A method for constructing a high-oriented structure of MXene based on soft lithography microfluidics and flow field simulation optimization

Abstract

The application discloses a kind of based on microfluidic shear field induced MXene high orientation structure construction method, belong to flexible electronic and micro-nano manufacturing technical field.This method uses PDMS substrate as carrier, provides the limited microchannel of laminar shear action by CAD design and combines multi-physics field simulation optimization, constructs programmable fluid shear field;Utilize shear stress to induce MXene nanosheet to overcome Brownian motion, realize accurate orientation and dense stacking along streamline direction, and lock high orientation structure on substrate surface by in-situ crosslinking.The significant reduction of MXene interlayer grain boundary scattering and the order of magnitude improvement of carrier mobility are realized, so as to give the device excellent anisotropic conductive performance and mechanical robustness.The preparation method includes microfluidic chip soft lithography, flow field simulation optimization, shear induction directional assembly and in-situ curing packaging and other steps, and the process controllability is strong.The high orientation structure has wide application prospect in the fields of flexible transparent electrode, bionic electronic skin and high-performance strain sensor.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and specifically to a method for constructing MXene highly oriented structures based on soft lithography microfluidics and flow field simulation optimization. Background Technology

[0002] With the explosive growth of flexible electronics, electronic skin, wearable health monitoring, and soft robotics, the requirements for conformal bonding, extreme deformation tolerance, and long-term operational stability of electronic devices are becoming increasingly stringent. While traditional rigid inorganic semiconductors and metal thin films possess excellent electrical properties, they are prone to fatigue cracking under repeated bending, stretching, or torsion, leading to interruptions in conductive pathways and failing to meet the development needs of next-generation stretchable electronic devices. Therefore, developing novel low-dimensional material systems that combine atomic-level thickness, tunable electrical properties, and intrinsic flexibility has become a core research direction in the field of flexible electronics.

[0003] With its ultra-thin structure, high carrier mobility and excellent mechanical flexibility, MXene not only has excellent conductivity but also hydrophilicity. It can be fabricated on a large scale through solution processing and is regarded as an ideal candidate material to break through the current performance bottleneck of flexible electronics. It is widely used in flexible transparent conductive films, high-performance sensors, energy storage devices and logic circuits.

[0004] However, the integration and application of MXene on flexible substrates still face significant technical bottlenecks. Due to the lack of effective orientation control during solution processing or transfer, MXene nanosheets are prone to disordered stacking, random aggregation, and wrinkling, leading to numerous grain boundaries and interface scattering centers. This lack of microstructural order severely hinders efficient carrier transport, resulting in device performance far below the intrinsic material level. Furthermore, traditional spin-coating and drop-coating methods struggle to achieve oriented and compact stacking of nanosheets at specific spatial locations, resulting in high interlayer contact resistance and difficulty in forming a stable interfacial bond with the flexible substrate. Especially under dynamic deformation conditions, disordered stacked MXene layers are prone to slippage or peeling, severely impacting the device's electrical stability and cycle life.

[0005] Currently, to improve the ordered arrangement of MXenes, studies have attempted to use the Langmuir-Blodgett (LB) film method or shear coating technology. However, these methods generally suffer from long preparation cycles, difficulty in large-area continuous production, or poor compatibility with flexible micro / nano fabrication processes. They are still unable to achieve precise programming of MXene orientation, stacking patterns, and heterogeneous interfaces while simultaneously meeting high-throughput manufacturing requirements. Therefore, there is an urgent need to provide a microfluidic preparation method for highly oriented MXene structures based on soft lithography and flow field simulation optimization. This method aims to address the technical challenges of poor wettability, disordered arrangement, and unstable interfacial contact of MXene nanosheets on flexible substrates, thereby enabling the large-scale fabrication of high-performance, high-reliability flexible electronic devices. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the present invention aims to provide a method for constructing highly oriented MXene structures based on soft lithography microfluidics and flow field simulation optimization. This method addresses the technical problems of disordered arrangement of MXene on flexible substrates, severe grain boundary scattering, and high interfacial contact resistance. It enables controllable orientation and dense stacking of MXene nanosheets in a fluid environment, thereby improving the carrier mobility and mechanical durability of flexible electronic devices.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] Step 1: Design the microchannel mask layout using CAD software, and fabricate a PDMS microfluidic chip with a specific shrinkage ratio using soft photolithography.

[0009] Step 2: Use multiphysics simulation software to numerically simulate the velocity distribution and shear stress field in the flow channel, and calibrate the optimal flow range and geometric parameters for inducing MXene orientation.

[0010] Step 3: Prepare a highly stable MXene dispersion with specific rheological properties, and use the strong shear field generated by the microfluidic chip to induce the nanosheets to align in a highly oriented manner;

[0011] Step four involves locking the oriented MXene structure onto the surface of a flexible substrate through in-situ curing or rapid solvent evaporation, followed by electrode lead-out and encapsulation.

[0012] Furthermore, the specific method for CAD modeling and soft lithography microfluidic chip fabrication is as follows:

[0013] 1) First, the microchannel mask layout was drawn using AutoCAD software. The design adopted a bifurcation channel structure, with the inlet width set at 2 mm, the main channel height controlled at 60 μm, and the channel width at 125 μm for four iterations, so as to form the maximum flow velocity gradient during the truncation induction stage.

[0014] 2) The designed CAD drawings are photolithographically copied onto a high-resolution film to create a mask;

[0015] 3) Using standard soft lithography, SU-8 series negative photoresist is spin-coated onto a clean silicon wafer, and the solvent is removed by pre-baking. Then, ultraviolet exposure is performed using a pre-designed film mask to cross-link the colloid in the illuminated area. After exposure, the cross-linking reaction is enhanced by post-baking, and the unexposed parts are dissolved and removed by developer, thus leaving a raised structure on the silicon wafer that complements the designed channel, namely the SU-8 positive mold.

[0016] 4) Mix the polydimethylsiloxane prepolymer and curing agent at a mass ratio of 10:1 and pour them onto the SU-8 positive mold; place the sample in an 80℃ heating environment for 2 hours for heat curing. After full cross-linking, peel it off from the mold and use a punch to make the inlet and outlet ports. After oxygen plasma treatment, bond it to the glass substrate to form a closed microfluidic chip channel.

[0017] Furthermore, the specific methods for flow field simulation analysis and shear rate calibration are as follows:

[0018] 1) Import the CAD model into COMSOL Multiphysics software and use the laminar two-phase flow physics field interface to refine the boundary layer mesh on the microchannel wall and contraction region to ensure the accuracy of shear stress calculation;

[0019] 2) Set the inlet to velocity inlet, the outlet to pressure outlet, and the working fluid property to MXene dispersion;

[0020] 3) Run the steady-state solver to extract the shear rate distribution cloud map along the centerline of the flow channel. Ensure that in the main channel region, the shear rate reaches a minimum of 0.11 s⁻¹ for small-sized MXene (~250 nm) and a shear rate in the range of (500 ~ 1000 s⁻¹) for high-concentration (>15 mg / mL) / large-layer MXene (liquid crystal phase), thereby overcoming the Brownian motion of MXene nanosheets, forcing them to undergo rotational orientation, and optimizing the flow channel geometry in reverse based on the simulation results.

[0021] Furthermore, the specific method for preparing the MXene dispersion and its microfluidic directional molding is as follows:

[0022] 1) Select MXene with a high aspect ratio (such as MXene Ti3C2T) x (MoS2 or graphene oxide GO), dispersed in deionized water at a concentration of 1–10 mg / mL;

[0023] 2) Add 0.1 wt% surfactant and treat with an ultrasonic cell disruptor for 1-2 hours until a uniform brownish-yellow colloid is formed;

[0024] 3) Load the prepared dispersion into a syringe, install it into a precision injection pump, and set the flow rate (50 μL / min) according to the parameters calibrated in the simulation. When the dispersion flows through the microchannel contraction zone, it is subjected to strong shear force, and the MXene nanosheets are flipped from a disordered "out-of-plane" state to an ordered "in-plane" state, and are closely arranged along the streamline direction.

[0025] Furthermore, the specific method for the in-situ curing and device encapsulation process is as follows:

[0026] 1) For solid films, the slurry flowing out in a specific direction is collected directly on a moving platform, and the solvent is quickly evaporated by heating and curing.

[0027] 2) Photolithography is used to pattern highly oriented thin films to define transistor channels or sensor electrodes;

[0028] 3) Spin-coat a layer of encapsulation film on the device surface to improve the long-term stability and corrosion resistance of the device in humid environments or biological bodies.

[0029] The MXene conductive layer formed by this invention exhibits significant anisotropic transport characteristics and mechanical robustness. When the device is subjected to external bending or stretching, the highly oriented nanosheets maintain structural integrity through van der Waals forces, avoiding crack propagation and conductive circuit breaks commonly found in traditional disordered thin films, thereby achieving high stability of flexible electronic devices under dynamic deformation.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] Digital precision control: Through CAD and CFD simulation, the abstract "shear force" is quantified into specific "flow rate" and "geometric dimensions", eliminating the blindness of process trial and error and realizing programmable control of MXene orientation.

[0032] High aspect ratio orientation: The strong shear field generated by the contraction-expansion flow channel design effectively suppresses the random stacking and wrinkling of nanosheets, achieving near single-crystal orientation and significantly improving the in-plane conductivity and thermal conductivity of the composite material.

[0033] Strong interfacial bonding: By utilizing microfluidic in-situ curing technology, the modulus mismatch between the rigid conductive layer and the flexible substrate is solved, thereby improving the fatigue resistance and cycle life of the device.

[0034] Good process compatibility: This method can be directly integrated with roll-to-roll processes, supporting large-area continuous fabrication of flexible transparent electrodes, electromagnetic shielding films, or tactile sensor arrays, breaking through the bottlenecks of low efficiency and small area of ​​traditional LB film methods. Attached Figure Description

[0035] Figure 1 The following is a CAD design of the microfluidic chip mask layout for this invention.

[0036] Figure 2 The present invention provides a flow velocity distribution cloud map within a microchannel obtained through COMSOL Multiphysics simulation.

[0037] Figure 3 The purpose of this invention is to investigate the quantitative influence of microfluidic channel geometric parameters on MXene orientation.

[0038] Figure 4 This invention combines SAXS (small-angle X-ray scattering) with the orientation analysis of highly oriented MXene structures. Detailed Implementation

[0039] The present invention will be further explained and described below with reference to the accompanying drawings and embodiments. The following embodiments will help those skilled in the art to better understand the invention.

[0040] like Figure 1 As shown, this invention presents a flexible MXene highly oriented structure based on microfluidic shear field-induced fabrication. The fabrication process is described below, including the following steps:

[0041] Step 1: The PDMS prepolymer and curing agent are mixed evenly at a mass ratio of 10:1. After vacuum degassing for 30 minutes, the mixture is poured onto the surface of the SU-8 positive mold and spread evenly using a spin coater at 500 rpm. It is then thermo-cured at 80 ℃ for 2 hours. After complete cross-linking, it is peeled off from the mold surface to obtain a flexible PDMS microfluidic chip with a microstructure. Subsequently, the flow channel mask pattern designed in CAD is imported into COMSOL software for flow field simulation. By adjusting the inlet flow rate and flow channel height, the shear rate is calibrated to reach 1 × 10⁻⁻⁻⁻⁶. 4 The optimal geometric parameters of m / s were determined to ensure that the fluid could induce the nanosheets to align when flowing through the contraction zone. After simulation optimization, the chip was subjected to oxygen plasma treatment and bonded to a glass substrate to obtain a microfluidic platform for MXene directional assembly. Figure 1 The image shown is the flow channel mask designed in CAD.

[0042] Step two: Connect the prepared microfluidic chip to the injection pump system and inject the prepared MXene (e.g., MXene) dispersion into the chip inlet; pump the dispersion into the microchannel at a flow rate of 50 μL / min. Figure 2 As shown, a strong shear field is formed in the confined space of the microchannel at this time; this proves that MXene has undergone a highly ordered directional arrangement in the channel; then, an ultraviolet light source is integrated at the channel outlet to perform instantaneous photo-crosslinking on the dispersion containing the photoinitiator, instantly "freezing" the directional structure in the wet soft network, thereby preparing a continuous and stable highly directional conductive layer; finally, the sample is placed in a 60°C oven to dry for 2 hours to remove residual solvent, and a layer of PDMS is spin-coated on the film surface for encapsulation and protection to improve the stability and peel resistance of the device.

[0043] Step three: To further investigate the quantitative influence of microfluidic channel geometry parameters on the micro-orientation behavior of MXene, systematic flow field control and structural characterization were performed on the prepared layered nanocomposite film. For example... Figure 3 As shown, by changing the key geometric dimensions and process parameters of the microchannel, the effects of the channel forming section length d, channel height h, inlet flow velocity v, and nanosheet mass ratio c on the film orientation order parameter (f) were quantitatively analyzed. The test results show that an excessively high nanosheet mass ratio (wt.%) leads to steric hindrance between nanosheets, hindering their directional alignment. When the ratio exceeds 2.5 mg / mL, the orientation order parameter begins to decrease. Figure 3 (a) As the length d of the contraction section increases, the shearing time of the fluid on the nanosheet prolongs, and the orientation order parameter shows a trend that when d exceeds 1.2 cm, the f value stabilizes above 0.90. Figure 3 (b); As the channel height h decreases, the shear rate within the channel increases exponentially. When the height decreases from 100 μm to 20 μm, the orientation order parameter uniformly decreases from 0.92 to 0.83. Figure 3 (c); Furthermore, the inlet flow rate v directly affects the magnitude of the shear force. When the flow rate is increased from 600 μL / min to 1000 μL / min, the Brownian motion of the nanosheets is effectively suppressed, and the orientation order parameter is significantly improved. Figure 3 (d); The above results were verified by two-dimensional SAXS images, confirming that the orientation sequence parameters can be programmable by precisely controlling the microfluidic physical parameters.

[0044] Step four: To further reveal the mesoscopic stacking characteristics and long-range order evolution of the highly oriented structure, synchrotron small-angle X-ray scattering (SAXS) characterization was performed on the thin films under different process conditions, such as... Figure 4As shown in (b, c, d). Comparative analysis of the characterization results shows that the thin film prepared in the low-flow-rate channel exhibits isotropic diffuse annular scattering. Figure 4 (c) indicates that the layer arrangement is disordered; while the film prepared at high shear rates has a highly concentrated scattering signal along a specific azimuth angle, forming an obvious arc-shaped / point-shaped scattering pattern. Figure 4 (d) demonstrates that the film prepared under optimal parameters proves that the layered structure has a significant preferred orientation. Furthermore, by performing azimuth angle (φ) slice analysis on the two-dimensional scattering spectrum and extracting the azimuth angle distribution curve, it can be seen that the half-width at half-maximum (FWHM) of the azimuth angle distribution is distributed near φ=180° (0° in the plane), indicating that MXene is preferentially and highly oriented along the longitudinal direction of the film (or the flow direction of the channel).

[0045] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. The technical solution adopted in this invention is a method for constructing MXene highly oriented structures based on microfluidic shear field induction, characterized in that, Includes the following steps: Step 1: Design the microchannel mask layout using CAD software, and fabricate a PDMS microfluidic chip with a specific micrometer size using soft photolithography. Step 2: Use multiphysics simulation software to numerically simulate the velocity distribution and shear stress field in the flow channel to achieve the optimal flow range and geometric parameters for inducing MXene orientation. Step 3: Prepare a highly stable MXene dispersion with specific rheological properties, and use the strong shear field generated by the microfluidic chip to induce the nanosheets to align in a highly oriented manner; Step four involves locking the oriented MXene structure onto the surface of a flexible substrate through in-situ curing or rapid solvent evaporation, followed by electrode lead-out and encapsulation.

2. The method for constructing MXene highly oriented structures based on microfluidic shear field induction according to claim 1, characterized in that, The specific fabrication method of the microfluidic chip is as follows: A shrink-expansion microchannel mask layout is drawn using AutoCAD, with an inlet width of 2mm, a main channel height of 60μm, and a fourth iteration channel width of 125μm. The design is photolithographically transferred to a film to create the mask. SU-8 negative photoresist is spin-coated onto a silicon wafer, and after UV exposure, baking, and development, an SU-8 positive mold is obtained. PDMS prepolymer and curing agent are mixed at a ratio of 10:1 and poured onto the positive mold. The mixture is then heat-cured at 80℃ for 2 hours. After peeling, holes are drilled to create the inlet and outlet ports. After oxygen plasma treatment, the mixture is bonded to a glass substrate to form a closed channel.

3. The method for constructing MXene highly oriented structures based on microfluidic shear field induction according to claim 1, characterized in that, The specific method for flow field simulation calibration is as follows: import the CAD model into COMSOL Multiphysics, use the laminar two-phase flow physics field interface, and refine the boundary layer mesh on the microchannel wall and the contraction region. Set the inlet as a velocity inlet and the outlet as a pressure outlet, and set the working fluid property to MXene dispersion; run the steady-state solver, extract the shear rate distribution cloud map of the channel centerline, and ensure that small-sized MXene (~250nm) corresponds to a minimum shear rate of 0.11s⁻¹, and high-concentration (>15mg / mL) / large-layer MXene corresponds to a range of 500~1000s⁻¹, and back-optimize the channel geometry.

4. The method for constructing MXene highly oriented structures based on microfluidic shear field induction according to claim 1, characterized in that, The specific preparation method of the MXene dispersion is as follows: MXene Ti3C2T is selected. x MoS2 or graphene oxide (GO) was dispersed in deionized water at a concentration of 1-10 mg / mL; 0.1 wt% surfactant was added, and the mixture was treated with an ultrasonic cell disruptor for 1-2 hours until a homogeneous colloid was formed; the rheological properties of the dispersion were tested using a rheometer to ensure that it remained stable at shear rates of 10³~10⁻⁶. 5 Within the range of s⁻¹, it exhibits shear-thinning behavior.

5. The method for constructing MXene highly oriented structures based on microfluidic shear field induction according to claim 1, characterized in that, The specific method for shear-induced high-orientation alignment is as follows: the dispersion is loaded into a syringe, installed in a precision injection pump, and pumped into the microchannel at a flow rate of 50 μL / min; the orientation of the nanosheets in the channel is monitored in real time using a high-speed microscopy system, and the azimuth half-width (FWHM) of the azimuth distribution is verified to be <15° by synchrotron small-angle X-ray scattering (SAXS), thus obtaining a highly oriented MXene flow.

6. The method for constructing MXene highly oriented structures based on microfluidic shear field induction according to claim 1, characterized in that, The specific method of in-situ curing and encapsulation is as follows: For solid films, the slurry flowing out in a specific direction is collected on a moving platform and cured at 60°C for 2 hours to evaporate the solvent; the highly oriented film is patterned using photolithography to define transistor channels or sensor electrodes; a PDMS encapsulation layer is spin-coated on the device surface and cured at 80°C for 1 hour to improve stability and corrosion resistance in humid environments.

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