higher throughput particle production.
The system supports integration with diagnostic tools and downstream processing elements, facilitating real-time characterization, control, and further particle manipulation on-chip.
Documented Applications
Particle synthesis from solution, including precipitation of insoluble or sparingly soluble inorganic salt crystals and other particle formation via changes in state or chemical reaction.
Production of nanoparticles, microparticles, nanocrystals, quantum dots, and composite particles through controlled nucleation and growth stages.
Non-particle producing reactions occurring purely in gas or liquid phases.
Generation of coaxial multi-phase flow streams yielding droplets, micelles, bubbles, aerosols, lamellar structures, and emulsions.
Flow cytometry applications involving cell and particle counting, detection, analysis, manipulation, and sorting using highly focused core streams.
Integration with on-chip functional elements including heaters, sensors, and optical components for advanced monitoring and control.
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