Periodic Reporting for period 4 - EVODIS (Exploiting vortices to suppress dispersion and reach new separation power boundaries)
Okres sprawozdawczy: 2020-09-01 do 2021-08-31
The 21st century is expected to develop towards a society depending ever and ever more on (bio-)chemical measurements of fluids and matrices that are so complex they are well beyond the current analytical capabilities. Incremental improvements can no longer satisfy the current needs of e.g. the proteomics field, requiring the separation of tens of thousands of components. The pace of progress in these fields is therefore predominantly determined by that of analytical tools, whereby liquid chromatography is the most prominent technique to separate small molecules as well as macromolecules, based on differential interaction of each analyte with support structures giving it a unique migration velocity. To improve its performance, a faster transport between these structures needs to be generated. Unfortunately the commonly pursued strategy, relying on diffusion and reducing the structure size, has come to its limits due to practical limitations related to packing and fabrication of sub-micron support structures, pressure tolerance and viscous heating.
A ground-breaking step to advance chromatographic performance to another level would be to accelerate mass transport in the lateral direction, beyond the rate of diffusion only. To meet this requirement, an array of microstructures and local electrodes can be defined to create lateral electroosmotic vortices in a pressure-driven column, aiming to accelerate the local mass transfer in an anisotropic fashion. The achievement of ordered arrays of vortices is intimately linked to this requirement, which is also of broader importance for mixing, anti-fouling of membrane and reactor surfaces, enhanced mass transfer in reactor channels, emulsification, etc. Understanding and implementing anisotropic vortex flows will therefore not only revolutionize analytical and preparative separation procedures, but will also be highly relevant in all flow systems that benefit from enhanced mass transfer.
A ground-breaking step to advance chromatographic performance to another level would be to accelerate mass transport in the lateral direction, beyond the rate of diffusion only. To meet this requirement, an array of microstructures and local electrodes can be defined to create lateral electroosmotic vortices in a pressure-driven column, aiming to accelerate the local mass transfer in an anisotropic fashion. The achievement of ordered arrays of vortices is intimately linked to this requirement, which is also of broader importance for mixing, anti-fouling of membrane and reactor surfaces, enhanced mass transfer in reactor channels, emulsification, etc. Understanding and implementing anisotropic vortex flows will therefore not only revolutionize analytical and preparative separation procedures, but will also be highly relevant in all flow systems that benefit from enhanced mass transfer.
The project aimed at enhancing (lateral) mass transport in microfluidic channels to improve chromatographic performance. In line with the proposal, we have studied 2 configurations in parallel wherein the channel walls are either capacitive (induced charge approach) or resistive (permanent charge approach), and wherein lateral movement is induced by a superimposed electroosmotic flow (EOF).
We started with electrically characterizing the materials constituting the channels allowing to predict e.g. appropriate frequencies and potentials for AC actuation of the EOF, but also to give guidance on the microfabrication processes by determining appropriate dimensions of layers, channels, etc.
After ‘brute force modeling’ requiring extensive computational power we first managed to show a numerical proof of concept of vortex chromatography and to define operational and design rules to achieve given performance gains. This was done for both retained and unretained conditions.
Next, we extensively developed fabrication procedures on gradually improved designs, taking into account results from electrical and fluidic characterization methods. We eventually successfully fabricated appropriate devices for both approaches (resistive and capacitive channel walls, respectively). In these devices we even managed to create vortex arrays with a varying number of vortices depending on the conditions and channel geometry.
Using the induced charge approach, we demonstrated a clear reduction of the dispersion as a result of the vortices under retained and unretained conditions (factor 3-5 reduction). We ended the project with scaling considerations on the technology (perspectives of more than 10-fold increase in performance), and have presented a roadmap for further maturation of the technology.
We started with electrically characterizing the materials constituting the channels allowing to predict e.g. appropriate frequencies and potentials for AC actuation of the EOF, but also to give guidance on the microfabrication processes by determining appropriate dimensions of layers, channels, etc.
After ‘brute force modeling’ requiring extensive computational power we first managed to show a numerical proof of concept of vortex chromatography and to define operational and design rules to achieve given performance gains. This was done for both retained and unretained conditions.
Next, we extensively developed fabrication procedures on gradually improved designs, taking into account results from electrical and fluidic characterization methods. We eventually successfully fabricated appropriate devices for both approaches (resistive and capacitive channel walls, respectively). In these devices we even managed to create vortex arrays with a varying number of vortices depending on the conditions and channel geometry.
Using the induced charge approach, we demonstrated a clear reduction of the dispersion as a result of the vortices under retained and unretained conditions (factor 3-5 reduction). We ended the project with scaling considerations on the technology (perspectives of more than 10-fold increase in performance), and have presented a roadmap for further maturation of the technology.
All above described results are unique research and beyond state of the art. The following can be added:
The realization of vortices in micron-scale channels that are furthermore not restricted by a given structural dimension to allow for resonance (in the case of conventional acoustic streaming) was not demonstrated in literature so far, nor its impact on dispersion reduction, nor the 3D PIV device for visualization.
The newly developed vortex chromatography method that we introduced and validated in EVODIS is a novel separation technology that can be used in a wide range of applications.
For the characterization of the vortices that have a 3D nature, conventional (2D) particle image velocimetry is inappropriate. We have developed a novel 3D methodology and instrument (pending patent, filed during project) that can be potentially used in a much broader context.
For the capacitive flow generation approach we came up with a novel approach to position the interface between the electrodes near the center of the channel in the height direction, making use of SOI substrates. This channel/electrode configuration allows to generate high electrical fields, in the central portion of a channel, allowing to, produce deeper channels with larger volumes. This is essential to allow for sufficient sample loadability and concomitant high sensitivity detection for chromatography operation. In a more general context, the method allows for fast lateral flows in high volume devices, which can be reactors, but also separation devices not relying on chromatographic principles.
For the permanent charge approach we (unexpectedly) learned that non-vertical walls are critical to allow for (sustained) vortices in AC-EOF mode.
To interpret the attainable performance gain we initially conducted flow simulations using Comsol Multiphysics wherein virtual injections of sample bands were performed. We learned to implement and validated the general dispersion theory of Brenner (Westerbeek et al, manuscript under consideration). Based on the vortex flows only, we can now predict chromatographic potential, requiring only a fraction of the computational power of the conventional full calculation, therewith making further improvements of vortex dispersion related research (in separations, but also in reactors).
The realization of vortices in micron-scale channels that are furthermore not restricted by a given structural dimension to allow for resonance (in the case of conventional acoustic streaming) was not demonstrated in literature so far, nor its impact on dispersion reduction, nor the 3D PIV device for visualization.
The newly developed vortex chromatography method that we introduced and validated in EVODIS is a novel separation technology that can be used in a wide range of applications.
For the characterization of the vortices that have a 3D nature, conventional (2D) particle image velocimetry is inappropriate. We have developed a novel 3D methodology and instrument (pending patent, filed during project) that can be potentially used in a much broader context.
For the capacitive flow generation approach we came up with a novel approach to position the interface between the electrodes near the center of the channel in the height direction, making use of SOI substrates. This channel/electrode configuration allows to generate high electrical fields, in the central portion of a channel, allowing to, produce deeper channels with larger volumes. This is essential to allow for sufficient sample loadability and concomitant high sensitivity detection for chromatography operation. In a more general context, the method allows for fast lateral flows in high volume devices, which can be reactors, but also separation devices not relying on chromatographic principles.
For the permanent charge approach we (unexpectedly) learned that non-vertical walls are critical to allow for (sustained) vortices in AC-EOF mode.
To interpret the attainable performance gain we initially conducted flow simulations using Comsol Multiphysics wherein virtual injections of sample bands were performed. We learned to implement and validated the general dispersion theory of Brenner (Westerbeek et al, manuscript under consideration). Based on the vortex flows only, we can now predict chromatographic potential, requiring only a fraction of the computational power of the conventional full calculation, therewith making further improvements of vortex dispersion related research (in separations, but also in reactors).