Microfluidic device and system for studying abnormal migration of solute of fractured porous medium system

Abstract

The utility model discloses a microfluid device and a system for researching abnormal migration of solute of a fractured porous medium system. The microfluid device for studying abnormal migration of the solute of the fractured porous medium system comprises a chip and a substrate, wherein the lower surface of the chip is bonded with the upper surface of the substrate; a crack and a porous medium area distributed around the crack are patterned on the lower surface of the chip; the porous medium area comprises a plurality of cylinders, gaps are reserved among the cylinders, and flow channels communicated with the cracks are formed; and a part or all of the cylinders in the porous medium area are provided with notches serving as blind ends. The microfluid system for studying abnormal migration of the solute of the fractured porous medium system comprises a fluid injection device, the microfluid device and a fluid collection device which are connected in sequence.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of microfluidic devices, specifically to a kind of microfluidic device and system for studying fissure porous medium system solute abnormal migration. BACKGROUND

[0002] Fissure structure widely exists in natural process, since its permeability is obviously higher than surrounding area, it often becomes the main passage of fluid flow and solute transport, so it is very important to analyze and predict fluid motion and solute transport in fissure system. At present, the research on fissure-low permeability matrix system and fissure-porous medium system is focused on numerical simulation, lacking the support of actual experimental data, it is difficult to verify the accuracy and effectiveness of numerical model. The traditional in-situ monitoring and soil column experiment method of fissure is limited in monitoring the flow and transport of matrix or porous medium inside and around fissure, has the shortcomings of limited observation data, weak repeatability, long experimental time, etc., which hinders further research.

[0003] The patent specification with publication number CN114112840A discloses a test device and method for studying the seepage characteristics of pore-fissure double medium, which comprises a flow injection control system, a test main body system and a monitoring and analysis imaging system. The test main body system comprises a mounting frame, a clamp assembly and a chip sample. The chip sample is clamped on the clamp assembly and comprises an upper cover layer, a middle core layer and a lower pad layer bonded as a whole. The middle core layer has a plurality of pore-fissure seepage zones in the middle. The pore-fissure seepage zones have pore channels and fissure channels. The middle core layer has inflow and outflow channels at both ends, which are connected with the pore-fissure seepage zones. The inflow channel has a water injection port. The outflow channel comprises three outflow branches, one of which is connected with the fissure channel, and the other two are connected with the pore channel. Each outflow branch has a water outlet, and the outflow branches converge into a total water outlet. UTILITY MODEL CONTENT

[0004] The utility model provides a kind of microfluidic device and system for studying fissure porous medium system solute abnormal migration. The utility model can visualize solute transport process in fissure-porous medium system, and record full-field data in whole process. The utility model also has the characteristics of strong repeatability and short experimental time, which can overcome the shortcomings of limited observation data, weak repeatability and long experimental time of existing experimental methods.

[0005] [1] A microfluidic device for studying fissure porous medium system solute abnormal migration, comprising a chip and a substrate, the lower surface of the chip and the upper surface of the substrate are bonded.

[0006] The lower surface of the chip is patterned with fissures and porous medium regions distributed around the fissures.

[0007] The porous medium region comprises a plurality of cylinders, and gaps are left between the cylinders to form flow channels communicating with the fissure;

[0008] Part or all of the cylinders in the porous medium region are provided with notches as blind ends.

[0009] In some embodiments, the microfluidic device, the depth of the notch on the cylinder can be 40% to 60% of the diameter of the cylinder.

[0010] In some embodiments, the microfluidic device, the arc length of the notch on the cylinder can account for 1 / 8 to 1 / 4 of the circumference of the cylinder.

[0011] In some embodiments, the microfluidic device, the cylinders in the porous medium region can be arranged in a longitudinal and transverse staggered array. Further, the orientations of the notches on the cylinders in different transverse rows can be different.

[0012] In some embodiments, the microfluidic device can further comprise a fluid injection inlet, a fluid injection buffer zone, a fluid injection connection zone, a fluid outflow connection zone, a fluid outflow buffer zone and a fluid outflow outlet; the fluid injection inlet, the fluid injection buffer zone and the fluid injection connection zone are sequentially communicated with one end of the fissure, and the other end of the fissure is sequentially communicated with the fluid outflow connection zone, the fluid outflow buffer zone and the fluid outflow outlet. Further, the fluid injection inlet and the fluid outflow outlet can be provided on the upper surface of the chip, and the fluid injection buffer zone, the fluid injection connection zone, the fluid outflow connection zone and the fluid outflow buffer zone can be patterned on the lower surface of the chip.

[0013] In some embodiments, the microfluidic device, the notch of the cylinder can be filled with hydrogel. The hydrogel itself and the filling method can adopt the prior art.

[0014] [2] A microfluidic system for studying abnormal solute transport in a fissure porous medium system, comprising a fluid injection device, the microfluidic device of [1] and a fluid collection device connected in sequence.

[0015] In some embodiments, the microfluidic system, a camera device for observation and recording can be arranged above the microfluidic device.

[0016] In some embodiments, the microfluidic system, a light emitting device for irradiating the microfluidic device can be arranged below the microfluidic device.

[0017] Compared with the prior art, the microfluidic device has the beneficial effects that:

[0018] In porous media flow, blind end often forms a closed area, and the flow in the blind end is quite different from the flow in the pores. Meanwhile, for solute transport in porous media, the blind end will intercept solute in many cases, leaving the solute in the blind end and not flowing out with the flow, thereby causing abnormal transport. Designing a blind end in a porous media cylinder helps to further explore the influence of the blind end on the flow and the influence of the blind end on the abnormal transport of solute.

[0019] On the basis of the above-mentioned designed cylinder containing a blind end, the blind end in the cylinder can be further filled with hydrogel. Such a chip structure with a solid hydrogel blind end filling can be used for conservative solute transport, release experiment and solute reaction experiment based on requirements. For the conservative solute transport experiment, after being washed with clean water, a solution containing solute can be directly injected, and the solute will flow in the structure and exchange and diffuse in the blind end. For the conservative solute release experiment and solute reaction experiment, a solution containing solute A can be first injected and left for a certain period of time, and then solute A in the pores is washed away with clean water, while solute A in the hydrogel is still retained; then clean water or solute B is slowly injected, and the release of solute A in the blind end hydrogel or the reaction of the released solute A in the hydrogel with the injected solute B can be observed. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A chip patterning structure schematic diagram of a microfluidic device for studying solute abnormal transport in a fractured porous media system is provided in the specific embodiment;

[0021] Figure 2 A local enlarged view of a porous media area of a microfluidic device for studying solute abnormal transport in a fractured porous media system is provided in the specific embodiment;

[0022] Figure 3 A structure schematic diagram of a microfluidic system for studying solute abnormal transport in a fractured porous media system is provided in the specific embodiment. DETAILED DESCRIPTION

[0023] The utility model will be further described below in combination with the drawings and specific embodiments. It should be understood that these embodiments are only used for illustrating the utility model and are not used for limiting the scope of the utility model.

[0024] A microfluidic device for studying solute abnormal transport in a fractured porous media system includes a chip and a substrate, and the lower surface of the chip is bonded to the upper surface of the substrate. Referring to Figure 1, the lower surface of the chip is patterned with a fluid injection buffer zone 2, a fluid injection connecting zone 3, a fissure 4, a porous medium zone 5 distributed around the fissure 4, a fluid outflow connecting zone 6 and a fluid outflow buffer zone 7; the upper surface of the chip is provided with a fluid injection port 1 and a fluid outflow port 8. The fluid injection port 1, the fluid injection buffer zone 2, the fluid injection connecting zone 3 and one end of the fissure 4 are sequentially connected, and the other end of the fissure 4 is sequentially connected with the fluid outflow connecting zone 6, the fluid outflow buffer zone 7 and the fluid outflow port 8. For example, the length of the fissure 4 and the porous medium zone 5 is 50 mm, the width of the fissure 4 is 0.5 mm, and the width of the porous medium zone 5 is 10.5 mm. Figure 1 For the fluid injection zone on the left side of the middle, a fluid injection connecting zone 3 is added, the left end of the fluid injection connecting zone 3 is connected with the fluid injection buffer zone 2, and the right end is connected with the inlet of the fissure 4, and the length of the fluid injection connecting zone 3 is 2 mm. The radius of the fluid injection buffer zone 2 is 1.5 mm, which is used to buffer the injected fluid and stabilize the fluid inflow velocity. The center of the fluid injection buffer zone 2 is the fluid injection port 1, and the radius of the fluid injection port 1 is 0.25 mm, which is used to connect the catheter to inject fluid during the experiment. Figure 1 For the fluid outflow zone on the right side of the middle, a fluid outflow connecting zone 6 is added, the left side of the fluid outflow connecting zone 6 is connected with the outlet of the fissure 4, and the right side is connected with the fluid outflow buffer zone 7, and the length of the fluid outflow connecting zone 6 is 5 mm. The radius of the fluid outflow buffer zone 7 is 1.5 mm, which is used to buffer the outflow fluid. The center of the fluid outflow buffer zone 7 is the fluid outflow port 8, and the radius of the fluid outflow port 8 is 0.25 mm, which is used to connect the catheter to outflow fluid during the experiment.

[0025] In combination Figure 2 The porous medium zone 5 comprises a plurality of cylinders 9, and gaps are left between the cylinders 9 to form flow channels communicating with the fissure 4. Part or all of the cylinders 9 in the porous medium zone 5 are provided with notches 10 as blind ends, which are used to study the influence of the blind ends in the porous medium on solute transport and solute reaction. The depth of the notches 10 provided on the cylinders 9 can be 40% to 60% of the diameter of the cylinders 9. The arc length where the notches 10 are provided on the cylinders 9 can account for 1 / 8 to 1 / 4 of the circumference of the cylinders 9. The cylinders 9 in the porous medium zone 5 are arranged in a staggered array, and the notches 10 on the cylinders in different rows are oriented differently. For example, as shown in Figure 2 For the original cylinders 9 with a radius of 0.2 mm, notches 10 are provided in the cylinders 9. Specifically, the blind end is a cuboid with a length (i.e. the depth of the notch 10) of 0.2 mm, a width of 0.1 mm and a height (i.e. the height of the flow channel) of the height of the cylinder 9, and the orientation has four directions of three o'clock, six o'clock, nine o'clock and twelve o'clock. In the porous medium, the blind ends of each row are oriented in the same direction, and the blind ends of adjacent columns are oriented differently.

[0026] In some embodiments, the notch 10 of the cylinder 9 of the microfluidic device described above can be filled with hydrogel. The hydrogel itself and the filling method can be of the prior art. An exemplary specific method is given here: 10 mL of 20% acrylamide, 1% bisacrylamide, 20 mg / mL photoinitiator 4-(2-hydroxyethoxy)phenyl-2-hydroxy-2-propyl ketone 200 mg are mixed thoroughly, and by changing the concentration of the polymer solution, the porosity and permeability of the resulting hydrogel can be adjusted. The fracture-porous medium structure containing blind-end cylinders is made into a PDMS chip, the microfluidic channel is filled with a hydrogel polymer solution, and then based on the porous medium-fracture mask of the pure cylinder, the other porosity flow parts are masked, and the hydrogel part in the cylinder 9 and the blind end is exposed to 350-360 nm wavelength ultraviolet light for 20 s for curing. The polymer solution exposed to ultraviolet light is cured into hydrogel, while the unexposed area remains fluid. Then the residual unreacted hydrogel is washed with distilled water containing buffer solution and sodium chloride, and the target structure is obtained, which is filled with solid hydrogel in the blind end of the cylinder 9.

[0027] Referring to Figure 3 A microfluidic system for studying the anomalous transport of solutes in fracture-porous medium systems includes a fluid injection device, the microfluidic device 11 described above filled or not filled with hydrogel, and a fluid collection device connected in sequence. The fluid injection device includes a syringe pump 17 and a syringe 18 mounted on the syringe pump 17, and the syringe 18 is connected to the fluid injection inlet 1 through a soft catheter 13 and an L-shaped joint 12 in sequence. The fluid collection device includes a waste tank 14, and the fluid flow outlet 18 is connected to the waste tank 14 through an L-shaped joint 12 and a soft catheter 13 in sequence. Above the microfluidic device 11 is provided with a camera device for observation and recording. The camera device includes a camera and lens 19 and a computer 20 connected to the camera and lens 19 for controlling the camera and lens 19. Below the microfluidic device 11 is provided with a light-emitting device for irradiating the microfluidic device 11. The light-emitting device includes a light-emitting plate 16 and a power supply 15 connected to the light-emitting plate 16 for controlling the light-emitting plate 16.

[0028] The utility model discloses can be based on the self-affine nature of natural fissure shape, uses Hirst index H to measure the roughness degree of fissure, generates fissure channel with different roughness based on algorithm using different H. The fissure channel can be specifically designed with reference to the prior art. The utility model discloses can use the same size cylinder, based on different spacing, repeatedly arrange to generate the uniform porous medium with different porosity. Different fissure channel and different porous medium are combined, the fissure shape and porous medium pore after combination are retained, and the cylinder in the fissure channel is removed to generate different fissure-porous medium system. Based on the generated fissure-porous medium system, a mask is made, a siliceous mold is made using ultraviolet soft lithography method using the mask, and a chip of PDMS (polydimethylsiloxane) material is made using the mold based on the pouring method. The chip is installed in an experimental platform with a stable light source and an optical camera, and a catheter is used to connect the chip with a syringe containing a colored experimental solute such as methyl blue and a waste liquid device. During the experiment, the solute is injected at a predetermined flow rate using a syringe pump, the colored solute migration in the chip is observed, and data is collected using an optical camera.

[0029] Because the PDMS material has good light transmittance, chemical inertness and hydrophobicity, the solute migration in the chip fissure-porous medium system structure can be observed and sufficient observation data can be recorded. After the experiment is completed, the chip can be cleaned and recycled for the next experiment or based on the mold for pouring again. Compared with the traditional experimental method, the utility model has the advantages of large amount of observation data, high observation resolution, short experiment time, low experiment cost, easy experiment platform construction and good repeatability.

[0030] During the solute migration experiment, the fluid containing the colored solute such as methyl blue dye enters the microfluidic device through the catheter through the fluid injection port, is buffered in the fluid inflow buffer zone, enters the inlet of the fissure channel through the fluid injection connection zone, and flows freely in the fissure-porous medium combination. Due to the difference in permeability and dispersion of the fissure region and the porous medium, the fluid and the solute will preferentially flow through the fissure region, and the flow and diffusion in the porous medium region will be lagged, causing abnormal migration. After the fluid and the solute reach the fissure outlet, they enter the fluid outflow buffer zone through the fluid outflow connection zone, and then leave the microfluidic device through the fluid outflow port. Due to the transparency of the PDMS material, the migration of the colored solute in the microfluidic device can be recorded by the camera with high precision.

[0031] The microfluidic device can be formed by bonding two parts, the first part is a PDMS chip processed by soft lithography, the microfluidic channel, fissure and porous medium area are patterned on the lower surface of the PDMS chip, and the height of the channel, fissure and porous medium area can be 150 mm. The second part is a substrate, which can be a glass sheet cleaned by alcohol and water. After the above two parts are cleaned by plasma, the lower surface of the PDMS chip is bonded to the upper surface of the glass sheet, and the microfluidic device is obtained.

[0032] The microfluidic device can be formed by bonding two parts, the first part is a PDMS chip processed by soft lithography, the microfluidic channel, fissure and porous medium area are patterned on the lower surface of the PDMS chip, and the height of the channel, fissure and porous medium area can be 150 mm. The second part is a substrate, which can be a glass sheet cleaned by alcohol and water. After the above two parts are cleaned by plasma, the lower surface of the PDMS chip is bonded to the upper surface of the glass sheet, and the microfluidic device is obtained.

[0033] In the following, an exemplary preparation and use method of the microfluidic device of the utility model will be stated, which comprises the following steps:

[0034] Step 1, use a silicon wafer with a radius of 50 mm as a mold base, blow the surface dust of the silicon wafer with high-purity nitrogen, and heat it at a temperature of 200 DEG C for 30 min to remove other impurities on its surface.

[0035] Step 2, after cooling the heated silicon wafer, pour 3-4 mL of photoresist SU-8 onto its smooth surface, tilt the silicon wafer to make the photoresist evenly cover it, fix it in a spin coater, and spin at a speed of 2200 r / min for 15 s to make the silicon wafer surface evenly cover the photoresist with a thickness of 150 um.

[0036] Step 3, place the silicon wafer after completing the spin coating on a heating table, heat it at 95 DEG C for 90 s, and then heat it at 65 DEG C for 390 s. After the heating is finished, cool the silicon wafer to room temperature.

[0037] Step 4, stack the light-shielding mask prepared in advance on the silicon wafer, fix the silicon wafer in a photoetching machine, open the air float to make the light-shielding mask tightly adhere to the surface of the silicon wafer, turn on the photoetching machine, and expose it to ultraviolet light for 20 s to make the part of the photoresist contacting the ultraviolet light react and crosslink.

[0038] Step 5, after the exposure is finished, place the silicon wafer on a heating table, heat it at 95 DEG C for 90 s, and then heat it at 65 DEG C for 390 s. After the heating is finished, cool the silicon wafer to room temperature.

[0039] Step 6, put the finished silicon wafer into the developing solution for development. The photoresist that did not contact the UV light during the exposure and did not crosslink is removed by the developing solution. Each time the silicon wafer is placed in the developing solution for 5 minutes of shaking, then the silicon wafer is removed and new developing solution is used for the next development. After 3 or more developments, the silicon wafer is ensured to have the photoresist completely removed.

[0040] Step 7, place the silicon wafer that has finished the development step on a heating stage and heat at 95°C for 15 minutes to remove the residual developing solution and to strengthen the attachment of the crosslinked photoresist portion to the silicon wafer.

[0041] Step 8, place the silicon wafer in a closed container and add 3-5 mL of trimethylchlorosilane to the container. After one night, the silicon wafer is removed and the trimethylchlorosilane is attached to the surface of the silicon wafer for the subsequent PDMS chip fabrication. The silicon wafer-crosslinked photoresist combination that has finished the above steps is collectively referred to as a PDMS mold, which can be used to repeatedly fabricate PDMS chips.

[0042] Step 9, mix 30 grams of PDMS reagent with 3 grams of curing agent and mix thoroughly. Place the mixture in a closed container and use a vacuum pump to remove air bubbles that are generated during the mixing for 45 minutes. Use aluminum foil to wrap the bottom and sides of the mold to form a mold channel. Pour the mixture that has finished the air removal into the mold channel to uniformly cover the surface of the mold. Use an ear bulb to blow away the air bubbles that are generated during the pouring.

[0043] Step 10, place the mold channel that contains the PDMS and curing agent mixture in an oven. For the oven, pre-adjust the oven rack to be in a horizontal plane. After using the oven to heat at 80°C for 120 minutes, cool the oven to room temperature. After the heating, the PDMS mixture is cured on the surface of the mold.

[0044] Step 11, remove the aluminum foil outside the mold and slowly remove the PDMS from the surface of the mold. Use a knife to cut the removed PDMS to obtain the portion of the PDMS that is needed. Use a punch with a radius of 0.25 mm to vertically punch the PDMS at the areas corresponding to the fluid injection port 1 and the fluid flow outlet 8. After the punching, remove the PDMS filament inside the punch needle. Seal the lower surface of the PDMS that has finished the cutting and punching (the surface that has the flow channel) using tape for later use.

[0045] Step 12, select a glass wafer with an appropriate size according to the size of the PDMS chip. Use 75% ethanol solution to clean the glass wafer and then dry the glass wafer for later use.

[0046] Step 13, place the cleaned glass slide and the PDMS chip with the tape removed into the plasma cleaner, make sure the parts that need to be bonded later, the top surface of the glass slide and the bottom surface of the PDMS chip, are facing upwards. Turn on the vacuum centrifuge and the plasma cleaner, and perform the plasma cleaning for about 2 minutes.

[0047] Step 14, after the cleaning is completed, take out the glass slide and the PDMS chip, align the top surface of the glass slide and the bottom surface of the PDMS chip, and press them slightly with fingers to improve the tightness of the bonding.

[0048] Step 15, place the bonded device into an oven, heat it at 80°C for 15 minutes, then cool it to room temperature, seal the surface of the chip with tape, and store it for later use.

[0049] Step 16, when performing the solute anomalous transport experiment, remove the tape on the surface of the chip, connect the fluid injection port and the fluid flow outlet of the chip to the soft catheter through the L-shaped joint, connect the catheter on one side of the fluid injection port to a 1 mL syringe, fill the syringe with the experimental fluid containing the color dye methyl blue, and connect the catheter on one side of the fluid flow outlet to the waste liquid storage container.

[0050] Step 17, load the syringe into the injection control unit of the syringe pump, fix the microfluidic device on the horizontal support, set a uniform light source below the support, and set an optical camera above the support, connect the optical camera to the computer, and adjust the exposure time, focal length of the optical camera, and light intensity of the uniform light source to obtain the best observation effect.

[0051] Step 18, complete the setting of the injection parameters of the syringe pump, perform the injection operation, set the camera picture saving parameters in the computer, and start the timed sampling of the optical camera picture data, so as to realize the observation and recording of the solute anomalous transport in the fracture-porous medium system during the experiment.

[0052] Step 19, after the completion of the anomalous transport experiment, use the dye solution with a known concentration prepared in advance to saturate the device, obtain the image data with a known concentration, and use it to determine the standard curve of solute concentration-image gray value.

[0053] Step 20, use the concentration-gray value standard curve obtained in step 19 to convert the gray value to concentration for the anomalous transport experiment image obtained, to obtain the concentration data of the experiment, based on which further analysis can be performed, such as analyzing the anomalous transport phenomenon and comparing it with the results of numerical simulation, so as to verify and optimize the numerical simulation method.

[0054] In addition, it should be understood that, after reading the above description of the present application, those skilled in the art can make various changes or modifications to the present application, and these equivalent forms also fall within the scope of the appended claims.

Claims

1. A microfluidic device for studying solute anomalous transport in fractured porous media systems, characterized in that, The chip and the substrate are bonded by the lower surface of the chip and the upper surface of the substrate; The lower surface of the chip is patterned with a slit and a porous medium region distributed around the slit; The porous medium region contains a plurality of cylinders with gaps between them, forming flow channels communicating with the slit; Some or all of the cylinders in the porous medium region are provided with notches as blind ends.

2. The microfluidic device of claim 1, wherein, The depth of the notches on the cylinders is 40% to 60% of the diameter of the cylinders; The arc length of the notches on the cylinders accounts for 1 / 8 to 1 / 4 of the circumference of the cylinders.

3. The microfluidic device of claim 1, wherein, The cylinders in the porous medium region are arranged in a staggered array, and the notches on the cylinders in different horizontal rows are oriented in different directions.

4. The microfluidic device of claim 1, wherein, The microfluidic device further comprises a fluid injection inlet, a fluid injection buffer zone, a fluid injection connection zone, a fluid outflow connection zone, a fluid outflow buffer zone and a fluid outflow outlet; The fluid injection inlet and the fluid outflow outlet are provided on the upper surface of the chip; The fluid injection buffer zone, the fluid injection connection zone, the fluid outflow connection zone and the fluid outflow buffer zone are patterned on the lower surface of the chip; The fluid injection inlet, the fluid injection buffer zone and the fluid injection connection zone are sequentially connected to one end of the slit, and the other end of the slit is sequentially connected to the fluid outflow connection zone, the fluid outflow buffer zone and the fluid outflow outlet.

5. The microfluidic device according to any one of claims 1 to 4, wherein The notches of the cylinders are filled with hydrogel.

6. A microfluidic system for studying solute anomalous transport in fractured porous media systems, characterized in that, The microfluidic device is connected to a fluid injection device and a fluid collection device in sequence.

7. The microfluidic system of claim 6, wherein, A camera device is provided above the microfluidic device for observation and recording.

8. The microfluidic system of claim 6 or 7, wherein, A light-emitting device is provided below the microfluidic device for irradiating the microfluidic device.

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