Microfluidic Fabrication Techniques for High-Pressure Testing of Microscale Supercritical CO2 Foam Transport in Fractured Unconventional Reservoirs

Summary

This paper describes a protocol along with a comparative study of two microfluidic fabrication techniques, namely photolithography/wet-etching/thermal-bonding and Selective Laser-induced Etching (SLE), that are suitable for high-pressure conditions. These techniques constitute enabling platforms for direct observation of fluid flow in surrogate permeable media and fractured systems under reservoir conditions.

Abstract

Pressure limitations of many microfluidic platforms have been a significant challenge in microfluidic experimental studies of fractured media. As a result, these platforms have not been fully exploited for direct observation of high-pressure transport in fractures. This work introduces microfluidic platforms that enable direct observation of multiphase flow in devices featuring surrogate permeable media and fractured systems. Such platforms provide a pathway to address important and timely questions such as those related to CO₂ capture, utilization and storage. This work provides a detailed description of the fabrication techniques and an experimental setup that may serve to analyze the behavior of supercritical CO₂ (scCO₂) foam, its structure and stability. Such studies provide important insights regarding enhanced oil recovery processes and the role of hydraulic fractures in resource recovery from unconventional reservoirs. This work presents a comparative study of microfluidic devices developed using two different techniques: photolithography/wet-etching/thermal-bonding versus Selective Laser-induced Etching. Both techniques result in devices that are chemically and physically resistant and tolerant of high pressure and temperature conditions that correspond to subsurface systems of interest. Both techniques provide pathways to high-precision etched microchannels and capable lab-on-chip devices. Photolithography/wet-etching, however, enables fabrication of complex channel networks with complex geometries, which would be a challenging task for laser etching techniques. This work summarizes a step-by-step photolithography, wet-etching and glass thermal-bonding protocol and, presents representative observations of foam transport with relevance to oil recovery from unconventional tight and shale formations. Finally, this work describes the use of a high-resolution monochromatic sensor to observe scCO₂ foam behavior where the entirety of the permeable medium is observed simultaneously while preserving the resolution needed to resolve features as small as 10 µm.

Introduction

Hydraulic fracturing has been used for quite some time as a means to stimulate flow especially in tight formations¹. Large amounts of water needed in hydraulic fracturing are compounded with environmental factors, water-availability issues², formation damage³, cost⁴ and seismic effects⁵. As a result, interest in alternate fracturing methods such as waterless fracturing and the use of foams is on the rise. Alternative methods may provide important benefits such as reduction in water use⁶, compatibility with water sensitive formations⁷, minimal to no plugging of the formation⁸, high apparent viscosity of the fracturing fluids⁹, recyclability¹⁰, ease of clean-up and proppant carrying capability⁶. CO₂ foam is a potential waterless fracturing fluid that contributes to more efficient production of petroleum fluids and improved CO₂ storage capacities in the subsurface with a potentially smaller environmental footprint compared to conventional fracturing techniques^6,7,11.

Under optimal conditions, supercritical CO₂ foam (scCO₂ foam) at pressures beyond the minimum miscibility pressure (MMP) of a given reservoir provides a multi-contact miscible system that is able to direct flow into less permeable parts of the formation, thereby improving sweep efficiency and recovery of the resources^12,13. scCO₂ delivers gas like diffusivity and liquid like density¹⁴ and is well suited for subsurface applications, such as oil recovery and carbon capture, utilization and storage (CCUS)¹³. The presence of the constituents of foam in the subsurface helps reduce the risk of leakage in long-term storage of CO₂¹⁵. Moreover, coupled-compressibility-thermal shock effects of scCO₂ foam systems may serve as effective fracturing systems¹¹. Properties of CO₂ foam systems for subsurface applications have been studied extensively at various scales, such as characterization of its stability and viscosity in sand-pack systems and its effectiveness in displacement processes^{3,6,12,15,16,17}. Fracture level foam dynamics and its interactions with porous media are less studied aspects that are directly relevant to the use of foam in tight and fractured formations.

Microfluidic platforms enable direct visualization and quantification of the relevant microscale processes. These platforms provide real-time control of the hydrodynamics and chemical reactions to study pore-scale phenomena alongside recovery considerations¹. Foam generation, propagation, transport and dynamics may be visualized in microfluidic devices emulating fractured systems and fracture-microcrack-matrix conductive pathways relevant to oil recovery from tight formations. Fluid exchange between fracture and matrix is directly expressed in accordance with the geometry¹⁸, thereby highlighting the importance of simplistic and realistic representations. A number of relevant microfluidic platforms have been developed over the years to study various processes. For example, Tigglaar and coworkers discuss fabrication and high-pressure testing of glass microreactor devices through in-plane connection of fibers to test flow through glass capillaries connected to the microreactors¹⁹. They present their findings related to bond inspection, pressure tests and in-situ reaction monitoring by ¹H NMR spectroscopy. As such, their platform may not be optimal for relatively large injection rates, pre-generation of multiphase fluid systems for in situ visualization of complex fluids in permeable media. Marre and coworkers discuss the use of a glass microreactor to investigate high-pressure chemistry and supercritical fluid processes²⁰. They include results as a finite-element simulation of stress distribution to explore the mechanical behavior of modular devices under the load. They use nonpermanent modular connections for interchangeable microreactor fabrication, and the silicon/Pyrex microfluidic devices are not transparent; these devices are suited for kinematic study, synthesis and production in chemical reaction engineering where visualization is not a primary concern. The lack of transparency makes this platform unsuitable for direct, in situ visualization of complex fluids in surrogate media. Paydar and coworkers present a novel way to prototype modular microfluidics using 3D printing²¹. This approach does not seem well-suited for high-pressure applications since it uses a photocurable polymer and the devices are able to withstand only up to 0.4 MPa. Most microfluidic experimental studies related to transport in fractured systems reported in literature focus on ambient temperature and relatively low-pressure conditions¹. There have been several studies with a focus on direct observation of microfluidic systems that mimic subsurface conditions. For example, Jimenez-Martinez and co-workers introduce two studies on critical pore-scale flow and transport mechanisms in a complex network of fractures and matrix^22,23. The authors study three-phase systems using microfluidics under reservoir conditions (8.3 MPa and 45 °C) for production efficiency; they assess scCO₂ usage for re-stimulation where the leftover brine from a prior fracturing is immiscible with CO₂ and the residual hydrocarbon²³. Oil-wet silicon microfluidic devices have relevance to mixing of oil-brine-scCO₂ in Enhanced Oil Recovery (EOR) applications; however, this work does not directly address pore-scale dynamics in fractures. Another example is work by Rognmo et al. who study an upscaling approach for high-pressure, in situ CO₂ foam generation²⁴. Most of the reports in literature that leverage microfabrication are concerned with CO₂-EOR and they often do not include important fabrication details. To the best of the authors’ knowledge, a systematic protocol for fabrication of high-pressure capable devices for fractured formations is currently missing from the literature.

This work presents a microfluidic platform that enables the study of scCO₂ foam structures, bubble shapes, sizes and distribution, lamella stability in the presence of oil for EOR and hydraulic fracturing and aquifer remediation applications. The design and fabrication of microfluidic devices using optical lithography and Selective Laser-induced Etching²⁹ (SLE) are discussed. Additionally, this work describes fracture patterns that are intended to simulate the transport of fluids in fractured tight formations. Simulated pathways may range from simplified patterns to complex microcracks based on tomography data or other methods that provide information regarding realistic fracture geometries. The protocol describes step-by-step fabrication instructions for glass microfluidic devices using photolithography, wet-etching and thermal bonding. An in-house developed collimated Ultra-Violet (UV) light source is used to transfer the desired geometric patterns onto a thin layer of photoresist, which is ultimately transferred to the glass substrate using a wet-etching process. As part of quality assurance, the etched patterns are characterized using confocal microscopy. As an alternative to photolithography/wet-etching, an SLE technique is employed to create a microfluidic device and a comparative analysis of the platforms is presented. The setup for flow experiments comprise gas cylinders and pumps, pressure controllers and transducers, fluid mixers and accumulators, microfluidic devices, high-pressure capable stainless-steel holders along with a high-resolution camera and an illumination system. Finally, representative samples of observations from flow experiments are presented.

Protocol

CAUTION: This protocol involves handling a high-pressure setup, a high-temperature furnace, hazardous chemicals, and UV light. Please read all relevant material safety data sheets carefully and follow chemical safety guidelines. Review pressure testing (hydrostatic and pneumatic) safety guidelines including required training, safe operation of all equipment, associated hazards, emergency contacts, etc. before starting the injection process.

1. Design geometrical patterns

1. Design a photomask comprising geometrical features and flow pathways of interest (Figure 1, Supplementary File 1: Figure S1).
2. Define the bounding box (surface area of the device) to identify the area of the substrate and confine the design to the dimensions of the desired medium.
3. Design inlet/outlet ports. Choose port dimensions (e.g., 4 mm in diameter in this case) to achieve a relatively uniform distribution of foam prior to entering the medium (Figure 1).
4. Prepare a photomask of the designed geometrical pattern by printing the design onto a sheet of transparent film or a glass substrate.
   1. Extrude the two-dimensional design to the third dimension and incorporate inlet and outlet ports (for use in SLE).
      NOTE: The SLE technique requires a three-dimensional drawing (Figure 2).

2. Transfer the geometric patterns to the glass substrate using photolithography

NOTE: Etchants and piranha solutions must be handled with extreme care. Use of personal protective equipment including facepiece reusable respirator, goggles, gloves and use of acid/corrosion resistant tweezers (Table of Materials) is recommended.

1. Prepare the solutions needed in the wet-etching process by following these steps (also see the electronic supporting information provided as Supplementary File 1).
   1. Pour an adequate amount of chrome etchant solution in a beaker such that the substrate can be submerged in the etchant. Heat up the fluid to approximately 40 °C.
   2. Prepare a solution of developer (Table of Materials) in deionized water (DI water) with a volumetric ratio of 1:8 such that the substrate is able to be fully submerge in the mixture.
2. Imprint the geometrical pattern on a borosilicate substrate coated with a layer of chromium and a layer of photoresist using UV irradiation.
   1. Using gloved hands, place the mask (glass substrate or the transparent film bearing the geometrical pattern) directly on the side of the borosilicate substrate that is covered with chrome and photoresist.
   2. Place the photomask and substrate combination under the UV light with the photomask facing the source.
      NOTE: This work uses UV light with a wavelength of 365 nm (to match the peak sensitivity of the photoresist) and at an average intensity of 4.95 mW/cm².
   3. Transfer the geometrical pattern into the layer of photoresist by exposing the stack of the substrate and the mask to UV light.
      NOTE: Optimum exposure time is a function of the thickness of the photoresist layer and the strength of UV radiation. Photoresist is sensitive to light and the entire process of imprinting the pattern must be performed in a dark room equipped with yellow lighting.
3. Develop the photoresist.
   1. Remove the photomask and substrate stack from the UV stage using gloved hands.
   2. Remove the photomask and submerge the substrate in the developer solution for approximately 40 s, thereby transferring the pattern to the photoresist.
   3. Cascade-rinse the substrate by flowing DI water from the top of the substrate and over all its surfaces a minimum of three times and allow the substrate to dry.
4. Etch the pattern in the chrome layer.
   1. Submerge the substrate in a chrome etchant heated to about 40 °C for approximately 40 s, thereby transferring the pattern from the photoresist to the chrome layer.
   2. Remove the substrate from the solution, cascade-rinse the substrate using DI water and allow it to dry.
5. Etch the pattern in the borosilicate substrate.
   NOTE: A buffered etchant (Table of Materials) is used to transfer the geometrical pattern to the glass substrate. Prior to the use of the buffered etchant, the backside of the substrate is coated with a layer of photoresist to shield it from the etchant. The thickness of this protective layer is immaterial to the overall fabrication process.
   1. Using a brush, apply several layers of hexamethyldisilazane (HMDS) on the uncovered face of the substrate and allow it to dry.
      NOTE: HMDS helps promote adhesion of photoresist to the surface of the borosilicate substrate.
   2. Apply one layer of photoresist on top of the primer. Place the substrate in an oven at 60‒90 °C for 30–40 min.
   3. Pour an adequate amount of the etchant into a plastic container and fully submerge the substrate in the etchant.
      NOTE: The etching rate is influenced by the concentration, temperature and duration of exposure. The buffered etchant used in this work etches an average of 1‒10 nm/min.
   4. Leave the patterned substrate in the etchant solution for a predetermined amount of time based on the desired channel depths.
      NOTE: Etching time may be reduced by intermittent bath sonication of the solution.
   5. Remove the substrate from the etchant using a solvent-resistant pair of tweezers and cascade-rinse the substrate using DI water.
   6. Characterize the etched features on the substrate to ensure desired depths have been achieved.
      NOTE: This characterization may be done using a laser scanning confocal microscope (Figure 3). In this work, a 10x magnification is used for data acquisition. Once channel depths are satisfactory, move to the cleaning and bonding stage.

3. Clean and bond

1. Remove photoresist and chrome layers.
   1. Remove the photoresist from the substrate by exposing the substrate to an organic solvent, such as N-Methyl-2-pyrrolidone (NMP) solution heated using a hot plate under a hood to approximately 65 °C for approximately 30 min.
   2. Cascade-rinse the substrate with acetone (ACS grade), followed by ethanol (ACS grade) and DI water.
   3. Place the cleaned substrate in chrome etchant heated using a hot plate under a hood to approximately 40 °C for about 1 min, thus removing the chrome layer from the substrate.
   4. Once the substrate is free from chrome and photoresist, characterize the channel depths using laser scanning confocal microscopy.
      NOTE: This work uses a 10x magnification for data acquisition (Figure 4).
2. Prepare the cover plate and the etched substrate for bonding.
   1. Mark the positions of the inlet/out holes on a blank borosilicate substrate (cover plate) by aligning the cover plate against the etched substrate.
   2. Blast through-holes in the marked locations using a micro abrasive sandblaster and 50 µm aluminum-oxide micro sandblasting media.
      NOTE: Alternatively, the ports may be created using a mechanical drill.
   3. Cascade rinse both the etched substrate and the cover plate with DI water.
   4. Perform an RCA wafer cleaning procedure to remove contaminants prior to bonding using standard technique. Perform the wafer cleaning steps under a hood due to the volatility of the solutions involved in the process.
   5. Bring a 1:4 by volume H₂O₂:H₂SO₄ piranha solution to a boil and submerge the substrate and the cover plate in the solution for 10 min under a hood.
   6. Cascade rinse the substrate and the cover plate with DI water.
   7. Submerge the substrate and the cover plate in the buffered etchant for 30–40 s.
   8. Cascade rinse the substrate and the cover plate with DI water.
   9. Submerge the substrate and the cover plate for 10 min in a 6:1:1 by volume DI water:H₂O₂:HCl solution that is heated to approximately 75 °C.
      NOTE: Etching and bonding are preferably performed in a cleanroom. If a cleanroom is not available, performing the following steps in a dust-free environment is recommended. In this work, steps 3.2.9–3.2.12 are performed in a glovebox to minimize the possibility of contamination of the substrates.
   10. Press the substrate and the cover plate tightly against each other while submerged.
   11. Remove the substrate and the cover plate from DI water:H₂O₂:HCl solution. Cascade rinse with DI water and submerge in DI water.
   12. Make sure the substrate and the cover plate are firmly attached together and carefully remove the two while pressed against each other from DI water.
3. Bond the substrates thermally.
   1. Place the stacked substrates (the etched substrate and the cover plate) between two smooth, 1.52 cm-thick, glass-ceramic plates for bonding.
   2. Place the glass-ceramic plates between two metallic plates made of Alloy X (Table of Materials), which is able to withstand the required temperatures without significant distortion.
   3. Center the glass wafers in the ceramic-metallic holder.
      NOTE: This work uses glass-ceramic plates that are 10 cm x 10 cm x 1.52 cm in thickness. The stacked setup is secured using 1/4” bolts and nuts (Figure 5).
   4. Hand-tighten the nuts and place the holder in a vacuum chamber for 60 min at approximately 100 °C.
   5. Remove the holder from the chamber and carefully tighten the nuts using approximately 10 lb-in of torque.
   6. Place the holder inside a furnace and execute the following heating program. Raise the temperature at 1 °C/min up to 660 °C; keep the temperature constant at 660 °C for 6 h followed by a cooling step at approximately 1 °C/min back down to room temperature.
   7. Remove the thermally bonded microfluidic device, rinse it with DI water, place it in HCl (12.1 M) and bath-sonicate (40 kHz at 100 W of power) the solution for one hour (Figure 6).

4. Fabricate laser-etched glass microfluidic devices

NOTE: Device fabrication was performed by a third-party glass 3D printing service (Table of Materials) via an SLE process and using a fused silica substrate as the precursor.

1. Write the desired pattern in a fused silica substrate using a linearly polarized laser beam oriented perpendicular to the stage generated via a femtosecond laser source with a pulse duration of 0.5 ns, a repetition rate of 50 kHz, pulse energy of 400 nJ, and a wavelength of 1.06 μm.
2. Remove the glass from the written pattern inside the fused silica substrate using a KOH solution (32 wt%) at 85 °C with ultrasound sonication (Figure 7).

5. Perform high-pressure testing

1. Saturate the microfluidic device with the resident fluid (e.g., DI water, surfactant solution, oil, etc. depending on the type of experiment) using a syringe pump.
2. Prepare foam-generating fluids and related instruments.
   1. Prepare the brine solution (resident fluid) with the desired salinity and dissolve the surfactant (such as lauramidopropyl betaine and alpha-olefin-sulfonate) with the desired concentration (according to surfactant’s critical micelle concentration) in the brine.
   2. Fill the tanks of the CO₂ and water pumps with adequate amounts of fluids per the experiment at room temperature.
   3. Fill the brine accumulator and flow lines with the surfactant solution using a syringe. This work uses an accumulator with a capacity of 40 mL.
   4. Rinse the brine line with the brine solution.
   5. Rinse the line connecting the accumulator to the device and the outlet lines with the resident fluid (the brine solution in this case).
   6. Place the saturated microfluidic device in a pressure-resistant holder and connect the inlet/outlet ports to the appropriate lines using 0.010” inner diameter tubing (Figure 8, Supplementary File 1: Figure S5).
   7. Increase the temperature of the circulating bath, which controls the temperature of the brine and CO₂ lines, to the desired temperature (e.g., 40 °C here (Figure 9)).
   8. Check all the lines to ensure the integrity of the setup prior to injection.
3. Generate the foam.
   1. Begin injecting the brine at a rate of 0.5 mL/min and check the flow of surfactant solution into the device and the backpressure line.
   2. Increase the backpressure and brine-pump pressure simultaneously in gradual steps (~ 0.006 MPa/s) while maintaining continuous flow from the outlet of the backpressure regulator (BPR). Increase the pressure up to ~7.38 MPa (minimum required scCO₂ pressure) and stop the pumps.
   3. Increase the CO₂ line pressure up to a pressure above 7.38 MPa (minimum scCO₂ pressure).
   4. Open the CO₂ valve and allow the scCO₂ mixed with the high-pressure surfactant solution to flow through an inline mixer to generate foam.
   5. Wait until flow is fully developed inside the device and the channels are saturated. Monitor the outlet for the onset of foam generation.
      NOTE: Auxiliary ports may be used to help pre-saturate the medium fully with the resident fluid (Figure 1). Inconsistencies in the rate of pressure build-up and sudden increases in BPR may lead to breakage (Figure 10). Fluid pressures and backpressure must be raised gradually to minimize the risk of damage to the device.
4. Perform real-time imaging and data analysis.
   1. Turn on the camera to capture detailed images of flow inside the channels. This work uses a camera featuring a 60 megapixel, monochromatic, full-frame sensor.
   2. Launch the dedicated shutter control software (Table of Materials). Select a shutter speed of 1/60, a focal ratio (f-number) of f/8.0, and select the appropriate lens.
   3. Launch the dedicated camera software (Table of Materials). Select the camera, the desired format (e.g., IIQL) and an ISO setting of 200 in the pulldown menu under the “CAMERA” setting of the software.
   4. Adjust the working distance of the camera to the medium as needed to focus on the medium. Capture images at prescribed time-intervals by pressing the capture button in the software.
5. Depressurize the system back to ambient conditions.
   1. Stop injection (gas and liquid pumps), close the CO₂ and brine pump inlets, open the rest of the line valves and turn off the heaters.
   2. Decrease the backpressure gradually (e.g., at a rate of 0.007 MPa/s) until the system reaches ambient pressure conditions. Decrease the brine and CO₂ pump pressures separately.
      NOTE: Decreasing the scCO₂ pressure may result in inconsistent or turbulent BPR outflow, therefore the pressure drawdown must be executed with requisite care.
6. Clean the microfluidic device thoroughly after each experiment as needed by flowing the following sequence of solutions through the medium: isopropanol/ethanol/water (1:1:1), 2 M HCl solution, DI water, a basic solution (DI water/NH₄OH/H₂O₂ at 5:5:1) and DI water.
7. Post-process collected images.
   1. Isolate the pore scape by excluding the background from the images.
   2. Correct minor misalignments by performing perspective transformation and implementing a local thresholding strategy as needed to account for non-uniform illumination²⁸_.
   3. Calculate geometrical and statistical parameters relevant to the experiment such as average bubble size, bubble size distribution and bubble shape for each foam microstructural images in the channel.

Results

This section presents examples of physical observations from scCO₂ foam flow through a main fracture connected to array of micro-cracks. A glass microfluidic device made via photolithography or SLE is placed inside a holder and in the field of view of a camera featuring a 60 megapixel, monochromatic, full-frame sensor. Figure 11 illustrates the process of fabrication microfluidic devices and their placement in the experimental setup. Figure 12 is illu...

Discussion

This work presents a protocol related to a fabrication platform to create robust, high-pressure glass microfluidic devices. The protocol presented in this work alleviates the need for a cleanroom by performing several of the final fabrication steps inside a glovebox. The use of a cleanroom, if available, is recommended to minimize the potential for contamination. Additionally, the choice of the etchant should be based on the desired surface roughness. The use of a mixture of HF and HCl as the etchant tends to reduce surf...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1/4” bolts and nuts			For fabrication of the metallic plates to sandwich the glass chip between them for thermal bonding
3.45 x 3.45 mm UV LED	Kingbright		To emitt LED light
3D measuring Laser microscope	OLYMPUS	LEXT OLS4000	To measure channel depths
40 mm x 40 mm x 10 mm 12V DC Cooling Fan	Uxcell		To cool the UV LED lights
120 mm x 38 mm 24V DC Cooling Fan	Uxcell		To cool the UV LED lights
5 ml (6 ml) NORM-JECT Syringe	HENKE SASS WOLF	Lot #16M14CB	To rinse the chip before each experiment
Acetone (Certified ACS)	Fisher Chemical	Lot #177121	For cleaning
Acid/ corossion resistive tweezer	TED PELLA		To handle the glass piece in corosive solutions
Acid/solvent resistance tweezers	TED PELLA, INC	#53009 and #53010	To handle the glass in corrosive solutions
Alloy X	AMERICAN SPECIAL METALS	Heat Number: ZZ7571XG11	Thermal bonding
Ammonium hydroxide (ACS reagent)	Sigma Aldrich	Lot #SHBG9007V	To clean the chip at the end of process
AutoCAD	Autodesk, San Rafael, CA		To design 2D patterns and 3D chips
BD Etchant for PSG-SiO2 systems	TRANSENE	Lot #028934	An improved buffered etch formulation for delineation of phosphosilica glass – SiO2 (PSG), and borosilica glass – SiO2 (BSG) systems
Blank Borofloat substrate	TELIC	CG-HF	Upper substrate for UV etching
Borofloat substrate with metalizations	TELIC	PG-HF-LRC-Az1500	Lower substrate for UV etching
Capture One photo editing software	Phase One		To Capture/Edit/Convert the pictures taken by Phase One Camera
Capture station	DT Scientific	DT Versa	To place of the chip in the field of view of the camera
Carbon dioxide gas (Grade E)	PRAXAIR	UN 1013, CAS Number 124-38-9	non-aqeous portion of foam
Chromium etchant 1020	TRANSENE	Lot #025433	High-purity ceric ammonium nitrate systems for precise, clean etching of chromium and chromium oxide films.
Circulating baths with digital temperature controller	PolyScience		To control the brine and CO2 temperatures
Computer		NVIDIA Tesla K20 Graphic Card - 706 MHz Core - 5 GB GDDR5 SDRAM - PCI Express 2.0 x16	To process and visualize the images obtained via the Phase One camera
Custom made high pressure glass chip holder			To tightly hold the chip and its connections for high pressure testing
Cutrain (Custom)			To protect against UV/IR Radiations
Deionized water (DI)			For cleaning
Digital camera with monochromatic 60 MP sensor	Phase One	IQ260	Visualization system
Ethanol, Anhydrous, USP Specs	DECON LABORATORIES, INC.	Lot #A12291505J, CAS# 64-17-5	For cleaning
Facepiece reusable respirator	3M	6502QL, Gases, Vapors, Dust, Medium	To protect against volatile solution inhalation
Fused Silica (UV Grade) wafer	SIEGERT WAFER	UV grade	Glass precursor for SLE printing
GIMP	Open-source image processing software		To characterize image texture and properties
Glovebox (vinyl anaerobic chamber)	Coy		To provide a clean, dust-free environment
Heated ultrasonic cleaning bath	Fisher Scientific		To accelerate the etching process
Hexamethyldisilazane (HMDS) Cleanroom® MB	KMG	62115	Primer for photoresist coating
Hose (PEEK tubing)	IDEX HEALTH & SCIENCE	Natural 1/16" OD x .010" ID x 5ft, Part # 1531	Flow connections
Hydrochloric acid, certified ACS plus	Fisher Chemical	Lot # 187244	Solvent in RCA semiconductor cleaning protocol
Hydrogen Peroxide	Fisher Chemical	H325-500	Solvent in RCA semiconductor cleaning protocol
ImageJ	NIH		To characterize image texture and properties
ISCO syringe pump	TELEDYNE ISCO	D-SERIES (100DM, 500D)	To pump the fluids
Kaiser LED light box	Kaiser		To illuminate the chip
Laser printing machine	LightFab GmbH, Germany.	FILL	Glass-SLE chip fabrication
Laser safety glasses	FreeMascot	B07PPZHNX4	To protect against UV/IR Radiations
LED Engin 5W UV Lens	LEDiL		To emitt LED light
Light Fab 3D Printer (femtosecond laser)	Light Fab		To selectively laser Etch of fused silica
LightFab 3D printer	LightFab GmbH, Germany		To SLE print the fused silica chips
MATLAB	MathWorks, Inc., Natick, MA		Image processing
Metallic plates
Micro abrasive sand blasters (Problast 2)	VANIMAN	Problast 2 – 80007	To craete holes in cover plates
MICROPOSIT 351 developer	Dow	10016652	Photoresist developer solution
Muffle furnace	Thermo Scientific	Thermolyne Type 1500	Thermal bonding
N2 pure research grade	Airgas	Research Plus - NI RP300	For drying the chips in each step
NMP semiconductor grade - 0.1μm Filtered	Ultra Pure Solutions, Inc	Lot #02191502T	Organic solvent
Oven	Gravity Convection Oven	18EG
Phase One IQ260 with an achromatic sensor	Phase One	IQ260	To visulize transport in microfluidic devices using an ISO 200 setting and an aperture at f/8.
Photomask	Fine Line Imaging	20,320 DPI FILM	Pattern of channels
Photoresist (SU-8)	MICRO CHEM	Product item: Y0201004000L1PE, Lot Number: 18110975	Photoresist
Polarized light microscope	OLYMPUS	BX51	Visual examination of micro channels
Ports (NanoPort Assembly)	IDEX HEALTH & SCIENCE	NanoPort Assembly Headless, 10-32 Coned, for 1/16" OD, Part # N-333	Connections to the chip
Python	Python Software Foundation		Image processing
Safety face shield	Sellstrom	S32251	To protect against UV/IR Radiations
Sealing film (Parafilm)	Bemis Company, Inc		Isolation of containers
Shutter Control Software	Schneider-Kreuznach		To adjust shutter settings
Smooth ceramic plates			Thermal bonding
Stirring hot plate	Corning®	PC-620D	To heat the solutions
Sulfuric acid, ACS reagent 95.0-98.0%	Sigma Aldrich	Lot # SHBK0108	Solvent in RCA semiconductor cleaning protocol
Syringe pump (Standard Infuse/Withdraw PHD ULTRA)	Harvard Apparatus	70-3006	To saturate the chip before each experiment
Torque wrench	Snap-on	TE25A-34190	To tighten the screws
UV power meter	Optical Associates, Incorporated	Model 308	To measure the intesity of UV light
UV power meter	Optical Associates, Incorporated	Model 308	To quantify the strength of UV light
UV radiation stand (LED lights)			To transfer the pattern to glass (photoresist layer)
Vaccum pump	WELCH VACCUM TECHNOLOGY, INC	1380	To dry the chip
Variable DC power supplies	Eventek	KPS305D	To power the UV LED lights