Method and device for enhancing mass transfer inside microdroplets
By using a hydrophobic substrate and mechanical vibration inside the microdroplets, the problem of low mixing and transport efficiency of droplets at the microscale is solved, achieving efficient material mixing and mass transfer, applicable to various scenarios and without pollution.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAN MICRO-CHEMICAL PRECISION TECHNOLOGY CO LTD
- Filing Date
- 2026-04-17
- Publication Date
- 2026-05-26
AI Technical Summary
Existing technologies have low efficiency in droplet mixing and transport at the microscale, slow mass transfer processes, and problems such as complex structure, high cost, easy contamination, or limited applicability.
By combining a hydrophobic substrate with mechanical vibration, strong convective circulation is generated inside the droplets through the control of substrate surface wettability and vibration frequency and amplitude, achieving rapid mixing and mass transfer.
It significantly improves the efficiency of material mixing and mass transfer by 1-2 orders of magnitude, is suitable for droplets from nanoliter to microliter, and is applicable to drug screening, microreactions and biochemical detection. It also eliminates the need for insertable stirring elements, thus avoiding cross-contamination.
Smart Images
Figure CN122076544A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of microfluidics, specifically to a method and apparatus for enhancing mass transfer within microdroplets. Background Technology
[0002] With the rapid development of technologies such as microfluidic chips, drug screening systems, single-cell analysis, and microreactors, micro- and even nano-scale droplets have become the core carriers for biochemical reactions and detection. In these microscale systems, the mixing and transport efficiency of substances directly determines the reaction rate, detection sensitivity, and analytical throughput.
[0003] However, fluid flow at the microscale is characterized by low Reynolds numbers (Re is typically much less than 1), with laminar flow being the dominant state and molecular diffusion becoming the primary mechanism for mixing. For small molecules in aqueous solutions, the diffusion coefficient D is typically in the range of 10. -9 The mass transfer rate is on the order of m² / s, which means that within a 100 μm droplet, achieving uniform mixing through diffusion alone would take tens of seconds or even minutes. This slow mass transfer process has become a major bottleneck restricting the analytical throughput of microfluidic chips and the reaction efficiency of microreactors.
[0004] To address the above issues, researchers have developed various methods for enhancing mass transfer within microdroplets, mainly including the following categories: 1. Integrating micro-stirring elements, micro-rotors, or magnetic stirring beads within microchannels or microcavities, and driving their rotation via an external magnetic field, achieves mechanical stirring of droplets. However, rotor structures are complex and difficult to fabricate, and the presence of the stirring element can easily cause sample contamination or cell damage. Furthermore, this method is difficult to handle ultra-microdroplets below the nanoliter level.
[0005] 2. Using an electric field to drive electroosmotic flow, electrothermal flow, or dielectrophoretic effects within or at the interface of droplets to achieve mixing enhancement. However, this method requires the application of high voltage (usually hundreds of volts), which can lead to problems such as electrolysis and Joule heating, and can easily damage biological samples (such as proteins and cells). In addition, electroosmotic flow is sensitive to the ionic strength and pH of the solution, limiting its applicability.
[0006] 3. High-frequency surface acoustic waves excited by a piezoelectric substrate can generate acoustic flow within droplets, achieving rapid mixing. However, high-frequency acoustic waves (MHz level) attenuate rapidly in liquids, mainly affecting the thin layer at the bottom of the droplet, with limited penetration into thick droplets or high-viscosity liquids. Furthermore, acoustic radiation may cause localized temperature rises, affecting thermosensitive samples. Additionally, the integration process between piezoelectric materials and microfluidic chips is complex and costly.
[0007] Based on this, the present invention designs a method and apparatus for enhancing mass transfer inside microdroplets to solve the above problems. Summary of the Invention
[0008] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a method and apparatus for enhancing mass transfer inside microdroplets.
[0009] To achieve the above objectives, the present invention provides the following technical solution: A method for enhancing mass transfer within microdroplets includes the following steps: Step 1: Substrate preparation: Prepare a hydrophobic substrate with a static contact angle θ ≥ a set threshold; By utilizing the low solid-liquid contact area, weak wall viscous dissipation, and low vibration damping characteristics of the hydrophobic substrate, droplet oscillation attenuation is reduced and vibration energy is retained. Step 2: Droplet fixation: The target droplet is applied to the surface of the hydrophobic substrate to form a fixed droplet; Step 3: Vibrational mass transfer: Apply vertical / horizontal periodic mechanical vibration to the hydrophobic substrate containing the fixed droplets, adjust the vibration frequency and amplitude, and use the low damping characteristics to efficiently convert the vibration energy into the internal circulating kinetic energy of the droplets, so as to realize the rapid mixing and transport of substances within the droplets.
[0010] Furthermore, the threshold is set at 110°.
[0011] Furthermore, the substrate surface of the hydrophobic substrate is a hydrophobic coating, micro / nano structure, or a chemically modified hydrophobic surface.
[0012] Furthermore, the volume of the fixed droplet is 1 nL-200 μL.
[0013] Furthermore, the vibration frequency of mechanical vibration is 10Hz-1000Hz and the amplitude is 1μm-500μm.
[0014] Furthermore, the central region of the hydrophobic substrate is treated with a hydrophilic coating to form a mixed wetting region of central hydrophilicity and peripheral hydrophobicity. The central hydrophilic region improves the efficiency of vibration energy input, while the peripheral hydrophobic region maintains low damping characteristics, thus synergistically enhancing internal flow.
[0015] A microdroplet internal mass transfer enhancement system, utilizing a microdroplet internal mass transfer enhancement method, includes: A vibration generating unit is used to generate mechanical vibrations with controllable frequency and amplitude. The base platform, set on the vibration generating unit, is used to support the hydrophobic base; The droplet loading unit is used to apply target droplets onto the surface of a hydrophobic substrate; The observation unit is used to monitor the internal flow state of the droplet in real time.
[0016] Furthermore, the vibration generating unit can be a piezoelectric ceramic actuator, an electromagnetic vibrator, or an eccentric motor.
[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention has the following advantages: High mass transfer efficiency: By controlling the wettability of the substrate surface to reduce droplet vibration damping, combined with mechanical vibration to generate strong convective circulation inside the droplet, the efficiency of material mixing and mass transfer is significantly improved by 1-2 orders of magnitude compared to pure diffusion.
[0018] Non-contact and pollution-free: No need for insertion stirring elements, avoiding cross-contamination, suitable for biological samples.
[0019] Parameters are controllable and easy to integrate: Vibration frequency, amplitude and substrate wettability can all be independently adjusted, making it easy to integrate with microfluidic chips.
[0020] Wide range of applications: It can handle droplets from nanoliters to microliters and is suitable for various scenarios such as drug screening, microreactions, and biochemical detection. Attached Figure Description
[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.
[0022] Figure 1 A top view of the vibration of a droplet on a hydrophilic substrate under a signal excitation; Figure 2 A top view showing the vibration of a droplet on a hydrophobic substrate under the same signal excitation; Figure 3 A side view of the vibration of a droplet (containing tracer particles) on a hydrophilic substrate under a signal excitation. Figure 4 A side view of the vibration of droplets (including tracer particles) on a hydrophobic substrate under the same signal excitation; Figure 5 A top view of two different colored droplets on a hydrophilic substrate mixing for 3 seconds under one signal excitation; Figure 6 A top view of two different colored droplets on a hydrophobic substrate mixing for 3 seconds under the same signal excitation; Figure 7 This image shows a comparison of the internal flow of droplets on a hydrophobic substrate with and without ethanol wetting in the central region. Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0024] Example 1: A method for enhancing mass transfer inside microdroplets, comprising the following steps: Step 1: Substrate preparation: Prepare a hydrophobic substrate with a static contact angle θ ≥ a set threshold; By utilizing the low solid-liquid contact area, weak wall viscous dissipation, and low vibration damping characteristics of the hydrophobic substrate, droplet oscillation attenuation is reduced and vibration energy is retained. Because of the small solid-liquid contact area, the wall viscosity dissipation of hydrophobic surfaces is significantly reduced, the droplet vibration damping is lower than that of hydrophilic surfaces, and the oscillation decay is slower, which is conducive to the maintenance and conversion of vibration energy inside the droplet. Step 2: Droplet fixation: The target droplet is applied to the surface of the hydrophobic substrate to form a fixed droplet; Step 3: Vibrational mass transfer: Apply vertical / horizontal periodic mechanical vibration to the hydrophobic substrate containing the fixed droplets, adjust the vibration frequency and amplitude, and use the low damping characteristics to efficiently convert the vibration energy into the internal circulating kinetic energy of the droplets, so as to realize the rapid mixing and transport of substances within the droplets.
[0025] Set the threshold to 110°.
[0026] The substrate is a glass sheet; The substrate surface of the hydrophobic substrate is a hydrophobic coating, micro / nano structure, or chemically modified hydrophobic surface.
[0027] The hydrophobic coating is a layer of hydrophobic silica nanoparticles; Micro-nano structures are micro-nano array structures that exist on the surface after laser etching, such as cylindrical arrays, square column arrays, and pointed cone arrays; Chemically modified hydrophobic surfaces are those modified through silanization, esterification, or polymer grafting methods, such as immersion modification using C18-TMS, HMDS, fatty acids, or ATRP-based reagents. Preferably, θ is in the range of 120°-160° to minimize wall viscous dissipation.
[0028] Preferably, the volume of the fixed droplet is 1 nL-200 μL.
[0029] Preferably, the mechanical vibration frequency is 10Hz-1000Hz and the amplitude is 1μm-500μm.
[0030] Preferably, the central region of the hydrophobic substrate is treated with hydrophilic material to form a mixed wetting region of central hydrophilicity and peripheral hydrophobicity. The central hydrophilic region improves the vibration energy input efficiency, while the peripheral hydrophobic region maintains low damping characteristics, thus synergistically enhancing internal flow. The central region accounts for 0%-90% of the contact area between the droplet and the hydrophobic substrate.
[0031] Hydrophilic treatment can be achieved through oxidation, hydroxylation, surface grafting of hydrophilic polymers, and organic solvent-assisted water wetting. For example, surface cleaning can be done with oxygen plasma, piranha solution, or polyacrylic acid immersion. Alternatively, the surface can be wetted with ethanol and then replaced with water.
[0032] A microdroplet internal mass transfer enhancement system, utilizing a microdroplet internal mass transfer enhancement method, includes: A vibration generating unit is used to generate mechanical vibrations with controllable frequency and amplitude. The base platform, set on the vibration generating unit, is used to support the hydrophobic base; The droplet loading unit is used to apply target droplets onto the surface of a hydrophobic substrate; Observation units (such as high-speed camera systems) are used to monitor the internal flow state of droplets in real time.
[0033] The vibration generating unit is a piezoelectric ceramic actuator, an electromagnetic vibrator, or an eccentric motor.
[0034] Specific examples are as follows: Case 1 of this application Substrate: Glass sheet coated with hydrophobic silica nanoparticles, with a contact angle of approximately 150°; Droplet: 20 μL deionized water; Vibration parameters: frequency 100Hz, amplitude 50μm (vertical vibration); Comparison Case 1 Substrate: Glass plate; Droplet: 20 μL deionized water Vibration parameters: frequency 100Hz, amplitude 50μm (vertical vibration); Results: High-speed camera footage showed that, under vibration excitation, the droplet flow on the control surface (contact angle 90°) in Comparison Case 1 was as follows: Figure 1 As shown, the internal average flow velocity is approximately 0.5 mm / s. The droplet flow in Example 1 of this application is as follows: Figure 2 As shown, the flow intensity increased by about 3 times, and the flow was greatly enhanced.
[0035] Case 2 of this application: Substrate: Glass sheet coated with hydrophobic silica nanoparticles, with a contact angle of approximately 150°; Droplet: 50 μL of deionized water containing 50 μm tracer particles; Vibration parameters: frequency 900Hz, amplitude 10-50μm (vertical vibration); Comparison Case 2 Substrate: Glass plate; Droplet: 50 μL of deionized water containing 50 μm tracer particles Vibration parameters: frequency 900Hz, amplitude 10-50μm (vertical vibration); Results: At an amplitude of 50 μm, the side view captured by high-speed imaging shows that, under vibration excitation, the droplet flow on the surface (contact angle ~90°) of Comparative Case 2 is as follows: Figure 3 As shown, the tracer particles showed almost no reaction under this vibrational excitation and gradually sank to the bottom, indicating that the internal flow of the droplet was very weak, and the PIV could not measure the internal flow velocity, with an average flow velocity of 0 mm / s. The droplet flow in Case 2 of this application is as follows... Figure 4 As shown, the tracer particles formed a relatively strong circulation inside the droplet, and the average flow velocity, measured by PIV, reached 1.6 mm / s. When the amplitude decreased, no internal flow was observed in the droplet of Comparative Case 2. However, in Application Case 2, when the amplitude was 40 μm, the average flow velocity inside the droplet on the hydrophobic surface reached 1.1 mm / s; when the amplitude was 30 μm, the internal flow reached 0.7 mm / s; when the amplitude was 20 μm, the average internal flow velocity reached 0.35 mm / s; and when the amplitude was 10 μm, the internal flow was weak and difficult to observe, approximately 0 mm / s.
[0036] Case 3 of this application: Substrate: Glass sheet coated with a hydrophobic fluorinated coating, with a contact angle of approximately 155°; Droplets: 20 μL of deionized water containing blue pigment and 20 μL of deionized water containing red pigment Vibration parameters: frequency 800Hz, amplitude 80μm (vertical vibration); Comparison Case 3 Substrate: Glass plate; Droplets: 20 μL of deionized water containing blue pigment and 20 μL of deionized water containing red pigment Vibration parameters: frequency 800Hz, amplitude 80μm (vertical vibration); Result: As Figure 5 As shown in Comparative Case 3, on the hydrophilic control surface (contact angle ~90°), two different colored droplets remained unevenly mixed after 3 seconds of vibration excitation, with color differences persisting within the droplets. However, as... Figure 6 As shown, two different colored droplets on the hydrophobically modified surface were completely mixed after 3 seconds of vibration excitation, and no obvious color difference was observed in the droplets.
[0037] Case 4 of this application: Substrate: A glass slide coated with hydrophobic silica nanoparticles. The central region (2 mm in diameter, accounting for 80% of the contact area between the droplet and the substrate) is pre-wetted with ethanol (contact angle ~90°), while the periphery remains in its original hydrophobic state (contact angle ~150°). Droplet: 50 μL of deionized water, containing 50 μm tracer particles; Vibration parameters: frequency 500Hz, amplitude 30μm (horizontal vibration); Results: In Case 4 of this application, the ethanol-wetting central region improved the vibration energy input efficiency, while the peripheral hydrophobic region maintained low damping characteristics, such as... Figure 7 As shown, the average internal flow velocity of the unwetted droplet is 0.9 mm / s, while the average internal flow velocity of the wetted droplet in the central region is 1.2 mm / s. The internal flow intensity of the droplet is increased by about 30% compared to the unwetted droplet.
[0038] In summary, when droplets are on hydrophobic surfaces, the solid-liquid contact area is significantly reduced, resulting in a substantial decrease in wall viscous dissipation. Instead, the bulk viscous dissipation within the droplet becomes the dominant effect. Hydrophobic droplets, due to their weak wall viscous dissipation and significant bulk viscous dissipation, exhibit significantly lower vibrational damping and slower oscillation decay compared to hydrophilic droplets. Under the same excitation conditions, hydrophobic droplets can retain vibrational energy for a longer period, are less prone to rapid decay due to wall friction, and maintain energy for a longer duration. More vibrational energy is retained within the droplet, converting into fluid kinetic energy to drive internal flow, rather than being dissipated at the solid-liquid interface, resulting in more efficient energy conversion. The low damping characteristic allows the droplet to respond to vibrations over a wider frequency range, forming a stable internal circulation at the resonant frequency. This internal circulation effectively breaks the diffusion boundary layer, enabling rapid mixing and mass transfer of substances within the microdroplet.
[0039] Therefore, the present invention has the following advantages: High mass transfer efficiency: By controlling the wettability of the substrate surface to reduce droplet vibration damping, combined with mechanical vibration to generate strong convective circulation inside the droplet, the efficiency of material mixing and mass transfer is significantly improved by 1-2 orders of magnitude compared to pure diffusion.
[0040] Non-contact and pollution-free: No need for insertion stirring elements, avoiding cross-contamination, suitable for biological samples.
[0041] Parameters are controllable and easy to integrate: Vibration frequency, amplitude and substrate wettability can all be independently adjusted, making it easy to integrate with microfluidic chips.
[0042] Wide range of applications: It can handle droplets from nanoliters to microliters and is suitable for various scenarios such as drug screening, microreactions, and biochemical detection.
[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for enhancing mass transfer within microdroplets, characterized in that: Includes the following steps: Step 1: Substrate preparation: Prepare a hydrophobic substrate with a static contact angle θ ≥ a set threshold; By utilizing the low solid-liquid contact area, weak wall viscous dissipation, and low vibration damping characteristics of the hydrophobic substrate, droplet oscillation attenuation is reduced and vibration energy is retained. Step 2: Droplet fixation: The target droplet is applied to the surface of the hydrophobic substrate to form a fixed droplet; Step 3: Vibrational mass transfer: Apply vertical / horizontal periodic mechanical vibration to the hydrophobic substrate containing the fixed droplets, adjust the vibration frequency and amplitude, and use the low damping characteristics to efficiently convert the vibration energy into the internal circulating kinetic energy of the droplets, so as to realize the rapid mixing and transport of substances within the droplets.
2. The method for enhancing mass transfer within microdroplets according to claim 1, characterized in that, Set the threshold to 110°.
3. The method for enhancing mass transfer within microdroplets according to claim 2, characterized in that, The substrate surface of the hydrophobic substrate is a hydrophobic coating, micro / nano structure, or chemically modified hydrophobic surface.
4. The method for enhancing mass transfer within microdroplets according to claim 1, characterized in that, The volume of the fixed droplet is 1 nL-200 μL.
5. The method for enhancing mass transfer within microdroplets according to claim 1, characterized in that, The vibration frequency of mechanical vibration is 10Hz-1000Hz and the amplitude is 1μm-500μm.
6. A method for enhancing mass transfer within microdroplets according to any one of claims 1-5, characterized in that, The central area of the hydrophobic substrate is treated with a hydrophilic coating to form a mixed wetting area with a central hydrophilic center and a peripheral hydrophobic surface.
7. A microdroplet internal mass transfer enhancement system, utilizing the microdroplet internal mass transfer enhancement method according to any one of claims 1-6, characterized in that, include: A vibration generating unit is used to generate mechanical vibrations with controllable frequency and amplitude. The base platform, set on the vibration generating unit, is used to support the hydrophobic base; The droplet loading unit is used to apply target droplets onto the surface of a hydrophobic substrate; The observation unit is used to monitor the internal flow state of the droplet in real time.
8. The microdroplet internal mass transfer enhancement system according to claim 7, characterized in that, The vibration generating unit is a piezoelectric ceramic actuator, an electromagnetic vibrator, or an eccentric motor.