Particle suspension evaporation method and system based on vibration substrate

Abstract

The invention belongs to the field of particle suspension evaporation, and relates to a particle suspension evaporation method and system based on a vibration substrate. According to the method, particle suspension liquid drops are deposited on a vibration substrate, and the substrate is driven to generate periodic vibration with specific frequency and amplitude, so that the liquid drops enter a resonance state. Under the resonance condition, complex convection is formed in the liquid drops, single circulation driven by evaporation is broken, the trend that particles continuously migrate to the edge is remarkably weakened, and therefore the coffee ring effect is effectively restrained. Compared with the prior art, the method has the advantages that the structure is simple, the operation is convenient, uniform deposition of particles can be realized without adding a surfactant or special surface modification, and the method has good universality and wide application prospect, and is suitable for the fields of biological detection, ink-jet printing, functional coating, micro-nano device manufacturing and the like.

Description

Technical Field

[0001] This invention belongs to the field of particle suspension evaporation, and more specifically, relates to a particle suspension evaporation method and system based on a vibrating substrate, which is used to suppress the coffee ring effect and achieve controllable and uniform deposition of particles on the substrate surface. Background Technology

[0002] The droplet evaporation process has long been a focus of attention. During the evaporation of suspensions containing solid particles, the evaporation rate is highest near the three-phase contact line, creating a compensating circulation from the edge to the center within the droplet. This drives the suspended particles to migrate and accumulate at the droplet edge, ultimately forming a ring-shaped deposition on the substrate surface, known as the "coffee ring effect." While this effect is prevalent in natural phenomena, it severely impacts performance in many applications. For example, in surface-enhanced Raman spectroscopy (SERS), biosensing, inkjet printing, functional coatings, and micro / nano device fabrication, uniform particle distribution is essential to ensure signal strength consistency and device performance stability. However, the uneven particle accumulation caused by the coffee ring effect leads to detection signal deviations, uneven film thickness, and localized failures, significantly limiting the development of related technologies.

[0003] To suppress the coffee ring effect, researchers have proposed various methods, such as altering substrate wettability, introducing electric or magnetic fields to control flow, using special solvent systems, or surface modification. While these methods improve particle distribution to some extent, they often suffer from stringent experimental conditions, complex apparatus, limited applicability, or high costs, hindering their widespread application. Therefore, finding a simple, universal, and efficient way to control the internal flow during droplet evaporation to achieve uniform particle deposition has become a critical scientific and technological problem that urgently needs to be solved in this field.

[0004] Therefore, it is necessary to provide a method and system for evaporating particulate suspensions based on a vibrating substrate to solve the above problems. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a method and system for evaporating particulate suspension based on a vibrating substrate, the purpose of which is to better suppress the coffee ring effect during the droplet evaporation process.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for evaporating a particulate suspension based on a vibrating substrate is provided, comprising the following steps: S1. Print the particulate suspension onto the substrate; S2. Observe the contact parameters of the droplets deposited in the particulate suspension, and calculate the reference vibration frequency of the deposited droplets using the following formula. :

[0007] in, Let be the radius of a spherical droplet of the same volume. The resonance order is... The effective density of the suspension; S3. Adjust the substrate vibration repeatedly according to the calculated reference vibration frequency f until the droplet reaches a resonance state; S4. As evaporation proceeds, calculate f in a timely manner and adjust the vibration frequency and amplitude of the substrate to keep the droplet in resonance.

[0008] Furthermore, the contact parameters include the contact radius between the droplet and the substrate. and static contact angle .

[0009] Furthermore, the radius of the spherical droplet of the same volume The calculation formula is: .

[0010] Furthermore, the order of the resonance mode of the droplet is 4.

[0011] According to another aspect of the present invention, a particulate suspension evaporation system based on a vibrating substrate is provided, including an inkjet printing system, an observation system, a signal output system, and a controller; The inkjet printing system includes an injection pump, a syringe, a nozzle, a substrate, and a vibration platform. The suspension is ejected from the nozzle by the injection pump and then deposited on the substrate. The contact parameters between the droplets and the substrate are observed by the observation system and transmitted to the controller. The controller calculates the reference vibration frequency. The signal output system outputs a suitable electrical signal according to the reference vibration frequency and drives the vibration platform to generate corresponding vibration so that the droplets and the substrate resonate.

[0012] Furthermore, the reference vibration frequency of the deposited droplet is calculated using the following formula. :

[0013] in, Let be the radius of a spherical droplet of the same volume. The resonance order is... This represents the effective density of the suspension.

[0014] Furthermore, the contact parameters include the contact radius between the droplet and the substrate. and static contact angle .

[0015] Furthermore, the radius of the spherical droplet of the same volume The calculation formula is: .

[0016] Furthermore, the order of the resonance mode of the droplet is 4.

[0017] In summary, the technical solutions conceived in this invention, compared with the prior art, can achieve the following beneficial effects: 1. This invention involves adding a suspended droplet of particles to the surface of a vibrating substrate. When the substrate vibrates periodically at a specific frequency and amplitude, the droplet couples with the substrate, entering a resonant state. In this state, the flow pattern inside the droplet changes from the traditional single evaporation-driven circulation to multi-directional turbulence and convection circulation, effectively disrupting the tendency of particles to continuously migrate towards the edges. Simultaneously, vibration-induced convection alters the spatial distribution of the droplet surface evaporation rate, making the overall evaporation process more uniform, thereby significantly weakening or even eliminating the "coffee ring effect" and achieving uniform deposition.

[0018] 2. This invention further integrates an observation system to monitor key contact parameters of droplets during the evaporation process (including contact angle, contact radius, and droplet morphology evolution) in real time. By comparing the droplet dynamic characteristics at different evaporation stages, the most suitable vibration frequency and amplitude can be selected and applied, ensuring that the droplets maintain a stable vibration state close to resonance throughout the evaporation process, thereby achieving optimal particle distribution. This method enables personalized control for suspensions with different particle sizes, concentrations, and volume fractions, ensuring the repeatability and reliability of experimental results.

[0019] 3. The evaporation deposition system proposed in this invention has a simple overall structure, mainly consisting of a common vibrating substrate, a signal generator, a power amplifier, and an observation module. These are all readily available standardized devices, making system setup and operation convenient. Furthermore, this method achieves deposition morphology control without relying on additional surfactants or complex chemical modifications, avoiding alterations to the suspension system composition and exhibiting high versatility. Evaporation experiments can be conducted on both hydrophilic and hydrophobic particle suspensions within this system, thus providing an efficient and controllable particle deposition method for multiple fields such as biosensing, functional coatings, and micro / nano device fabrication. Attached Figure Description

[0020] Figure 1 This is a flowchart of the suspension evaporation process constructed according to a preferred embodiment of the invention; Figure 2 This is a schematic diagram of the suspension printing system according to a preferred embodiment of the present invention; Figure 3 The preferred embodiment of the present invention features evaporation patterns on a vibrating substrate (a) and a stationary substrate (b).

[0021] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-Injection pump, 2-Injector, 3-Controller, 4-Baseboard, 5-High-speed camera, 6-Vibrator, 7-XY moving platform, 8-Power amplifier, 9-Light source, 10-Signal generator. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] For particulate suspensions, the evaporation rate is highest near the three-phase contact line. A compensating circulation spontaneously forms within the droplets, moving from the edges to the center. This drives the suspended particles to migrate and gradually accumulate at the droplet edges, ultimately forming a distinct coffee-colored ring on the substrate surface. This effect severely impacts the uniformity and functional stability of the deposited layer. Therefore, this invention first provides a method and system for evaporative deposition of particulate suspensions based on a vibrating substrate, such as… Figure 1-2 As shown, the core idea is to change the flow pattern inside the droplets by periodically vibrating the substrate, thereby suppressing unidirectional particle migration and achieving uniform deposition. Specifically, by measuring the basic parameters of the deposited droplets using a high-speed camera and adjusting the vibration frequency and amplitude of the substrate in real time based on the measurement results, the problem of uneven evaporation and deposition of particle suspensions on conventional substrates is solved.

[0024] The specific steps include: S1. The particulate suspension is printed onto a pre-defined substrate surface using an inkjet printing system. The inkjet printing system includes an injection pump (preferably a flow pump), a syringe, a nozzle, and a vibration platform (including a vibrator and an XY moving platform), which can ensure precise control of the droplet deposition position and the consistency of droplet volume.

[0025] S2. A high-speed camera system is used to observe the contact parameters of the droplets during the evaporation process in real time. These contact parameters include at least the contact radius and the static contact angle. Based on the observation data, the reference vibration frequency of the droplets is calculated using the following formula. ;

[0026] in, The radius of a spherical droplet with the same volume as the deposited droplet. The resonance order of the droplet can take values ​​such as 2, 4, 6, 8, etc. (even numbers). The surface tension of the suspension, This represents the effective density of the suspension.

[0027] S3. Based on the calculated reference frequency, repeatedly adjust the output parameters of the signal output module and determine whether a resonance state has been reached by observing the droplet vibration morphology. When the droplet exhibits periodic vibration with maximum amplitude, it indicates that it is in the optimal resonance condition. The signal output module includes a signal generator and a power amplifier. The signal generator generates a sinusoidal electrical signal, and the power amplifier amplifies the electrical signal to drive the exciter.

[0028] S4. During the continuous evaporation of the droplet, the vibration frequency and amplitude of the substrate are adjusted appropriately based on the feedback to ensure that the droplet is always in a state close to resonance. This method can maintain internal turbulence and convection circulation throughout the evaporation process, effectively preventing particles from migrating unidirectionally to the edge until the droplet is completely dried.

[0029] This embodiment uses an aqueous solution of polystyrene (PS) particles as the experimental subject, with an effective suspension density of approximately for The particle diameter is approximately The mass fraction is The suspension is injected into a syringe via a syringe pump and then uniformly printed onto the surface of a glass substrate through an inkjet printing nozzle.

[0030] Specifically, the volume of droplets printed in each iteration of the printing system is approximately [missing information]. The extrusion flow rate of the suspension is approximately... This flow rate can both avoid nozzle clogging and ensure the controllability of the droplet formation process, thereby improving the repeatability and reliability of deposition experiments.

[0031] Subsequently, a high-speed camera system was used to observe the morphology of the droplets after deposition in real time and measure the contact radius of the droplets. With contact angle Radius of a spherical droplet of the same volume The calculation formula is:

[0032] according to The reference resonant frequency was calculated.

[0033] Contact radius of the measured droplet Approximately Contact angle Approximately The reference was calculated. The vibration frequency is approximately .

[0034] The preferred order of the droplet's resonance mode is 4. In the 4th-order resonance mode, the internal flow structure is more complex and the circulation intensity is greater. Due to the strong convection, the evaporation rate on the droplet surface tends to be spatially uniform, thereby accelerating the overall evaporation process. Experiments show that, under the same environmental conditions, the droplet evaporation rate in the 4th-order vibration mode is significantly higher than that in other non-resonant states, making it the preferred working condition for achieving rapid and uniform deposition.

[0035] Specifically, the output frequency of the signal generator is set to The output voltage amplitude is (Peak-to-peak voltage).

[0036] Specifically, by adjusting the gain knob, the output voltage of the power amplifier is approximately The output current is approximately This effectively drives the exciter to generate the required mechanical vibration, thereby ensuring that the substrate maintains a stable periodic vibration state throughout the droplet evaporation process. By coordinating the setting of the above electrical signal and power amplification parameters, the droplet can be kept under near-resonance conditions, achieving an ideal internal convection mode and uniform particle deposition effect.

[0037] As a preferred embodiment of the present invention, a particulate suspension evaporation system based on a vibrating substrate is provided, such as... Figure 2 As shown, this is a system used to implement the above-mentioned particulate suspension evaporation deposition method. The system includes a printing system, an observation system, and a signal output system.

[0038] The printing system includes a flow pump 1, a syringe 2, a substrate 4, a vibrator 6, and an XY moving platform 7. The flow pump 1 is connected to the syringe 2, allowing the suspension to be smoothly ejected from the nozzle to form droplets. The substrate 4 is connected to the vibrator 6, which is fixed on the XY moving platform 7 to enable the droplets to freely deposit on the substrate.

[0039] The observation system includes a controller 3, a high-speed camera 5, and a light source 9. In this example, the light source 3 is a high-intensity LED. Before using the observation system, the focal length and aperture of the high-speed camera should be adjusted to enable the observation of a bright and uniform real image.

[0040] The signal output system includes a power amplifier 8 and a signal generator 10. The output terminal of the signal generator 10 is connected to the input terminal of the power amplifier 8. The electrical signal generated by the signal generator 10 is amplified by the power amplifier 8 and then drives the exciter 6 to operate. The signal generator 10 is used to adjust the vibration frequency of the exciter, and the power amplifier 8 is used to adjust the vibration amplitude of the exciter.

[0041] Injector 2 draws in a portion of the suspension, and flow pump 1 applies pressure to injector 2, thereby driving the suspension to be ejected from the nozzle, and the resulting droplets are deposited on substrate 4. The contact angle and contact radius between the droplets and the substrate are observed through an observation system. Signal generator 10 and power amplifier 8 output appropriate electrical signals based on the measured parameters, and drive exciter 6 to generate vibration.

[0042] like Figure 3 As shown, the evaporation deposition patterns of the suspension after drying on vibrating and stationary substrates are compared. Under stationary substrate conditions, during droplet evaporation, particles continuously migrate to the vicinity of the three-phase contact line, eventually forming a distinct ring-shaped deposition on the substrate surface, a typical "coffee ring effect." Under vibrating substrate conditions, due to the strong convective disturbance generated by the droplets at the resonant frequency, the particle migration path is disrupted and redistributed, resulting in a nearly uniform particle layer with reduced edge accumulation. This comparative result directly verifies that the vibrating substrate evaporation deposition method proposed in this invention can effectively suppress the coffee ring effect and significantly improve the uniformity of particle deposition.

[0043] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of particle suspension evaporation based on a vibrating substrate, characterized in that, The method comprises the following steps: S1, printing a particle suspension on a substrate; S2. The contact parameters of the deposited droplet of the particle suspension are observed and the reference oscillation frequency of the deposited droplet is calculated by the following formula : wherein, R is the radius of a spherical droplet of the same volume, n is the resonance order, ρeff is the effective density of the suspension; S3, repeatedly adjusting the vibration of the substrate according to the calculated reference vibration frequency f until the droplet reaches a resonance state; S4, as evaporation proceeds, timely calculating f and adjusting the vibration frequency and amplitude of the substrate so that the droplet always remains in resonance.

2. The vibrating substrate-based particle suspension evaporation method according to claim 1, wherein The contact parameters include a contact radius of the droplet with the substrate and a static contact angle .

3. The vibrating substrate-based particle suspension evaporation method according to claim 2, wherein The radius of the spherical droplet under the same volume The calculation formula is: 。 4. The vibrating substrate-based particle suspension evaporation method according to any one of claims 1 to 3, characterized by, The order of the resonance mode of the droplet is 4.

5. A vibrating substrate based particle suspension evaporation system, characterized by, The method comprises an inkjet printing system, an observation system, a signal output system and a controller. The inkjet printing system comprises a syringe pump, a syringe, a nozzle, a substrate and a vibration platform; the suspension is sprayed from the nozzle under the action of the syringe pump and then deposited on the substrate; the contact parameters between the droplet and the substrate are observed by the observation system and transmitted to the controller; the controller calculates a reference vibration frequency; the signal output system outputs a suitable electrical signal according to the reference vibration frequency and drives the vibration platform to generate corresponding vibration so that the droplet and the substrate resonate.

6. A vibrating substrate based particle suspension evaporation system according to claim 5, wherein, The reference oscillation frequency of the deposited droplet is calculated by the following formula : wherein, R is the radius of the spherical droplet, n is the resonance order, ρeff is the effective density of the suspension.

7. The vibrating substrate-based particle suspension evaporation system of claim 5, wherein, The contact parameters include a contact radius of the droplet with the substrate and a static contact angle .

8. The vibrating substrate-based particle suspension evaporation system of claim 7, wherein, The radius of the spherical droplet under the same volume The calculation formula is: 。 9. The vibrating substrate-based particle suspension evaporation system according to any one of claims 5 to 8, wherein The order of the resonance mode of the droplet is 4.

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